A    TEXT     BOOK 


OF 


PHYSIOLOGY. 


TEXT    b66k 


PHYSIOLOGY. 


M.  FOSTER,  M.A.,  M.D.,  F.R.S., 

PRjSLKCTOR   in    physiology   and    fellow    of   trinity   college,    CAMBRIDGE. 


WITH  ILL  USTRA  TIONS. 


THIRD     EDITION,      REVISED. 


MACMILLAN     AND     CO., 
1880. 


ar34 

/8gO 


PREFACE 
TO   THE    SECOND    EDITION. 


So  short  a  time  has  passed  since  the  appearance  of 
the  first  edition  that  it  has  not  seemed  desirable  to  make 
any  important  changes.  My  previous  decision  not  to 
introduce  figures  of  instruments  has  been  so  generally 
disapproved,  that  I  have  waived  my  own  judgment  and 
inserted  a  number  of  illustrations,  which  I  trust  will  be 
found  to  assist  the  reader.  The  areas  of  the  cerebral 
convolutions,  in  spite  of  the  difficulties  surrounding  the 
true  interpretation  of  the  phenomena  resulting  from  their 
stimulation,  are  of  such  interest,  especially  to  the  medical 
profession,  that  I  have  introduced  illustrative  figures  for 
which  I  have  to  thank  the  kindness  of  Dr.  Ferrier. 

Otherwise  my  efforts  have  been  chiefly  directed  to 
removing  inaccuracies  and  obscurities,  iu  the  hope  of 
rendering  the  work  more  worthy  of  the  favour  with  which 
it  has  been  received.  It  will  be  observed  that  the  largest 
changes  and  additions  occur  in  the  small  print. 

I  have  to  thank  Dr.  Pye-Smith  and  other  friends  as 
well  as  previously  unknown  correspondents  for  their 
valuable  suggestions  ;  and  I  am,  as  before,  greatly 
indebted  for  the  help  given  me  by  my  former  pupils, 
Mr.  Dew-Smith,  Mr.  Langley,  and  Mr.  Lea. 

Trinitv  College,  Camrridge, 
December,   1S77. 


PREFACE 
TO    THE    THIRD    EDITION. 


The  most  important  changes  in  the  present  edition 
are  to  be  found  in  the  section  on  Muscle  and  Nerve  ; 
I  have  rearranged  this  section  altogether,  hoping  thereby 
to  render  this  difficult  subject  more  easy  for  the  reader. 
The  other  changes,  though  numerous,  are  for  the  most 
part  slight,  and  very  largely  confined  to  the  small  print. 
I  have  again  to  offer  my  best  thanks  to  my  friends  who 
have  assisted  me  in  this  as  in  the  two  former  editions. 


Trinity  College,  Cambridge, 
September,   1879. 


CONTENTS. 


PAGS 

INTRODUCTORY     I 


BOOK   I. 

BLOOD.     THE  TISSUES  OF  MOVEMENT. 
THE  VASCULAR  MECHANISM. 


CHAPTER  I. 

Br.ooD,  pp.   13 — 41. 

Sec.  I.     The  Coagulalion  of  Blood      .......  14 

Sec.  2.      The  Chemical  Composition  of  Blood       .....  30 

Sec.  3.      The  Hist  iry  of  the  Corpuscles  ......  35 

Sec.  4.      The  Quantity  of  Blood,  and  its  distribution  in  the  Body  .         .  40 

CHAPTER  n. 
The  Contractile  Tissues,  pp.  42 — 122. 

Sec.  I.      The  Phenomena  of  Muscle  and  Nerve     ...  ..43 

Muscular  and  nervous  Irritability,  p.  43.  The  I'licnomena 
of  a  simple  mu'-cular  contraction,  p.  46.  Tetanic  con- 
tractions, p.  52. 


Viii  CONTENTS. 

PAGB 

Sec.  2.     The  changes  in  a  Muscle  during  Muscular  Contraction   ,         .         57 
The  change   in  form,   p.    57.     Electrical   Changes,    p.    62. 
Chemical  Changes,  p.  68.     The  Changes  in  a  Nerve  during 
the  passage  of  a  Nervous  Impulse,  p.  75. 

Sec.  3.  '    The  Nature  of  the  Changes  through  which  an  Electric  Current 

is  able  to  generate  a  Nervous  Impulse   .....  7^ 

The  action  of  ihe  Constant  Current,  p.  78. 

Sec.  4.      The  Muscle-nerve  Preparation  as  a  Machine   ....         86 
The  nature  and  mode  of  application  of  the  Stimulus  as 
affecting  the  amount  and  character  of  the  Contraction,  p.  86. 
The  influence  of  the  Load,   p.  go.     The  influence  of  the 
Size  and  Form  of  the  muscle,  p.  92. 

Sec.  5.      The  Circumstances  which  determine  the  Degree  of  Ii-ritability 

of  Muscles  and  Nerves         ...  ....  92 

The  effects  of  severance  from  the  Central  Nervous  System, 
p.  93.  The  Influence  of  Temperature,  p.  95.  The  Influ- 
ence of  Blood  Supply,  96.  The  Influence  of  Functional 
Activity,  p.  98. 

•    Sec.  6.     A  fzirther  discussion  of  some  points  in  the  Physiology  of  Muscle 

and  Nerve  .........       loi 

The  Electrical  Phenomena  of  Muscle  and  Nerve,  p.  lOi. 
The  energy  of  Muscle  and  Nerve  and  the  nature  of  the 
Chemical  Changes,  p.  116. 

Sec.  7.  Unstriated  Muscular  Tissue  .         ,         .         .         .         .         .  119 

Sec.  8.  Cardiac  Muscles    .........  120 

Sec.  9.  Cilia     ...........  121 

Sec.  10.  Migrating  Cells    .........  122 


CHAPTER  III. 

The  Fundamental  Properties  of  Nervous  Tissues, 
pp.   123—135. 

Automatic  Actions,  p.  127.     Reflex  Actions,  p.  128.     Inhibition,  p.  132. 


CON  Tt  NTS.  ix 

CHAPTER  IV. 
The  V.\scular  Mechanism,  pp.   136 — 235. 

PAGE 

I.  The  Physical  Phenomena  of  the  Circulation    .       136 

Sec.  I.     Main  gitura!  facts  of  the  Circulation 137 

The  capillary  Circulation,  p.  137.  The  flow  in  the  Arteries, 
p.  139.  The  flow  in  the  Veins,  p.  147.  Hydraulic 
principles  of  the  Circulation,  p.  148. 

Sec,  2.     The  Heart    ..........        154 

The  Phenomena  of  the  Normal  Beat,  p.  155.  The 
Mechanism  of  the  Valves,  p.  164.  The  sounds  of  the 
Heart,  p.  16S.  The  work  done,  p.  171.  Variations  in  the 
Heart's  Beat,  p.  172. 

Sec.  3.     Tlu  Pulse      .         .         .         .         .         .         .         .         .         .       1 73 

II.  The  Vital  Pheno.mena  of  the  Circulation        .       184 

Sec.  4.     Changes  in  the  beat  of  tJu  Heart     .         .         .         .         .         .       1S6 

Nervuus  Mechanism  of  the  beat,  p.  1S7.  Inhibition  of  the 
beat,  p.  1 89.  The  effects  ou  the  circulation  of  changes  in 
the  heart's  beat,  p.  199. 

Sec.  5.     Changes  in  the  calibre  of  the  minute   arteries,      Vasa-ntotor 

actions        ..........       200 

Vaso-motor  Nerves,  p.  203.  Vaso-constrictor  and  Vaso- 
dilator Nerves,  p.  220.  The  effects  of  local  vascular  con- 
striction or  dilation,  p.  224. 

Sec.  6.     Changes  in  the  Capillary  Districts  .....       226 

Sec.  7.     Changes  in  the  Quantity  of  Blood 229 


The  Mutual  Relations  and  the  Coordination  of  the  Vascular 
Factors 


2"nI 


CONTENTS. 


BOOK   II. 


THE    TISSUES    OF    CHEMICAL    ACTION    WITH    THEIR 
RESPECTIVE  MECHANISMS.     NUTRITION. 


CHAPTER  I. 

The  Tissues  and  Mechanisms  of  Digestion,  pp.  239^328, 

PAGB 

Sec.  I.     TTie  Properties  of  the  Digestive  Jtiices     .         .         ...         .       239 

Saliva,  p.  239.  Gastric  Juice,  p.  245.  Bile,  p.  254, 
Pancreatic  Juice,  p.  257-     Succus  Entericus,  p.  264. 

Sec.  2.      The  act  of  secretion  in  the  case  of  the  Digestive  yuices  and  the 

Nervous  Mechanisms  which  regulate  it  ....       265 

Sec.  3.      The  Muscular  Mechanisms  of  Digestion.  ....       293 

Mastication,  p.  293.  Deglutition,  p,  293.  Peristaltic  action 
of  the  small  intestine,  p.  296.  Movements  of  the  oesophagus, 
p.  299.  Movements  of  the  stomach,  p.  300.  Movements 
of  the  large  intestine,  p.  302.  Defaecation,  p.  302. 
Vomiting,  p.  304. 

Sec.  4.     The  Changes  which  the  food  undergoes  in  the  Alimentary  Canal      307 

Sec.  5.     Absorption  of  the  Products  of  Digestion  .         .         .         .         .316 
The  Course  taken  by  the  several  products  of  digestion,  p.  322. 


CHAPTER  II. 
The  Tissues  and  Mechanisms  of  Respiration,  pp.  329 — 397. 

Sec.  I.     The  Mechanics  of  Pulmonary  Respiration       ....       33*^ 
The   Rhythm  of   Respiration,   p.   332-.     The    Respiratory 
Movements,  p.  334. 


CONTENTS.  xi 

o  ^  /■  PACE 

Sec.  2.     C/ianga  of  the  Air  in  Ketpiralion  .....  .       340 

Sec.  3.  The  Respiratory  Changes  in  the  Blood  .....  343 
The  relations  of  oxygen  in  the  blood,  p.  345.  Ha.moglobin; 
its  properties  and  derivatives,  p.  348.  Colour  of  venous  and 
arterial  blood,  p.  353.  The  relations  of  the  carbonic  acid 
in  the  blood,  p.  358.  The  relations  of  the  nitrogen  in  the 
blood,  p.  360. 

Sec.  4.      The  Respiratory  Changes  in  the  Lungs  .....        360 
Tiie  entrance  of  oxygen,  p.  360.     The  exit  of  carbonic  acid, 
p.  361. 

Sec.  5.      The  Respiratory  Changes  in  the  Tissues  .....       363 

Sec.  6.      The  Nervous  Mechanism  of  Respiration  .         .         .         .       369 

Sec.  7.     The  Effects  of  Respiration  on  the  Circulation  ....       378 

Sec.  8.  Tlie  Effects  of  Changes  in  the  Air  breathed  ....  388 
The  effects  of  deficient  air.  Asphyxia.  Phenomena  of 
asphyxia,  p.  388.  The  circulation  in  asphyxia,  p.  390.  The 
effects  of  an  increased  supply  of  air.  Apnoea,  p.  392.  The 
effects  of  changes  in  the  composition  of  the  air  breathed, 
p.  394.  The  effects  of  changes  in  the  pressure  of  the  air 
breathed,  p.  394. 

Sec.  9.     Modified  Respiratory  Movements     ......       395 

Sighing,  Yawning,  Hiccough,  Sobbing,  Coughing,  Sneezing: 
Laughter,  p.  395. 


CHAPTER  III. 

Secretio.n  by  the  Skin,  pp.  398 — 406. 

The  Nature  and  Amount  of  Perspiration      ......        399 

Cutaneous  Respiration  .         .         .         .         .  .  .         .         .401 

The  Secretion  of  Perspiration      ........       402 

The  Ner^'ous  Mechanism  of  Perspiration,  p.  402. 

Absorption  by  the  Skin  .  .......      405 


Xll  CONTENTS. 


CHAPTER   IV. 

Secretion  by  the  Kidneys,  pp.  407 — 423. 

PAGE 

Sec.  I.      The  Composition  of  Urine      .......       407 

Sec.  2.     The  Secretion  of  Urine .         .         .         .         .         .         .         .411 

The  relation  of  the  secretion  of  urine  to  arterial  pressure, 
p.  411.     Secretion  by  the  renal  epithelium,  p.  414. 

Sec.  3.     Micturition  ..........       419 


CHAPTER  V. 

The  Metabolic  Phenomena  of  the  Body,  pp.  424—495. 

Sec.  I.     Metabolic  Tissues .       425 

The  History  of  Glycogen,  p.  425.  The  History  of  Fat, 
Adipose  Tissue,  p.  437.  The  Mammary  Gland,  p.  441. 
The  Spleen,  p.  444. 

Sec.  2.      The  History  of  Urea  and  its  allies  .....       446 

Sec.  3.     The  Statistics  of  Ntitrition     .......       454 

Comparison  of  Income  and  Outcome,  p.  458.  Nitrogenous 
Metabolism,  p.  462.  The  effects  of  Fatty  or  Amyloid  Food, 
p.  464. 

Sec.  4.     The  Energy  of  the  Body        .......       468 

The  income  of  energy,  p.  468.  The  expenditure,  p.  469. 
The  Sources  of  Muscular  Energy,  p.  470.  The  Sources  and 
Distribution  of  Heat,  p.  474.  Regulation  by  variations  in 
loss,  p.  478.     Regulation  by  variations  in  production,  p.  480. 

Sec.  5-      The  Influence  of  the  Nervous  System  on  Nutrition  .         .         .       488 

Sec.  6.     Dietetics        ..........       491 


CONTENTS.  xiii 

BOOK    III. 

THE  CENTRAL   NERVOUS  SYSTEM  AND    ITS    INSTRUMENTS. 

CHAPTER  I. 
Sensory  Nkuvics,  pp.  499 — 509. 

CHAPTER  H. 

Sight,  pp.  510—573. 

PACE 

Sec.  I.     Dioptric  Mechanisms     ........       510 

The  Formation  of  the  Image,  p.  510.  Accommodation,  p. 
512.  Movements  of  the  Pupil,  p.  520.  Imperfections  in 
the  Dioptric  apparatus,  p.  525. 

Sec.  2.      Visual  Sensations  ........       529 

The  origin  of  Visual  Impulses,  p.  529.  Simple  Sensations, 
p.  539.     Colour  Sensations,  p.  544. 

Sec.  3.      Visual  Perceptions         ........       552 

Modified  Perceptions,  p.  554. 

Sec.  4.     Bitiocular  Vision  .........       559 

Corresponding  or  identical  points,  p.  559.  Movements  of 
the  eyeballs,  p.  560.     The  Horopter,  p.  566. 

Sec.  5.      Visual  y udgmaits  ........       568 

Sec.  6.      The  Protective  Mechanisms  of  the  Eye 572 

CHAPTER  HI. 
Hearing,  Smell,  and  Taste,  pp.  574— 58S. 

Sec  I.     Hearing 574 

The  acoustic  apparatus,  p.  575.  Auditory  Sensations,  p. 
577.     Auditory  Judgments,  p.  583. 

Sec.  2.     Smell 584 

Sec.  3.      Taste     ...........       5S6 


XIV  CONTENTS. 

CHAPTER  IV. 

Feeling  and  Touch,  pp.  589 — 598. 

PAGE 

Sec.  I.     General  Sensibility  and  Tactile  Perceptions      .         ,         .         •       589 
Sec.  2.     Tactile  Sensations  .         .         .         .         ,         .         ,         -591 

Sensations  of  Pressure,  p.  591.     Sensations  of  Temperature, 

p.  592. 
Sec.  3.      Tactile  Perceptions  and  Jzidgments  .....       594 

Sec.  4.     The  Muscular  Sense       .         .         .         .         ,         .         .         ,       596 

CHAPTER  V. 
The  Spinal  Cord,  pp.  599 — 621. 

Sec.  I.     As  a  centre  of  Reflex  Action  ......       599 

In  the  Frog,  p.  599.     In  the  Mammal,  p.  606.     The  time 
of  Reflex  Actions,  p.  608. 
Sec.  2.     As  a  Centre  or  Group  of  Centres  of  Autotnatic  Action     .         .       609 
Sec.  3.     As  a  Co7iductor  of  Afferent  and  Efferent  Impulses  .         .         .611 

CHAPTER  VL 
The  Brain,  pp.  622 — 671. 

Sec.  I.      On   the  Phenomena   exhibited  by  an   aniinal  deprived  of  its 

Cerebral  Hemispheres  .......       622 

Sec.  2.      The  Mechanisms  of  Cooi'dinafed  Movements     ....        627 

Forced  Movements,  p.  636, 
Sec.  3.      The  Functions  of  the  Ce^'ebral  Convolutions     ....       638 

Sec.  4.      The  Functions  of  other  parts  of  the  Brain         ....        650 

Corpora  striata  and  optic  thalami,  p.  652.     Corpora  quad- 
rigemina,  p.  657.     Cerebellum,  p.  660.     Crura  Cerebri  and 
Pons  Varolii,  p.  663.     Medulla  oblongata,  p.  664. 
Sec.  5.      The  Rapidity  of  Cerebral  Operations        .....       665 

Sec.  6.     The  Cranial  Nerves       ........       667 

CHAPTER  VII. 

Special  Muscular  Mechanisms,  pp.  672 — 685. 

Sec.  I.      The  Voice 672 

Sec.  2.     Speech  ...         ........  6.78 

Vowels,  p.  678.     Consonants,  p.  679. 

Sec.  3.     Locomotor  Mechanisms  ........  68? 


CONTENTS.  XV 


BOOK    IV. 
THE  TISSUES  AND  MECHANISMS  OF  REPRODUCTION. 

CHAPTER  I. 

Menstruation,  pp.  691 — 693. 

CHAPTER  n. 
Impregnation,  pp.  694,  695. 

CHAPTER  ni. 

The  Nutrition  of  the  Embryo,  pp.  696 — 702. 

CHAPTER  IV. 
Parturition,  pp.  703 — 706. 

CHAPTER  V. 
The  Phases  of  Life,  pp.  707 — 719. 

CHAPTER  VI. 
Death,  pp.  720,  722. 

APPENDIX. 
On  the  Chemical  Basis  of  the  Animal  Body,  pp.  725 — 788. 

INDEX,  p.  789. 


INTRODUCTORY. 


Among  the  simpler  organisms  known  to  Biologists,  perhaps  the 
most  simple  as  well  as  the  most  common  is  that  which  has  received 
the  name  of  Amoeba.  There  are  many  varieties  of  Amoeba,  and 
probab'y  many  of  the  forms  which  have  been  described  are,  in 
reality,  merely  amoebiform  phases  in  the  lives  of  certain  animals 
or  plants ;  but  they  all  possess  the  same  general  characters. 
Closely  resembling  the  white  corpuscles  of  vertebrate  blood,  they 
are  wholly  or  almost  wholly  composed  of  undifferentiated  pro- 
toplasm, in  the  midst  of  which  lies  a  nucleus,  though  this  is 
sometimes  absent.  In  many  a  distinction  may  be  observed 
between  a  more  solid  external  layer  or  ecfosarc,  and  a  more  fluid 
granular  interior  or  oidosan ;  but  in  others  even  this  primary 
difterentiation  is  wanting.  P.y  means  of  a  continually  occurring 
flu.x  of  its  protoplasmic  substance,  the  amoeba  is  enabled  from 
moment  to  moment  not  only  to  change  its  form  but  also  to  shift 
its  position,  liy  flowing  roui  d  the  substances  which  it  meets,  it, 
in  a  way,  swallows  them  ;  and  having  digested  and  absorbed  such 
parts  as  are  suitable  tor  food,  ejects  or  rather  flows  away  from  the 
useless  remnants'.  It  thus  lives,  moves,  eats,  grows,  and  after  a 
time  dies,  having  been  during  its  whole  life  hardly  anything  more 
than  a  minute  lump  of  protoplasm.  Hence  to  the  Physiologist  it 
is  of  the  greatest  interest,  since  in  its  life  the  problems  of 
physiology  are  reduced  to  their  simplest  forms. 

Now  the  study  of  an  amoeba,  with  the  help  of. knowledge 
gained  by  the  examination  of  more  complex  bodies,  enables  us 
to  state  that  the  undifferentiated  protoplasm  of  which  its  body  is 
so  largely  composed  possesses  certain  fundamental  vital  properties. 

T.     It  is  contractile.     There  can  be  little  doubt  that  the 
changes  in  the  protoplasm  of  an  amoeba  which  bring  about  its 

'   Huxley  and  Martin,  EUtnentary  Biology,  I.ess)n  III. 
F    P.  I 


2  PROPERTIES    OF   PROTOPLASM. 

peculiar '  amoeboid  '  movements,  are  identical  in  their  fundamental 
nature  with  those  which  occurring  in  a  muscle  cause  a  contraction  : 
a  muscular  contraction  is  essentially  a  regular,  an  amoeboid  move- 
ment, an  irregular  flow  of  protoplasm.  The  substance  of  the 
amoeba  may  therefore  be  said  to  be  contractile. 

2.  It  is  irritable  and  automatic.  When  any  disturbance, 
such  as  contact  with  a  foreign  body,  is  brought  to  bear  on  the 
amoeba  at  rest,  movements  result.  These  are  not  passive  move- 
ments, the  effects  of  the  push  or  pull  of  the  disturbing  body  pro- 
portionate to  the  force  employed  to  cause  them,  but  active  mani- 
festations of  the  contractility  of  the  protoplasm  ;  that  is  to  say, 
the  disturbing  cause,  or  '  stimulus,'  sets  free  a  certain  amount  of 
energy  previously  latent  in  the  protoplasm,  and  the  energy  set 
free  takes  on  the  form  of  movement.  Any  living  matter  which, 
when  acted  on  by  a  stimulus,  thus  suffers  an  explosion  of  energy, 
is  said  to  be  '  irritable.'  The  irritability  may,  as  in  the  amoeba, 
lead  to  movement;  but  in  some  cases  no  movement  follows  the 
application  of  the  stimulus  to  irritable  matter,  the  energy  set  free 
by  the  explosion  taking  on  some  other  form  than  movement,  ex.  gr. 
heat.  Thus  a  substance  may  be  irritable  and  yet  not  contractile, 
though  contractiUty  is  a  very  common  manifestation  of  irritability. 

The  amoeba  (except  in  its  prolonged  quiescent  stage)  is  rarely 
at  rest.  It  is  almost  continually  in  motion.  The  movements 
cannot  always  be  referred  to  changes  in  surrounding  circumstances 
acting  as  stimuli  ;  in  many  cases  the  energy  is  set  free  in  con- 
sequence of  internal  changes,  and  the  movements  which  result  are 
called  spontaneous  or  automatic'  movements.  We  may  therefore 
speak  of  the  protoplasm  of  the  amoeba  as  being  irritable  and 
automatic. 

3.  It  is  receptive  and  assimilative.  Certain  substances 
serving  as  food  are  received  into  the  body  of  the  amoeba,  and 
there  in  large  measure  dissolved.  The  dissolved  portions  are 
subsequently  converted  from  dead  food  into  new  living  protoplasm, 
and  become  part  and  parcel  of  the  substance  of  the  amoeba. 

'  This  word  has  recently  acquired  a  meaning  almost  exactly  opposite  to  that 
which  it  originally  bore,  and  an  automatic  action  is  now  by  many  understood 
to  mean  nothing  more  than  an  action  produced  by  some  machinery  or  other. 
In  this  worlc  I  use  it  in  the  older  sense,  as  denoting  an  action  of  a  body,  the 
cau-^es  of  which  appear  to  lie  in  the  body  itself.  It  seems  preferable  to  '  spon 
taneous,'  inasmuch  as  it  does  n  it  necessarily  carry  with  it  the  idea  of  irregularity, 
and  bears  no  reference  to  a  '  will.' 


INTRODUCTORY.  3 

4.  It  is  metabolic  and  secretory.  Pari  passu  with  the 
reception  of  new  material,  there  is  going  on  an  ejection  of  old 
material,  for  tiie  increase  of  the  aniaba  by  the  addition  of  food  is 
not  indefinite.  In  otlier  words,  the  jjrotoplasm  is  continually 
undergoing  chemical  change  (metabolism),  room  being  made  for 
the  new  protoplasm  by  the  breaking  up  of  the  old  protoplasm  into 
products  which  are  cast  out  of  the  body  and  got  rid  of.  These 
products  of  metabolic  action  have,  in  many  cases  at  all  events, 
subsidiary  uses.  Some  of  them,  for  instance,  we  have  reason  to 
think,  are  of  value  for  the  purpose  of  dissolving  and  effecting  other 
preliminary  changes  in  the  raw  food  introduced  into  the  body  of 
the  amoeba  ;  and  hence  are  retained  within  the  body  for  some  little 
time.  Such  products  are  generally  spoken  of  as  'secretions.' 
Others  which  pass  more  rapidly  away  are  generally  called  '  excre- 
tions.' The  distinction  between  the  two  is  an  unimportant  and 
frequently  accitlental  one. 

The  energy  expended  in  the  movements  of  the  amoeba  is 
su[)!)lied  by  the  chemical  changes  going  on  in  the  protoplasm,  by 
the  breaking  up  of  bodies  possessing  much  latent  energy  into 
bodies  possessing  less.  Thus  the  metabolic  changes  which  the 
food  (as  distinguished  from  the  undigested  stuff  mechanically 
lodged  for  a  Avliile  in  the  body)  undergoes  in  passing  through  the 
protojjlasm  of  the  amoeba  are  of  three  classes :  those  preparatory 
to  and  culminating  in  the  conversion  of  the  food  into  protoplasm, 
those  concerned  in  the  discharge  of  energy,  and  those  tending  to 
economise  the  immediate  products  of  the  second  class  of  changes 
by  rendering  them  more  or  less  useful  in  carrying  out  the  first. 

5.  It  is  respiratory.  Taken  as  a  whole,  the  metabolic 
changes  are  pre-eminently  processes  of  oxidation.  One  article  of 
food,  i.e.  one  substance  taken  into  the  body,  viz.  oxygen,  stands 
apart  from  all  the  rest,  and  one  product  of  metabolism  peculiarly 
associated  with  oxidation,  viz.  carbonic  acid,  stands  also  somewhat 
apart  from  all  the  rest.  Hence  the  assumjition  of  oxygen  and  the 
excretion  of  carbonic  acid,  together  with  such  of  the  metabolic 
processes  as  are  more  especially  oxidative,  are  frequently  spoken 
of  together  as  constituting  the  respiratory  processes. 

6.  It  is  reproductive.  The  individual  amoeba  represents  a 
unit.  This  unit,  after  a  longer  or  shorter  life,  having  increased  in 
si/e  by  the  addition  of  new  protoplasm  in  excess  of  that  which  it 
is  continually  using  uj),    may,  by  fission    (or   by   other   mems) 

'    I'lii-i  term  w.xs  introduced  liy  Schwann  (tSjg).     Mi'ros.  Untersurh.  p.  229. 

I — 2 


4  THE   FUNDAMENTAL   TISSUES. 

resolve  itself  into  two,  (or  more)  parts,  each  of  which  is  capable 
of  living  as  a  fresh  unit  or  individual. 

Such  are  the  fundamental  vital  qualities  of  the  protoplasm  of 
an  amoeba ;  all  the  facts  of  the  life  of  an  amoeba  are  mani- 
festations of  these  protoplasmic  qualities  in  varied  sequence  and 
subordination. 

The  higher  animals,  we  learn  from  morphological  studies,  may- 
be regarded  as  groups  of  amoebae  peculiarly  associated  together. 
All  the  physiological  phenomena  of  the  higher  animals  are 
similarly  the  results  of  these  fundamental  qualities  of  protoplasm 
peculiarly  associated  together.  The  dominant  principle  of  this 
association  is  the  physiological  division  of  labour  corresponding  to 
the  morphological  differentiation  of  structure.  Were  a  larger  or 
'higher'  animal  to  consist  simply  of  a  colony  of  undiffer- 
entiated amoebce,  one  animal  differing  from  another  merely  in  the 
number  of  units  making  up  the  mass  of  its  body,  without  any 
differences  between  the  individual  units,  progress  of  function 
would  be  an  impossibility.  The  accumulation  of  units  would 
be  a  hindrance  to  welfare  rather  than  a  help  Hence, 
in  the  evolution  of  living  beings  through  past  times,  it  has 
come  about  that  in  the  higher  animals  (and  plants)  certain  groups 
of  the  constituent  amoebiform  units  or  cells  have,  in  company 
with  a  change  in  structure,  been  set  apart  for  the  manifestation  of 
certain  only  of  the  fundamental  properties  of  protoplasm,  to  the 
exclusion  or  at  least  to  the  complete  subordination  of  the  other 
properties. 

These  groups  of  cells,  thus  distinguished  from  each  other  at 
once  by  the  differentiation  of  structure  and  by  the  more  or  less 
marked  exclusiveness  of  function,  receive  the  name  of  '  tissues,' 
Thus  the  units  of  one  class  are  characterized  by  the  exaltation  of 
the  contractility  of  their  protoplasm,  their  automatism,  metabolism 
and  reproduction  being  kept  in  marked  abeyance.  These  units 
constitute  the  so-called  muscular  tissue.  Of  another  tissue,  viz. 
the  nervous,  the  marked  features  are  irritability  and  automatism, 
with  an  almost  complete  absence  of  contractility  and  a  great 
restriction  of  the  other  qualities.  In  a  third  group  of  units,  the 
activity  of  the  protoplasm  is  largely  confined  to  the  chemical 
changes  of  secretion,  contractility  and  automatism  (as  manifested 
by  movement)  being  either  absent  or  existing  to  a  very  slight 
degree.  Such  a  secreting  tissue,  consisting  of  epithelium-cells, 
forms  the  basis  of  the  mucous  membrane  of  the  alimentary  canal. 
In  the  kidney,  the  substances  secreted  by  the  cells,  being  of  no 
further  use,  are  at  once  ejected  from  the  body.     Hence  the  renal 


INTRODUCTORY.  5 

tissue  may  be  spoken  of  as  excretory.  In  the  epiiheliuni-cells  of 
the  hmgs,  the  protoplasm  plays  an  altogether  subordinate  part  in 
the  assumption  of  ox\gcn  and  the  excretion  of  carbonic  acid. 
Still  we  may  perhaps  be  permitted  to  speak  of  the  pulmonary 
epithelium  as  a  respiratory  tissue. 

In  aildiiion  to  these  distinctly  secretory  or  excretory  tissues, 
there  exist  groups  of  cells  specially  reserved  for  the  carrying  on  of 
chemical  changes,  the  products  of  which  are  neither  cast  out  of 
the  body,  nor  collected  in  cavities  for  digestive  or  other  uses. 
The  work  of  these  cells  seems  to  be  of  an  intermediate  character ; 
they  are  engaged  either  in  elaborating  the  material  of  food  that  it 
may  be  the  more  easily  assimilated,  or  in  preparing  used-up  material 
for  final  excretion.  They  receive  their  materials  from  the  blood 
and  return  their  products  back  to  the  blood.  They  may  be  called 
the  metabolic  tissues  par  excellence.  Such  are  the  fat-cells  of 
adipose  tissue,  the  hepatic  cells  (as  far  as  the  work  of  the  liver 
other  than  the  secretion  of  bile  is  concerned),  and  probably  many 
other  celkilar  elements  in  various  regions  of  the  body. 

Each  of  the  various  units  retains  to  a  greater  or  less  degree  the 
power  of  reproducing  itself,  and  the  tissues  generally  are  capable 
of  regeneration  in  kind.  But  neither  units  nor  tissues  can  re- 
produce other  parts  of  the  organism  than  themselves,  much  less 
the  entire  organism.  For  the  reproduction  of  the  complex  indi- 
vidual, certain  units  are  set  apart  in  the  form  of  ovary  and  testis. 
In  these  all  the  properties  of  protoplasm  are  distinctly  subordinated 
to  the  work  of  growth. 

Lastly,  there  are  certain  groups  of  units,  certain  tissues,  which 
are  of  use  to  the  body  of  which  they  forni  a  part,  not  by  reason  of 
their  manifesting  any  of  the  fundamental  qualities  of  protoplasm, 
but  on  account  of  the  physical  and  mechanical  properties  of 
certain  substances  which  their  protoplasm  has  been  able  by  virtue 
of  its  metabolism  to  manufacture  and  to  deposit.  Such  tissues 
are  bone,  cartilage,  connective  tissue  in  large  part,  and  the  greater 
portion  of  the  skin. 

We  may  therefore  consider  the  complex  body  of  a  higher 
animal  as  a  compound  of  so  many  tissues,  each  tissue  correspond- 
ing to  one  of  tlie  fundamental  qualities  of  protoplasm,  to  the 
development  of  which  it  is  specially  devoted  by  the  division  of 
labour.  It  must  however  be  remembered  that  there  is  a  distinct 
limit  to  the  division  of  labour.  In  each  and  every  tissue,  in 
addition  to  its  leading  quality,  there  are  more  or  less  pronounced 
remnants  of  all  tiie  other  protoplasmic  qualities.  Thus,  tliough 
we  may  call  one  tissue /(/r  excellence  metabolic,  all  the  tissues  are 
to  a  greater  or  less  extent  metabolic.     The  energy  of  each,  what 


6  THE   FUNDAMENTAL   TISSUES. 

ever  be  its  particular  mode,  has  its  source  in  the  breaking-up  of 
the  protoplasm.  Chemical  changes,  including  the  assumption  of 
oxygen  and  the  production  complete  or  partial  of  carbonic  acid, 
and  therefore  also  entailing  a  certain  amount  of  secretion  and 
excretion,  must  take  place  in  each  and  every  tissue.  And  so  with 
all  the  other  fundamental  properties  of  protoplasm  ;  even  con- 
tractility, which  for  obvious  mechanical  reasons  is  soonest  reduced 
where  not  wanted,  is  present  in  many  other  tissues  besides  muscle. 
And  it  need  hardly  be  said  that  each  tissue  retains  the  power 
of  assimilation.  However  thoroughly  the  material  of  food  be 
prepared  by  digestion  and  subsequent  metabolic  action,  the  last 
stages  of  its  conversion  into  living  protoplasm  are  effected  directly 
and  alone  by  the  tissue  of  which  it  is  about  to  form  a  part. 

Bearing  this  qualification  in  mind,  we  may  draw  up  a  physio- 
logical classification  of  the  body  into  the  following  fundamental 
tissues  : — 

1.  The  eminently  contractile  ;   the  muscles. 

2.  „  ,,        irritable  and  automatic ;  the  nervous  system. 

3.  ,,  ,,       secretory,  or    excretory ;    digestive,  urinary, 

and  pulmonary,  &c.,  epithelium. 

4.  „  „       metabolic ;  fat-cells,  hepatic  cells,  lymphatic 

and  ductless  glands,  &c. 

5.  „  „        reproductive ;  ovary,  testis. 

6.  The  indififerent  or  mechanical ;  cartilage,  bone,  &c. 

All  these  separate  tissues,  with  their  individual  characters,  are 
however  but  parts  of  one  body ;  and  in  order  that  they  may 
be  true  members  working  harmoniously  for  the  good  of  the  whole, 
and  not  isolated  masses  each  serving  its  own  ends  only,  they  need 
to  be  bound  together  by  coordinating  bonds.  Some  means  of 
communication  must  necessarily  exist  between  them.  In  the 
mobile  homogeneous  body  of  the  amoeba,  no  special  means  of 
communication  are  required.  Simple  diffusion  is  sufficient  to 
make  the  material  gained  by  one  part  common  to  the  whole  mass, 
and  the  native  protoplasm  is  physiologically  continuous,  so  that  an 
explosion  set  up  at  any  one  point  may  be  immediately  propagated 
throughout  the  whole  irritable  substance.  In  the  higher  animals, 
the  several  tissues  are  separated  by  distances  far  too  great  for  the 
slow  process  of  diffusion  to  serve  as  a  sufficient  means  of  com- 
munication, and  their  primary  physiological  continuity  is  broken 
by  their  being  imbedded  in  masses  of  formed  material,  the 
product  of  the  indifferent  tissues,  which  being  devoid  of  irritability, 
present   an    effectual   barrier   to   the    propagation   of    molecular 


IMKODLCTORY,  7 

explosions.  It  thus  becomes  necessary  tliat  in  the  increasing 
complexity  of  animal  forms,  the  process  of  differentiation  should 
be  accompanied  by  a  corresponding  integration,  that  the  isolated 
tissues  should  be  made  a  whole  by  bonds  uniting  tiiem  together. 
These  bonds  moreover  must  be  of  two  kinds. 

In  the  first  place  there  must  be  a  ready  and  ra|)id  distribution 
and  interchange  of  material.  The  contractile  tissues  must  be 
abundantly  supplied  with  material  best  adapted  by  previous 
elaboration  for  direct  assimilation,  and  the  waste  products  arising 
from  their  activity  must  be  at  once  carried  away  to  the  metabolic 
or  excretory  tissues.  And  so  with  all  the  other  tissues.  There 
must  be  a  free  and  speedy  intercourse  of  material  between  each 
and  all.  This  is  at  once  and  most  easily  effected  by  the  regular 
circulation  of  a  common  fluid,  the  blood,  into  which  all  the 
elaborated  food  is  discharged,  from  which  each  tissue  seeks  what 
it  needs,  and  to  which  each  returns  that  for  which  it  has  no  longer 
any  use.  Such  a  circulation  of  fluid,  being  in  large  measure  a 
mechanical  matter,  needs  a  machinery,  and  calls  forth  an  expendi- 
ture of  energy.  The  machinery  is  supplied  by  a  special  construc- 
tion of  the  primary  tissues,  and  the  energy  is  arranged  for  by  the 
presence  among  these  of  contractile  and  irritable  matter.  Thus 
to  the  fundamental  tissues  there  is  added,  in  the  higher  animals,  a 
vascular  bond  in  the  shape  of  a  mechanism  of  circulation. 

In  the  second  i)lace  no  less  important  than  the  interchange 
of  material  is  the  interchange  of  energy.  In  the  amoeba  the 
irritable  surface  is  physiologically  continuous  with  the  more 
internal  protoplasm,  while  each  and  every  part  of  the  body  has 
automatic  powers.  In  the  higher  animal,  portions  only  of  the 
skin  remain  as  eminently  irritable  or  sensitive  structures,  while 
automatic  actions  are  chiefly  confined  to  a  central  mass  of  irritable 
nervous  matter.  Both  forms  of  irritable  matter  are  separated,  by 
long  tracts  of  indifferent  material,  from  those  contractile  tissues 
through  which  they  chiefly  manifest  the  changes  going  on  in  them- 
selves. Hence  the  necessity  for  long  strands  of  eminently 
irritable  tissue  to  connect  the  skin  and  contractile  tissues  as  well 
with  each  other  as  with  the  automatic  centres.  Similar  strands  are 
also  needed,  though  perhaps  less  urgently,  to  connect  the  other 
tissues  with  these  and  with  each  other.  To  the  vascular  bond 
there  must  be  added  an  irritable  bond,  along  the  strands  of  which 
impulses,  set  up  by  changes  in  one  or  another  part,  may  travel  in 
determinate  courses  for  the  regulation  of  the  energy  of  distant 
spots.  In  other  word-^,  ])art  of  the  irritable  tissues  must  be 
specially  arranged  to  form  a  coordinating  nervous  system. 

Still  further  complications  have  yet  to  be  considered.      In  the 


«  CENTRAL  NERVOUS  MECHANISM. 

life  of  a  minute  liomogeneous  amoeba,  possessing  no  special  form 
or  structure,  there  is  little  scope  for  purely  mechanical  operations. 
As  however  we  trace  oat  the  gradual  development  of  the  more 
complex  animal  forms,  we  see  coming  forward  into  greater  and 
greater  prominence  the  arrangement  of  the  tissues  in  definite 
ways  to  secure  mechanical  ends.  Thus  the  entire  body  acquires 
particular  shapes,  and  parts  of  the  body  are  built  up  into 
mechanisms,  the  actions  of  which  are  to  the  advantage  of  the 
individual.  Into  the  composition  of  these  mechanisms  or 
'  organs '  the  active  fundamental  tissues,  as  well  as  the  passive 
or  indifferent  tissues,  enter ;  and  the  working  of  each  mechanism, 
the  function  of  each  organ,  is  dependent  partly  on  the  mechanical 
conditions  offered  by  the  passive  elements,  partly  on  the  activity 
of  the  active  elements.  The  vascular  mechanism,  of  which  we  have 
just  spoken,  is  such  a  mechanism.  Similarly  the  urgent  necessity 
for  the  access  of  oxygen  to  all  parts  of  the  body  has  given  rise 
to  a  complicated  respiratory  mechanism ;  and  the  needs  of  copious 
alimentation,  to  an  alimentary  or  digestive  mechanism. 

Further,  inasmuch  as  muscular  movement  is  one  of  the  chief 
ends,  or  the  most  important  means  to  the  chief  ends,  of  animal 
life,  we  find  the  animal  body  abounding  in  motor  mechanisms,  in 
which  the  prime  mover  is  muscular  contraction,  while  the  ma- 
chinery is  supplied  by  complicated  arrangements  of  muscles  with 
such  indifferent  tissues  as  bone,  cartilage,  and  tendon.  In  fact, 
the  greater  part  of  the  animal  body  is  a  collection  of  muscular 
machines,  some  serving  for  locomotion,  others  for  special  man- 
oeuvres of  particular  members  and  parts,  others  as  an  assistance  to 
the  senses,  and  yet  others  for  the  production  of  voice,  and  in  man, 
of  speech. 

Lastly,  the  simple  automatism  of  the  amoeba,  with  its  simple 
responses  to  external  stimuli,  is  replaced  in  the  higher  animals  by 
an  exceedingly  complex  volition  afl^ected  in  multitudinous  ways  by 
influences  from  the  world  without ;  and  there  is  a  correspondingly 
complex  central  nervous  system.  And  here  we  meet  with  a  new 
form  of  differentiation  unknown  elsewhere.  While  the  contrac- 
tility of  the  amoebal  protoplasm  differs  but  slightly  from  the  con- 
tractility of  the  vertebrate  striated  muscle,  there  is  an  enormous 
difference  between  the  simple  irritabiUty  of  the  amoeba  and  the 
complex  action  of  the  vertebrate  nervous  system.  Excepting  the 
nervous  or  irritable  tissues,  the  fundamental  tissues  have  in  all 
animals  the  same  properties,  being,  it  is  true,  more  acute  and 
perfect  in  one  than  in  another,  but  remaining  fundamentally  the 
same.  The  elementary  muscular  fibre  of  a  mammal  is  a  mass  of 
but  shghtly  differentiated  protoplasm,   forming  a  whole   physio- 


INTRODUCTORY.  9 

logically  continuous,  and  in  no  way  constituting  a  mechanism. 
Each  fibre  is  a  counterpart  of  all  others  ;  and  the  muscle  of  one 
animal  dilTcrs  from  that  of  anotlier  in  such  particulars  only  as  are 
wliolly  subordinate.  In.  the  nervous  tissues  of  the  higher  animals, 
on  the  contrary,  we  find  properties  unknown  to  those  of  the  lower 
ones ;  and  in  projjortion  as  we  ascend  the  scale,  we  observe  an 
increasing  diflerenliation  of  the  nervous  system  into  unlike  parts. 
Thus  we  have,  what  does  not  exist  in  any  other  tissue,  a  mechanism 
of  nervous  tissue  itself,  a  central  nervous  mechanism  of  complex 
structure  and  complex  function,  the  comjjlexity  of  which  is  due 
not  primarily  to  any  mechanical  arrangements  of  its  parts,  but  to 
the  further  dilTerentiation  of  that  fundamental  quality  of  irritability 
and  automatism  which  belongs  to  all  irritable  tissues,  and  to  all 
native  prott)])lasm. 

In  the  following  pages  I  propose  to  consider  the  facts  of  physi- 
ology very  much  according  to  the  views  which  have  been  just 
sketched  out.  Tiie  funtlamental  properties  of  most  of  the  ele- 
mentary tissues  will  first  be  reviewed,  and  then  the  various  special 
mechanisms.  It  will  be  found  convenient  to  introduce  early  the 
account  of  the  vascular  mechanism,  and  of  its  nervous  coordinating 
mechanism,  while  the  mechanisms  of  respiration  and  alimentation 
will  be  best  considered  in  connection  with  the  respiratory  and 
secretory  tissues.  The  description  of  the  purely  motor  mechanisms 
will  be  brief;  and,  save  in  a  few  instances,  confined  to  a  statement 
of  general  principles.  The  special  functions  of  the  central  nervous 
system,  including  the  senses,  must  of  necessity  be  considered  by 
themselves.  The  tissues  and  mechanism  of  reproduction  and  the 
phenomena  of  the  decay  and  death  of  the  organism  will  naturally 
form  the  subject  of  the  closing  chapters. 


BOOK    I, 


BLOOD.      THE  TISSUES   OF    MOVEMENT.      THE 
VASCULAR   MECHANISM. 


CHAPTER    I. 
BLOOD. 


Blood,  when  flowing  m  a  normal  condition  through  the  blood- 
vessels, consists  of  an  almost  colourless  fluid,  the  plas.min 
which  are  suspended  a  number  of  more  solid  bodies,  the Td  and 
whie  corpuscles.  Were  we  anxious  to  give  a  forma  'compere 'ess 
to  the  classification  of  the  various  parts  of  the  body  into  tissues 
^'e  might  speak  ot  the  blood  as  a  tissue  of  which  tL  corn  rles 
are  the  essentia  cellular  elements,  while  the  plasma  is  a  imkl 
matr.v  We  might  compare  it  to  a  cartilage,  ?he  firm  mat  ixo 
which  had  become  completely  liquefied 'so  that  the  cart  Le 
corpuscles  were  perfectly  free  to  move  about  ^ 

In  regarding  blood  as  tissue,  however,  we  come  uoon  the 
difficulty  that  It,  unlike  all  the  other  tissues,  possesses  no  one 
characteristic  property.  The  protoplasm  of  the^vl  ke  conxiscTeJ 
neci  rdX .  ";';r'^  protoplasm,  in  no  respect  fitted  o  an; 
special  duty;  and  though,  as  we  shall  see,  the  red  corpuscles 
have  a  definite  respiratory  function,  inasmuch  as  they  aroZferl 
of  oxygen  from  the  lungs  to  the  several  tissues,   still   this  re  S! 

hZTJieT'^r  °f  ^'- ^'^^y --y  labou'rs  of  th  blood. 
wiU  be  therefore  far  more  profitable,  indeed  necessary,  to  trea 
the  blood,  not  as  a  tissue  by  itself  but  as  the  great  means  of 
communication  of  material  between  the  tissues  properly  sTcal  ed 
Its  real  usefulness  lies  not  so  much  in  any  one  property  of  eith^^^ 
s  corpuscles  or  us  plasma,  as  in  its  nature  fi  ting  it  to  ser  eas 
tie  great  medium  of  exchange  between  all  parts Vf  the  body 
J  he  receptive  tissues  pour  into  it  the  material  which  t  ley  W 

hilts       T  '"^'^"?'  '^''  '""''''''"^  ^'^-^^"^^  -'^'^draw  from'it  the 

hmgs  wmch  are  no  longer  of  any  use,  and  the  irritable  t^^^e  con 

rac  lie,  and   indeed    all    the   tissues,    seek   in  it    he  s'ubstances 

(mcluding_  oxygen)    which    they  need  for    the    ma  ffe    u  on    of 

er^ergy  or  tor  the  storing  up  of  differentiated  material   a^d  ""turn 

to  It  the  waste  products  resulting  from  their  activity.     AH  over  the 


J4  COAGULATION   OF   BLOOD.  [BOOK   L 

;rref.  ^.^  the  e^e^a.  -   --g^^nvkr «" 

the   whole  individual.     Just  as  tne  wnu         5  ^^ 

them  their  immediate  air  and  food.  composition 

From  this  it  follows,  on  the  one  hand,  tiiat  tne  cm  P 

that  the  united  action  of  all  the  tissues  must  lenu 

maintain  an  average  uniform  compos;t-n  of  die  whole  n.a 

blood.     The  special  changes  which  blood        known  t  p 

Sh  ^:  'prSfnted  by  blood,  ^""^ht  - -^4="'°  ' 

the  most  important,  is  the  property  .t  possesses  of  clottmg  or 

coagulating  when  shed. 

Sec.   I.     The  Coagulation  of  Blood 

Blood,  when  shed  from  the  blood-vessels  of  ^  l^^j^g  ^^^f^/^jj 
perLly  fluid.     In  a  ^Ho^jime  ^t  be^^^^^^ 

elly      The  vessel  into  which  it  has  been   shed,  can  ayhis  s  age 
ie  Lerted  without  a  drop  of  the  ^^^-^.,^-;:f;/^^  ,d   if   fSl 
of  the  same  bulk  as  the  Ff^^^^  y/^^/^^^^^^X'rior  of  the  vessel, 
removed,  presents  a  complete  mould  ot  the  ^"^f  }"\"  ,  1 

.  IfX  blood  in  this  jelly  stage  be  left  -^^-^^^^l^;,,?  ^.^P 
a  few  drops  of  an  almost  colouriess  A-d  ^"^^^^jf^^  numbed  and 
anceon  the  surface  of   the  jelly.      ,\"^^".!;^'"'\' superficial  layer 

l^sS.  -  ?-,e^i:tr:rtmrconsiste„cy,'no^ 


CHAP.   I.]  BLOOD.  ,5 

lie  shrinking  andc(;ndensat.on  of  the  clot,  and  the  correspond 
ing  increase  of  the  serum,  continue  for  some  time      The    Zer 
surface  o    the  clot  is  generally  cupped.     A    pordon  of  L  ^J^o 
e.xam.ned  under  the  microscopi  is  seen  to  consist  of  a  florko 
fine  g lanular  fibrils,  in  the  meshes  of  which  are  entangled    he  red 

seen ;;.'  rf^'^^r'*-"  '^  ^'"  ,'^''^°^-  ^"  ^'^  ^-"-  nofhmg  a'n  be 
substance  called  Jibnn.  Hence  we  may  speak  of  he  clot  a.; 
consisting  of  fibrin  and  corpuscles;   and  the  act  of  clottin.  o 

ion'of" t"  blood"°"'^^  "  ^°"^'^"'^"  °^  ^^^  naturallytirpor- 

seZration  of  r.     """  '"f"'"  /"to  fibrin  and  serum,  followed  by 

separation  of  the  serum  from  the  fibrin  and  corpuscles  ^ 

In  man,  blood  when  shed  becomes  viscid  in  about  two  or  three 

A  te^  th:^  1"'^  '"!•"'  ^'f  J^">'"^^^^^  •"  ^b°"^  five  or  ten  minutes 
feln       V'P''  of  another  few  minutes  the  first  drops  of  serum  are 

hour's  Thr?"''"?"  ^'  ^'"'•"•'^''^  ^^"^P'^^^  '"  f™'-  one  to  sclera! 
hours  The  times  however  will  be  found  to  vary  according  to  tlfe 
condition  of  the  individual,  the  temperature  of  he  ^ir  fnc^  li^ 
rn-.:^^re7aptlit:or^^^  '-r  -^'^'^'^''^^  ^lood  is'^heT'  ^Imong 

.iscia  ty  sets  in.     In  consequence  there  appears  on  the  surface  nf 

the  blood  an  upper  la3er  of  colourless  plasma,  contamhn    in  i?s 

the  rp'd^P°T."'/"''^">'  ^~°^°"^^^^^  ^°^P"^^l-^  (whch  are  ilht'er  than 

'   he     o^^allld    '  bift-  ''°^'^  1'"  ^^'^-^^  P^^^^  °^  ^'-  blood  form  ng 

eenbthe  blood  ^or'°'''      ^  "T''"''   ^"^>' ^°^^  ^^  sometime! 

body.  "'^"'  ''^    ^"fl^'""iatory  conditions   of  the 

th/n!'J'  ^"^^^  ''°'''^  ^^^^^  '^^^  appearance  in  horse's  blood  even  at 
brsurroSd'h'''^  °'  '^'^  "'■••     ^^  ^  P-^'^-^  of  house's  blool 

at  abouT  o"  r      ^  ^  ?°^'"^  "'^"^"'■^  °^  '^^  ^"^1  ^^^^  and  thus  kept 
Under    h.?''°'°'"''"  "'''^>'  ^"  "^"^^^^  indefinitely  postponed 
X les  ta^es   n'r;''"';'  '  "°'"'  ,^°"P'^^^^^  descent'^of  th'e  co?: 
transmren^  ni  ^       r  ''^"1-  ^  considerable  quantity  of  colourless 
A  Son  nr^  f'"'^  ^'■"^  ^""^"^  blood-corpuscles  may  be  obtained 
exi^Hv  ."  \  '"'"""'"  '""'"°^'^^  '"'■on^  the  freezing^mixture  ciot^ 

fon;  '^  "-.^r    ;^^ -^- b'-d.     It  first  becomes  viscid  an"  U^n 
shrunken  clot'nd.       ^"^^^Jl^^ntly    separates   into    a   colourless 
an'^st^tid^V^t  of"l?rclot.''"  ^'"^^'^  ^'^"  ^'^  ^°^P"-'-  -^  "- 
If  a  few  cubic  centimetres  of  the  same  plasma  be  diluted  with 


1 6  COAGULATION  OF  BLOOD.       [BOOK  L 

50  times  its  bulk  of  a  75  p.c.  solution  of  sodium  chloride'  coagu- 
lation is  much  retarded,  and  the  various  stages  may  be  more  easily 
watched.  As  the  fluid  is  becoming  viscid,  fine  fibrils  of  fibrin  will 
be  seen  to  be  developed  in  it,  especially  at  the  sides  of  the  con- 
taining vessel.  As  these  fibrils  multiply  in  number,  the  fluid 
becomes  more  and  more  of  the  consistence  of  a  jelly,  and  at  the 
same  time  somewhat  opaque.  Stirred  or  pulled  about  with  a 
needle,  the  fibrils  shrink  up  into  a  small  opaque  stringy  mass  ;  and 
a  very  considerable  bulk  of  the  jelly  may  by  agitation  be  resolved 
into  a  minute  fragment  of  shrunken  fibrin  floating  in  a  quantity  of 
what  is  really  diluted  serum.  If  a  specimen  of  such  diluted  plasma 
be  stirred  from  time  to  time,  as  soon  as  coagulation  begins,  with  a 
needle  or  glass  rod,  the  fibrin  may  be  removed  piecemeal  as  it 
forms,  and  the  jelly-stage  may  be  altogether  done  away  with. 
When  fresh  blood  which  has  not  yet  had  time  to  coagulate  is 
stirred  or  whipped  with  a  bundle  of  rods  (or  anything  presenting 
a  large  amount  of  rough  surface),  no  jelly-like  coagulation  takes 
place,  but  the  rods  become  covered  with  a  mass  of  shrunken 
fibrin.  Blood  thus  whipped  until  fibrin  ceases  to  be  deposited,  is 
found  to  have  entirely  lost  its  power  of  coagulation. 

Putting  all  these  facts  together,  it  is  very  clear  that  the  pheno- 
mena of  the  coagulation  of  blood  are  caused  by  the  appearance  in 
the  plasma  of  fine  fibrils  of  fibrin.  As  long  as  these  are  scanty, 
the  blood  is  simply  viscid.  When  they  become  sufficiently  nume- 
rous, they  give  the  blood  the  firmness  of  a  jelly.  Soon  after  their 
formation  they  begin  to  shrink ;  and  in  their  shrinking  enclose  in 
their  meshes  the  corpuscles,  but  squeeze  out  the  fluid  parts  of  the 
blood.  Hence  the  appearance  of  the  shrunken  coloured  clot  and 
the  colourless  serum. 

Fibrin,  whether  obtained  by  whipping  freshly- shed  blood,  or  by 
washing  either  a  normal  clot,  or  a  clot  obtained  from  colourless 
plasma,  exhibits  the  same  general  characters.  It  belongs  to  that 
class  of  complex  unstable  nitrogenous  bodies  called /r<?/^/i^^  which 
form  a  large  portion  of  all  living  bodies  and  an  essential  part  of 
all  protoplasm^.  It  gives  the  ordinary  proteid  reactions.  It  is 
insoluble  in  water  and  in  dilute  saline  solutions ;  and  though  it 
swells  up  in  dilute  hydrochloric  acid,  it  is  not  thereby  appreciably 
dissolved  3. 

Minor  differences  have  been  stated  to  exist  in  the  characters  of 
fibrin  obtained,  in  various  ways  and  from  various  sources,  ex.  gr.  by 

*  A  solution  of  sodium  chloride  of  this  strength  will  hereafter  be  spoken  of 
as  'normal  saline  solution.' 

*  See  Appendix.  3  For  further  details  see  Appendix. 


CIIAl'.   I.J  BLOOD.  17 

wliipping,  or  by  washing  a  blood-colt,  from  venous  or  from  arterial 
blood.  But  these  difTorcnces  arc  unimportant.  The  characters  are 
said  to  vary  also  in  different  animals. 

Coagulation  then  i.s  brought  about  by  the  introduction  into  the 
blood-i)lasmaof  a  substance,  fibrin,  wliich  previously  did  not  exist 
there  as  such.  Such  a  substance  must  have  antecedents,  or  an 
antecedent — what  are  they,  or  what  is  it  ? 

If  blood  be  received  direct  from  the  blood-vessels  into  one- 
third  its  bulk  of  a  saturated  so'ution  of  some  neutral  salt,  such  as 
magnesium  sulphate,  and  the  two  gently  but  thoroughly  mixed, 
coagulation,  especially  at  a  moderately  low  temperature,  will  be 
deferred  for  a  very  long  time.  If  the  mixture  be  allowed  to  stand, 
the  corpuscles  will  sink,  and  a  colourless  plasma  will  be  obtained 
similar  to  the  plasma  gained  from  horse's  blood  by  cold,  except 
that  it  contains  an  excess  of  the  neutral  salt.  The  presence  of 
the  neutral  salt  has  acted  in  the  same  direction  as  cold  :  it  has 
prevented  the  occurrence  of  coagulation.  It  has  not  destroyed 
the  fibrin  ;  for  if  some  of  the  plasma  be  diluted  with  ten  times 
its  bulk  (or  even  a  less  quantity)  of  wator,  it  will  coagulate 
speedily  in  quite  a  normal  fashion,  with  the  production  of  quite 
normal  fibrin. 

If  some  of  the  colourless  tran.sparent  plasma,  obtained  either 
by  the  action  of  neutral  salts  from  any  blood,  or  by  the  help  of 
cold  from  horse's  blood,  be  treated  with  some  solid  neutral  salt, 
such  as  sodium  chloride,  to  saturation,  a  white  flaky  somewhat 
sticky  precipitate  will  make  its  appearance.  If  this  precipi- 
tate be  removed,  the  fluid  is  no  longer  coagulable  (or  very 
slightly  so),  even  though  the  neutral  salt  present  be  removed  by 
dialysis,  or  its  influence  lessened  by  dilution.  With  the  removal 
of  the  substance  precipitated,  the  plasma  has  lost  its  power  of 
coagulating. 

If  the  precipitate  itself,  after  being  washed  with  a  saturated 
solution  of  tiie  neutral  salt  (in  which  it  is  insoluble)  so  as  to  get 
rid  of  all  serum  and  other  constituents  of  the  plasma,  be  treated 
with  a  small  quantity  of  water,  it  readily  dissolves',  and  the 
solution  rapidly  filtered  gives  a  clear  colourless  filtrate,  which  is  at 
first  perfectly  fluid.  Soon,  however,  thj  fluidity  gives  way  to 
viscidity,  and  this  in  turn  to  a  jelly  condition,  and  finally  the  jelly 
shrinks  into  a  clot  floating  in  a  clear  fluid ;  in  other  words,  the 

•  The  substance  itself  is  not  soluble  in  distilled  water,  but  a  quantity  of  the 
neutral  ^aIts  always  clin^^rs  to  the  precipitate,  and  thus  the  addiiion  of  water 
virtually  gives  rise  to  a  dilute  saline  solution,  in  which  the  substance  is  re.idiN 
soluble. 


l8  PLASMINE.  [book   I, 

filtrate  clots  like  plasma.  Thus  there  is  present  in  cooled  plasma, 
and  in  plasma  kept  from  clotting  by  the  presence  of  neutral  salts, 
a  something,  precipitable  by  saturation  with  neutral  salts,  a 
something  which,  since  it  is  soluble  in  very  dilute  saline  solutions, 
cannot  be  fibrin  itself,  but  which  in  solution  speedily  gives  rise  to 
the  appearance  of  fibrin.  To  this  substance  its  discoverer,  Denis^, 
gave  the  name  oi  plasmitie.  We  are  justified  in  saying  that  the 
coagulation  of  blood  is  the  result  of  the  conversion  of  plasmine 
into  fibrin. 

The  question  now  arises.  What  is  the  exact  nature  of  plasmine  ? 
Is  it  for  instance  a  mixture  of  two  or  more  substances  which  by 
their  interaction  produce  fibrin  ?  This  view  is  suggested  by  the 
fact  that  plasmine  cannot  be  kept  i?i  sohttio/i  for  any  length  of 
time  without  changing  into  fibrin,  except  when  submitted  to 
certain  influences,  such  as  cold.  It  is  moreover  supported  by 
the   following  facts. 

The  disease  known  as  hydrocele  is  characterized  by  the  presence 
in  the  tunica  vaginalis  (or  serous  sac  of  the  testis)  of  an  abnormal, 
and  often  very  considerable  quantity  of  a  clear,  colourless,  or 
faintly  yellow  fluid  very  similar  in  appearance  to  the  serum  of 
clotted  blood.  This  secretion,  when  drawn  from  the  living  body 
without  admixture  of  blood,  will  in  the  great  majority  of  cases 
remain  perfectly  fluid,  and  enter  into  decomposition  without  having 
shewn  any  tendency  whatever  to  clot.  In  a  few  exceptional  cases 
a  coagulation,  generally  slight,  but  quite  similar  to  that  of  colour- 
less blood-plasma,  may  be  observed. 

If  a  small  quantity  of  hydrocele  fluid  which  has  been  observed 
not  to  clot  spontaneously  be  mixed  with  some  serum  or  whipped 
blood,  the  mixture  will  after  a  longer  or  shorter  time  clot  in  a 
completely  normal  manner.  That  is  to  say,  two  fluids  neither  of 
which  apart  clot  spontaneously,  will  clot  spontaneously  when 
mixed  together.  (In  some  cases  no  clot  is  formed  ;  specimens  of 
hydrocele  fluid  are  occasionally  met  with  in  which  coagulation 
cannot  be  thus  produced.) 

If  serum  be  treated  to  saturation  with  solid  sodium  chloride  or 
magnesium  sulphate,  a  flaky  precipitate  very  similar  in  general 
appearance  to  plasmine  will  make  its  appearance.  Like  plasmine, 
this  precipitate  is  soluble  in  very  dilute  neutral  saline  solutions,  and 
in  consequence  as  thus  prepared  readily  dissolves  when  treated 
with  distilled  water,  since  a  certain  amount  of  sodium  chloride 
clings  to  it.  Unlike  plasmine,  its  filtered  solution  will  not  clot. 
If,  however,  some  of  the  solution  be  added  to  hydrocele  fluid,  a 
clotting  takes  place  just  as  when  serum  itself  is  added.  The  rest 
'  Ann,  d.  Sci.  Nat.,  (iv.)  x.  p.  25. 


I 


CHAP.   l]  BLOOD.  19 

of  the  serum  from  which  this  substance  has  been  removed  will  not, 
after  the  removal  by  dialysis  of  the  excess  of  salt,  cause  clotting  in 
hydrocele  fluitl.  Kvitlently  it  is  the  presence  of  this  constituent, 
not  coagiilable  of  itself,  wliich  gives  to  serum  its  power  pf  producing 
a  coagulation  in  hydrocele  Ihiid.  The  substance  in  question  may 
also  be  prepared  by  diluting  blood-scrum  with  ten  or  twenty  times 
its  bulk  of  water  and  ])assing  a  brisk  stream  of  carbonic  acid 
through  it.  The  mixture  speedily  becomes  turbid,  and  if  left  to 
stan<l  a  copious  white  a^iorphous  somewhat  granular  precipitate 
settles  down.  The  substance  so  thrown  down  has  received  the 
name  oi  parai^/obiilin  ox  fibrinoplasiic globulin  ox  jihritioplastin.  It 
may  also  be  thrown  down  by  very  cautiously  adding  ililute  acetic 
acid  to  dilute  serum.  It  is,  like  fibrin,  a  proteid  :  but  it  differs  in 
many  respects  from  fibrin.  It  does  not  occur  in  the  form  of  fibrils, 
and  though  insoluble  in  distilled  water,  is  very  readily  soluble  in 
dilute  neutral  saline  solutions.  There  are  many  proteids  very 
closely  allied  to  it ;  and  these  are  frequently  classed  together  as 
globulins^. 

If,  on  the  other  hand,  hydrocele  fluid,  specimens  of  which  have 
been  observed  to  coagulate  on  the  addition  of  serum  or  paraglobu- 
lin,  be  treated  in  the  same  way  either  with  carbonic  acid  or  with 
sodium  chloride  to  saturation,  a  precipitate  is  obtained  similar  to, 
but  more  flaky  and  less  granular  in  nature  than,  that  produced  in 
serum.  A\'hcn  this  precipitate,  to  which  the  name  oi fibrinogen  has 
been  given,  is  dissolved  in  dilute  neutral  saline  solution,  and  the 
solution  added  to  serum,  the  mixture  coagulates  spontaneously, 
while  the  hydrocele  fluid  from  which  the  substance  has  been 
remove.  1  no  longer  causes  coagulation  in  serum.  Thus  paraglo- 
bulin  from  scrum  causes  coagulation  of  hydrocele  fluid,  and  fibrin- 
ogen from  hydrocele  fluid  causes  coagulation  of  serum,  though 
neither  alone  coagulates  spontaneously.  And  serum  deprived  of 
its  paraglobulin,  and  hydrocele  fluid  deprived  of  its  fibrinogen, 
have  lost  all  power  of  coagulating  each  other. 

Lastly,  if  solid  paraglobulin  and  fibrinogen,  prepared  by  the 
sodium  chloride  method,  be  together  dissolved  in  dilute  saline 
solution,  the  fluid  mixture  will  coagulate  spontaneously  with  the 
production  of  quite  normal  fibrin. 

These  facts  seem  to  shew  that  plasmine  is  a  mijrture  of 
fibrinogen  and  paraglobulin  ;  indeed  an  artificial  mixture  of  the 
two  latter,  obtained  from  serum  and  hydrocele  fluid  respectively, 
would  be  undislingiiishable  from  the  former  obtained  from 
plasma.      It   must   however  be  remembered   that  no  one  has  yet 

'  For  further  details  see  Appoi.dix. 

2 — 2 


20  PARAGLOBULIN   AND   FIBRINOGEN.        [BOOK  I. 

succeeded   in   separating   natural   plasmine   into   fibrinogen  and 
fibrinoplastin''. 

There  are  moreover  facts  which  shew  that  the  above  state- 
ments do  not  cover  the  whole  ground  ;  there  is  evidence  of  the 
existence  of  yet  another  factor  in  the  process. 

1.  If  fibrinogen  and  paraglobulin  be  isolated  by  the  carbonic 
acid  method,  their  mixture  in  a  saline  solution  clots  with  great 
difficulty  or  not  at  all ;  when  they  are  prepared  by  the  saturation 
method,  their  mixture  gives  a  good  firm  clot.  This  suggests  that 
something  retained  by  the  latter  method  is  lost  by  the  former. 

2.  Normal  blood-plasma  must  naturally  contain  an  excess  of 
paraglobulin,  since  after  coagulation  the  serum  still  contains  a 
considerable  quantity  of  that  body.  Yet  even  in  blood-plasma, 
paraglobulin,  under  certain  circumstances,  will  favour  coagulation. 
If  three  parts  of  plasma  be  mixed  with  one  part  of  a  solution  of 
magnesium  sulphate  (one  of  the  salt  to  three  and  a  half  of  water), 
the  mixture  diluted  with  eight  parts  of  water  will  afford  a  dilute 
plasma,  in  which  spontaneous  coagulation  will  either  not  occur  at 
all  or  come  on  very  slowly  indeed.  .  In  this  dilute  plasma  the 
paraglobulin  is  still  in  excess.  Nevertheless  the  addition  of  a 
further  quantity  of  paraglobulin,  prepared  by  saturation  with 
sodiuili  chloride,  will  speedily  cause  coagulation.  From  this  it 
may  be  inferred  that  in  adding  the  paraglobulin  thus  prepared 
something  else  is  added  as  well. 

3.  If  blood-serum  or  defibrinated  blood  be  poured  into 
about  twenty  times  its  bulk  of  strong  spirit,  and  the  mixture 
allowed  to  stand  for  some  three  weeks,  or  longer,  all  the  proteid 
matters  including  the  paraglobulin  become  coagulated  and  almost 
wholly  insoluble  in  water.  Hence  if  the  spirit  be  filtered  off  from 
the  copious  precipitate,  and  the  latter  dried  at  a  low  temperature 
(below  40°)  and  extracted  with  distilled  water,  the  aqueous 
extract  contains  no  palpable  amount  of  proteid  material  and 
gives  but  slight  reactions  with  proteid  tests.  A  small  quantity  of 
tUis  aqueous  extract  of  blood,  however,  though  free  from  para- 
globulin, will  when  added  to  the  dilute  plasma,  spoken  of  above, 
bring  about  a  rapid  coagulation. 

^  "We  owe  the  discovery  of  fibrinoplastin  and  fibrinogen  to  A.  Schmidt, 
whose  earlier  papers  wiJl  be  found  in  Reichert  and  du  Bois-Reymond's  Archiv, 
1861,  p.  545,  and  1862,  p.  428.  Schnaidt's  later  results,  which  are  discusred 
in  the  succeeding  portions  of  this  i-ection,  are  contained  in  papers  published  in 
Pfliiger's  Ai'chiv,  VI.  (1872)  p.  413  ;  XI.  (1875)  pp.  291  and  515  ;  XIII.  (1876) 
pp.  93  and  146. 


CHAP.    I  ]  bLOUD.  2 1 

4.  If  the  pericardial  cavity  of  a  large  mammal  (ox,  horse, 
sheep)  be  laid  open  imvicdiatcly  after  death,  the  lluid  removed  will 
coagulate  spontaneously  and  rapidly.  The  clot  will  on  examina- 
tion be  lound  to  consist  of  a  meshwork  of  normal  fibrin  in  which 
arc  entangled  a  multitude  of  white  corpuscles.  If  the  opening  of 
the  body  be  deferred  to  some  twenty  or  more  hours  after  death, 
the  pericardial  lluid  will  be  four:d  either  not  to  coagulate  at  all  or 
to  coagulate  very  slowly  and  feebly. 

When,  however,  paraglobulin  prepared  by  the  saturation 
method  is  added  to  such  a  ])cricardial  fluid  a  rapid  and  complete 
coagulation  is  generally  brought  about.  But  precisely  the  same 
coagulation  may  in  many  cases  be  brought  about  by  the  simple 
addition  of  the  aqueous  extract  just  described.  Most  pericardial 
fluids  in  f;ict  behave  extremely  like  the  dilute  plasma  spoken  of 
above.  Moreover  some  specimens  of  hydrocele  fluid  will  clot 
spontaneously  on  tlie  addition  of  the  aqueous  extract  without  any 
paraglobulin  being  added  at  all. 

Here  then  are  indications  of  the  existence  of  a  substance 
which  is  neither  fibrinogen  nor  paraglobulin,  but  which  neverthe- 
less appears  to  be  as  necessary  as  either  of  the  other  two  for  the 
occurrence  of  coagulation.  This  third  substance  will  not  bring 
about  coagulation  with  fibrinogen  alone  or'  with  paraglobulin 
alone.  It  will  not  bring  about  coagulation  in  fluids  such  as  many 
hydrocele  fluids,  from  which  paraglobulin  is  apparently  absent, 
nor  serum,  from  which  fibrinogen  is  absent  It  is  efticacious  only 
in  such  cases  where  there  are  reasons  for  thinking  that  both 
paraglobulin  and  fibrinogen  are  present.  But  its  most  important 
feature  is  tlie  following.  In  the  cases  in  which  coagulation  is 
brought  about  by  the  addition  of  paraglobulin  to  fibrinogenous 
liquids,  the  quantity  of  fibrin  produced  certainly  depends  on  the 
quantity  of  fibrinogen  present  and  appears  also  to  be,  to  a  certain 
extent,  determined  by  the  quantity  of  paraglobulin  added ; 
whereas  the  addition  of  the  aqueous  extract  only  afl'ects  the 
rapidity  with  which  coagulation  sets  in,  and  not  at  all  the  quantity 
of  fibrin  ])roduced.  In  other  words,  the  aqueous  extract  does 
not  contribute  to  the  substance  of  the  fibrin,  but  favours,  or  is 
essential  to,  the  union  of  tlie  two  fibrin  factors.  That  is  to  say, 
the  substance  in  the  aqueous  extract  which  thus  affects  coagulation 
belongs  to  tliat  class  of  substances  which  promote  the  union  of 
other  bodies,  or  cause  changes  in  other  bodies,  without  themselves 
entering  into  union  or  undergoing  change.  These  substances 
we  shall  hereafter  learn  to  speak  of  as  '  ferments  ' ;  and  this  ]iar- 
ticular  substance  has  been  called  by  its  discoverer,  A.  Schmidt*, 

•  Op.cit. 


22  FIBRIN-FERMENT.  [BOOK   I. 

fibrin-ferment.  Obviously  the  ferment  is  present  in  blood-plasma, 
in  plasmine,  and  in  paraglobulin  as  prepared  by  the  saturation 
method,  but  is  apparently  in  large  measure  lost  when  paraglobulin 
is  prepared  by  the  carbonic  acid  method. 

In  conclusion  then  we  may  say,  that  coagulation  is  the  result 
of  the  interaction  of  two  bodies,  paraglobulin  and  fibrinogen, 
brought  about  by  the  agency  of  a  third  body,  fibrin-ferment. 
Where  these  three  bodies  are  all  present,  as  in  blood-plasma,  in 
plasmine,  in  pericardial  fluid  taken  from  the  body  immediately 
after  death,  spontaneous  coagulation  is  witnessed  :  where  the 
ferment  is  absent,  but  the  other  factors  are  present,  as  in  many 
cases  of  pericardial  fluid  removed  some  time  after  death, 
coagulation  will  take  place  on  the  addition  of  ferment  alone  : 
where  both  ferment  and  paraglobulin  are  absent,  as  in  many  cases 
of  hydrocele  fluid,  both  these  must  be  added  before  coagulation 
can  come  on. 


The  exact  nature  of  the  process  by  which  the  presence  of  all  three 
factors  leads  to  the  formation  of  fibrin  cannot  be  at  present  defined 
more  closely  than  by  the  phrase  '  interaction.'  Beyond  the  broad 
fact  that  the  quantity  of  fibrin  formed  is  affected  by  the  quantity  of 
paragtobulin  and  fibrinogen  present,  we  have  no  knowledge  of  quanti- 
tative relations  between  the  two  constituents.  That  they  do  not  unite 
simply  together,  as  a  base  with  an  acid,  seems  to  be  clearly  shewn  by 
the  fact,  that  in  artificial  coagulations  the  quantity  of  fibrin  formed 
is  by  weight  always  less  than  that  of  the  paraglobulin  used ;  indeed  is 
frequently  less  than  that  of  the  fibrinogen  calculated  to  be  present. 
Hammarsten^  argues  that  the  paraglobulin  does  not  enter  in  any  way 
into  the  fibrin,  the  latter  being  simply  transformed  fibrinogen.  He 
explains  the  fibrinoplastic  properties  of  paraglobulin  as  due  to  that 
substance  obviating  certain  hindrances  to  the  formation  of  the  fibrin, 
for  instance,  preventing  the  solution  by  saline  or  other  bodies  of  the 
fibrin  while  it  is  in  what  may  be  called  a  nascent  condition,  i.e.  in  a 
stage  intennediate  between  fibrinogen  and  fibrin.  According  to  him 
the  quantity  of  paraglobulin  present  in  a  coagulating  fluid,  though  of 
marked  effect  on  the  quantity  of  fibrin  produced,  has  no  effect  on  the 
total  quantity  of  fibrinogen  used  up,  i.e.  transformed  into  fibrin  or 
into  something  else 

Some  authors  go  so  far  as  to  believe  that  paraglobulin  in  itself  has 
no  share  in  the  matter,  and  that  its  apparent  fibrinoplastic  qualities 
are  always  due  to  a  quantity  of  the  ferment  being  entangled  in  it 
during  its  preparation  They  regard  the  formation  of  fibrin  as  being 
simply  a  transformation  of  fibrinogen  by  means  of  the  fibrin  ferment. 
But  this  view  is  clearly  untenable  so  long  as  the  statement  that  the 
quantity  of  fibrin  formed  is  affected  by  the  presence  of  paraglobulin 


Pfliiger's  Archiv,  xiv.  (1877),  211. 


k 


CilAP.    I.]  BLOOD.  23 

is  not  disproved.  Tiie  assertion  of  Hammarsten',  that  paraglobulin 
may  be  deprived  of  its  fibrinuplastic  powers  by  exposure  to  a  tempera- 
ture of  56""  or  58°  C.  without  any  change  in  its  ordinary  charajters 
points  it  is  true  in  that  direction,  but  his  further  statement  that 
specimens  of  hydrocele  fluid  whicH  refuse  to  clot  on  the  simple 
addition  of  the  ferment,  but  do  so  on  the  further  addition  of  para- 
globulin,  may  yet  contain  a  considerible  qu.mtity  of  a  body  app.irenlly 
identical  with  para;4lobulin,  shew  that  further  study  of  the  whole 
subject  is  still  required. 

This  conception  of  coagulation  as  a  chemical  process  between 
certain  factors  renders  easy  of  comprehension  the  influence  of 
various  conditions  on  the  coagulation  of  blood.  The  quickening 
inlluence  of  heat,  the  retarding  effect  of  cold,  the  favourabl.; 
action  of  motion  and  of  contact  with  surfaces,  and  hence  the 
results  of  whipping  and  the  influence  exerted  by  the  form  and 
surface  of  vessels,  become  intelligible.  The  greater  the  number 
of  points,  that  is  the  larger  and  rougher  the  surface  presented  by 
the  vessel  into  which  blood  is  shed,  the  more  quickly  coagulation 
comes  on,  for  contact  with  surfaces  favours  chemical  union.  So 
also  the  presence  of  spongy  platinum,  or  of  an  inert  powder  like 
charcoal,  quickens  the  coagulation  of  tardily  clotting  fluids,  such 
as  many  cases  of  pericardial  fluid. 

The  action  of  neutral  salts  is  still  obscure.  Schmidt  has  shewn 
that  the  presence  of  a  neutral  salt,  such  as  sodium  chloride,  is 
essential  to  the  process,  coagulation  not  occurring  even  where  all 
three  factors  are  present,  if  no  neutral  salt  accompany  them  ;  thus 
bringing  tibrin  coa^uilation  after  all  into  the  same  category  as  the 
coagulaiion  of  albu.nin  by  heat :  see  Appendix.  The  presence  of 
hienioglobin  also,  independently  of  the  fibrinoplistin  which  may  be 
present  in  the  red  corpuscles,  appears  to  favour  coagulation. 

Having  thus  arrived  at  an  approximative  knowledge  of  the 
nature  of  coagulation,  we  are  in  a  better  position  for  discussing 
the  question,  \\'hy  does  blood  remain  fluid  in  tlie  vessels  of  the 
living  body  and  yet  clot  when  shed  ? 

The  older  views  may  be  at  once  summarily  dismissed.  The 
clotting  is  not  due  to  loss  of  temperature,  for  cold  retards  coagu- 
lation, and  the  blood  of  cold-blooded  animals  bjhaves  just  like 
that  of  warm-blooded  animals  in  clotting  when  shed.  It  is  not 
due  to  loss  of  motion,  ibr  motion  favours  coagulation.  It  is  not 
due  to  exposure  to  air,  whereby  either  an  increased  access  of 
oxygen  or  an  escape  of  volatile  matters  is  facilitated,  for  on  the 
one  hand  the  blood  is  fully  exposed  to  the  air  in  the  lungs,  and 

»  TRviger's  Arc/iiv,  xviii.  (187S),  p.  38 


24  INFLUENCE  OF   LIVING  BLOOD-VESSELS.      [BOOK   I. 

on  the  other  shed  blood  clots  when  received,  without  any  exposure 
to  the  atmosphere,  in  a  closed  tube  over  mercury. 

All  the  facts  known  to  us  point  to  the  conclusion,  that  when 
blood  is  contained  in  healthy  living  blood-vessels,  a  certain  relation 
or  equilibrium  exists  between  the  blood  and  the  containing  vessels 
of  such  a  nature  that  as  long  as  this  equilibrium  is  maintained  the 
blood  remains  fluid,  but  that  when  this  equilibrmm  is  disturbed  by 
events  in  the  blood  or  in  the  blood-vessels  or  by  the  removal  of 
the  blood,  the  blood  undergoes  changes  which  result  in  coagu- 
lation. The  most  salient  facts  in  support  of  this  conclusion  are  as 
follows. 

1.  After  death,  when  all  motion  of  the  blood  has  ceased, 
the  blood  remains  for  a  long  time  fluid.  It  is  not  till  some  time 
afterwards,  at  an  epoch  when  post-mortem  changes  in  the  blood 
and  in  the  blood-vessels  have  had  time  to  develop  themselves, 
that  coagulation  begins.  Thus  some  hours  after  death  the  blood 
in  the  great  veins  may  be  found  perfectly  fluid.  Yet  such  blood 
has  not  lost  its  power  of  coagulating ;  it  still  clots  when  removed 
from  the  body,  and  clots  too  when  received  over  mercury  without 
exposure  to  air,  shewing  that  the  fluidity  of  the  highly  venous 
blood  is  not  due  to  any  excess  of  carbonic  acid  or  absence  of 
oxygen.  Eventually  it  does  clot  even  within  the  vessels,  but 
never  so  firmly  and  completely  as  when  shed.  It  clots  first  in 
the  larger  vessels,  remaining  for  a  very  long  time,  for  many  hours 
in  fact,  fluid  in  the  smaller  veins,  where  the  same  bulk  of  blood 
is  exposed  to  the  influence  of,  and  reciprocally  exerts  an  influence 
on,  a  larger  surface  of  the  vascular  walls  than  in  the  larger  veins. 
Thus  if  the  foot  of  a  sheep  be  ligatured  and  amputated,  the  blood 
in  the  small  veins  will  be  found  fluid  and  yet  coagulable  for  many 
hours. 

2.  If  the  vessels  of  the  heart  of  a  turtle  (or  any  other  cold- 
blooded animal)  be  ligatured,  and  the  heart  be  cut  out  and 
suspended  so  that  it  may  continue  to  beat  for  as  long  a  period 
as  possible,  the  blood  will  remain  fluid  within  the  heart  as  long  as 
the  pulsations  go  on,  i.e.  for  one  or  two  days  (and  indeed  for  some 
time  afterwards),  though  a  portion  taken  away  at  any  period  of 
the  experiment  will  clot  very  speedily.'^ 

3.  If  the  jugular  vein  of  a  large  animal,  such  as  an  ox-  or 
horse^  be  ligatured  when  full  of  blood,  and  the  ligatured  portion 

»  Briicke,  Brit,  and  For.  Med.  Chir.  Review,  xix.  p.  183  {1857). 


CHAI'.    l]  BLOOD.  25 

excised,  the  blood  in  many  cases  remains  perfectly  fluid,  along  the 
greater  part  of  the  length  of  the  piece,  for  twenty-four  or  even 
forty-eight  hours.  The  piece  so  ligatured  may  be  suspended  in  a 
framework  and  opened  at  the  top  so  as  to  imitate  a  living  test- 
tube,  and  yet  the  blood  will  often  remain  long  .fluid,  though  a 
Dortion  removed  at  any  time  into  another  vessel  will  clot  in  a 
few  minutes.  If  two  such  living  test-tubes  be  prepared,  the 
blood  may  be  poured  from  one  to  the  other  without  coagulation 
taking  place.' 

The  above  facts  illustrate  the  absence  of  coagulation  in  intact 
or  slightly  altered  living  blood-vessels ;  the  following  shew  that 
coagulation  may  take  place  even  in  the  living  vessels. 

4.  If  a  needlQ  or  piece  of  wire  or  thread  be  introduced  into 
the  living  blood-vessel  of  an  animal,  either  during  life  or  im- 
mediately after  death,  the  piece  will  be  found  encrusted  with 
fibrin. 

5.  If  in  a  living  animal  a  blood-vessel  be  ligatured,  the 
ligature  being  of  such  a  kind  as  to  injure  the  inner  coat,  coagu- 
lation takes  place  at  the  ligature  and  extends  for  some  distance 
from  it.  Thus  if  the  jugular  vein  of  a  rabbit  be  ligatured  roughly 
in  two  places,  clots  will  in  a  few  hours  be  found  in  the  ligatured 
portion,  reaching  upwards  and  downwards  from  each  ligature,  the 
middle  portion  being  the  least  coagulated.  Clots  will  also  be 
found  on  the  far  side  of  each  ligature.  The  clots  will  still  appear 
if  the  ligature  be  removed  immediately  after  being  applied, 
provided  that  in  the  process  the  inner  coat  has  been  wounded. 
If  the  ligatures  be  applied  in  such  a  way  as  not  to  injure  the 
inner  coat,  coagulation  will  not  take  place,  though  the  blood 
may  remain  for  many  hours  perfectly  at  rest  between  the  ligatures. 

6.  "When  an  artery  is  ligatured  a  conspicuous  clot  is  formed 
on  the  cardiac  side  of  the  ligature.  The  clot  is  largest  and  firmest 
in  die  immediate  neighbourhood  of  the  ligature,  gradually  thinning 
away  from  thence  and  reaching  usually  as  far  as  where  a  branch 
is  given  off.  Between  this  branch  and  the  ligature  there  is  stasis ; 
the  walls  of  the  artery  suffer  from  the  want  of  renewal  of  blood, 
and  thus  favour  the  proj^agation  of  the  coagulation.  On  the 
distal  side  of  the  ligature  where  the  artery  is  much  shrunken,  the 
clot  which  is  formed,  though  naturally  small  and  inconspicuous,  is 
similar. 

'  Lister,  Proc,  Roy.  Soc,  xil.  p.  580  (1S5S). 


26  SOURCES   OF   THE   FIBRIN-FACTORS.        [BOOK   I. 

7.  Any  injury  of  the  inner  coat  of  a  blood-vessel  causes  a 
coagulation  at  the  spot  of  injury.  Any  treatment  of  a  blood- 
vessel tending  to  injure  its  normal  condition  causes  local 
coagulation. 

8.  Disease  involving  the  inner  coat  of  a  blood-vessel  causes 
a  coagulation  at  the  part  diseased.  Thus  inflammation  of  the 
lining  membrane  of  the  valves  of  the  heart  in  endocarditis  is 
frequently  accompanied  by  the  deposit  of  fibrin.  In  aneurism 
the  inner  coat  is  diseased,  and  layers  of  fibrin  are  commonly 
deposited.  So  also  in  fatty  and  calcareous  degeneration  without 
any  aneurismal  dilation  there  is  a  tendency  to  the  formation  of 
clots. 

9.  Similar  phenomena  are  seen  in  the  case  of  serous  fluids 
which  coagulate  spontaneously.  If,  as  soon  after  death  as  the 
body  is  cold  and  the  fat  is  soUdified,  the  pericardium  be  carefully 
removed  from  a  sheep  by  an  incision  round  the  base  of  the  heart, 
the  pericardial  fluid  may  be  kept  in  the  pericardial  bag  as  in  a 
living  cup  for  many  hours  without  clotting,  and  yet  a  small  portion 
removed  with  a  pipette  clots  at  once,  and  a  thread  left  hanging 
into  the  fluid  soon  becomes  covered  with  fibrin. 

The  only  interpretation  which  embraces  these  facts  is  that  so 
long  as  a  certain  normal  relation  between  the  lining  surfaces  of 
the  blood-vessels  and  the  blood  is  maintained,  coagulation  does 
not  take  place ;  but  when  this  relation  is  disturbed  by  the  more  or 
less  gradual  death  of  blood-vessels,  or  by  their  more  sudden 
disease  or  injury,  or  by  the  presence  of  a  foreign  body,  coagu- 
lation sets  in.  Two  additional  points  may  here  be  noticed. 
I.  Stagnation  of  blood  favours  coagulation  within  the  blood- 
vessels, apparently  because  the  blood-vessels,  like  other  tissues,' 
demand  a  renewal  of  the  blood  on  which  they  depend  for  the 
maintenance  of  their  vital  powers.  2.  The  influence  of  surface 
is  seen  even  in  the  coagulation  within  the  vessels.  In  cases  of 
coagulation  from  gradual  death  of  the  blood-vessels,  as  in  the 
case  of  an  excised  jugular  vein,  the  fibrin,  when  its  deposition  is 
sufficiently  slow,  is  seen  to  appear  first  at  the  sides,  and  from 
thence  gradually,  frequently  in  layers,  to  make  its  way  to  the 
centre.  So  in  aneurism,  the  deposit  of  fibrin  is  frequently  lami- 
nated. In  cases  where  coagulation  results  from  disease  of  the 
lining  membrane,  the  rougher  the  interior,  the  more  speedy  and 
complete  the  clotting.  So  also  a  rough  foreign  body,  presenting 
a  large  number  of  surfkces  and  points  of  attachment,  more  readily 
produces  a  clot  when  introduced  into  the  living  blood-vessels  than 
a  perfectly  smooth  one. 


CHAP.    I.]  BLOOD.  27 

Clear  as  it  seems  to  be  that  some  vital  relation  of  blood  to 
blood-vessel  is  the  dominant  condition  affecting  coagulation,  it  is  by 
no  means  easy  to  state  distinctly  what  is  the  exact  nature  of  that 
relation.  Some  authors'  speak  of  the  blood-vessels  as  exercising 
a  restraining  influence  on  the  natural  tendency  of  the  blood  to 
coai^ulate.  Others  =»  regard  the  living  blood-vessel  (and  indeed 
living  matter  in  general)  as  being  wholly  inert  towards  the  fibrin- 
factorp.  These  they  consider  need  the  presence,  the  contact 
iqlluence  of  some  body,  in  order  that  they  may  act  on  each  other 
to  form  fibrin  ;  thus  contact  with  the  sides  of  the  vessel  into  which 
blood  is  shed,  or  with  the  surface  of  a  foreign  body  introduced 
into  a  living  vessel,  is,  according  to  them,  liie  determining  cause  of 
coagulation.  They  suppose  that  living  matter  exercises  no  such 
contact  influence. 

Before  this  point  can  be  decided,  further  knowledge  is  needed 
conccrr>ing  the  exact  condition  of  the  tibrin-factors  in  living  blood 
within  the  body.  While  the  blood  is  flowing  uncoagulated  through 
the  vessels  are  all  the  three  fibrin-factors,  pardglobulin,  fibrinogen  and 
ferment,  already  present  in  plasma  ?  Or  are  they  all,  or  is  one  or  two 
absent,  and  if  so  is  the  appearance  of  them,  or  of  one  of  them,  in  the 
plasma,  the  necessary  invisible  forerunner  of  coagulation  ?  Our  scanty 
information  on  this  point  may  be  summarized  as  follows. 

1.  In  all  spontaneously  coagulable  fluids  white  corpuscles  are 
present,  and  the  more  abundant  they  are,  the  mere  pronounced  is  the 
coagulation.  Thus  the  spontaneously  coagulating  pericardial  fluid  is 
exceedingly  rich  in  white  corpuscles,  and  the  clot  formed  seems  under 
the  microscope  to  be  almost  entirely  composed  of  them,  so  completely 
do  they  hide  the  threads  of  fibrin.  In  the  specimens  of  pericardial 
and  of  hydrocele  fluid  which  do  not  coagulate  spontaneously  white 
corpuscles  are  absent,  or  at  least  scanty. 

2.  The  deposition  of  fibrin  round  a  thread  if  dipped  into  a  coagu- 
lable fluid  or  dniwn  through  a  blood-vessel  and  left  there,  is  preceded 
by  an  accumulation  of  white  corpuscles.  These  cluster  in  great 
numbers  round  the  thread,  and  when  the  mass  is  examined  under 
the  microscope  the  corpuscles  seem  to  serve  as  starting  points  for  the 
development  of  the  threads  of  fibrin. 

3.  In  the  experiment  of  keeping  blood-fluid  but  coagulable  in  an 
excised  jugular  vein  (of  the  horse),  it  is  observed  that  when,  as  in 
course  of  time  happens,  the  corpuscles  have  sunk  to  the  bottom  of  the 
piece  of  vein,  the  upper  la\ers  of  clear,  corpuscle-free,  plasma  clot  very 
feebly  indeed  when  removed  from  the  vein,  whereas  the  lower  layers 
rich  in  corpuscles  clot  most  firmly. 

4.  When  horse's  blood  is  received  from  a  blood-vessel  into  an  ice-cold 
dilute  solution  of  chloride  of  sodium,  and  the  mixture  kept  just  short 

'  Briickc,  op.  cit.  »  Lister,  op.  cU. 


28  SOURCES   OF   THE  FIBRIN-FACTORS.  [BOOK   I. 

oi  actually  freezing,  the  whole  mass  of  corpuscles  sinks  rapidly.  It  is 
then  observed  that  the  dilute  plasma  free  from  corpuscles  clots  feebly, 
whereas  the  lower  layers  of  the  same:  dilute  plasma,  containing  all  the 
corpuscles,  gives  an  abundant  coagulation.  Plasma  of  horse's  blood 
may  bs  diluted  with  twelve  times  its  bulk  of  distilled  water  and  fil- 
tered, without  coagulation  setting  in,  provided  that  the  whole  operation 
is  conducted  at  a  temperature  just  short  of  freezing.  The  filtered  diluted 
plasma,  which  is  found  to  be  exceedingly  free  from  white  corpuscles, 
these  being  left  on  the  filter,  clots  feebly ;  the  amount  of  fibrin  it 
produces  is  less  than  half  that  obtainable  from  the  same  diluted 
plasma  unfiltered\ 

These  facts  point  very  decidedly  to  the  conclusion  that  the  white 
corpuscles  have  some  share  in  bringing  about  coagulation  ;  they 
moreover  suggest  that  one  or  more  of  the  fibrin-factors  have  their 
source  in  the  white  corpuscles,*  and  that  coagulation  is  due  to  the 
passage  of  these  elements  from  the  body  of  the  corpuscle  into  the 
plasma.     The  latter  view  is  corroborated  by  the  following  facts. 

5.  In  defibrinated  blood  or  blood-serum  a  certain  amount  of 
fibrin-ferment  is  present.  If  however  blood  be  treated  with  alcohol 
immediately  on  leaving  the  blood-vessels,  very  little  ferment  indeed  is 
found  to  be  present.  The  quantity  is  found  to  increase  from  the 
moment  of  leaving  the  vessels  to  the  onset  of  coagulation.  The 
fibrin-ferment  therefore  is  developed  from  some  part  of  the  blood. 

If  horse's  blood  be  kept  at  freezing  temperature,  the  formation  of 
ferment  is  arrested.  If  after  the  corpuscles  have  sunk  the  undermost 
layers  of  the  blood,  containing  almost  exclusively  red  corpuscles,  be 
removed,  little  or  no  ferment  can  be  obtained  from  this  portion,  either 
when  examined  immediately,  or  after  being  allowed  to  clot  at  an  ordinary 
temperature.  In  a  portion  taken  from  the  upper  layers  (colourless 
plasma)  of  the  same  blood,  while  there  is  little  or  no  ferment  present 
before  the  co.igulation  of  the  specimen,  there  is  abundance  afterwards. 
If  a  similar  portion  of  the  same  colourless  plasma  be  filtered  in  the  cold, 
the  filtrate,  which  is  nearly  free  from  white  corpuscles,  is  very  poor  in 
ferment  both  before  and  after  the  feeble  and  slow  coagulation  which 
the  fluid  undergoes  ;  the  material  on  the  filter,  consisting  almost 
entirely  of  white  corpuscles,  is  very  rich  in  ferment.  These  facts 
seem  to  shew  that  the  fibrin-ferment  which  is  present  in  bood-serum 
has  its  source,  not  in  the  red  but  in  the  white  corpuscles,  and  that  the 
passage  of  the  ferment  from  the  white  corpuscle  into  the  plasma  is  a 
precursor  of  coagulation. 

6.  The  coagulation  of  filtered  diluted  plasma  has  been  said  to  be 
both  feeble  and  slow.  The  tardiness  of  the  coagulation  is  due  to  the 
paucity  of  ferment ;  the  feebleness,  i.e.  the  small  quantity  of  fibrin 
produced,  must  be  due  to  the  scantiness  of  one  or  both  of  the  fibrin- 
factors.  On  adding  paraglobuhn  the  quantity  of  fibrin  produced  is  the 
same  as  that  given  by  the  same  cjuantity  of  unfiltered  plasma.  The 
filtered  plasma  is  therefore  deficient  in  paraglobuhn.  The  material  left 
on  the  filter  is  rich  in  paraglobuhn.     The  inference  which  A.  Schmidt 

'  A.  Schmidt,  op.  cit. 


CHAP.    I.J  liLOUD.  29 

draws  from  these  facts,  is  that  paraj^lobiilin,  like  the  fibrin-ferment, 
has  its  origin  in  the  white  corpuscles,  but  that  fibrinogen  is  a  normal 
constituent  of  the  plasma. 

7.  If  a  drop  of  horse's  plasma  kept  from  coagulating  by  cold  be 
examined  under  the  microscope,  it  will  be  found  to  contain  a  large 
number  of  white  corpuscles,  mixed  with  which  according  to  A.  Schmidt 
are  corpuscles  of  an  intermediate  character  between  white  and  red,  i.e. 
nucleated  cells  whose  protoplasm  is  loaded  with  coloured  hiemoglobin 
granules.  As  the  drop  is  watched,  a  large  number  of  the  white 
corpuscles  and  all  the  intermediate  forms  are  seen  to  break  up  into  a 
granular  detritus.  'I'liis  breaking  up  of  the  white  corpuscles  is  the 
precursor  of  coagulation,  the  threads  of  fibrin  seeming  to  start  from 
the  remains  of  the  corpuscles.  Putting  all.  these  facts  together, 
Schmidt  concludes  that  when  blood  is  shed,  a  number  of  white  and 
intermediate  corpuscles  fall  to  pieces,  by  which  act  a  quantity  of 
fibrin-ferment  and  of  paraglobulin  is  discharged  into  the  plasma. 
These  meeting  there  with  the  already  present  fibrinogen  give  rise  to. 
fibrin,  and  coagulation  results.  In  other  mammals  coagulation  even 
at  low  temperatures  is  too  rapid  to  permit  of  the  changes  in  the 
corpuscles  being  watched  as  satisfactorily  as  in  the  horse,  but  even  in 
these  evidences  of  the  existence  of  intermediate  forms  may  be  met 
with. 

This  view  exclades  the  red  corpuscles,  as  far  as  mammals  are 
concerned,  fiom  any  direct  share  in  coagulation.  Whether  this  ulti- 
mately prove  to  be  correct  or  not,  there  are  facts  which  shew  that  the 
nucleated  red  corpuscles  of  other  vertebrates,  which  it  must  be 
remembered  are  the  homologues  of  the  intermediate  forms,  have  a 
much  clearer  connection  with  the  process.  If  the  defibrinated  blood 
of  the  frog  or  the  bird  be  allowed  to  stand  until  the  corpuscles  have 
subsided,  the  latter,  separated  as  much  as  possible  from  the  serum, 
and  treated  with  a  considerable  quantity  of  distilled  water,  yield  a 
filtrate  which  coagulates  spontaneously.  That  is  to  say,  the  water 
breaks  up  the  red  corpuscles  and  sets  free  a  quantity  of  fibrin-factors 
which  otherwise  would  have  remained  latent.  The  amount  of  fibrin 
thus  obtained  may  be  considerably  greater  than  the  quantity  originally 
appearing  in  the  blood.  It  is  worthy  of  notice,  that  in  this  case  the 
corpuscle  is  the  source,  not  only  of  the  fibrin-ferment  and  paraglobulin, 
but  also  of  the  fibrinogen. 

Accepting  this  view  as  approximately  correct,  the  coagulation  of 
shed  blood  may  be  referred  to  the  circumstance,  that  even  the  com- 
paratively slight  changes  which  must  take  place  in  the  blood  on  its 
leaving  the  vessels  are  sufficient  to  entail  the  death,  and  so  the 
breaking  up,  of  a  number  of  the  delicate  white  corpuscles.  The 
formation  of  clots  within  the  body  is  not  so  easy  to  explain.  We  are 
driven  in  these  cases  to  suppose  that  injured  and  diseased  spots  or 
foreign  bodies  first  attract,  and  then,  as  it  were  by  irritation,  cause  the 
death  of  a  certain  number  of  corpuscles. 

But  in  any  case,  if  tliis  view  be  admitted,  it  must  also  be  granted 
that  the  blood-vessels  do  in  some  manner  or  other  exercise  a  re- 
straining influence  on  the  formation  of  fibrin. .    For  many  of  these 


30  CHEMICAL   COMPOSITION   OF   BLOOD.       [BOOK  I. 

corpuscles  must,  in  the  natural  course  of  events,  die  and  break  up  in 
the  blood-stream,  without  causing  coagulation.  Further,  defibrinated 
blood  contains  both  fibrin-ferment  and  paraglobulin  ;  it  ought,  there- 
fore, when  injected  into  the  vessels  which  already  in  the  natural  blood 
contain  fibi'inogen,  to  occasion  a  rapid  and  speedy  general  coagulation. 
This  it  does  not.  The  coagulations  which  occur  after  transfusion  of 
defibrinated  blood  are  partial  and  uncertain.  We  might  infer  from 
this  that  the  system  has  some  power  of  rapidly  either  destroying 
ferment  or  changing  the  properties  of  paraglobulin.  In  support  of 
this  it  has  been  stated,  that  a  quantity  of  fibrin-fennent  injected  into 
the  system  may  be  detected  in  the  blood  immediately  afterwards  (and 
is  present  then  without  causing  coagulation),  but  speedily  disappears. 
The  loss  of  spontaneous  coagulability  in  pericardia]  fluid  inight  be 
attributed  to  an  escape  -by  migration  of  the  white  corpuscles  away 
froin  the  pericardial  cavity,  but  this  is  inconsistent  with  the  fact  that 
in  the  majority  of  cases  the  ferment  alone  disappears  while  the  para- 
globulin remains.  According  to  the  facts  given  above,  the  white 
corpuscles  in  escaping  would  carry  away  both  ferment  and  paraglo- 
bulin, leaving  the  fibrinogen  alone.  Moreover  it  must  be  remembered 
that,  as  was  mentioned  on  p.  22,  Schmidt's  view  of  the  fibrinoplastic 
function  of  paraglobalin  is  not  accepted  by  all  investigators  ;  and 
some  authors^  while  agreeing  with  Schmidt  that  the  white  corpuscles 
are  the  source  of  the  fibrin-factors,  differ  from  him  in  so  far  that  they 
believe  that  the  fibrinogen  as  well  as  the  fibrin-ferment  arise  from 
these  bodies,  paraglobulin  according  to  them  having  nothing  to  do 
with  the  matter. 

Lastly,  we  should  remember  that  all  the  above,  even  if  correct,  is 
only  an  approximative  solution.  The  coagulation  of  muscle-plasma 
is  a  coagulation  in  which  white  corpuscles  cannot  serve  as  dei  ex 
mackma ;  moreover,  as  we  shall  see  later  on,  the  rigor  mortis  of  the 
white  corpuscle  itself  is  a  coagulation  ;  and  for  this  its  own  sub- 
sequent disintegration  cannot  be  regarded  as  an  adequate  cause. 

Sec.  2.     The  Chemical  Composition  of  Blood. 

The  average  specific  gravity  of  human  blood  is  1055,  varying 
from  1045  to  1075  within  the  limits  of  health.  The  reaction  of 
blood  as  it  flows  from  the  blood-vessels  is  found  to  be  distinctly 
alkaline. 

According  to  Zuntz^,  the  alkalescence  of  shed  blood  rapidly 
diminishes  up  to  the  onset  of  coagulation.  Other  observers  have 
however  maintained  that  the  serum  is  more  alkahne  than  the  un- 
coagulated  blood,  or  cruor. 

Blood  may,  in  general  terms,  be  considered  as  consisting  by 
weight  of  from  about  one-third  to  somewhat  less  than  one-half  of 

'  Fredericq,  L.,  Recherches  sur  ta  Coagulation  du  Sang.     Bruxelles,  1877. 
"  Centralbt.  f.  med.  Wiss.,  1867,  p.  801. 


CHAP.    I..]  BLOOD,  31 

corpuscles,  the  rest  being  plasma,  the  corpuscles  being  supposed 
ta  retain  the  amount  of  water  proper  to  them. 

Hoppe-Scyler  gives,  in  1000  parts  of  the  venous  blood  of  the 
horse,  Corpuscles  326,  Plasma  674'.  As  will  be  seen  in  the  suc- 
ceeding sections,  the  number  of  corpuscles  in  a  specimen  of  blood 
is  found  to  vary  considerably,  not  only  in  different  animals  and 
in  different  individuals,  but  in  the  same  individual  at  different 
times. 

Conspicuous  and  striking  as  are  the  results  of  coagulation, 
massive  as  appears  to  bo  the  clot  which  is  f(;rmed,  it  must  be 
remembered  that  by  far  the  greater  part  of  the  clot  consists  of 
corpuscles.  The  amount  by  weight  of  fibrin  required  to  bind 
together  a  number  of  corpuscles  in  order  to  form  even  a  large  firm 
clot  is  exceedingly  small.  Thus  the  average  quantity  by  weight 
of  fibrin  in  human  blood  is  said  to  be  '2  p.  c,  but  the  amount 
which  can  be  obtained  from  a  given  quantity  of  plasma  varies 
extremely;  the  variation  being  due  not  only  to  circumstances 
affecting  the  blood,  but  also  to  the  method  employed. 

The  difficulties  indeed  of  acquiring  an  exact  knowledge  of  the 
chemical  constitution  of  the  plasma,  which  as  we  have  seen  from  the 
foregoing  section  is  probably  undergoing  changes  from  the  moment 
of  being  shed,  are  very  great ;  our  information  concerning  the 
composition  of  the  serum  and  of  the  corpuscles  is  much  more 
trustworthy. 

Composition  of  serum.  In  100  parts  of  serum  there  are  in 

round  numbers    Water     90  parts 

Proteid  Substances       8  to  9      „ 

Fats,  Extractives^,  and  Saline  Matters  2  to  i      „ 

The  porteid  substances  predentin  serum  are  : — (i)  The  so- 
called  serum-albiimiti^  (2)  paraglobulin.  The  paraglobulin,  as  has 
been  stated  in  the  preceding  section,  may  be  removed  from  the 
serum  in  several  ways  :  viz.,  by  passing  carbonic  acid  through  or 
by  cautiously  adding  dilute  acetic  acid  to  the  diluted  serum,  or 
by  saturating  the  undiluted  serum  with  sodium  chloride  or  mag- 
nesium sulphate.  When  this  has  been  done  a  considerable  quantity 
of  proteid  material  is  still  left  in  the  serum  in  the  form  known  as 
serum  albumin,  distinguished  from  paraglobulin  among  other 
characters  by  its  being  soluble  in  distilled  water,  and  therefore  not 

'  For  the  various  methods  of  determination  see  Hoppe-Seyler,  Ildb.  PhysioU 
Chan.  Analyse,  p.  327. 

'  Tiiis  word  i>;  used  to  den  >te  soluble  substances  of  varied  origin  and  nature, 
occurring  in  small  quantities,  and  therefore  requiring  to  be  'extracted'  by 
spucial  means. 


32  COMPOSITION   OF   SERUM.  [BOOK   I. 

requiring  for  its  solution  the  presence  of  a  neutral  salt^  When 
serum,  after  the  cautious  addition  of  acetic  acid  in  order  to  neu- 
tralize its  alkalinity,  is  heated  to  about  75°  C.  both  the  serum 
albumin  and  paraglobulin  are  thrown  down  in  the  form  known  as 
coagulated  proteids,  substances  characterized  by  their  great  inso- 
lubility. This  '  coagulation  '  by  heat  of  these  and  other  proteids 
is,  it  perhaps  need  hardly  be  said,  not  to  be  confounded  with  the 
coagulation  of  plasma  due  to  the  appearance  of  fibrin. 

Many  authors  have  distinguished  between  the  deposit  caused  by 
the  passage  of  carbonic  acid  through  the  dilute  serum,  and  the 
further  precipitate  of  proteid  material,  which  may  be  gained  by  the 
subsequent  addition  of  dilate  acetic  acid.  The  former  is  generally 
fibrinoplastic,  i.e.  will  give  rise  to  fibrin  when  added  to  fibrinogenous 
liquids.  The  latter  will  not  do  so,  and  has,  on  this  account,  and 
for  the  reason  that  it  is,  or  speedily  becomes  insoluble  in  dilute 
neutral  saline  solution,  been  distinguished  from  paraglobulin  under 
the  name  of  se7'iuji-casein  or  alkali  albn7nin'^.  The  presence  or 
absence  of  fibrinoplastic  powers  appears,  in  the  present  state  of  our 
knowledge,  at  all  events,  to  be  an  unsatisfactory  character  by  which 
to  distinguish  one  form  of  proteid  from  another,  and  it  seems  on  the 
whole  the  best  to  recognize  only  one  proteid  as  existing  in  serum 
besides  serum-albumin,  and  to  call  it  paraglobulin s.  Hammarsten* 
finds  that  saturation  with  magnesium  sulphate  is  a  more  trustworthy 
means  of  throwing  down  paraglobulin  than  the  saturation  with  sodium 
chloride  generally  employed  ;  and  by  the  use  of  this  method  has  come 
to  the  conclusion  that  the  quantity  of  paraglobulin  present  in  serum 
has  been  greatly  underrated.  It  has  hitherto  been  generally  spoken  of 
as  existing  in  small  quantities  only,  but  Hammarsten  has  estimated  it 
as  varying  in  different  animals  from  1788  p.  c.  (rabbit)  to  4'S65  p.  c. 
(horse),  the  serum-albumin  ranging  from  4'436  p.  c.  (rabbit)  to  2*677 
p.  c.  (horse).  In  human  blood  he  found  3' 103  p.  c.  paraglobulin,  and 
4*5 1 6  p.  c.  serum-albumin. 

The  fats,  which  are  scanty,  except  after  a  meal  or  in  certain 
pathological  conditions,  are  the  neutral  fats,  stearin,  palmitin,  and 
olein,  with  a  certain  quantity  of  their  respective  alkaline  soaps. 
Lecithin  s  and  cholesterin  occur  in  very  small  quantities  only. 
Among  the  extractives  present  in  serum  may  be  put  down  all  the 
nitrogenous  and  other  substances  which  form  the  extractives  of 
the  body  and  of  food,  such  as  urea,  kreatin,  sugar,  lactic  acid,  &c. 

^  For  further  details  see  Appendix. 

*  See  Appendix. 

3  Cf.  Weyl,  Zt.f.  physiolog.  Chem.,  I.  (1877)  p.  72. 

*  Pfliiger's  Archiv,  XVII.  (1878)  p.  413. 

5  For  detailed  accounts  of  the  characters  of  the  several  chemical  substances 
mentioned  in  this  and  succeeding  chapters  consult  the  Appendix  under  the 
appropriate  headings. 


CHAP.    I.]  BLOOD.  33 

A  very  large  number  of  these  have  been  discovered  in  the  blood 
under  various  circunis'ances,  the  consideration  of  v/hich  must 
be  left  for  the  present.  The  peculiar  odour  of  blood-serum  is 
probably  due  to  the  presence  of  volatile  bodies  of  the  fatty  acid 
series.  The  faint  yellow  colour  of  serum  is  due  to  a  special 
yellow  pigment.  The  most  characteristic  and  important  chemical 
feature  of  the  saline  constitution  of  the  serum  is  the  preponder- 
ance of  sodium  salts  over  those  of  potassium.  In  this  respect 
the  serum  offers  a  marked  contrast  to  the  corpuscles  (see  below). 
Less  marked,  but  still  striking,  is  the  abundance  of  chlorides  and 
the  poverty  of  phosphates  in  the  serum  as  compared  with  the 
corpuscles.  The  salts  may  in  fact  briefly  be  described  as  consist- 
ing chiefly  of  sodium  chloride,  with  small  quantities  of  sodium 
carbonate,  sodium  sulphate,  sodium  phosphate,  calcium  phosphate, 
and  magnesium  phosphate. 

Composition  of  the  red  corpuscles.  The  corpuscles 
contain  less  water  than  the  serum.  In  loo  parts  of  wet  corpuscles 
there  are  of  Water  56*5  pans 

Solids  43-5     ,, 

The  solids  are  almost  entirely  organic  matter,  the  inorganic  salts  in 
the  corpuscles  amounting  to  less  than  i  p.  c.  Of  the  organic 
matter  again  by  flir  the  larger  part  consists  of  hremoglobin.  In 
100  parts  of  the  dried  organic  matter  of  the  corpuscles  of  human 
blood,  Jiidell'  found,  as  the  mean  of  two  observations, 

Haemoglobin  9° '54  Lecithin  -54 

Proteid  Substances  S'67  Cholesterin  '25 

The  composition  and  properties  of  haemoglobin  will  be  considered 
in  connection  with  respiration.  Of  the  proteid  substances  which 
form"  the  stroma  of  the  non- nucleated  red  corpuscles  this  much 
may  be  said,  that  they  belong  to  the  globulin  family.  The  amount 
of  fibrinoplastic  paraglobulin,  and  the  exact  nature  of  the  other 
members  of  the  group  present,  must  be  considered  as  yet  unde- 
termined. As  regards  the  inorganic  constituents,  the  corpuscles 
are  distinguished  by  the  relative  abundance  of  the  salts  of  potas- 
sium and  of  phosphates. 

The  distribution  of  inorganic  salts  in  blood  may  be  seen  from  the 
following  analysis  by  C.  Schmidt  of  the  ash  of  plasma  and  corpuscles 
respectively  (the  iron  which  belongs  almost  exclusively  to  the  lucmo- 
globin=  of  the  red  corpuscles  and  exists  in  mere  traces  only  in  the 
serum  or  plasma  being  omitted). 

'  Hoppe-Seyler,  Untcrsuch.  III.  390. 

'  lia-nugl  )bin  contains  -4  to  "5  p.c.  of  Fe,  and  the  quantity  of  iron  in  the 
blood  will  depend  on  the  quantity  of  haemoglobin. 

F.  P.  3 


34-  COMPOSITION   OF   THE   CORPUSCLES.       [BOOK  I. 

In  looo  parts  Corpuscles.  In  looo  parts  Plasma. 

Potassium  chloride     3*679  ~ 

„  sulphate      '132 

„         phosphate  a -343 
Sodium  .„  '633 

Calcium  „  "094 

Magnesium      „  '060 

Soda  •341 


7-282 


Potassium  chloride 
„          sulphate 

•359 
•281 

Sodium  phosphate 

Calcium        „ 

Magnesium  „ 

Soda 

Sodium  chloride 

■271 

•298 

•218 

I  "532 

5546 

8-505 

It  must  be  remembered  that  the  arrangement  of  bases  and  acids  in 
such  an  analysis  is  an  artificial  one,  and  moreover,  that  the  ash  does 
not  represent  the  inorganic  salts  present  in  a  natural  condition  in  the 
blood.  Thus  for  instance,  the  phosphates  in  the  ash  are  largely 
derived  by  oxidation  from  tKe  phosphorus  present  in  the  lecithin,  and 
the  sulphates  similarly  from  the  sulphur  of  proteid  substances.  Cn 
the  other  hand,  carbonic  anhydride  is  absent  from  the  above  table, 
though  carbonates  undoubtedly  exist  in  the  serum.  Free  soda  is  put 
down  as  a  constituent  of  the  ash,  because  in  the  ash  the  bases  pre- 
ponderate over  the  acids  (even  when  carbonic  anhydride  is  reckoned 
with  them) ;  this  alone  shews  how  little  the  salts  of  the  ash  correspond 
to  those  really  present  in  the  blood.  Among  the  natural  saline 
constituents  of  serum  may  be  enumerated  sodium  chloride,  calcic 
phosphate,  which  is  enabled  to  exist  in  a  state  of  solution  in  the 
alkaline  blood  by  reason  of  its  being  combined  in  some  way  or  other 
with  the  proteids,  and  sodium  carbonate. 

Composition  of  the  white  corpuscles.  If  it  be  permitted  to  infer 
the  composition  of  the  white  corpuscles  from  that  of  the  pus-cor- 
puscles which  they  so  closely  resemble,  they  would  seem  to  consist 
of— 

1.  Several  proteid  substances,  viz.  ordinary  albumin,  an  albumin 
like  that  of  muscle  coagulating  at  48°,  an  alkali  albumin,  a  substance 
closely  resembling  myosin  and  yet  differing  from  it,  and  a  peculiar 
form  of  proteid  material  soluble  with  difficulty  in  hydrochloric  acid. 
The  nuclei  contain  nuclein.     See  Appendix:. 

2.  Lecithin,  extractives,  glycogen,  and  inorganic  salts,  there  being 
in  the  ash  a  preponderance  of  potassium  salts  and  of  phosphates  ; 
after  the  death  of  the  corpuscle  the  glycogen  appears  to  be  converted 
into  sugar. 

Both  the  corpuscles  and  the  plasma  (or  serum)  contain  gases. 
These  will  be  considered  in  connection  with  respiration. 

The  main  facts  of  interest  then  in  the  chemical  composition 
of  the  blood  are  as  follows.  The  red  corpuscles  consist  chiefly  of 
haemoglobin.  The  solids  of  serum  consist  chiefly  of  serum- 
albumin,'  the  quantity  of  fibrin-factors  and  of   alkali   albuminate 

'  Miescher.     Hoppe-Seyler,  Untersuchungen,  iv.  441. 


CHAI'.    I.  I  BLOOn.  35 

being  small.  The  serum  or  plasma  contrnsts  with  the  corpuscles, 
inasmuch  as  the  former  contains  chiefly  chlorides  and  sodium  salts 
while  the  latter  are  richer  in  jjhosphates  and  potassium  salts.  The 
extractives  of  the  blood  are  remark;ible  rather  for  their  number 
and  variability  than  for  their  abundance,  the  most  constant  and 
important  being  periiaps  urea,  kreatin,  sugar,  and  lactic  acid. 

Sec.  3.     The  History  of  the  Corpuscles. 

In  the  living  body  red  blood-corpuscles  are  continually  bjing 
destroyed,  and  new  ones  as  continually  being  produced.  The 
proofs  of  this  are, 

I.  The  number  of  the  red  corpuscles  in  the  blood  at  any 
given  time  varies  much. 

The  number  of  corpuscles  in  a  specimen  of  blood  is  determined 
by  mixing  a  small  but  carefully  measured  quantity  of  the  blood  with 
a  large  quantity  of  some  indifferent  fluid,  and  then  actually  counting 
the  corpuscles  in  a  1-nown  minimal  bulk  of  the  mixture. 

This  may  be  done  either  by  Vierordt's  plan  (somewhat  moflified 
by  Gowers'),  in  which  a  minimal  quantity  of  the  diluted  blood, 
measured  in  a  fine  capillary  tube,  is  spread  on  a  surface  marked  out 
in  square  areas,  and  the  number  of  corpuscles  in  each  square  area 
counted  under  the  microfcope,  or  by  Malassez^,  in  which  the  diluted 
blood  is  drawn  into  a  capillary  tube  of  flattened  sides,  and  the  number 
of  corpuscles  counted  in  siiit  in  the  tube  by  means  of  an  ocular 
marked  out  in  squares,  the  microscope  being  so  adjusted  that  each 
area  of  the  ocular  corresponds  to  a  certain  capacity  of  the  capillary 
tube. 

The  average  number  of  red  corpusqjes  in  human  blood  is 
about  5  millions  in  a  cubic  millimetre ;  in  mammals  generally  it 
ranges  from  3  to  18  millions.  The  number  varies  in  different 
parts  of  the  vascular  system,  being  greater  in  the  capillaries  and 
in  the  veins  than  in  the  arteries.  It  is  increased  by  meals,  and 
diminished  by  fasting  ;  of  course,  the  number  of  corpuscles  present 
in  any  given  bulk  of  blood  being  merely  the  expression  of  the 
proportion  of  corpuscles  to  the  amount  of  plasma,  variations 
in  the  number  counted  might  and  in  certain  cases  are  probably 
caused  by  an  increase  or  decrease  in  the  quantity  of  plasma, 
occurring  while  the  actual  number  of  corjiuscles  is  stationary. 
But  many  ol  the  variations  cannot  be  so  accounted  for ;  they 
must  be  due  to  an  increase  or  decrease  of  the  total  number  of 
corpuscles  in  the  body.     After  a  very  large  reduction  of  the  total 

■■  Gruftdrist  tier  Phvsiol ^e,  p.  9.  '  Lancet,  1877,  II.  p.  497 

3  Archive^  lie  J'/tysiologie,  1874,  p.  32. 

3—2 


36  ORIGIN   OF   THE   RED   CORPUSCLES.      [BOOK  I, 

number  of  red  corpuscles,  as  by  haemorrhage  or  disease  (ansemia), 
the  normal  proportion  may  be  regained  even  within  a  very  short 
time. 

2.  There  are  reasons  for  thinking  that  the  urinary  and  bile- 
pigments  are  derivatives  of  haemoglobin.  If  this  be  so,  an 
immense  number  of  corpuscles  must  be  destroyed  daily  (and 
replaced  by  new  ones)  in  order  to  give  rise  to  the  amount  of 
urinary  and  bile-pigment  discharged  daily  from  the  body. 

3.  When  the  blood  of  one  animal  is  injected  into  the  vessels 
of  another  {ex.  gr.  that  of  a  bird  into  a  mammal),  the  corpuscles 
of  the  first  may  for  some  time  be  recognised  in  bloqcl  taken  from 
the  second  ;  but  eventually  they  wholly  disappear.  This  of  course 
is  no  strong  evidence,  since  the  destruction  of  foreign  corpuscles 
might  take  place  even  though  the  proper  ones  had  a  permanent 
existence. 

Origi?t  of  the  Red  Corpuscles. 

In  the  embryo  red  corpuscles  are  produced, 

1.  From  metamorphosis  of  certain  mesoblastic  cells  in  the 
vascular  area. 

2.  By  division  of  the  corpuscles  thus  formed. 

3.  In  a  somewhat  later  stage,  by  the  transformation  of 
nucleated  white  corpuscles,  which  probably  arise  in  the  liver  and 
spleen,  and  pass  thence  into  the  blood.  The  cell-substance 
becomes  impregnated  with  haemoglobin,  and  the  nucleus  breaks  up 
and  disappears. 

4.  By  the  direct  transformation  of  the  protoplasm  of  undiffe- 
rentiated connective-tissue  corpuscles,'  the  red  corpuscle  appearing 
first  as  a  minute  speck  in  the  protoplasmic  cell-substance,  and  sub- 
sequently enlarging  very  much  after  the  fashion  of  an  oil-globule. 

In  the  adult,  division  of  existing  corpuscles  is  at  least 
exceedingly  rare,  if  it  occurs  at  all.  In  the  spleen-pulp  small 
nucleated  coloured  corpuscles  have  been  observed  similar  to  those 
met  with  in  the  embryo  ;  transitional  forms,  shewing  the  presence  of 
haemoglobin  in  the  cell-substance  and  degeneration  of  the  nucleus, 
have  been  seen.  In  the  wide  capillaries  of  the  red  medulla  of 
bones  similar  transitional  forms  have  been  observed,  and  they 
have  also  been  noticed  in  circulating  blood. 

According  to  Alex.  Schmidt,^  in  living  unchanged  blood  these  forms 
are  abundant ;  they  break  up  and  disappear,  however,  immediately 

'  Schafei",  Froc.  Roy.  Soc,  xxii.  243.  =  Op.  cit 


CIIAl'.    I.]  IJLOOD.  j7 

that  the  blood  is  shed,  unless  sperial  precautions  (application  of  cold, 

&o.)  be  used. 

From  these  several  facts  it  is  concluded  that  the  red  corpuscles 
take  origin  from  colourless  nucleated  corpuscles  similar  to,  if  not 
identical  with,  the  ordinary  white  corpuscles  of  the  blood. 

In  the  case  of  animals  with  nucleated  red  corpuscles  the  change 
consists  chiefly  in  a  transformation  ot  the  nitive  protoplasm  of  the 
white  corpuscle  into  haemoglobin  and  stroma.  In  the  case  of  animals 
with  non-nucleated  red  corpuscles,  most  observers  '  agree  in  the  opinion 
that  the  nu  leus  of  the  white  corpuscle  breaks  up  and  disappears,  so 
that  the  red  corpusjle  represents  only  the  modified  cell-substance  of  its 
progenitor.  Wharton  Jones,  supported  by  Huxley,  resting  chiefly  on 
the  parallelism  in  size  and  form  between  the  nuclei  of  the  white  cor- 
puscles and  the  entire  red  corpuscles  in  different  orders  and  families  of 
mammals,  con  dudes  that  the  latter  is  in  reality  the  naked  coloured 
nucleus  of  the  former. 

Hayem  ^  describes  the  red  corpuscles  as  arising  from  a  kind  of 
uncolourcd  corpuscle  quite  distinct  from  the  ordinary  white  corpuscles. 
To  th^jse,  which  have  been  overlooked  on  accoimt  of  tlieir  great 
transparency,  aad  which  are  as  numerous  or  even  more  numerous 
than  the  or  limuy  white  corpuscles,  he  proposes  to  give  the  name  of 
hcEinatoblasls. 

There  are  reasons  for  believing  that  riot  only  may  the  number 
of  red  cori)usclos  vary,  but  also  the  quantity  of  haemoglobin 
present  in  tlie  individual  corpuscles  dififer  under  difi'erent  circum- 
stances. Malassez3,  by  comparing  the  tnit  of  a  quantity  of  blood 
the  numbers  of  whose  corpuscles  had  been  estimated,  with  that  of 
a  graduated  solution  of  picrocarminate  of  ammonia,  has  been 
able  to  estimate  the  amouiit  of  haemoglobin  present  in  the  cor- • 
puscles  under  ditierent  circumstances.  He  finds  that  in  anajmia 
the  poverty  of  the  corpuscles  in  haemoglobin  is  even  more 
striking  than  the  scantiness  of  the  corpuscles,  and  is  sooner 
affected  by  the  administration  of  iron. 

Ori^^in  of  Whke  Corpuscles. 

That  the  white  corpuscles  are  continually  being  removed  is 
evident  from  the  fact  that  they  vary  extremely  in  number  at 
different  times  and  under  various  circumstances.  They  are  very 
largely  increased  by  taking  food.  Thus  during  fasting  they  may 
be  se-Mi  in  a  drop  of  blood  to  bear  to  the  red  the  proi)ortion  of 
I  in  8co  or  looo.  After  a  meal  this  proportion  rises  to  i  in  300 
or  400. 

'  Koliiker,  Neuni.inn,  Schmidt. 

'  Compt.  Kepid.,  T.  85  (1877),  p.  12S5. 

'  Archwes  de  Physiohgiey  1877,  p.  i.     Cf.  also  Ilayem,  ibui.^.  649. 


38  THE   WPIITE   CORPUSCLES.  [BOOK   I. 

The  fact  that  in  the  lymphatic  glands,  and  other  adenoid  structures, 
corpuscles,  similar  to,  if  not  identical  with  white  blood-corpuscles,  are 
to  be  seen  of  very  various  sizes,  many  with  double  nuclei  and  some 
indeed  actually  dividing  into  two  corpuscles',  suggests  that  these 
organs  are  the  birth-places  of  the  white  corpuscles.  The  lymph  is 
continually  pouring  into  the  blood  a  crowd  of  white  corpuscles,  which 
for  the  most  part  make  their  appearance  in  the  lymph-vessels  after  the 
latter  have  traversed  the  lymphatic  glands.  And  this  view  is  further 
supported  by  the  fact  that  in  the  disea.se  leuch^mia,  where  the  white 
corpuscles  may  be  so  abundant  as  to  nuniber  as  many  as  i  to  lo  red, 
the  spleen,  the  lymphatic  glands,  and  other  forms  of  adenoid  tissue, 
are  enlarged.  (The  pheno  r.ena  are  however  capable  of  a  converse 
interpretation,  viz.  that  the  white  corpuscles,  failing  to  become  con- 
verted into  red  corpuscles,  are  crowded  into  the  lymphatic  organs). 

At  the  same  time  it  is  open  for  us  to  suppose  that  any  proliferating 
tissue  may  give  rise  to  new  corpuscles  ;  and  Klein  ^  states  that  he  has 
seen  them  Ijudded  off  from  the  reticulum  of  the  spleen.  The  white 
corpuscles  have  also  been  observed  to  divided 

We  may  conclude  therefore  that  the  white  corpuscles  probably 
arise,  by  division  chiefly,  froni  the  leucocytes  of  adenoid  tissue, 
but  that  other  sources  may  exist. 

Juife  of  the    White  Corpuscles. 

As  we  have  seen,  it  is  extremely  probable  that  a  large  number 
of  the  white  corpuscles  end  by  giving  birth  to  red  corpuscles  ;  btit 
it  is  also  possible  that  a  not  inconsiderable  nuinber  die  in  the 
blood  and  are  there  broken  up  and  disappear. 

On  the  other  hand  we  know  that  in  an  inflamed  area  the 
'white  corpuscles  migrate  in  large  numbers  into  the  extravascular 
portions  of  the  tissues,  and  there  are  reasons  for  thinking  that  not 
only  the  pus  corpuscles  and  '  exudation '  corpuscles  which  are  the 
common  products  of  inflammation,  but  even  the  new  tissue 
elements  (connective-tissue  cells  and  fibres,  blood-vessels,  &c.), 
which  miake  their  appearance  as  the  result  of  the  so-called  'pro- 
ductive '  inflammations,  are  the  descendants,  immediate,  or  remote, 
of  such  migratory  corpuscles.  But  a  discussion  of  this  question 
would  lead  us  too  far  away  from  the  purpose  of  this  work. 

Fate  of  the  Red  Co7'puscles. 

In  the  spleen  we  find,  as  Kolliker  long  since  pointed  out, 
large  protoplasmic  cells  in  which  are  included  a  number  of  red 

'  Ranvier,  Trai'J cT histologic,  p.  l6l. 
'  Q.  y.  Micros.  Sci.,  xv.  (1875)  P-  370« 
3  Klein,  Hdb.  Phys.  Lab.,  p.  8. 


CHAP.    I.]  BLOOD.  39 

corpuscles  :  and  these  red  corpuscles  may  be  observed  in  various 
stages  of  ap])arcnt  disintegration.  It  is  probable  therefore  that 
tiie  s])leen  is  the  grave  of  many  of  the  red  corpuscles. 

Since  scrum  of  fresh  blood  contains  no  dissolved  hcemoglobin, 
it  is  clear  that  the  haemoglobin  of  the  broken-up  corpuscles  must 
speedily  be  transformed  into  some  other  body.  Into  what  other 
body  ?  In  old  blooil-clots  (as  in  those  of  cerebral  haemorrhage) 
there  are  freijuently  found  minute  crystals  of  a  body  which  has 
received  the  name  lucmatoidin.  There  can  be  no  doubt  that  the 
hoematoidin  of  these  clots  is  a  derivative  from  the  haemoglobin  of 
the  escaped  blood.  We  know'  that  hemoglobin  contains,  besides 
a  proteid  residue,  a  residue  not  proteid  in  nature,  called  haematin. 
We  know  further  that  haematin  may  lose  the  iron  which  it  contains 
(and  which  appears  to  be  loosely  attached),  and  yet  remain  a 
coloured  body.  So  that  there  is  no  difficulty  in  the  passage  from 
the  proteid-and-iron  containing  haemoglobin  to  the  proteid-and- 
iron  free  htematoidin.  But  haematoidin,  not  only  in  the  form  and 
appearance  of  its  crystals,  but  also,  as  far  as  can  be  ascertained 
by  the  analysis  of  the  small  quantities  at  disposal,  in  its  chemical 
composition,  is  identical  with  bilirubui,  the  primary  pigment  of 
bile.  Moreover,  the  injection  of  haemoglobin,  or  of  dissolved  red 
corpuscles,  into  the  vessels  of  a  living  animal,  gives  rise  to  a  large 
amount  of  bile-pigment  in  the  urine,  and  at  the  same  time  increases 
enormously  the  relative  quantity  of  bilirubin  in  the  bile.  Thus 
though  no  one  has  yet  succeeded  in  producing  bilirubin  artificially 
from  haemoglobin,  facts  point  very  strongly  to  the  view  that  the 
red  corpuscles  are  used  up  to  supply  bile-pigment. 

It  must  be  added  however  that,  according  to  Preyer',  the  spectra 
of  haematoidin  and  bilirubin  are  quite  distinct,  and  that  many  ob- 
servers have  failed  to  obt  lin  bile-pigment  in  the  urine  as  the  result  of 
injection  of  a  solution  of  haemoglobin.  Blood-clots  frequently  contain, 
besides  or  in  place  of  haematoidin,  a  yellow  substance  named  lutein, 
which  is  certainly  distinct  from  bilirubin.  Lutein  is  the  substance 
which  gives  to  corporea  lutea  their  characteristic  colour. 

Our  knowlc'lgc  of  urinary  pigments  is  so  imperfect  that  httle  can 
be  said  as  to  their  relation  to  haemoglobin.  We  cannot  at  present 
definitely  trace  the  normal  urinary  pigment  back  to  haemoglobin, 
however  probable  such  a  source  may  seem  ;  but  Jaffd  finds  in  many 
urines,  especially  those  of  fever-patients,  a  body  called  ttrobilin, 
identical  with  hydrohiliriibin  obtained  from  bilirubin  by  reduction 
with  sodium  amalgam'. 

'  See  Chapter  on  Changes  of  Blood  in  Respiration, 
"  DU  Blu'Krystallc. 

^  Cf.  Lichennann,    I'fliiger's  Archiv,  XI.  (1875)   p.  181.     Disque,  7Jsckr.  f, 
Physiol,  Chcm.  II.  (1878),  p.  259. 


40   THE  QUANTITY  OF  BLOOD  IN  THE  BODY.  [BOOK  I. 

Sec.  4.     The  Quantity  of  Blood,  and  its  Distribution  in 

THE  Body. 

The  total  quantity  of  blood  present  in  an  animal  body  is 
estimated  in  the  following  way.  As  much  blood  as  possible  is 
allowed  to  escape  from  the  vessels  ;  this  is  measured  directly. 
The  vessels  are  then  washed  out  with  water  or  normal  saline 
solution,  and  the  washings  carefully  collected,  mixed  and  measured. 
A  known  quantity  of  blood  is  diluted  with  water  or  normal  saline 
solution  until  it  possesses  the  same  tint  as  a  measured  specimen 
of  the  washings.  This  gives  the  amount  of  blood  {or  rather  of 
haemoglobin)  in  the  measured  specimen,  from  which  the  total 
quantity  in  the  whole  washings  is  calculated.  Lastly,  the  whole 
body  is  carefully  minced  and  washed  free  from  blood.  The 
washings  are  collected  and  filtered,  and  the  amount  of  blood  in 
them  estimated  as  before  by  comparison  with  a  specimen  of  diluted 
blood.  The  quantity  of  blood  in  the  two  washings,  together  with 
the  escaped  blood,  gives  the  total  quantity  of  blood  in  the  body. 
Estimated  in  this  way,  the  total  quantity  of  blood  in  the  human 
body  may  be  said  to  be  about  xs^^  °f  the  body-weight. 

There  are  several  sources  of  error  in  the  above  method.  One  is 
that  venous  blood  has  less  colouring  power  than  arterial  blood.  This 
has  been  met  by  Gscheidlen  by  poisoning  the  animal  with  carbonic 
oxide,  by  which  all  the  haemoglobin  is  reduced  to  one  state,  and  there- 
fore has  throughout  the  same  colouring  power.  The  quantity  of 
hcemoglobin  in  the  muscular  fibre  itself  is  a  source  of  error,  but 
probably  a  very  slight  one.  The  difficulty  of  getting  a  clear  infusion 
of  the  minced  tissues  is  more  serious.  According  to  Ranke'  the  total 
blood  in  the  body  of  a  rabbit  amounts  to  -^q  of  the  body-weight,  in  a 
dog  to  jig-,  in  a  cat  to  gV,  in  a  frog  to  ^g. 

The  blood^  is  distributed  as  follows  in  round  numbers  : — 

About  one-fourth  in  the  heart,  lungs,  large  arteries  and  veins, 
j>  ?)  >j     3>  liver, 

,,  „  „     „   skeletal  muscles, 

„  „  ,,     „  other  organs. 

Since  in  the  heart  and  great  blood-vessels  the  blood  is  simply 
in  transit,  without  undergoing  any  great  changes  (and  in  the  lungs, 
as  far  as  we  know,  the  changes  are  limited  to  respiratory  changes), 
it  follows  that  the  changes  which  take  place  in  passing  through  the 
liver  and  skeletal  muscles  far  exceed  those  which  take  place  in 
the  rest  of  the  body. 

»  Blut-vertheilung,  187 1.  *  Ranke,  op.  cit. 


ciiAr.  i.j 


BLOOD. 


41 


Rankc  found  the  distribution  to  be  as  follows. 


R.-ibbit. 


In  the  Viscera. 

Per  cent,  of  Per  cent,  of 

a  oial  Blood.  Organ  Weight. 

(■Living.                  63-4  i8-o 

\  Dead  and  Rigid.  61*23  20'6 

590  240 


In  the  Carcase. 

Per  cent,  of  Per  cent,  of 

Total  llloud.  Organ  Weight. 

36*6  27 

3877  27 

41 'o  3-4 


1  n  the  various  organs  of  the  rabbit : 


Per  cent,  of  Total  Blood 


bplcen  .... 

■23 

Brain  and  Cord 

•     i":24 

Ki  Ineys     .     .     . 

1-6:; 

Skin      .... 

210 

Intestines .     .     . 

6-30 

lioncs,  &.C.      .     . 

.     8-24 

He  :rt,  Lungs,  Grea 

t 

Blood-vessels. 

2276 

Skeletal  Muscles 

29-20 

Liver    

2930 

Per  cent,  of  Organ  Weight. 


Skin 

Bones .... 
Al.  Canal  .  . 
Muscles  .  .  . 
Brain  and  Cord 
Kidney  .  .  . 
Spleen  .  .  . 
Liver  .... 
(Heart,  Lungs,  and 
Great  Vessels    . 


I  "07 

2-36 

346 

5-14 

5"52 

11-86 

12*50 

28-71 

63-n). 


CHAPTER   II. 

THE  CONTRACTILE  TISSUES. 

The  greater  number  of  the  movements  of  the  complex  animal 
body  are  carried  on  by  means  of  the  skeletal  striated  muscles.  A 
skeletal  muscle  when  subjected  to  certain  influences  contracts,  i.e. 
shortens,  bringing  its  two  ends  nearer  together ;  and  the 
shortening  acting  upon  various  bony  levers  or  by  help  of  other 
mechanical  arrangements,  produces  a  movement  of  some  part  of 
the  body.  The  striated  tissue  of  which  the  skeletal  muscles  are 
composed  is  the  chief  contractile  tissue.  The  peculiar  muscular 
tissue  of  the  heart  is  another  contractile  tissue ;  under  certain  in- 
fluences the  fibres  into  which  it  is  arranged,  shorten  and  thus  give 
rise  to  the  beat  of  the  heart,  A  similar  shortening  or  contraction 
of  the  fusiform  fibre  cells  of  plain  muscular  tissue,  gives  rise  to 
movements  or  to  changes  of  calibre,  &c.,  of  the  alimentary  canal, 
the  urinary  bladder,  the  uterus,  the  arterieS,  and  the  like. 

At  first  sight  '  contraction '  of  any  one  of  these  forms  of 
differentiated  muscular  tissue  seems  wholly  unlike  an  amoeboid 
movement  of  an  amoeba  or  of  a  white  corpuscle  of  the  blood. 
And  yet  the  transition  from  the  one  to  the  other  is  very  slight.  A 
typical  amoeba  may  be  regarded  as  spherical  in  form,  and  when  it 
is  executing  its  movements  the  pseudopodic  bulging  of  its 
protoplasm  may  be  seen  to  occur  now  on  this  now  on  that  part  of 
its  circumference  and  to  take  now  this  and  noiv  that  direction. 
The  fibre  cell  of  plain  muscular  tissue  is  a  nucleated  proto- 
plasmic mass  of  a  distinctly  fusiform  shape,  and  when  it  executes 
its  movements,  i.e.  contracts,  the  bulging  of  its  protoplasm  is 
always  a  lateral  bulging  in  a  direction  at  right  angles  to  the  long 
axis  of  the  fibre  cell.  Since  as  we  shall  see  there  is  no  change  of 
total  bulk,  this  thickening  of  the  fibre  by  means  of  the  lateral 
bulging  is  necessarily  accompanied  by  a  shortening  of  its  length. 
The  contraction  of  muscular  tissue  is  in  fact  a  limited  and  definite 


CHAP.   II.]  THE   CONTRACTILE   TISSUES.  43 

amoeboid  movement  in  which  intensity  and  rapidity  are  gained  at 
the  expense  of  variety. 

Besides  these  movements  which  are  carried  out  in  the  body  by 
means  of  ditVerentiated  muscular  tissue,  there  are  others  brought 
about  by  the  pecuhar  structures  known  as  cilia,  among  which  we 
may  include  the  motile  tails  of  spei matozoa  ;  and  ordinary  amue- 
boid  movements  are  not  wanting,  being  conspicuously  shewn  by 
the  so-called  migrating  cells.  We  may  include  both  these  under 
the  heading  of  contractile  tissues. 

Of  all  tliese.  various  forms  of  contractile  tissue  the  skeletal 
striated  muscles,  on  account  of  the  more  complete  development 
of  their  functions,  will  be  better  studied  first ;  the  others,  on 
account  of  their  very  simplicity,  are  in  many  respects  less  satis- 
factorily understood. 

All  the  ordinary  striated  skeletal  muscles  are  connected  with 
nerves.  We  have  no  reason  for  thinking  that  their  contractility  is 
called  into  play,  under  normal  conditions,  otherwise  than  by  the 
agency  of  nerves. 

Muscles  and  nerves  being  thus  so  closely  allied,  and  having 
besides  so  many  properties  in  common,  it  will  conduce  to  clear- 
ness and  brevity  if  we  treat  them  together. 

Sec.  I.     The  Phenomena  of  Muscle  and  Nerve. 
Muscular  and  Nervous  Irritability. 

The  skeletal  muscles  of  a  frog,  the  brain  and  spinal  cord  of 
which  have  been  destroyed,  do  not  exhibit  any  spontaneous  move- 
ments or  contnctions,  even  though  the  nerves  be  otherwise  quite 
intact.  Left  untouched  the  whole  body  may  decompose  without 
any  contraction  of  any  of  the  muscles  having  been  witnessed. 
Neither  the  skeletal  muscles  nor  the  nerves  distributed  to  them 
possess  any  power  of  automatic  action. 

If  however  a  muscle  be  laid  bare  and  be  more  or  less  violently 
disturbed,  if  for  instance  it  be  pinched,  or  touched  with  a  hot 
wire,  or  brought  in  contact  with  certain  chemical  substances,  or 
subjected  to  the  action  of  galvanic  currents,  it  will  contract  when- 
ever it  is  thus  disturbed.  Though  not  possessing  any  automatism, 
the  muscle  is  (and  continues  for  some  time  after  the  general  death 
of  the  animal  to  be)  irritable.  Though  it  remains  quite  quiescent 
when  left  untouched,  its  powers  are  then  dormant  only,  not 
absent.  These  require  to  be  roused  or  'stimulated'  by  some 
change  or  disturbance  in  Order  that  they  may  manifest  themselves. 
The  substances  or  agents  which  are  thus  able  to  evoke  the 
activity  of  an  irritable  muscle  are  spoken  of  as  stimuli. 


44  MUSCULAR    IRRITABII-ITY.  [BOOK   I. 

But  to  produce  a  contraction  in  a  muscle  the  stimulus  need 
not  be  applied  directly  to  the  muscle  ;  it  may  be  applied,  indirectly 
by  means  of  the  nerve.  Thus  if  the  trunk  of  a  nerve  be  pinched, 
or  subjected  to  sudden  heat,  or  dipped  in  certain  chemical  sub- 
stances, or  acted  upon  by  various  galvanic  currents,  contractions 
are  seen  in  the  muscles  to  which  branches  of  the  nerve  are 
distributed. 

The  nerve  like  the  muscle  is  irritable,  it  is  thrown  into  a  state 
of  activity  by  a  stimulus ;  but  unlike  the  muscle  it  does  not 
itself  contract.  The  changes  set  up  in  the  nerve  by  the  stimulus] 
are  not  visible  changes  of  form ;  but  that  changes  of  some  kind 
or  other  are  set  up  and  propagated  along  the  nerve  down  to  the 
muscle  is  shewn  by  the  fact  that  the  muscle  contracts  when  a  part 
of  the  nerve  even  at  some  distance  from  itself  is  stimulated. 
Both  nerve  and  muscle  are  irritable,  but  only  the  muscle  is  con- 
tractile, i.e.  manifests  its  irritability  by  a  contraction.  The  nerve 
manifests  its  irritability  by  transmitting  along  itself,  without  any 
visible  alteration  of  form,  certain  molecular  changes  set  up  by  the 
stimulus.  We  shall  call  these  changes  thus  propagated  along  a 
nerve,  '  nervous  impulses'. 

We  have  stated  above  that  the  muscle  is  irritable  in  the  sense 
that  it  may  be  thrown  into  contractions  by  stimuli  applied  directly 
to  itself.  But  it  might  fairly  be  urged  that  the  contractions  so 
produced  are  in  reality  due  to  the  fact  that,  although  the  stimulus 
is  apparently  applied  directly  to  the  muscle,  it  is,  after  all,  the 
fine  nerve-branches,  so  abundant  in  the  muscle,  which  are  actually 
stimulated.  The  following  facts  however  go  far  to  prove  that  the 
muscular  fibres  themselves  are  capable  of  being  directly  stimulated 
without  the  intervention  of  any  nerves.  When  a  frog  (or  other 
animal)  is  poisoned  with  urari,  the  nerves  may  be  subjected  to 
the  strongest  stimuli  without  causing  any  contractions  in  the 
muscles  to  which  they  are  distributed :  yet  even  ordinary  stimuli 
applied  directly  to  the  muscle  readily  cause  contractions.  If 
before  introducing  the  urari  into  the  system,  a  ligature  be  passed 
underneath  the  sciatic  nerve  in  one  leg,  for  instance  the  right,  and 
drawn  tightly  round  the  whole  leg  to  the  exclusion  of  the  nerve, 
it  is  evident  that  the  urari  when  injected  into  the  back  of  the 
animal,  will  gain  access  to  the  right  sciatic  nerve  above  the 
ligature,  but  not  below,  while  it  will  have  free  access  to  the  whole 
left  sciatic.  If,  as  soon  as  the  urari  has  taken  effect,  the  two 
sciatic  nerves  be  stimulated,  no  movement  of  the  left  leg  will  be 
produced  by  stimulatmg  the  left  sciatic,  whereas  strong  contractions 
of  the  muscles  of  the  right  leg  below  the  ligature  will  follow 
stimulation  of  the  right  sciatic,  whether  the  nerve  be  stimulated 


CiiAT.  11. J         .m:  coNrKAciii.i!:  ussues.  45 

above  or  below  the  li:,'atiire.  Now  since  the  upper  parts  of  both 
sciatics  are  etiually  exposed  to  the  action  of  the  poison,  it  is  clear 
that  the  failure  of  llie  left  nerve  to  cause  contraction  is  not 
attributable  to  any  change  having  taken  place  in  the  upper  portion 
of  the  nerve,  else  wliy  should  not  the  right,  which  has  in  its  upper 
portion  been  equally  exposed  to  the  action  of  the  poison,  also 
fail?  Evidently  the  poison  acts  on  some  parts  of  the  nerve 
lower  down.  If  a  single  muscle  be  removed  from  the  circulation 
(by  ligaturing  its  blood-vessels),  previous  to  the  poisoning  with 
urari,  that  muscle  will  contract  when  any  part  of  the  nerve  going 
to  it  is  stimulated,  though  no  other  nuiscle  in  the  body  will  con- 
tract when  its  nerve  is  stimulated.  Here  the  whole  nerve  right 
down  to  the  muscle  has  been  exposed  to  the  action  of  the  poison  ; 
and  yet  it  has  lost  none  of  its  power  over  tlie  muscle.  On  the 
other  hand,  if  the  muscle  be  allowed  to  remain  in  the  body,  and 
so  be  exposed  to  the  action  of  the  ])oison,  but  the  nerve  be 
divided  high  up  and  the  lower  part  connected  with  the  muscle 
gently  lifted  up  and  kept  separate  from  the  rest  of  the  tissues 
of  the  body  before  the  urari  is  introduced  into  the  system,  so  as 
to  be  protected  from  the  inHuence  of  the  poison,  it  is  found  that 
stimulation  of  the  nerve  produces  no  contractions  in  the  muscle, 
though  stimuli  applied  directly  to  the  muscle  at  once  cause  it  to 
contract.  From  these  facts  it  is  clear  that  urari  poisons  the  ends 
of  the  nerve  within  the  muscle  long  before  it  affects  the  trunk,  and 
it  is  exceedingly  probable  that  it  is  the  very  extreme  ends  of  the 
nerves  (possibly  tiie  end-plates,  for  urari  poisoning,  at  least  when 
profound,  causes  a  slight  but  yet  distinctly  recognisable  effect  in 
the  microscopic  appearance  of  these  structures^)  which  are 
affected.  The  phenomena  of  urari  poisoning  therefore  go  far  to 
prove  that  miiscles  are  capable  of  being  made  to  contract  by 
stimuli  applied  directly  to  the  muscular  fibres  themselves ;  and 
there  are  other  facts  which  support  tins  view. 

This  question  of  'independent  mus.ular  irritability'  was  once 
thought  to  be  of  importance.  In  old  times,  the  swelling  of  a  muscle 
during  contraction  was  held  to  be  caused  by  the  animal  spirits  descend- 
ing into  it  along  the  nerves;  and  when  the  dotrine  of  'spirits'  was 
given  up,  it  was  still  taught  that  tlic  vital  activity  of  the  muscle  was 
something  bestowed  ujjon  it  by  the  action  of  the  nerve,  and  not  pro- 
perly belonging  to  itself.  We  owe  to  Haller  the  establishment  of  the 
trutli,  that  the  contraction  of  a  muscL"  is  a  manifestation  of  the  muscle's 
own  energy,  excited  it  may  be  by  nervous  action,  but  not  caused  by  it. 
Haller  spoke  of  the  muscle  as  possessing  a  vis  /fisi'/d,  while  he  called 
the  nervous  action,   which  ex.itcs  contraction,  the  vis  iieh'osa.     He 

-  Kuhnc,  Untinuch.  Physiol.  Inst.  Heidelberg,  Hd.  U.  (1S7S)  p.  1S7. 


46 


MUSCULAR   CONTRACTION. 


[book  I. 


used  the  word  irritability  as  almost  synonymous  with  contractility,  a 
meaning  which  is  still  adopted  by  many  authors.  In  this  work  we 
have  used  it  in  the  wider  sense,  first  employed  by  Giisson,  which  in- 
cludes other  manifestations  of  energy  than  the  change  of  form  which 
constitutes  a  contraction.  Since  Haller's  time,  the  question  whether 
muscles  possess  an  independent  irritability  has  shifted  its  ground  ;  it 
now  means,  not  whether  muscles  are  instable  or  no,  but  simply 
whether  their  irritability  can  be  called  into  action  in  other  ways  than 
by  the  mediation  of  nerves.  In  addition  to  the  urari  argument  juit 
described,  we  may  state  that  portions  of  muscular  fibres,  entirely  des- 
titute of  nerves,  such  as  the  lower  end  of  the  sartorius  of  the  frog,  may 
be  stimulated  directly  with  contractions  as  a  result  ;  that  the  chemical 
substances  which  act  as  stimuli  when  applied  directly  to  muscles, 
differ  somewhat  from  those  which  act  as  stimuli  to  nerves,  and  lastly, 
that  a  portion  of  muscle-fibre  quite  free  from  nerves  may  be  seen  under 
the  microscope  to  contract.  In  the  succeeding  portions  of  this  work 
abundant  evidence  will  be  afforded  that  the  activity  of  contractile 
protoplasm  is  in  no  way  essentially  dependent  on  the  presence  of 
nervous  elements. 


The  Phenonmia  of  a  Simple  Muscular  Contraction. 

If  the  far  end  of  the  nerve  of  a  muscle-nerve  preparation  (the 
gastrocnemius  for  instance  of  the  frog  with  the  attached  sciatic 
nerve  dissected  out),  Figs,  i  and  2,  be  laid  on  the  electrodes  of 
an  induction-machine,  the  passage  of  a  single  induction-shock 
(either  making  or  breaking)  will  produce  no  visible  change  in  the 


Fig.  2.  The  muscle-nerve  preparaiion  of  Fig.  i,  with  the  clamp,  electrodes,  and  electrode- 
holder,  are  here  shewn  on  a  larger  scale.  The  letters  as  in  Fig.  i.  The  form  of 
electrode-holder  figured  is  a  convenient  one  for  general  purposes,  but  many  other  forms 
are  in  use. 


Fig. 


Diagram  illustrating  Apparatus  arf 


-J.  The  moist  chamber  containing  the  muscle-nerve  preparation.  (The  mwscle-nerve 
by  the  clamp  cl,  which  firmly  grasps  the  end  of  the  femur  _/,  is  connected  by  mea 
nerve  «,  with  the  portion  of  the  spinal  column  ^i  still  attached  to  it,  is  placed  on  I 
glass  case  gl.  is  kept  saturated  with  moisture,  and  the  electrode-holder  is  so  con 
into  contact -with  the  nerve. 

B.  The  revolving  cylinder  bearing  the  smoked  paper  on  which  the  lever  writes. 

C.  Du  Bois-Reymond's  key  arranged  for  short-circuiting.      The  wires  x  and  y  of  the 
with  the  wires  x ,  y' ,  and  these  are  secured   in  the  key.  one  on  either  side.     To 
induction-machine  D.     This   secondary  coil  can  be  made  to  slide  up  and  down  c 
connected  directly  with  one   pole,  for  instance  the  copper  pole  c.  p.  of  the  battery , 
another  binding  screw  b  of  the  key  to  the  zinc  pole  z.  p.-  of  the  battery. 

Supposing  everything  to  be  arranged,  and  the  battery  charged,  on  depressing  the  han 
from  c.  p.  through  x"  Xo  pr.  c,  and  thence  through  y"  to  a,  thence  to  b,  and  so  througl 
and  the  primary  circuit  is  in  consequence  immediately  broken. 

At  the  instant  that  the  primary  current  is  either  made  or  broken,  an  induced  curren 
Reymond's  key  be  raised  (as  shewn  in  the  thick  line  in  the  figure),  the  wires  x",  x'.  x,  tl 
and  the  nerve  consequently  experiences  a  making  or  breaking  induction-shock  whenev 
be  shut  down,  as  in  the  dotted  line  /i'  in  the  figure,  the  resistance  of  the  cross  bar  is  so 
that  the  whole  secondary  (induced)  current  passes  from  .t"  toy"  (or  from  y"  to  .r").  alon 
not  affected  by  any  changes  in  the  current.  ' 


To  face  pa^e  46. 


E. 


•:d  fok  Experiments  with  Mi'«ci,e  and  Xerve. 

electrode-holder  are  shewn  0:1  a  larger  scale  in  Fig.  2  )  The  muscle  ///,  supported 
the  S  hook  j  and  a  thread  with  the  lever  /.  placed  below  ihe  moist  chamber.  The 
lectiode-holder  el.  in  contact  with  the  wires  x,  y.  The  whole  of  the  interior  of  the 
ed  that  a  piece  of  moistened   blotting  paper   may  be  placed  on  it  without  coming 


■ode-holder  are  connected  through  binding  screws  in  the  floor  of  the  moist  chamber 
ime  key  are  attached  the  wires  x"  y"  coming  from  the  secondary  coil  s.  c.  of  the 
he  primarj-  coil  /r.  c.  with  which  are  connected  the  two  wires  x"'  and  y" .  x"'  is 
'"  is  carried  to  a  binding  screw  a  of  the  Jlorse  key  /",  and  is   continued  as  j*"  from 

a,  of  the  Morse  key  F.  a  current  will  be  made  in  the  primarj-  coil  pr.  c.  passing 
0  s.  /.     On  removing  the  finger  from  the  handle  of  /',  a  spring  thrusts  up  the  handle. 

>r  the  instant  developed  in  the  secondar>'  coil  s.  c.  If  the  cross  bar  A  in  the  du  Bois- 
ve  between  the  electrodes  and  the  wires  v,  y'.  y"  form  the  complete  secondary  circuit, 
;  primar)'  current  is  made  or  broken.  If  the  cross  bar  of  the  du  Bois-Kcymond  key 
It  compared  with  that  of  the  ner\'e  and  of  the  wires  going  from  the  key  to  the  nerve, 
cross  bar,  and  none  passes  into  the  nerve.     The  nerve  being  thus  short-circuited,  is 


[book  I. 


TVTvnnwAPW. 


CILM'.    11.]  THE   CONrKACriLli   TISSUES.  49 

Fig.  4.  The  figure  i>  diagrammatic,  the  csicntials  only  of  the  instrument  being  shewn.  The 
sinokfil  kI:l<!s  plalc  A  swings  on  the  '"  scconJs  "  pen  liiliuii  A'  by  means  of  carefully  adjusted 
be.irings  at  C.  I  he  contrivances  by  wluch  the  gl.iss  plate  can  be  reiuoved  and  replaced  at 
pleasure  arc  not  shewn.  A  second  glass  plaie  s  ■  arranged  that  the  first  glass  plate  may  be 
moved  lip  anJ  down  without  aber.ng  the  swini;  of  the  pcniiilum  is  also  omitted,  before 
commcni'ing  an  experiment  the  pen  luliiin  is  raided  up  (in  the  (igiiic  to  the  r.ght),  and  is  kept 
in  that  position  by  the  t  o  h  a  catching  on  the  sprin;;-calc'i  6  ( )n  depressing  the  catc'i  6  the 
glass  plate  issct  free,  swings  .no  the  new  position  indicated  by  the  dotted  lines,  and  is  held  in 
that  position  by  the  tooth  a'  c.iiching  on  the  catch  //.  In  the  course  of  its  swing  the  tooth  /t' 
c  m  ng  into  c  ntact  with  the  projeciing  steel  rod  f,  knocks  it  on  one  side  in'.o  the  X)Osi'ion 
inJ.caied  ^y  ihc  do;ted  line  c.  ]1  he  rod  c  is  in  electric  continuity  with  the  wire  .r  of  the 
primary  cil  of  a.i  induction-machine.  The  screw  ti  is  siinda.ly  in  electric  continuiiy  with 
the  v/.re y  of  the  same  primary  coil  The  screw  ti and  the  rod  c  are  armed  with  platinum  at 
the  points  in  wliich  they  are  in  con'act,  and  both  are  insulated  by  means  of  the  eb  m.tc  block 
e.  As  tong  as  c  and  (/arc  in  contact  the  circuit  of  the  primary  coil  to  which  x  and^  bcl  mg 
is  closed.  When  in  its  swing  tlie  tooth  tt'  knocks  c  away  from  d,  at  that  instant  the  circuit  iS 
broken,  and  a  "  break. ng  '  sh  ^ck  is  sen-  through  t'le  ek'CtroJcs  connected  with  the  S'.-cond.ary 
co.l  of  the  machmc.  and  so  through  the  nerve.  The  lever  /,  the  end  only  of  which  is  shewn 
ill  the  figure,  is  brought  t.>  be.ar  on  the  glass  pi  ite,  and  when  at  rest  de^cribes  a  straight  line, 
or  more  exactly  an  arc  (if  a  circle  of  large  r.idais.  'J'he  tuning-fork y",  the  ends  only  uf  the 
two  limbs  of  which  are  shewn  in  the  figure  placed  immediately  below  the  lever,  serves  to 
mark  the  time. 

the  lever  being  stationary,  the  point  of  the  lever  describes  an  arc  on 
the  glass  plate.  The  rate  at  which  the  glass  plate  travels,  z'.e.  the 
time  it  takes  for  the  lever-point  to  describe  a  line  of  a  given  len^^th  on 
the  glass  plate,  may  be  calculated  from  the  length  of  the  pendulum, 
but  it  is  simpler  and  easier  to  place  a  vibrating  tuning-fork  imme- 
diately under  the  point  of  the  lever.  '  If  the  vibrations  of  the  tuning- 
fork  are  known,  then  the  number  of  vibrations  \vhi."h  are  marked  on  the 
plate  between  any  two  points  on  the  line  described  by  the  lever  gives 
the  time  taken  by  the  lever  in  passing  from  one  point  to  the  other. 
An  easy  arrangement  permits  the  exact  time  at  which  the  shock  is  sent 
through  the  nerve  to  be  marKicd  on  the  line  of  the  lever.  To  avoid 
too  many  markings  on  the  plate  the  pendulum  after  describing  an  arc 
is  caught  by  a  spring  catch  on  the  opposite  side. 

A  complete  muscle-curve,  such  as  that  shewn  in  Fig.  3.  taken 
from  the  gastrocnemius  of  a  frog,  teaches  us  the  following  facts  : 

1.  That  although  the  passage  of  the  induced  current  from 
electrode  to  electrode  is  practically  instantaneous,  its  effect, 
measured  from  the  entrance  of  the  shock  into  the  nerve  to  the 
return  of  the  muscle  to  its  natural  length  after  the  shortening, 
takes  an  appreciable  time.  In  the  figure,  the  whole  curve  from 
a  to  d  takes  up  about  the  same  time  as  eighteen  double  vibrations 
of  the  tuning-fork.  Since  each  double  vibration  represents  ysu  o( 
a  second,  the  duration  of  the  whole  curve  was  j\j-  sec, 

2.  In  the  first  portion  of  this  period,  from  a  to  />,  there  is  no 
visible  change,  no  shortening  of  the  muscle,  no  raising  of  the 
lever. 

3.  It  is  not  until  l>,  that  is  to  say  after  the  lapse  of  ^  i.e.  about 

I  So 

J  J  sec.  that  the  shortening  begins.     The  shortening  as  shewn  by 

the  curve  is  at   first  slow,   but  soon   becomes   more  rapid,  and 

F.  P.  4 


50 


THE   MUSCLE   CURVE. 


[book  I. 


then  slackens  again  until  it  reaches  a  maximum  at  c ;  the  whole 
shortening  occupying  about  2V  ^^^- 

4.  Arrived  at  the  maximum  of  shortening,  the  muscle  at 
once  begins  to  relax,  the  lever  descending  at  first  slowly,  then 
very  rapidly,  and  at  last  more  slowly  again,  until  at  d  the  muscle 
has  regained  its  natural  length ;  the  whole  return  from  the 
maximum  of  contraction  to  the  natural  length  occupying  y|o,  i.e. 
about  -^  sec. 

Thus  a  simple  muscular  contraction,  a  simple  spasm  as  it  is 
sometimes  called,  produced  by  a  momentary  stimulus,  such  as  an 
instantaneous  induction-shock,  consists  of  three   main   phases  : 

1.  A  phase  antecedent  to  any  visible  alteration  in  the  muscle. 
This  phase,  during  which  invisible  preparatory  changes  are  taking 
place  in  the  nerve  and  muscle,  is  often  called  the  *  latent  period.' 

2.  A  phase  of  shortening  or  contraction,  more  strictly  so 
called. 

3.  A  phase  of  relaxation  or  return  to  the  original  length. 

In  the  case  we  are  considering,  the  electrodes  are  supposed  to 
be  applied  to  the  nerve  at  some  distance  from  the  muscle.  Con- 
sequently the  latent  period  of  the  curve  comprises  not  only  the 
preparatory  actions  going  on  in  the  muscle  itself,  but  also  the 
changes  necessary  to  conduct  the  immediate  effect  of  the  induction- 
shock  from  the  part  of  the  nerve  between  the  .electrodes,  along  a 
considerable  length  of  nerve  down  to  the  muscle.  It  is  obvious 
that  these  latter  changes  might  be  eliminated  by  placing  the 
electrodes  on  the  muscle  itself  or  on  the  nerve  close  to  the  muscle. 


yv/vv/v/vwv/N.'^^ 


Fig,  s-     Curves  illustrating  the  measurement    of    the   Velocity  of  a  Nervous 
Impulse.     (Diagrammatic.)    To  be  read  from  left  to  right. 

The  same  muscle-nerve  preparation  is  stimulated  (i)  as  far  as  possible  from  the  muscle,  (2) 
as  near  as  possible  to  the  muscle  ;  both  contractions  are  registered  by  the  pendulum 
myographion  exactly  in  the  same  way. 

In  (i)  the  stimulus  enter?  the  nerve  at  the  time  indicated  by  the  line  a,  the  contraction, 
shewn  by  the  dotted  hne,  begins  at  U  ;  the  whole  latent  period  therefore  is  indicated  by  the 
distance  from  aXa  b'. 

In  (2)  the  stimulus  enters  the  nerve  at  exactly  the  same  time  a  ;  the  contraction,  shewn  by 


CHAP.    II]  THE   CONTRACTILE   TISSUES.  5t 

the  unbroken  line,  hefiins  at  6;  the  latent  period  tlicrefore  is  indicated  by  the  distuncc 
between  a  nnd  d. 

'i  he  lime  taken  up  by  tlie  nervo;is  impulse  in  pa<!Mn(;  al  mj;  the  length  of  nerve  between  i 
and  3  i<  therefore  m  lica:ed  by  the  distance  between  t  and  6',  which  may  be  measured  by  the 
tisning-fiirk  curve  bcl  >w.  \.E.— No  v.ilu^  is  given  in  the  figure  for  the  vibrati  jns  of'the 
tunini;-fork,  since  the  figure  i>  di.tjjrammaMC,  ihe  distance  between  the  two  curves,  as 
compared  with  the  length  of  cither,  having  been  purposely  exaggerated  for  the  sake  ol 
simphcity. 

If  this  were  done,  the  nuiscie  and  lever  being  exactly  as  before, 
and  care  were  taken  tiiat  the  induction-shock  entered  into  the 
nerve  at  the  new  sjjot.  at  the  moment  when  the  point  of  the  lever 
had  reached  exactly  the  same  point  of  the  travelling  surface  as 
before,  a  curve  like  that  shewn  by  the  plain  line  in  Fig.  5  would 
be  gained.  It  resembles  the  first  curve  (indicated  in  the  figure  by 
a  dotted  line)  in  all  points,  except  that  the  latent  period  is 
shortencil  ;  the  contraction  begins  rather  earlier.  From  this  we 
learn  two  facts : 

1.  The  greater  part  of  the  latent  period  is  taken  up  by  changes 
in  the  muscle  itself,  preparatory  to  the  actual  visible  shortening,  for 
the  two  latent  periods  do  not  dither  much.  Of  course,  even  in  the 
second  case,  the  latent  period  includes  the  changes  going  on  in  the 
short  piece  of  nerve  still  lying  between  the  electrodes  and  the 
muscular  fibres.  To  eliminate  this  with  a  view  of  determining  the 
latent  period  in  the  muscle  itself,  the  electrodes  should  be  placed 
directly  on  the  muscle  poisoned  with  urari.  If  this  were  done,  it 
would  still  be  found  that  the  latent  period  was  chiefly  taken  up  by 
changes  in  the  muscular  as  distinguished  from  the  nervous  elements. 

2.  Such  difference  as  does  exist  indicates  the  time  taken  up 
by  the  propagation,  along  the  piece  of  nerve,  of  the  changes  set 
up  at  the  far  end  of  the  nerve  by  the  induction-shock.  These 
changes  we  shall  hereafter  speak  of  as  constituting  a  nervous 
impulse  ;  and  the  above  experiment  shews  that  it  takes  some  ap- 
preciable time  for  a  nervous  impulse  to  travel  along  a  nerve.  In 
the  figure  the  difterence  between  the  two  latent  periods,  the 
distance  between  ^  and  l>',  seems  almost  too  small  to  measure 
accurately  ;  but  if  a  long  piece  of  nerve  be  used  for  the  experi- 
ment, and  the  recording  surface  be  made  to  travel  very  fast,  the 
difference  between  the  duration  of  the  latent  period  when  the 
induction -shock  is  sent  in  at  a  point  close  to  the  muscle,  and  that 
when  it  is  sent  in  at  a  point  as  far  away  as  possible  from  the 
muscle,  may  be  satisfactorily  measured  in  fractions  of  a  second. 
If  the  length  of  nerve  between  the  two  ]>oints  be  accurately 
measured,  the  rate  at  which  a  nervous  impulse  travels  along  the 
nerve  to  a  muscle  can  be  easily  calculated.  This  has  been  found 
to  be  in  the  frog  about  28,  and  in  man  about  ^^  metres  per  second, 

4—2 


52  TETANIC   CONTRACTIONS.  [BOOK   I. 

Thus  when  a  momentary  stimulus,  such  as  a  single  induction - 
shock,  is  sent  into  a  nerve  connected  with  a  muscle,  the  following 
events  take  place  : 

1.  The  generation  at  the  spot  stimulated  of  a  nervous  impulse, 
and  the  propagation  of  the  impulse  along  the  nerve  to  the  muscle. 
The  time  taken  up  by  this  varies  accordmg  to  the  lengtli  of  the 
nerve.     For  the  same  length  of  nerve  it  is  tolerably  constant. 

2.  The  setting  up  of  certain  molecular  changes  in  the  muscle, 
unaccompanied  by  any  visible  alteration  in  its  form,  constituting 
the  latent  period,  and  occupying  on  an  average  about  yo-o'^^'^  sec. 
The  time  taken  up  by  the  latent  period  varies  somewhat  according 
to  circumstances. 

3.  The  shortening  of  the  muscle  up  to  a  maximum,  occupying 
about  YW'u  ^^^* 

4.  The  return  of  a  muscle  to  its  former  length,  occupying 
about  Y^-jy  sec.  Both  these  last  events  vary  much  in  duration 
according  to  circumstances'. 

Tetaiiic  Contractions. 

If  a  single  induction-shock  be  followed  at  a  sufficiently  short 
interval  by  a  second  shock  of  the  same  strength,  the  first  simple 
contraction  or  spasm  will  be  followed  by  a  second  spasm,  the  two 
bearing  some  such  relation  to  each  other  as  that  shewn  by  the 
curve  in  Fig.  6,  where  the  interval  between  the  two  shocks  was 
just  long  enough  to  allow  the  first  spasm  to  have  passed  its 
maximum  before  the  latent  period  of  the  second  was  over.  It 
will  be  observed  that  the  second  curve  is  almost  in  all  respects 


Fig.  6.     Tracing  of  a  Double  Muscle  Curve.    To  be  read  from  left  to  right. 
While  themuscle  =  was  engaged  in  the  first  contraction  (whose  complete  course,  had  nothing 
intervened,  is  indicated  by  the  dotted  line),  a  second  induction-shock  was  thrown  in,  at  such 
a  time  that  the  second  ccntraction  began  just   as  the  first  was  beginning  to  decline.     The 
second  curve  is  seen  to  start  from  the  first,  as  does  the  first  from  the  base-line. 

'  The  measurements  here  stated  are  those  ordinarily  given.  The  curve 
described  in  the  previous  text  happened  to  have  a  rather  long  latent  period,  and 
the  lengthening  to  be  of  shorter  instead  of  longer  duration  than  the  shortening. 

*  In  this  and  the  other  curves  of  this  section  the  tracings  figured  vi^ere  taken 
i:oxa.frog^s  muscle. 


CHAP.    II.]  THE   CONTRACTILE   TISSUES.  53 

like  the  first  except  that  it  starts,  so  to  speak,  from  tlie  first  curve 
instead  of  from  the  base  Hne.  Tlie  second  nervous  impulse  has 
actfil  on  the  already  contracted  muscle,  and  made  it  contract 
again  just  as  it  would  have  done  if  there  had  been  no  first 
impulse,  and  the  muscle  hail  been  at  rest.  The  two  contractions 
are  added  toi^ether  and  the  lever  raised  nearly  double  tlie  height 
it  would  have  been  by  either  alone.  A  more  or  less  similar  result 
would  occur  if  the  second  contraction  began  at  any  other  phase 
of  the  first.  The  combined  effect  is,  of  course,  greatest  when  the 
secontl  contraction  begins  at  the  maximum  of  the  first,  being  less 
both  before  and  afterwarils.  If  in  the  same  way  a  third  shock 
follows  the  second  at  a  siifiiciently  short  interval,  a  third  curve 
is  piled  on  the  top  of  the  second.  The  same  with  a  fourth,  and 
so  on. 

When  however  repeated  shocks  are  given  it  is  found  that  the 
height  of  each  contraction  is  rather  less  than  the  preceding  one, 
and  this  diminution  becomes  more  marked  the  greater  the  number 
of  shocks.  Hence,  after  a  certain  number  of  shocks,  the  succeed- 
ing impulses  do  not  cause  any  further  shortening  of  the  muscle, 
any  further  raising  of  the  lever,  but  merely  keep  up  the  con- 
traction already  existing.  The  curve  thus  reaches  a  maximum, 
whicli  it  maintains,  subject  to  the  depressing  effects  of  exhaustion 
as  long  as  the  shocks  are  repeated.  When  these  cease  to  be 
given,  the  muscle  returns,  in  the  usual  way,  at  first  very  rapidly, 
and  then  more  slowly,  to  its  natural  length.  When  the  shocks  do 
not  succeed  each  other  too  rapidly,  the  individual  contractions 
may  readily  be  traced  along  the  whole  curve,  as  is  seen  in  Fig.  7, 


vv%/W\rv« 


Kic.  7.  Muscle  throw.v  into  Tetanus,  when  the  Primary  Current  op  am 
Inuuction-.machine  is  repeatedly  broken  at  intervals  of  sixteen  in  a 
SECOND.     To  be  read  from  left  to  right. 


54  TETANIC   CONTRACTIONS.  [BOOK  I. 

Fig.  7.  The  upper  line  is  that  described  by  the  muscle.  The  lower  marks  time,  the  intervals 
between  the  elevations  indicating  seconds.  The  intermediate  line  shows  when  the  shocks 
were  sent  in,  each  mark  on  it  corresponding  to  a  shock.  The  lever,  which  describes  a  stra.ght 
line  before  the  shocks  are  allowed  to  fail  into  the  nerve,  rises  almost  vertically  (the  recording 
surface  travelling  in  this  case  slowly)  as  soon  as  the  first  shock  enters  the  nerve  at  a.  Having 
risen  to  a  certain  height,  it  beg.ns  to  fall  again,  but  in  its  fall  is  raised  once  more  by  the 
second  shock,  and  that  to  a  greater  height  than  before.  The  third  and  succeeding  shocks 
have  similar  effects,  the  muscle  continuing  to  become  shorter,  though  the  shortening  at  each 
shock  is  less.  After  a  while  the  increase  in  the  to.al  shortening  of  the  muscle,  though  the 
individual  contractions  are  sdll  visible,  almost  ceases.  At  b,  the  shocks  cease  to  be  sent  into 
the  nerve  ;  the  contractions  almost  immediately  disappear,  and  the  lever  forthwith  commences 
to  descend.  The  muscle  being  lightly  loaded,  the  descent  is  very  gradual ;  the  muscle  had 
njt  regained  its  natural  length  when  the  tracing  was  stopped. 

where  the  primary  current  of  the  induction-machine  was  repeatedly- 
broken  at  intervals  of  sixteen  in  a  second.  When  the  shocks 
succeed  each  other  more  rapidly,  the  individual  contractions,  visible 
at  first,  may  become  fused  together  and  lost  to  view  as  the  tetanus 


A 


Fig.    8.    Tetanus  produced  with   the  ORDirrARY    Magnetic   Interruptor   of   an 
Induction-.machine.      (Recording   surface  travelling  slowly.)     To  be  read  from  left 
■     to  right. 

The  interrupted  current  being  thrown  in  at  a  the  lever  rises  rapidly,  but  at  h  the  muscle 
reaches  the  ma.'cimum  of  contraction.  This  is  continued  till  c,  when  the  current  is  shut  off 
and  relaxation  commences. 

continues  and  the  muscle  becomes  tired.  When  the  shocks 
succeed  each  other  still  more  rapidly  (the  second  contraction 
beginning  in  the  ascending  portion  of  the  first),  it  becomes  diffi- 
cult or  impossible  to  trace  out  the  single  contractions.  The  curve 
then  described  by  the  lever  is  of  the  kind  shewn  in  Fig.  8,  where 
the  primary  current  of  an  induction-machine  was  rapidly  made  and 
broken  by  the  magnetic  interruptor,  Fig.  9.  The  lever,  it  will  be 
observed,  rises  at  a  after  the  latent  period  (which  is  not  marked), 
first  rapidly,  and  then  more  slowly,  in  an  apparently  unbroken 
line  to  a  maximum  at  about  ^,  maintains  the  maximum  so  long 
as  the  shocks  continue  to  be  given,  and  when  these  cease  to  be 
given,  as  at  c,  gradually  descends  to  the  base-line.  This  condition 
of  muscle,  brought  about  by  rapidly  repeated  shocks,  this  fusion 
of  a  number  of  simple  spasms  into  an  apparently  smooth,  con- 
tinuous effort,  is  known  as  tetanus,  or  tetanic  contraction.  The 
above  facts  are  most  clearly  shewn  when  induction-shocks,  or  at 


CHAP.   II. J  THE  CONTRACTILE   TISSUES. 


55 


Fig.  9.     The  MagnktiC  Intbrruptor. 

The  figure  is  introduced  to  illustrate  the  action  of  this  instrument  as  commonly  used 
by  physiologists. 

The  two  wires  jr  an  J  ^  from  the  battery  are  connected  with  the  two  brass  pillars  a  .and  d 
by  mean-i  of  screws.  Directly  contact  is  thus  made  the  current,  indicated  in  the  figure  by  the 
thick  interrupted  line,  passes  in  the  direction  of  the  arrows,  up  the  pillar  a,  along  the  steel 
spring  ^.  as  far  as  the  scr^w  c,  ihe  point  of  which,  armed  with  platinum,  is  in  contact  with  a 
small  platinum  plate  on  .4.  The  current  passes  from  6  through  c  and  a  connecting  wire  into 
the  primary  coil  /».  Upon  its  entering  into  the  primary  coil,  an  induced  (making)  current  is 
for  the  instant  developed  in  the  secondary  coil  (not  shewn  in  the  figure).  From  the  primary 
coil  /»  the  current  passes,  by  a  connecting  wire,  through  the  double  spiral,  m,  anJ.  did  nothing 
happen,  would  continue  10  p.ass  frotrj  nt  by  a  connecting  wire  to  the  pillar  tf,  .and  so  by  the 
wire  _y  to  the  battery.  The  whole  of  this  course  is  indicated  by  the  thick  interrupted  line 
with  its  arrows. 

As  the  current  however  passes  through  the  spirals  m.  the  iron  cores  of  these  are  made 
magnetic.  They  in  consequence  draw  down  the  iron  bar  c.  fixed  at  the  end  of  the  spring  6, 
the  flexibility  of  the  spring  allowing  this.  But  when  e  is  drawn  down,  the  platinum  plate  on 
the  upper  surface  o(  i  is  also  drawn  away  from  the  screw  c.  and  a  similar  platinum  plate  on 
the  M/z/fr  surface  of  i  is  brotight  info  contact  with  the  platinum-armed  point  of  the  screw  /", 
the  screws  being  so  arranged  th.at  this  takes  place.  In  consequence  of  this  change  the  current 
can  no  longer  p.ass  from  i  to  c.  <  >n  the  contrary,  it  passes  from  6  x.o /,  and  so  down  the  pillar 
d,  in  the  direction  indicated  by  the  thin  interrupted  line,  ani  o  it  to  the  battery  by  the  wire 
y.  Thus  the  current  is  '  short-circuited  '  from  the  primary  coil ;  and  the  instant  that  the 
current  is  thus  cut  off  from  the  primary  coil,  an  induced  (breaking)  citrren:  is  for  the  moment 
developed  in  the  scconjarj-  coil.  But  the  current  is  cut  off  no:  only  from  the  primary  coil, 
but  .also  from  the  spirals  tn ;  in  consequence  their  cores  cease  to  be  magnetised,  the  bar  e 
ceases  to  be  attnicted  by  them,  and  the  spring  6,  by  virtue  of  its  elasticity,  resumes  its  fcfrmer 
position  in  cont,act  with  the  screw  c  This  return  of  the  spring  however  re-establishes  the 
current  in  the  primary  coil  an1  in  the  spirals,  ani  the  spring  is  drawn  down,  to  be  released 
once  more  in  the  same  manner  as  before.  Thus  as  long  as  the  current  is  passing  along  x.  the 
con'aci  of  6  is  constantly  alternating  between  c  and  /.  ani  the  current  is  constantly  p,assing 
into  and  bcinT  shut  off  from  ;*.  the  periods  of  .altcniailon  being  determined  by  the  periods  o? 
vibration  of  the  spring  A.  With  each  p.assage  of  the  current  into,  or  withdrawal  from  the 
primary  coil,  an  induced  (making  and,  respectively,  breaking)  shock  is  developed  in  the 
■Dcondary  coil. 


56  TETANIC   CONTRACTIONS.  [BOOK   I. 

least  galvanic  currents  in  some  form  or  other,  are  employed.  They 
are  seen,  however,  whatever  be  the  form  of  stimulus  employed. 
Thus  in  the  case  of  mechanical  stimuli,  while  a  single  blow  may 
cause  a  single  spasm,  a  pronounced  tetanus  may  be  obtained  by 
rapidly  striking  successively  fresh  portions  of  a  nerve.  With 
chemical  stimulation,  as  when  a  nerve  is  dipped  in  acid,  it  is 
impossible  to  secure  a  momentary  application ;  hence  tetanus, 
generally  irregular  in  character,  is  the  normal  result  of  this  mode 
of  stimulation.  In  the  living  body,  the  contractions  of  the 
striated  muscles,  brought  about  either  by  the  will  or  by  reflex 
action,  are  generally  tetanic  in  character.  Even  very  short  sharp 
movements,  such  as  a  sudden  jerk  of  the  limbs,  are  in  reality 
examples  of  tetanus  of  short  duration. 

When  it  has  once  been  realised  that  an  ordinary  tetanic 
muscular  movement  is  essentially  a  vibratory  movement,  that  the 
apparently  rigid  and  firm  muscular  mass  is  really  the  subject  of  a 
whole  series  of  vibrations,  a  series  namely  of  simple  spasms,  it 
will  be  readily  understood  why  a  tetanized  muscle,  like  all  other 
vibrating  bodies,  gives  out  a  sound.  That  a  contracting  (tetanized) 
muscle  does  give  out  a  sound,  the  so-called  muscular  sound,  is 
easily  proved  by  listening,  with  a  stethoscope  to  a  contracted 
biceps,  or  by  stopping  the  ears  and  listening  to  the  contractions  of 
one's  own  masseter  and  temporal  muscles. 

When  a  muscle  is  thrown  into  tetanus  by  interrupted  shocks 
applied  directly  to  the  nerve  or  to  the  muscle,  the  note  is  the  same 
as  that  of  the  interrupter  determining  the  number  of  the  shocks. 
This  is  naturally  the  case,  since  the  note  of  the  muscle-sound  is 
determined  by  the  rapidity  of  the  spasms  or  vibrations  which  go 
to  make  up  the  tetanus,  and  these  are  determined  by  the  rapidity 
with  which  the  stimulus  is  repeated. 

When  a  muscle  is  thrown  into  tetanus  by  the  will  or  by  reflex 
action  or  by  direct  stimulation  of  the  spinal  cord,  in  fact,  in  any 
way  through  the  action  of  the  central  nervous  system,  the  same 
note  is  always  heard,  viz.  one  indicating  19*5  vibrations  per 
second. 

The  note  actually  heard  is  one  indicating  39  (36  to  40)  vibrations 
per  sec.  This  is,  however,  an  harmonic  of  the  primary  note  of  the 
whole  sound. 

It  need  hardly  be  said  that  a  single  muscular  contraction,  a 
single  vibration,  cannot  cause  a  muscular  sound. 

The  general  observations  which  have  been  described  in  this 
section  may,  when  proper  precautions  are  taken,  be  carried  out 
on  a  muscle-nerve  preparation  from  a  frog  for  a  very  considerable 


CHAP   II.]  THE   CONTRACTILE   TISSUES.  57 

time  after  its  removal  from  the  body.  After  some  hours  however, 
or  it  may  be  days,  the  length  of  time  varying  according  to  cir- 
cumstances, it  will  be  found  that  no  stimulus,  however  powerful, 
will  cause  any  contraction,  when  applied  either  to  the  nerve  or  to 
the  muscle.  Both  muscle  and  nerve  are  then  said  to  have  lost 
their  irritability ;  and  a  short  time  afterwards  the  muscle  may  be 
observed  to  pass  into  a  peculiar  condition  known  as  rii^or  mortis, 
in  which  it  loses  all  the  suppleness  and  extensibility  characteristic 
of  the  living  irritable  muscle.  The  causes  of  this  loss  of  irri- 
tability as  well  as  the  features  and  nature  of  this  rigor  mortis  we 
shall  study  in  detail  presently. 

The  muscles  and  nerves  of  a  mammal,  or  indeed  of  any  warm- 
blooded animal,  lose  their,  irritability,  and  the  muscles  become 
rigid  in  a  very  short  time  (it  may  be  a  few  minutes)  after  removal 
from  the  body.  Hence  these  are  less  suitable  for  experiments 
than  the  muscles  and  nerves  of  the  frog,  though  their  general 
phenomena  are  exactly  the  same. 

We  must  now  attempt  to  study  in  greater  detail  the  changes 
which  take  place  in  a  muscle  and  nerve  during  the  contraction  of 
the  former  and  the  passage  of  an  impulse  along  the  latter,  with  a 
view  to  the  better  understanding  of  both  events. 


Sec.  2.     The  Changes  in  a  Muscle  during  Muscular 
Contraction. 

The  Change  in  Form. 

We  have  seen  that  at  the  close  of  the  latent  period  the  muscle 
shortens,  that  is,  each  fibre  shortens,  at  first  slowly,  then  more 
rapidly,  and  lastly  more  slowly  again.  The  shortening  (which  in 
severe  tetanus  may  amount  to  three-fifths  of  the  length  of  the 
muscle)  is  accompanied  by  an  almost  exactly  corresponding 
thickening,  so  that  there  is  hardly  any  actual  change  in  bulk.  If 
a  muscle  be  placed  horizontally,  and  a  lever  laid  upon  it,  the 
thickening  of  the  muscle  will  raise  up  the  lever,  and  cause  it  to 
describe  on  a  recording  surface  a  curve  exactly  like  that  described 
by  a  lever  attached  to  the  end  of  the  muscle.  There  appears  to 
be  a  minute  diminution  of  bulk  not  amounting  to  more  than  one 
thousandth. 

If  a  long  muscle  of  parallel  fibres,  poisoned  with  urari,  so  as  to 
eliminate  the  action  of  its  nerves,  be  stimulated  at  one  end,  the 
contraction  may  be  seen,  almost  with  the  naked  eye,  to  start  from 
the  end  stimulated,  and  to  travel  along  the  muscle.     If  two  levers 


58  THE   CONTRACTION   WAVE.  [BOOK   I. 

be  made  to  rest  on,  or  be  suspended  from,  two  points  of  such  a 
muscle  placed  horizontally,  the  points  being  at  a  known  distance 
from  each  other  and  from  the  pomt  stimulated,  the  progress  of 
the  contraction  may  be  studied.  It  is  found  that  the  contraction 
starting  from  the  spot  stimulated,  passes  along  the  muscle  in  the 
form  of  a  wave  diminishing  in  vigour  as  it  proceeds.  The  velocity 
with  which  this  contraction  wave  travels  in  the  muscles  of  the 
frog  is  about  3  or  4  metres  a  second ;  and  since  it  takes,  in  round 
numbers,  from  about  "05  to  'i  sec.  for  the  contraction  to  pass 
over  any  point  of  the  fibre,  the  wave-length  of  the  contraction 
wave  must  be  from  about  200  to  400  mm. 

Bernstein'  gives  the  velocity  of  the  contraction  wave  in  the  frog  as 
about  3  to  4  (3"869),  its  duration  as  "0533  to  "0894  sec,  and  hence  its 
wave-length  as  from  198  to  200  mm.  In  the  dog,  Bernstein  and 
Steiner^  find  the  velocity  of  the  wave  about  the  same,  viz.  3 '5 89,  but 
the  duration  much  longer,  viz.  '27  to  "4975  sec,  indicating  a  much 
more  extended  wave  ;  but  this  was  probably  due  to  the  abnormal 
condition  of  the  muscle,  since  the  duration  of  the  wave  in  the 
untouched  muscles  of  the  rabbit  more  nearly  agreed  with  that  of  the 
frog.  Hermann  3  makes  the  rate  in  the  frog  about  3  metres  or  rather 
less,  Aeby  had  previously  given  "8 — 1'2  metres  per  sec,  and  Engel- 
mann  I'ly  m.  per  sec.  as  the  velocity. 

The  velocity  is  increased  by  an  elevation  and  diminished  by  a 
lowering  of  temperature,  but  is  not  affected  by  variations  in  the 
load. 

Seeing  that  the  extreme  limit  of  the  length  of  a  muscular  fibre 
is  about  30  or  40  mm.,  it  is  evident  that  even  when  the  stimu- 
lation begins  at  one  end,  the  whole  fibre  is  not  only  in  a  state  of 
contraction  at  the  same  time,  but  almost  in  the  same  phase  of  the 
contraction  wave.  In  an  ordinary  contraction  occurring  in  the 
living  body  the  stimulus  is  never  applied  to  one  end  of  the  fibre ; 
the  nervous  impulse  which  in  such  cases  acts  as  the  stimulus  to 
the  muscle,  falls  into  the  fibre  at  about  its  middle,  where  the  nerve 
ends  in  an  end-plate,  and  the  contraction  wave  starting  from  the 
end-plate  travels  along  the  muscular  fibre  in  both  directions.  In 
such  a  case  therefore,  still  more  even  than  in  the  urarised  muscle 
stimulated  artificially  at  one  end,  must  the  whole  fibre  be  occupied 
at  the  same  time  by  the  wave  of  contraction. 

Changes  in  microscopic  structure.  When  portions  of 
living   irritable    muscle    are    examined    under    the    microscope, 

'  Utitersuch.  il.  d.  Erregungsvorgang  im  Nerven-  und  Muskelsystenie,  1871, 
p.  84. 

^  Pfliiger's  ^rc/^iz/,  X.  (1875)48. 

3  Archivf.  Anat,  u.  I'hys.,  1875,  p.  526. 


CHAP     II.]  THE   CONTRACTILE   TISSUES. 


59 


contraction  wavts  similar  to  those  just  described,  but  fecljlcr  and 
of  shorter  length,  may  be  observed  passing  along  the  fibres.  By 
appropriate  treatment  with  osmic  acid  or  other  reagents,  these 
short  contraction  waves  may  be  fixed,  and  the  structure  of  the 
contracted  portion  compared  at  leisure  with  that  of  the  portions 
of  the  fibre  at  rest.  In  Fig.  lo,  representing  a  fibre  of  the  muscle 
of  an  insect  (in  which  these  changes  can  be  more  satisfactorily 


Fig.  io.  Muscular  fibre  undergoing  contraction. 

The  muscle  is  that  of  Telef>honis  tiielanurjts  treated  withosmic  acid.  The  fibre  at  c  is  at 
rest,  .It  a  the  conlractiorj  begins,  at  b  it  has  reached  its  maximum.  The  right  hand  side  of 
the  figure  shows  the  same  fibre  as  seen  in  polariied  hght.     (After  lingelmann.) 

Studied  than  in  vertebrate  muscle),  the  contraction  wave  begins 
near  a,  and  has  reached  about  its  maximum  at  b,  while  at  c  the 
fibre  is  at  rest,  the  contraction  wave  not  having  reached  it  (or 
having  passed  over  it,  for  the  beginning  and  end  of  the  wave  are 
exactly  alike).  It  will  be  seen  that  at  b,  each  disc  of  the  fibre  is 
shorter  and  broader  than  at  c  Further,  while  at  c  the  dim  band 
X  is  conspicuous,  and  the  light  band  y,  with  its  accessory  markings 
y',  is  together  lighter  than  the  dim  band  x,  at  b  in  the  fully  con- 
tracted part  of  the  fibre  the  dim  band  appears  light  as  compared 
with  the  black  line  v'  occupying  the  middle  of  the  previously  light 
band.  In  the  contracted  muscle  then  there  is  a  reversal  of  the 
state  of  things  in  the  resting  muscle,  the  light  band  (or  part  of 
the  light  band)  of  the  latter  in  contracting  becomes  dark,  and  the 


60  THE   CHANGE   OF   FORM.  [BOOK  I. 

dim  band  of  the  latter  becomes  by  comparison  light.  Between 
rest  and  full  contraction  there  is  an  intermediate  stage,  as  at  «',  in 
which  the  distinction  between  dim  and  bright  bands  seems  to  be 
largely  lost.  The  subject  however  is  one  offering  peculiar  diffi- 
culties in  the  way  of  investigation,  and  while  most  observers  agree 
in  the  broad  facts  which  have  just  been  stated,  there  is  great 
diversity  of  opinion  concerning  further  details  and  especially  as  to 
the  interpretation  of  the  various  appearances  observed.  The 
accessory  markings  in  the  middle  of  the  light  band  have,  in 
particular,  been  the  subject  of  controversies  into  which  we  cannot 
enter  here. 

When  the  fibre  is  examined  in  polarized  light  it  is  seen  that  the 
dim  band  is  anisotropic,  and  the  light  band  wholly  isotropic,  the 
accessory  markings  y'  of  the  light  band  not  being  recognizable  in 
polarized  light.  This  is  the  case  during  all  the  phases  of  the  con- 
traction. At  no  period  is  there  any  confusion  between  the  anisotropic 
and  isotropic  material ;  these  maintain  their  relative  positions,  both 
become  shorter  and  broader  ;  but  it  will  be  observed  that  the  isotropic 
substance  diminishes  in  height  to  a  much  greater  extent  than  does  tbe 
anisotropic  substance.  The  latter  in  fact  appears  to  increase  in  bulk 
at  the  expense  of  the  former'. 

Relaxation.  The  shortening  as  we  have  seen  is  followed  by 
a  relaxation,  the  muscle  returning  to  its  original  length.  This  is 
brought  about  by  the  elastic  reaction  of  the  muscular  substance 
itself  The  application  of  an  extending  force,  though  useful,  is 
not  necessary. 

The  muscles  in  their  natural  position  in  the  body,  where  they  are 
to  a  certain  extent  on  the  stretch,  return  completely  and  rapidly  to 
their  former  length,  even  after  a  powerful  and  prolonged  contraction. 
Out  of  the  body  the  return,  especially  in  muscles  which  are  not  loaded, 
is  slower,  and  is  frequently  incomplete.  The  amount  of  this  deficiency 
of  relaxation  depends  on  the  nutritive  condition  of  the  muscle.  When 
a  muscle  is  stimulated  by  induction  shocks  repeated  with  a  certain 
rapidity  this  deficiency  of  relaxation,  or  '  contraction  remainder'  as  it 
has  been  called,  becomes  very  conspicuous"^. 

A  muscular  contraction  appears  then  to  be  essentially  a  trans- 

Fig.  II. 

location  of   molecules.      If   we  were  to  represent  a  portion  of 

'  Engelmann,  Pfliiger's  Archiv,  xviii.  (1878)  p.  i. 
»  Cf.  Tiegel,  Pfliiger's  Archiv,  xill.  (1876)  p.  71. 


CHAP,    II.]  THE   CONTRACTILE   TISSUES.  6l 

muscular  substance  at  rest  by  four  rows  of  molecules  four  abreast 
as  in  Fig.  ii,  the  contraction  might  be  represented  by  the  four 
rows  of  four  shifting  into  two  rows  of  eight ;  and  the  subsequent 
relaxation  by  a  return  into  the  four  rows.  We  cannot  at 
present  give  any  satisfactory  molecular  explanation  of  this  trans- 
location, even  when  we  have  studied  the  chemical  and  other 
events  to  be  described  immediately  which  accompany  and  are 
doubtless  the  cause  of  the  change  of  form.  And  there  is  a 
remarkable  physical  characteristic  of  the  contracted  state  which 
shews  how  complex  and  peculiar  is  the  act  of  contraction.  Living 
muscle  at  rest  is  very  extensible,  but  a  stretched  muscle  after  the 
extending  cause  has  been  removed,  returns  rapidly  and  com- 
pletely to  its  former  length.  In  physical  language  muscle  is 
spoken  of  as  possessing  slight  but  perfect  elasticity.  It  might  be 
imagined  that  during  a  contraction  this  extensibility  would  be 
diminished  in  order  that  none  of  the  resistance  which  the  muscle 
had  to  overcome,  no  part  of  the  weight  for  instance  which  had  to 
be  lifted,  should  be  wasted  in  stretching  the  muscle  itself  On 
the  contrary  we  find  that  during  a  contraction  there  is  a  marked 
increase  of  extensibility ;  thus  if  a  muscle  at  rest  be  loaded  with  a 
given  weight,  say  50  grammes,  and  its  extension  observed,  and  be 
then  while  unloaded  thrown  into  tetanus,  and  the  load  applied 
during  the  tetanus,  the  extension  in  the  second  case  will  be 
distinctly  greater  than  in  the  first.  During  the  contraction  there 
is  so  to  speak  a  greater  mobility  of  the  muscular  molecules,  and 
the  loaded  nmscle  has  in  contracting  to  overcome  its  own  tendency 
to  lengthen  on  extension  before  it  can  produce  any  effect  on  the 
weight  which  it  has  to  lift. 

When  a  muscle  is  exten^led  by  a  series  of  weights  increasing  in 
magnitude,  the  curve  (obtained  by  making  the  weights  abscissae  and 
the  extensions  ordi nates)  is  not  a  straight  line,  as  is  the  case  with 
dead  elastic  bodies,  but  a  hyperbola. 

The  elasticity  or  extensibility  of  the  muscular  substance  is 
essentially  a  vital  property,  i.e.  is  dependent  on  the  same  nutritive 
factors  as  the  irritability  of  the  muscular  substance.  As  the 
muscular  substance  bjcomes  weary  with  too  much  work  or 
impoverished  by  scanty  nutrition,  its  elasticity  suffers  pari  passu 
with  its  irritability.  The  exhausted  muscle  when  extended  does 
not  return  so  readily  to  its  proper  length  as  the  fresh  active 
muscle,  and,  as  we  shall  see,  the  dead  muscle  does  not  return 
at  all. 


62 


MUSCLE   CURRENTS. 


Electrical  Changes. 


[book  I. 


Muscle-currents.  If  a  muscle  be  removed  in  an  ordinary 
manner  from  the  body,  and  two  non-polarizable  electrodes', 
connected  with  a  delicate  galvanometer  of  many  convolutions, 
be  placed  on  two  points  of  the  surface  of  the  muscle,  a  deflection 
of  the  galvanometer  will  take  place  indicating  the  existence  of  a 
current  passing  through  the  galvanometer  from  the  one  point  of 
the  muscle  to  the  other,  the  direction  and  amount  of  the  deflec- 
tion varying  according  to  the  position  of  the  points.  The 
'  muscle-currents '  thus  revealed  are  seen  to  the  best  advantage 
when  the  muscle  chosen  is  a  cylindrical  or  prismatic  one  with 
parallel  fibres,  and  when  the  two  tendinous  ends  are  cut  off  by 
clean  incisions  at  right  angles  to  the  long  axis  of  the  muscle. 
The  muscle  then  presents  an  (artificial)  transverse  section  at  each 
end  and  a  longitudinal  surface.  We  may  speak  of  the  latter  as 
being  divided  into  two  equal  parts  by  an  imaginary  transverse 
line  on  its  surface  called  the  'equator,'  containing  all  the  points 
of   the   surface    midway  between    the   two    ends.     Fig.   13  is  a 


'  These  (Fi^.  12)  consist  essentially  of  a  slip  of  thoroughly  amalgamated 
zinc  dipping  into  a  saturated  solution  of  zinc  sulphate,  which  in  turn  is  brought 
into  connection  with  the  nerve  or  muscle  by  means  of  a  plug  or  bridge  of  china- 
clay  moistened  with  dilute  sodium  chloride  solution  ;  it  is  important  that  the 
zinc  should  be  thoroughly  amalgamated.  This  form  of  electrodes  gives  rise  to 
less  polarization  than  do  simple  platinum  or  copper  electrodes.  The  clay  affords 
a  connection  between  the  zinc  and  the  tissue  which  neither  acts  on  the  tissue 
nor  is  acted  on  by  the  tissue.  Contact  of  any  tissue  with  copper  or  platmum 
is  in  itself  sufficient  to  develop  a  current. 


Fig.  12.    NoN-PoLARizABLE  Electrodes. 
a,  the  glass  tube  ;  z,  the  amalgamated  zinc  slips  connected  with  their  respective  wires  ; 
z.  s.,  the  zinc  sulphate  solution ;  ch.  c,  the  plug  of  cliina  clay  ;  c',  the  portion  of  the  china- 
clay  plug  projeciing  from  the  end  of  the  tube  ;  this  can  be  moulded  into  any  required  form. 


CHAP.    11.]  THE   CONTRACTILE   TISSUES. 


63 


diagrammatic  representation  of  such  a  muscle,  the  Hne  ab  being 
the  equator.  In  such  a  muscle  the  development  of  the  muscle 
currents  is  found  to  be  as  follows. 

The  greatest  deflection  is  observed  whep  one  electrode  is 
placed  at  the  mid-point  or  equator  of  the  muscle,  and  the  other 
at  either  cut  end ;  and  the  deflection  is  of  such  a  kind  as  to  shew 


Fic.  13.     Diagram  illostratinc  the  electric  currents  op  nerve  avd  muscle. 
Being  purely  diagrammatic,  it  may  serve  for  a  piece  either  of  ner\-e  or  of  muscle,  except 
that  the  currents  at  the  transverse  section  cannot  be  shewTi  in  a  nerve.     The  arrows  shew  the 
direction  of  the  current  through  the  galvanometer. 

ai.  the  equator.  TTie  strongest  currents  are  tho«  shewn  by  rhe  dark  lines,  as  from  a,  at 
equator,  to  jr  or  to  y  at  the  cut  ends.  The  current  from  a  to  f  is  weaker  than  from  a  to  x, 
though  both,  as  shewn  by  the  arrows,  have  the  same  direction.  A  current  is  shewn  from  e. 
which  is  near  the  equator,  toy,  which  is  farther  from  the  equator.  The  a:rrent  (in  muscle) 
from  a  point  in  the  circumference  to  a  point  nearer  the  centre  of  the  transverse  section  is 
shewn  at  ^A.  From  d  to  ^  or  firom  x  10  y  there  is  no  current,  as  indicated  by  the  dotted 
lines. 


that  positive  currents  are  continually  passing  from  the  equator 
through  the  galvanometer  to  the  cut  end,  that  is  to  say,  the  cut 
end  is  negative  relatively  to  the  equator.  The  currents  outside 
the  muscle  may  be  considered  as  completed  by  currents  in  the 
muscle  from  the  cut  end  to  the  equator.  In  the  diagram  Fig.  13, 
the  arrows  indicate  the  direction  of  the  currents.  If  the  one 
electrode  be  placed  at  the  equator  ab,  the  effect  is  the  same  at 
whichever  of  the  two  cut  ends  x  ox  y  the  other  is  placed.  If,  one 
electrode  remaining  at  the  equator,  the  other  be  shifted  from  the 
cut  end  to  a  spot  c  nearer  to  the  equator,  the  current  continues 
to  have  the  same  direction,  but  is  of  less  intensity  in  proportion 
to   the  nearness  of  the  electrodes  to  each  other.      li  the  two 


64  MUSCLE  CURRENTS.  [BOOK  I. 

electrodes  be  placed  at  unequal  distances  e  and/,  one  on  either  side 
of  the  equator,  there  will  be  a  feeble  current  from  the  one  nearer 
the  equator  to  the  one  farther  off,  and  the  current  will  be  the 
feebler,  the  more  nearly  they  are  equidistant  from  the  equator. 
If  they  are  quite  equidistant,  as  for  instance  when  one  is  placed  on 
one  cut  end  x^  and  the  other  on  the  other  cut  end  y,  there  will  be 
no  current  at  all. 

If  one  electrode  be  placed  at  the  circumference  of  the  trans- 
verse section  and  the  other  at  the  centre  of  the  transverse  section, 
there  will  be  a  current  through  the  galvanometer  from  the  former  to 
the  latter ;  there  will  be  a  current  of  similar  direction  but  of  less 
intensity  when  one  electrode  is  at  the  circumference  g  of  the 
transverse  section  and  the  other  at  some  point  h  nearer  the  centre 
of  the  transverse  section.  In  fact  the  points  which  are  relatively 
most  positive  and  most  negative  to  each  other  are  points  on  the 
equator  and  the  two  centres  of  the  transverse  sections ;  and  the 
intensity  of  the  current  between  any  two  points  will  depend  on  the 
respective  distances  of  those  points  from  the  equator  and  from  the 
centres  of  the  transverse  sections. 

Similar  currents  may  be  observed  when  the  longitudinal  surface 
is  not  the  natural  but  an  artificial  one  ;  indeed  they  may  be 
witnessed  in  even  a  piece  of  muscle  provided  it  be  of  cylindrical 
shape  and  composed  of  parallel  fibres. 

These  natural  'muscle-currents'  are  not  mere  transitory 
currents  disappearing  as  soon  as  the  circuit  is  closed  ;  on  the 
contrary  they  last  a  very  considerable  time.  They  must  there- 
fore be  maintained  by  some  changes  going  on  in  the  muscle,  by 
continued  chemical  action  in  fact.  They  disappear  as  the  ir- 
ritability of  the  muscle  vanishes,  and  therefore  may  be  supposed 
to  be  connected  with  those  nutritive,  so-called  vital  changes 
which  maintain  the  irritability  of  the  muscle. 

Muscle-currents  such  as  have  just  been  described,  may,  we 
repeat,  be  observed  in  any  cylindrical  muscle  suitably  prepared, 
and  similar  currents,  with  variations  which  need  not  be  discussed 
here,  may  be  seen  in  muscles  of  irregular  shape  with  obliquely 
or  otherwise  arranged  fibres.  And  du  Bois-Reymond,  to  whom 
chiefly  we  are  indebted  for  our  knowledge  of  these  currents, 
has  been  led  to  regard  them  as  essential  and  important  properties 
of  living  muscle.  He  has  moreover  advanced  the  theory  that 
muscle  may  be  considered  as  composed  of  electro-motive  particles 
or  molecules,  each  of  which  like  the  muscle  at  large  has  a  positive 
equator  and  negative  ends,  the  whole  muscle  being  made  up  of 
these  molecules  in  somewhat  the  same  way  (to  use  an  illustration 
which  must  not  however  be  strained  or  considered  as  an  exact  one) 


CHAP.    IJ.]  nil.;    CONTRACTILE   TI.SSUKS. 


6S 


as  a  mn-nct  may  he  supposed  to  be  made  up  of  magnetic  particles 
each  with  its  north  and  south  pole. 

There  are  reasons  however  for  thinking  that  these  muscle- 
currents  have  no  such  fundamental  origin,  that  they  are  in  fact  of 
surface  and  mdeed  of  artificial  origin.  Without  entering  laryely 
into  the  controversy  on  this  question  (some  details  of  whir  h  will 
he  found  in  a  subsequent  section  in  small  print),  the  followinc 
imi)ortant  facts  may  be  mentioned. 

I.  When  a  muscle  is  examined  while  it  still  retains  untouched 
Its  natural  tendinous  terminations,  the  currents  are  much  less  than 
when  artihcial  transverse  sections  have  been  made.  The  natural 
tendinous  end  is  less  negative  than  the  cut  surface.  In  some  cases 
It  may  be  even  positive  relatively  to  the  longitudinal  surface.  But . 
the  tendinous  end  becomes  at  once  negative  when  it  is  dipped  in 
water  or  acid,  indeed  when  it  is  in  any  way  injured.  The  less 
roughly  in  fact  a  muscle  is  treated  the  less  evident  are  the  muscle- 
currents,  an.l  Hermann  has  shewn  that  if  proper  care  be  taken  a 
muscle  may  be  so  removed  from  the  body  as  to  give  only  currents 
which  are  hardly  appreciable.  ;         <-  iib 

,  2.  Engelmann-  has  shewn  that  the  surface  of  the  uninjured 
mactive;  ventricle  of  tlie  frog's  heart  is  isoelectric,  i.e.  that  no 
current  is  obtained  when  the  electrodes  are  placed  on  any  two 
points  of  the  surface.  If  however  any  part  of  the  surface  be  in- 
jured, or  if  the  ventricle  be  cut  across  so  as  to  expose  a  cut 
surface  the  injured  spot  or  the  cut  surface  becomes  at  once  most 
powerfully  negative  towards  the  uninjured  surface,  a  strong  current 
being  developed  which  passes  through  the  galvanometer  from  the 
uninjured  surface  to  the  cut  surface  or  to  the  injured  spot  The 
negativity  thus  developed  in  a  cut  surflice  passes  off  in  the 
course  of  some  hours,  but  may  be  restored  by  making  a  fresh  cut 
and  exposing  a  fresh  surface. 

Now  when  a  muscle  is  cut  or  injured  the  substance  of  the  fibres 
dies  at  the  cut  or  injured  surlace.  And  certain  authorities,  amono- 
whom  the  most  prominent  is  Hermann,  have  been  led  by  the 
above  and  other  facts  to  the  conclusion  that  muscle-currents  do 
not  exi.st  naturally  in  untouched  muscles,  that  the  muscular  sub- 
stance IS  naturally,  when  living,  isoelectric,  but  that  whenever 
a  portion  of  the  muscular  substance  dies,  it  becomes  7i>liile  dyin<' 
negative  to  the  living  substance,  and  thus  gives  rise  to  current.? 
1  hey  exp  am  the  typical  currents  (as  they  might  be  called) 
manifested  by  a  muscle  with  a  natural  longitudinal   surface  and 

•  Pfliiger's  Archiv,  xv.  (1877)  p.  116. 

'  The  necessity  of  its  being  inactive  will  be  seen  hubscquently. 


66  NEGATIVE   VARIATION.  [BOOK   I. 

artificial  transverse  sections,  by  the  fact  that  the  dying  cut  ends 
are  negative  relatively  to  the  rest  of  the  muscle. 

Du  Bois-Reymond  and  those  with  him  offer  special  explanations 
of  the  above  facts  and  of  other  objections  which  have  been  urged 
against  the  theory  of  naturally  existing  electro-motive  molecules. 
Into  these  we  cannot  enter  here.  We  must  rest  content  with  the 
statement  that  in  an  ordinary  muscle  currents  such  as  have  been 
described  may  be  witnessed,  but  that  strong  arguments  may  be 
adduced  in  favour  of  the  view  that  these  currents  are  not  '  natural ' 
phenomena  but  essentially  of  artificial  origin.  It  will  therefore  be 
best  to  speak  of  them  as  '  currents  of  rest.' 

Negative    variation    of   the    Muscle-current.      The 

controversy  whether  the  '  currents  of  rest '  observable  in  a 
muscle  be  of  natural  origin  or  not,  does  not  affect  the  truth  or 
the  importance  of  the  fact  that  an  electrical  change  takes  place 
in  a  muscle  whenever  it  enters  into  a  contraction.  When  currents 
of  rest  are  observable  in  a  muscle  these  are  found  to  undergo 
a  diminution  at  the  onset  of  a  contraction,  and  this  diminution 
is  spoken  of  as  '  the  negative  variation  '  of  the  currents  of  rest. 
The  negative  variation  may  be  seen  when  a  muscle  is  thrown  into 
a  single  contraction,  but  is  most  readily  shewn  when  the  muscle 
is  tetanized.  Thus  if  a  pair  of  electrodes  be  placed  on  a  muscle, 
one  at  the  equator,  and  the  other  at  or  near  the  transverse  section, 
so  that  a  considerable  deflection  of  the  galvanometer  needle, 
indicating  a  considerable  current  of  rest,  be  gained,  the  needle  of 
the  galvanometer  will,  when  the  muscle  is  tetanized  by  an  inter- 
rupted current  sent  through  its  nerve  (at  a  point  too  far  from  the 
muscle  to  allow  any  escape  of  the  current  into  the  electrodes 
connected  with  the  galvanometer),  swing  back  towards  zero ;  it 
returns  to  its  original  deflection  when  the  tetanizing  current 
is  shut  off. 

This  negative  variation  may  not  only  be  shewn  by  the  galvano- 
meter, but  it,  as  well  as  the  current  of  rest,  may  be  used  as  a 
galvanic  shock  and  so  employed  to  stimulate  a  muscle,  as  in  the 
experiment  known  as  'the  rheoscopic  frog.'  For  this  purpose 
very  irritable  muscles  and  nerves  in  thoroughly  good  condition  are 
required.  Two  muscle-nerve  preparations  A  and  ^  having  been 
made  and  each  placed  on  a  glass  plate  for  the  sake  of  insulation, 
the  nerve  of  the  one  B  is  allowed  to  fall  on  the  muscle  of  the 
other  A  in  such  a  way  that  one  point  of  the  nerve  comes  in 
contact  with  the  equator  of  the  muscle,  and  another  point  with 
one  end  of  the  muscle  or  with  a  point  at  some  distance  from  the 
equator.     At  the  moment  the  nerve  is  let  fall  and  contact  made,  a 


CHAP.    II.]  THE   CONTRACTILE   TISSUES.  6-J 

current,  viz.  the  'cuircnt  of  rest'  of  the  muscle  A,  passjs  through 
the  nerve;  tliis  acts  as  a  stimulus  to  the  nerve,  and  so  causes  a 
contraction  in  the  muscle  connected  with  the  nerve.  Thus  the 
muscle  A  acts  as  a  battery,  tlie  comi)letion  of  the  circuit  of 
which  by  means  of  the  nerve  of  B  serves  as  a  stimulus,  causing 
the  muscle  B  to  contract. 

If  while  the  nerve  of  B  is  still  in  contact  with  the  muscle  of 
A,  the  nerve  of  the  latter  is  tetanized  with  an  interrupted  current, 
not  only  is  the  muscle  of  A  thrown  into  tetanus  but  also  that 
of  B ;  the  reason  being  as  follows.  At  each  spasm  of  which  the 
tetanus  of  A  is  made  up,  there  is  a  negative  variation  of  the 
muscle-current  of  A.  Each  negative  variation  in  the  muscle- 
current  of  A  serves  as  a  stimulus  to  the  nerve  of  B,  and  is  hence 
the  cause  of  a  spasm  in  the  muscle  of  B ;  and  the  stimuli 
following  each  other  rapidly,  as  being  produced  by  tetanus  of  A 
they  must  do,  the  spasms  in  B  to  which  they  give  rise  are  also 
fused  into  a  tetanus  in  B.  B  in  fact  contracts  in  harmony  with 
A.  This  experiment  shews  that  the  negative  variation  accom- 
panying the  tetanus  of  a  muscle,  though  it  causes  only  a  single 
swing  of  the  galvanometer,  is  really  made  up  of  a  series  of 
negative  variations,  each  single  negative  variation  corresponding 
to  the  single  spasms  of  which  the  tetanus  is  made  up. 

But  an  electrical  change  may  be  manifested  even  in  cases 
when  no  currents  of  rest  exist.  VVe  have  stated  (p.  65)  that  the 
surface  of  the  uninjured  inactive  ventricle  of  the  frog's  heart  is 
isoelectric,  no  currents  being  observed  when  the  electrodes  of  a 
galvanometer  are  placed  on  two  points  of  the  surface.  Neverthe- 
less a  most  distinct  current  is  developed  whenever  the  ventricle 
contracts.  This  may  be  shewn  either  by  the  galvanometer  or  by 
the  rheoscopic  frog.  If  the  nerve  of  an  irritable  muscle-nerve 
preparation  be  laid  over  a  pulsating  ventricle,  each  beat  is 
responded  to  by  a  spasm  of  the  muscle  of  the  preparation.  In 
the  case  of  ordinary  muscles  two  instances  occur  in  which  it  seems 
impossible  to  regard  the  electrical  change  manifested  during 
the  contraction  as  t!ie  mere  diminution  of  a  preexisting  current. 

Accordingly  Hermann  and  those  who  with  him  deny  the 
existence  of  '  natural '  muscle-currents  speak  of  a  muscle  as 
developing  during  a  contraction  a  '  current  of  action,'  occasioned 
as  they  believe  by  the  muscular  substance  as  it  is  entering  into  the 
state  of  contraction  becoming  negative  towards  the  muscular 
substance  which  is  still  at  rest,  or  has  returned  to  a  state  of  rest. 
In  fact,  they  regard  the  negativity  of  muscular  substance  as 
characteristic  alike  of  a  beginning  death  and  of  a  beginning 
contraction.     And  they  believe  that  in  a  muscular   contraction 

5—2 


68  CHEMICAL   CHANGES.  [BOOK   I. 

a  wave  of  negativity  starting  from  the  end-plate  when  indirect, 
or  from  the  point  stimulated  when  direct  stimulation  is  used, 
passes  along  the  muscular  substance  to  the  ends  or  end 
of  the  fibre._  We  cannot  enter  more  fully  here  into  a  dis- 
cussion of  this  difficult  subject,  but  some  account  of  the  various 
facts  and  arguments  brought  forward  by  the  advocates  of  the 
conflicting  views  will  be  found  in  a  subsequent  section  in  small 
print. 

Whichever  view  be  taken  of  the  nature  of  these  muscle  currents, 
and  of  the  electric  change  during  contraction,  whether  we  regard  that 
change  as  a  'negative  variation'  or  as  a  'current  of  action,'  it  is 
important  to  remember  that  it  takes  place  entirely  during  the 
latent  period.  It  is  not  in  any  way  the  result  of  the  change  of 
form,  it  is  the  forerunner  of  that  change  of  form.  Just  as  a 
nervous  impulse  passes  down  the  nerve  to  the  muscle  without  any 
visible  changes,  so  a  molecular  change  of  some  kind,  unattended 
by  any  visible  events,  marked  only  by  an  electrical  change,  runs 
along  the  muscular  fibre  from  the  end-plates  to  the  terminations  of 
the  fibre,  preparing  the  way  for  the  visible  change  of  form  which 
is  to  follow.  This  molecular  invisible  change  is  the  work  of  the 
latent  period,  and  careful  observations  have  shewn  us  that  it,  like 
the  visible  contraction  which  follows  at  its  heels,  travels  along  the 
fibre  from  a  spot  stimulated  (from  the  end-plates  when  the  stimulus 
is  applied  indirectly  through  a  nerve,  or  from  the  point  touched  by 
the  electrodes  when  the  stimulus  is  a  direct  one)  towards  the  ends 
of  the  fibres,  in  the  form  of  a  wave  having  about  the  same  velocity 
as  the  contraction,  viz.  about  3  metres  a  second. 

Chemical  Changes. 

Before  we  attack  the  important  problem,  What  are  the  chemical 
changes  concerned  in  a  muscular  contraction  ?  we  must  study  in 
some  detail  the  chemical  features  of  muscle  at  rest.  And  here  we 
are  brought  face  to  face  with  the  chemical  diff"erences  between 
,  living  and  dead  muscles.  All  muscles,  within  a  certain  time  after 
removal  from  the  body,  or  while  still  within  the  body,  after 
'  general '  death  of  the  body,  lose  their  irritability.  The  loss  of 
irritability  even  when  rapid,  is  gradual,  but  is  succeeded  by  an 
event  of  some  suddenness,  the  entrance  into  the  condition  known 
as  rigor  mof'tis,  the  occurrence  of  which  is  marked  by  the  follow- 
ing features.  The  muscle,  previously  possessing  a  certain  trans- 
lucency,  becomes  much  more  opaque.  Previously  very  extensible 
and  elastic,  it  becomes  rigid  and  inextensible  and  at  the  same  time 
loses  its  elasticity ;  the  muscle  now  requires  considerable  force  to 


CUM'.    II.]  THE   CONTRACTILE   TISSUES.  69 

stretch  it,  and  when  the  force  is  removed,  does  not,  as  before, 
return  to  its  natural  length.  To  the  touch  it  has  lost  much  of  its 
former  softness,  and  becomes  firmer  and  more  resistent.  The 
entrance  into  rigor  mortis  is  characterised  by  a  shortening  or  con- 
traction, which  may,  under  certain  circumstances,  be  considerable. 
•The  energy  of  this  contraction  is  not  great,  so  that  when  opposed, 
no  actual  shortening  takes  place.  When  rigor  mortis  has  been 
fully  ileveloped,  no  muscle-currents  whatever  are  observed.  The 
onset  of  this  rigidity  may  be  considered  as  the  token  of  the  death 
of  the  muscle  itself.  As  we  shall  see,  the  chemical  features  of  the 
dead  rigid  muscle  are  strikingly  different  from  those  of  the  living 
muscle. 

If  a  dead  muscle,  from  which  all  flit,  tendon,  fascia,  and 
connective  tissue  have  been  as  much  as  possible  removed,  and 
which  has  been  freed  from  blood  by  the  injection  of  saline 
solution,  be  minced  and  repeatedly  washed  with  water,  the  wash- 
ings will  contain  certain  forms  of  albumin  and  certain  extractive 
bodies,  of  which  we  shall  speak  directly.  When  the  washing  has 
been  continued  until  the  wash-water  gives  no  proteid  reaction,  a 
large  portion  of  muscle  will  still  remain  undissolved.  If  this  be 
tieated  with  a  10  p.  c.  solution  of  sodium  chloride,  a  large  portion 
of  it  will  become  imperfectly  dissolved  into  a  viscid  fluid  which 
filters  with  difficulty.  If  the  viscid  filtrate  be  allowed  to  fall  drop 
by  drop  into  a  large  quantity  of  distilled  water,  a  -"'hite  flocculent 
matter  will  be  precipitated.  This  llocculent  precipitate  is  myosin. 
It  is  a  proteitl,  giving  the  ordinary  proteid  reactions,  and  having 
the  same  general  elementary  composition  as  other  proteids.  It 
is  soluble  in  dilute  saline  solutibns,  especially  those  of  sodium 
chloride,  and  may  be  classed  in  tlie  globulin  family,  though  it  is 
not  so  soluble  as  paraglobulin.  Dissolved  in  saline  solutions  it 
readily  coagulates  when  heated,  i.e.  is  converted  into  coagulated 
proteid  ',  and  it  is  worthy  of  notice  that  it  coagulates  at  a  lower 
temperature,  viz.  55° — 60°  C,  than  does  serum-albumin,  para- 
globulin and  many  other  proteids ;  it  is  precipitated  and  after  long 
action  coagulated  by  alcohol,  and  is  precipitated  by  an  excess  of  the 
sodium  chloride.  By  the  action  of  dilute  acids  it  is  very  readily 
converted  into  what  is  called  syntonin  or  acid-albumcn%  by  the 
action  of  dilute  alkalis  into  alkali-albumin.  Speaking  generally  it 
may  be  said  to  be  intermediate  in  its  character  between  fibrin  and 
globulin.  On  keeping,  and  especially  on  drying,  its  solubility  is 
much  diminished. 

Of  the  substances  which  are  left  in  washed  muscle  from  which 

'  See  Appendix  "  See  Appendix. 


70  CHEMICAL   CHANGES.  [BOOK   I. 

the  myosin  has  thus  bten  extracted  by  sodium  chloride  sohition 
little  is  known.  If  washed  muscle  be  treated  directly  with  dilute 
hydrochloric  acid,  the  greater  part  of  the  material  of  the  muscle 
passes  at  once  into  syntonin.  The  quantity  of  syntonin  thus 
obtained  may  be  taken  as  representing  the  quantity  of  myosin 
previously  existing  in  the  muscle.  The  portion  insoluble  in* 
dilute  hydrochloric  acid  consists  in  part  of  the  substance  of  the 
sarcolemma,  of  the  nuclei,  and  of  the  tissue  between  the  bundles, 
and  in  part  probably  of  certain  elements  of  the  fibres  themselves. 

If  living  contractile  frog's  muscle,  freed  as  before  as 
much  as  possible  from  blood,  be  frozen  %  and  while  frozen,  minced, 
and  rubbed  up  in  a  mortar  with  four  times  its  weight  of  snow 
containing  i  p.  c.  of  sodium  chloride,  a  mixture  is  obtained 
which  at  a  temperature  just  below  o°C.  is  sufficiently  fluid  to 
be  filtered,  though  with  difficulty.  The  slightly  opalescent  filtrate, 
or  muscle-plasma  as  it  is  called,  is  at  first  quite  fluid,  but  will  when 
exposed  to  the  ordinary  temperature  become  a  solid  jelly,  and 
afterwards  separate  into  a  clot  and  serum.  It  will  in  fact  coagulate 
like  blood-plasma,  with  this  difference,  that  the  clot  is  not  firm 
and  fibrillar,  but  loose,  granular  and  flocculent.  During  the  co- 
agulation the  fluid,  which  before  was  neutral  or  slightly  alkaline, 
becomes  distinctly  acid. 

The  clot  is  myosin.  It  gives  all  the  reactions  of  myosin 
obtained  from  dead  muscle. 

The  serum  contains  albumin  and  extractives. 

Besides  ordinary  serum-albumin  coagulating  at  75°,  Kiihne''  (to 
whom  we  owe  our  knowledge  of  the  above)  found  a  peculiar  form  of 
albumin  or  soluble  proteid  coagulating  at  45°,  irrespective  of  the 
degree  of  acidity  acquired  by  the  serum.  There  is  present  also  a 
proteid  substance  whose  coagulation  point  varies  widely  (sometimes  as 
low  as  25°),  being  dependent  on  the  acidity  of  the  serum  ;  this  latter 
appears  to  be  a  form  of  alkali-albumin,  its  coagulation  point  being 
probably  connected  with  the  salts  present  in  the  serum  (see  Appendix). 
Such  muscles  as  are  red  also  contain  a  small  quantity  of  haemoglobin, 
to  which  indeed  their  redness  is  due. 

Thus  while  dead  muscle  contains  myosin,  serum-albumin,  and 
extractives  with  certain  insoluble  matters  and  certain  gelatinous 
elements  not  referable  to  the  muscle  substance  itself,  living  muscle 
contains  no  myosin,  but  some  substance  or  substances  which  bear 
somewhat  the  same  relation  to  myosin  that  the  fibrin  factors  do  to 

»  Since,  as  we  shall  presently  see,  a  muscle  may  be  frozen  and  thaw  eel  again 
without  losing  any  of  its  vital  powers,  we  are  at  liberty  to  regard  the  frozen 
muscle  as  a  still  living  muscle. 

*  Protoplasma,  Leipzig,  1864. 


CHAP.  "11.]  THE   CONTRACTlLi:   TISSUES.  71 

fibrin,  and  which  becomes  or  become  myosin  on  the  death  of  the 
nniscle. 

We  may  in  fact  speak  of  rigor  mortis  as  characterized  by  a 
coagulation  of  the  muscle-plasma,  comparable  to  the  coagulation 
of  blood  plasma,  but  differing  from  it  inasmuch  as  the  product  is 
not  fibrin  but  myosin.  The  rigidity,  llie  loss  of  suppleness,  and 
the  diminished  transluccncy  appear  to  be  at  all  events  largely, 
though  probably  not  wholly,  due  to  the  change  from  the  fluid 
plasma  to  the  solid  myosin.  We  might  compare  a  living  muscle 
to  a  number  of  fine  transparent  membranous  tubes  filled  wilh 
blood-j)lasma.  When  this  blood-plasma  entered  into  the  'jelly ' 
stage  of  coagulation,  the  system  of  tubes  would  present  many  of 
the  phenomena  of  rig()r  mortis.  They  would  lose  much  of  their 
suppleness  and  transluccncy,  and  acquire  a  certain  amount  of 
rigidity. 

But  there  is  one  verj'  marked  and  important  difference  between 
rigor  mortis  of  muscle  and  the  coagulation  of  blood :  blood 
during  its  coagulation  undergoes  only  a  slight  change  in  its 
reaction  ;  muscle  during  the  onset  of  rigor  mortis  becomes 
distinctly,  it  might  be  said  intensely  acid. 

A  living  muscle  at  rest  is  in  reaction  neutral,  or,  from  some 
remains  of  lymph  adhering  to  it,  faintly  alkaline.  Tested  by 
litmus  paper  it  is  frequently  amphicroitic,  i.e.  it  will  turn  blue 
litmus  red  and  red  litmus  blue, — but  the  change  from  red  to  blue 
is  more  marked  than  that  from  blue  to  red.  If  on  the  other  hand 
the  reaction  of  a  thoroughly  rigid  muscle  be  tested,  it  will  be 
found  to  be  most  distinctly  acid.  This  development  of  acid  is 
witnessed  not  only  in  the  solid  untouched  fibre  but  also  in 
expressed  muscle-plasma.  The  red  colouration  of  the  blue  litmus 
thus  obtained  is  permanent,  and  cannot  therefore  be  due  to 
carbonic  acid. 

From  rigid  muscle  there  may  be  obtained  a  quantity  of  lactic 
acid,  or  rather  of  a  variety  of  lactic  acid  known  as  sarcolactic 
acid'.  It  is  probable  that  the  change  in  the  reaction  is  due 
to  the  formation  of  this  acid. 

The  appearance  of  rigor  mortis  is  characterized  then  by  the 
occurrence  of  a  nitrogenous  proteid  body,  myosin,  not  pre- 
viously existing  as  such  in  the  living  irritable  fibre,  and  of  a 
carbon  acid,  sarcolactic  acid.  But  there  is  another  most  import- 
ant acid,  which  is  developed  at  the  same  time.  Irritable  living 
muscular  substance  like  all  living  protoplasm  is  continu.dly 
respiring,  continually  consuming  oxygen  and  giving  out  carbonic 
acid.  In  the  body,  the  arterial  blood  going  to  the  muscle  gives 
'  Sec  Appendix. 


72  CHEMICAL   CHANGES.  '    [BOOK   I. 

up  some  of  its  oxygen,  and  gains  a  quantity  of  carbonic  acid,  thus 
becoming  venous  as  it  passes  through  the  muscular  capillaries. 
After  removal  from  the  body,  the  living  muscle  continues  to  take 
up  from  the  surrounding  atmosphere  a  certain  quantity  of  oxygen 
and  to  give  out  a  certain  quantity  of  carbonic  acid. 

At  the  onset  of  rigor  mortis  there  is  a  very  large  and  sudden 
increase  in  this  production  of  carbonic  acid,  in  fact  a  burst  as  it 
were  of  that  gas.  This  is  a  phenomenon  deserving  special  atten- 
tion. Knowing  that  the  carbonic  acid  which  is  the  outcome  of 
the  respiration  of  the  whole  body  is  the  result  of  the  oxidation  of 
carbon -holding  substances,  we  might  very  naturally  suppose  that 
the  increased  production  of  carbonic  acid  attendant  on  the 
development  of  rigor  mortis  is  due  to  the  fact  that  during  that 
event  a  certain  quantity  of  the  carbon-holding  constituents  of  the 
muscle  are  suddenly  oxidized.  But  such  a  view  is  negatived  by 
the  following  facts.  In  the  first  place,  the  increased  production 
of  carbonic  acid-  during  rigor  mortis  is  not  accompanied  by  any 
corresponding  increase  in  the  consumption  of  oxygen.  In  the 
second  place,  a  muscle  (of  a  frog  for  instance)  contains  in  itself 
no  free  or  loosely  attached  oxygen;  when  subjected  to  the  action 
of  a  mercurial  air  pump  it  gives  off  no  oxygen  to  a  vacuum, 
offering  in  this  respect  a  marked  contrast  to  blood,  and  yet,  when 
placed  in  an  atmosphere  free  from  oxygen,  it  will  not  only  continue 
to  give  off  carbonic  acid  while  it  remains  alive,- but  will  also 
exhibit  at  the  onset  of  rigor  mortis,  the  same  increased  production 
of  carbonic  acid  that  is  shewn  by  a  muscle  placed  in  an  atujo- 
sphere  containing  oxygen.  It  is  obvious  that  in  such  a  case  the 
carbonic  acid  does  not  arise  from  the  direct  oxidation  of  the 
muscle  substance,  for  there  is  no  oxygen  present  at  the  time  to 
carry  on  that  oxidation.  We  are  driven  to  suppose  that  during 
rigor  mortis,  some  complex  body,  containing  in  itself  ready  formed 
carbonic  acid  so  to  speak,  is  split  up  and  thus  carbonic  acid  set 
free,  the  process  of  oxidation  by  which  that  carbonic  acid  was 
formed  out  of  the  carbon-holding  constituents  of  the  muscle 
having  taken  place  at  some  anterior  date. 

It  is  found  moreover  that  there  is  a  certain  amount  of  parallelism 
between  the  intensity  of  the  rigor  mortis,  the  degree  of  acid  reaction 
{i.e.  the  amount  of  sarcolactic  acid  formed)  and  the  quantity  of  car- 
bonic acid  given  out.  If  we  suppose,  as  we  fairly  may  do,  that  the 
intensity  of  the  rigidity  is  dependent  on  the  quantity  of  myosin 
deposited  in  the  fibres,  the  parallelimi  between  the  three  products, 
myosin,  sarcolactic  acid,  and  carboni:  acid,  would  suggest  the  idea 
that  all  three  are  the  results  of  the  splitting  up  of  the  same  highly 
complex  substance.  But  we  have  not  at  present  succeeded  in  isolating 
or  in  otherwise  definitely  proving  the  existence  of  such  a  body. 


CHAP.    II.]  THE   CONTRACTILE    Tl.SSUES.  73 

Living  resting  muscle  then  is  alkaline  or  neutral  in  reaction,  and 
the  substance  cf  its  fibres  contains  a  coagulable  plasma.  Dead 
rigid  muscle  on  the  other  hand  is  acid  in  reaction,  from  the  pre- 
sence of  sarcolaclic  acid  ;  it  no  longer  contains  a  coagulable  plasma, 
but  is  laden  with  the  solid  myosin.  And  the  change  from  the 
living  irritable  condition  to  that  of  rigor  mortis  is  accompanied  by 
a  large  ami  sudden  development  of  carbonic  acid. 

We  may  now  return  to  the  question,  Wliat  are  the  chemical 
changes  which  take  place  when  a  living  resting  muscle  enters  into 
a  contraction  ?  These  changes  are  most  evident  after  the  muscle 
has  been  subjected  to  a  prolonged  tetanus  ;  but  there  can  be  no 
doubt  that  tlie  chemical  events  of  a  tJtanus  are,  like  the  physical 
events,  simply  the  sum  of  the  results  of  the  constituent  single 
contractions. 

In  the  first  place,  the  muscle  becomes  acid,  not  so  acid  as  in 
rigor  mortis,  but  still  sufficiently  so,  after  a  vigorous  tetanus,  to 
turn  blue  litmus  distinctly  red.  The  reddening  like  that  of  rigor 
mortis  is  permanent,  and  therefore  cannot  be  due  to  carbonic 
acid  ;  it  is  probably,  as  in  the  case  of  rigor  mortis,  caused  by  a 
development  of  sarcolactic  acid. 

In  the  second  place,  a  considerable  quantity  of  carbonic  acid 
is  set  free  ;  and  the  production  of  carbonic  acid  in  muscular  con- 
traction runs  altogether  parallel  to  the  production  of  carbonic  acid 
during  rigor  mortis.  It  is  not  accompanied  by  any  corresponding 
increase  in  the  consumption  of  oxygen.  This  is  evident  even  in  a 
muscle  through  which  the  circulation  of  blootl  is  still  going  on,  for 
though  the  blood  passing  through  a  contracting  muscle  gives  up 
more  o.xygen  than  the  blood  passing  through  a  resting  muscle,  in- 
crease in  the  amount  of  oxygen  taken  up  falls  below  the  increase 
in  the  carbonic  acid  given  out,  but  it  is  still  more  markedly  shewn 
in  a  muscle  removed  from  the  body.  For  in  such  a  muscle  both 
the  contraction  and  the  increase  in  the  production  of  carbonic  acid 
will  go  on  in  the  absence  of  oxygen.  A  frog's  muscle  suspended 
in  an  atmosphere  of  nitrogen  will  remain  irritable  for  some 
considerable  time,  and  at  each  vigorous  tetanus  an  increase  in  the 
production  of  carbonic  acid  may  be  readily  ascertained. 

Moreover  there  seems  to  be  a  correspondence  between  the 
energy  of  the  contraction  and  the  amount  of  carbonic  acid  and 
sarcolactic  acid  produced,  so  that  we  are  naturally  led  to  the  view 
that  in  a  muscular  contraction  as  in  rigor  mortis,  some  highly  com- 
plex substance  splits  up,  and  thus  gives  rise  to  these  two  acids. 
But  here  the  resemblance  between  rigor  mortis  and  contraction 
ends.  We  have  no  evitlence  of  the  formation  during  a  contraction 
of  any  botiy  like  myosin.      Rigor  mortis  and  contraction  are  alike 


74  CHEMICAL   CHANGES,  [BOOK    1. 

in  so  far  as  they  both  have  for  their  basis  a  complex  chemical  pro- 
cess giving  rise  to  the  formation  of  certain  acids,  and  in  both 
events  we  have  a  rise  of  temperature  indicating  that  heat  has  been 
set  free.  But  the  contracted  and  rigid  muscle  differ  essentially  in  the 
fact  that  while  the  former,  as  compared  with  living  resting  muscle, 
increases  in  extensibility  and  loses  none  of  its  translucency,  the 
latter  becomes  less  extensible,  less  elastic,  and  less  translucent. 
Corresponding  to  this  marked  difference,  we  find  myosin  formed 
in  the  rigid  muscle,  but  we  cannot  find  it  in  the  contracted 
muscle 

It  is  stated  by  Hermann  that  in  frog's  muscle  separated  from  the 
body,  the  quantity  of  carbonic  acid  given  out  during  rigor  mortis  is  in 
inverse  proportion  to  the  quantity  given  out  by  the  contractions  which 
have  taken  place  since  the  removal  of  the  muscle  from  the  blood- 
current.  The  more  the  muscle  has  contracted  during  this  period  the 
less  the  amount  of  carbonic  acid  given  out  in  the  final  rigor,  and  vice 
versa.  From  this  it  is  inferred  that  at  the  moment  of  separation  froni 
the  body,  the  muscle  contains  a  certain  capital  of  carbonic-acid-pro- 
ducing material  (to  wit,  tlie  substance  whose  explosive  decomposition 
we  have  supposed  to  give  rise  to  this  and  other  bodies)  which  may  be 
expended  either  in  rigor  mortis  or  in  contraction,  but  which,  from  the 
absence  of  blood,  cannot  be  replaced.  Consequently  the  expenditure 
in  the  direction  of  contraction  must  come  out  of  the  share  allotted  to 
rigor  mortis.     To  this  point  we  shall  return. 

The  other  chemical  changes  in  muscle  have  not  yet  been  clearly 
made  out.  Indeed  our  whole  information  concerning  the  other 
chemical  constituents  of  muscle  is  at  present  imperfect. 

Fats  are  present  in  considerable  quantities,  and  the  extractives 
are  varied  and  immerous.  The  most  important  are  kreatin,  sarco- 
lactic  or  paralactic  acid  (a  variety  of  lactic  acid,  diflfering  from  it 
chiefly  in  the  solubility  of  its  salts,  and  in  the  amount  of  water  of 
crystallization  contained  in  them),  and  sugar.  To  these  may  be 
added  xanthin,  hypoxanthin  (sarkin),  inosit  (especially  in  the 
cardiac  muscles),  inosinic  acid  and  traces  of  uric  acid.  Except  in 
.pathological  conditions  (and  in  the  plagiostome  fishes)  urea  is  con- 
spicuous by  its  absence.  In  living  muscle  glycogen  is  frequently 
present,  and  is  at  the  death  of  the  muscle  transformed  into  sugar. 
Dextrin  has  also  been  found  ;  and  a  special  fermentable  muscle- 
sugar  has  been  described.  It  has  been  much  debated  whether 
kreatin  or  kreatinin,  or  both,  are  present  in  muscle  ;  the  evidence 
goes  to  shew  that  kreatin  alone  is  present. 

The  ashes  of  muscle,  like  those  of  the  red  corpuscles,  are 
characterized  by  the  preponderance  of  potassium  salts  and  of 
phosphates ;  these  form  in  fact  nearly  80  p.  c.  of  the  whole 
ash. 


CHAF.   11]  THE   CONTRACTILE   TISSUES.  75 

The  general  comi)Osiiion  of  human  muscle  is  shewn  in  the 
following  table  of  v.  Bibra. 

Water 744-5 

Solids 

Myosin  and  other  matters,  clastic  ele- 
ments, &c.,  insoluble  in  water       ...     i55'4 
Soluble  proteids  ...  ...  ...       193 

Gelatin  ...  ...         ...         ...      207 

Extractives         ...  ...  ...  ...      37*1 

Fats        ...  ...  ...  ...  ...       230 

255-5 

Hclmholtz  shewed  long  ago  that  by  continued  contraction  the 
subitances  in  muscle  which  are  soluble  in  water,  i.e.  the  aqueous 
e.xtractivcs,  are  diminished,  while  those  which  are  soluble  in  alcohol 
are  increased.  In  other  words,  during  contraction  some  substance  or 
substances  soluble  in  water  are  converted  into  another  or  other  sub- 
stances insoluble  in  water  but  soluble  in  alcohol.  Ranke '  concluded 
from  his  observations  that  the  proteids  are  slightly  diminished,  and 
that  sugar  and  tats  are  produced  ;  but  the  data  for  these  conclusions 
arc,  at  present  at  all  events,  insufficient.  It  has  been  suggested  that 
the  glycogen  naturally  present  in  muscle  is  during  contraction  con- 
verted into  sugar.  The  failure  to  obtain  any  satisfactory  evidence  of 
the  production  of  nitrogenous  crystalline  bodies  us  the  result  of 
contraction  is  of  interest  ;  for  though  urea  is  conspicuous  by  its 
absence  from  muscle  both  during  rest  and  after  contra rtion,  some 
observers  have  thought  that  the  kreatin  in  muscle  is  increased  by 
contraction  :  this  has  not  been  definitely  proved. 

The  Changes  in  a  Nerve  during  the  passage  of  a  Nervous 
Impulse. 

The  change  in  the  form  of  a  muscle  during  its  contraction  is  a 
thing  which  can  be  seen  and  felt ;  but  the  changes  in  a  nerve  during 
its  activity  are  invisible  and  impalpable.  We  stimulate  one  end  of 
a  nerve,  and  since  we  see  this  followed  by  a  contraction  of  the 
muscle  attached  to  the  other  end,  we  know  that  some  changes  or 
other  constituting  a  nervous  impulse  have  been  propagated  along 
the  nerve,  but  these  are  changes  which  we  cannot  see.  Nor  have 
we  satisfactory  evidence  of  any  chemical  events  or  of  any  produc- 
tion of  heat,  accompanying  a  nervous  impulse.  We  may  fairly 
suppose  that  some  chemical  changes  form  the  basis  of  a  nervous 
impulse,  and  that  these  changes  set  free  a  certain  amount  of  heat, 
but  these  if  they  occur  are  too  slight  to  be  recognized  satisfactorily 
by  the  means  at  present  at  our  disposal.     In  fact,   beyond  the 

'    7'<tamis,  1S65. 


^6  CHANGES  DURING  A  NERVOUS  IMPULSE.  [BOOK  I. 

terminal  results  of  a  nervous  impulse,  such  as  a  muscular  contrac- 
tion in  the  case  of  a  nerve  going  to  a  muscle,  or  some  affection  of 
the  central  nervous  system  in  the  case  of  a  nerve  still  in  connection 
with  its  nervous  centre,  there  is  one  event  and  one  event  only 
which  we  are  able  to  recognize  as  the  objective  token  of  a 
nervous  impulse,  and  that  is  the  so-called  negative  variation  of  the 
nerve-current.  For  a  piece  of  nerve  removed  from  the  body 
exhibits  nearly  the  same  electric  phenomena  as  a  piece  of  muscle. 
It  has  an  equator  which  is  electrically  positive  as  compared  to  its  two 
cut  ends.  In  fact  the  diagram  Fig.  13,  and  the  description  which 
it  was  used  on  p,  6^^  to  illustrate,  may  be  applied  to  nerve  as  well 
as  to  muscle,  except  that  the  currents  are  in  all  cases  much  more 
feeble  in  the  case  of  nerves  than  of  muscles,  and  the  special 
currents  from  the  circumference  to  the  centre  of  the  transverse 
sections  cannot  well  be  shewn  in  a  slender  nerve  ;  indeed  it  is 
doubtful  if  they  exist  at  all. 

Du  Bois-Reymond '  found  the  electro-motive  force  of  the  sciatic 
nerve  of  a  frog  to  amount  to  '022  Daniel),  while  that  of  the  rabbit  did 
not  exceed  "026  Daniell.  Engelmaan  ^  however  obtained  for  the 
sciatic  of  the  frog  a  value  of  -046  iJaniell. 

During  the  passage  of  a  nervous  impulse  the  '  natural  nerve- 
current  '  undergoes  a  negative  variation,  just  as  the  '  natural  muscle- 
current  '  undergoes  a  negative  variation  during  a  contraction.  There 
are  however  difficulties  in  the  case  of  the  nerve  similar  to  those  in 
the  case  of  the  muscle,  concerning  the  i^re-existence  of  any  such 
'  natural '  currents  ;  hence  we  may  say  that  in  a  nerve  during  the 
passage  of  a  nervous  impulse,  as  in  a  muscle  during  a  muscular 
contraction,  a  '  current  of  action  '  is  developed. 

This  '  current  of  action  '  or  '  negative  variation '  may  be  shewn 
either  by  the  galvanometer  or  by  the  rheoscopic  frog.  If  the 
nerve  of  the  '  muscle-nerve  preparation  '  B  (see  p.  67)  be  placed  in 
an  appropriate  manner  on  a  thoroughly  irritable  nerve  A  (to  which 
of  course  no  muscle  need  be  attached),  i.e.  touching  say  the  equator 
and  one  end  of  the  nerve,  then  single  induction-shocks  sent  into 
the  far  end  of  ^  will  cause  single  spasms  in  the  muscle  of  B,  while 
tetanization  of  A,  i.e.  rapidly  repeated  shocks  sent  into  A^  will 
cause  tetanus  of  the  muscle  of  B. 

That  this  current,  whether  it  be  regarded  as  an  independent 
'  current  of  action  '  or  as  a  negative  variation  of  a  '  pre-existing  ' 
current,  is  an  essential  feature  of  a  nervous  impulse  is  shewn  by 
the  fact  that  the  degree  or  intensity  of  the  one  varies  with  that  of 

'   Gesatnmeite  Abhandl,  (1877),  \1.2y1. 
*  Pfliiger's  Archiv,  XV.  (1877),  P-  2ii. 


CHAP.    11.]  THE   CONTRACTILE   TISSUES.  "JJ 

the  other.  They  botli  travel  too  at  the  same  rate.  In  describing 
the  muscle-curve,  and  tlic  method  of  measuring  the  muscular 
latent  period,  v/e  have  incidentally  shewn  (p.  51)  how  the  velocity 
of  the  nervous  impulse  is  measured  also,  and  stated  that  the  rate 
in  the  nerves  of  a  frog  is  about  28  metres  a  second.  Bernstein  by 
means  of  an  apparatus  which  is  described  on  p.  106  finds  that  the 
negative  variation  travels  along  an  isolated  piece  of  nerve  at  the 
same  rate.  He  also  finds  tliat  it,  like  the  molecular  change  in  a 
muscle  preceding  the  contraction,  and  indeed  like  the  contraction 
itself,  passes  over  any  given  spot  of  the  nerve  in  the  form  of  a 
wave,  rising  ra[)i(lly  to  a  maximum  and  then  more  gradually  de- 
clining again.  He  has  been  able  to  measure  the  length  of  the 
wave,  and  this  he  finds  to  be  about  iS  mm.,  taking  '0007  sec.  to 
pass  over  any  one  point. 

When  an  isolated  })iece  of  nerve  is  stimulated  in  the  middle, 
the  negative  variation  is  propagated  equally  well  in  both  directions, 
and  that  whether  the  nerve  be  a  chiefly  sensory  or  a  chiefly  motor 
nerve,  or  indeed  if  it  be  a  nerve-root  composed  exclusively  of 
motor  or  of  sensory  fibres.  Taking  the  negative  variation  as  the 
token  of  a  nervous  impulse,  we  infer  from  this  that  when  a  nerve- 
fibre  is  stimulated  artificially  at  any  part  of  its  course,  the  nervous 
impulse  set  going  travels  in  both  directions. 

We  used  just  now  the  phrase  '  tetanization  of  a  nerve,' 
meaning  the  application  to  a  nerve  of  rapidly  repeated  shocks 
such  as  would  produce  tetanus  in  the  muscle  to  which  the  nerve 
was  attacheil,and  we  shall  have  frequent  occasion  to  employ  the 
phrase.  It  will  however  of  course  be  understood  that  there  is  in 
the  nerve  as  far  as  we  know  no  summation  of  nervous  impulses 
comparable  to  the  summation  of  muscular  contractions.  The 
series  of  shocks  sent  in  at  the  far  end  of  the  nerve  start  a  series 
of  impulses,  these  traVel  down  the  nerve  and  reach  the  muscle  as 
a  series  of  distinct  impulses  ;  and  the  first  changes  in  the  muscle, 
the  molecular  latent-period  changes,  also  form  a  series  the 
members  of  which  are  di.stinct.  It  is  not  until  these  molecular 
changes  become  transformed  into  visible  changes  of  form  that  any 
fusion  or  summation  takes  place. 

Putting  together  the  facts  contained  in  this  and  the  preceding 
sections,  tlie  following  may  be  taken  as  a  brief  approximate 
history  of  what  takes  place  in  a  muscle  and  nerve  when  the  latter 
is  subjected  to  a  single  induction-shock.  At  the  instant  that  the 
induced  current  passes  into  the  nerve,  changes  occur,  of  whose 
nature  we  know  nothing  certain  except  that  they  cause  a  '  nega- 
tive variation  '  of  the  '  natural '   nerve-current.      These  changes 


78  ACTION   OF   THE   CONSTANT   CURRENT.   [BOOK   I. 

propagate  themselves  along  the  nerve  in  both  directions  as  a 
nervous  impulse  in  the  form  of  a  wave,  having  a  wave-length  of 
about  1 8  mm.,  and  a  velocity  (in  frog's  nerve)  of  about  28m.  per 
sec.  Passing  down  the  nerve-fibres  to  the  muscle,  flowing  along  the 
branching  and  narrowing  tracts,  the  wave  at  last  breaks  on  the 
end-plates  of  the  fibres  of  the  muscle.  Here  it  is  transmuted 
into  a  muscle-impulse,  with  a  shorter  steeper  wave,  and  a  greatly 
diminished  velocity  (about  3  m.  per  sec).  This  muscle-impulse, 
of  which  we  know  hardly  more  than  that  it  is  m.arked  by  a 
negative  variation  in  the  muscle-current,  travels  from  each  end- 
plate  in  both  directions  to  the  end  of  the  fibre.  What  there 
becomes  of  it  we  do  not  know,  but  it  is  immediately  followed  by 
the  visible  contraction-wave,  travelling  behind  it  at  about  the  same 
rate,  but  with  a  vastly  increased  wave-length.  The  fibre,  as  the 
wave  passes  over  it,  swells  and  shortens,  bringing  its  two  ends 
together,  its  molecules  during  the  change  of  forni  arranging  them- 
selves in  such  a  way  that  the  extensibility  of  the  fibre  is  increased, 
while  at  the  same  time  an  explosive  decomposition  of  material 
takes  place,  leading  to  a  discharge  of  carbonic  and  sarcolactic 
acids,  and  probably  of  other  unknown  things,  with  a  considerable 
development  of  heat. 

Sec.  3.  Thk  Nature  of  the  Changes  through  which  an 
Electric  Current  is  able  to  generate  a  Nervous 
Impulse. 

Action  of  the  Constant  Current. 

In  the  preceding  account,  the  stimulus  applied  in  order  to 
give  rise  to  a  nervous  impulse  has  always  been  supposed  to  be  an 
induction  shock,  single  or  repeated.  This  choice  of  stimulus  has 
been  made  on  account  of  the  almost  momentary  duration  of  the 
induced  current.  Had  we  used  a  current  lasting  for  some  con- 
siderable time,  the  problems  before  us  would  have  become  more 
complex  in  consequence  of  our  having  to  distinguish  between  the 
events  taking  place  while  the  current  was  passing  through  the 
nerve  from  those  which  occurred  at  the  moment  when  the  current 
was  thrown  into  the  nerve  or  at  the  moment  when  it  was  shut  off 
from  the  nerve.  These  complications  do  arise  when  instead  of 
employing  the  induced  current  as  a  stimulus,  we  use  a  cojistant 
current,  i.e.  when  we  pass  through  the  nerve  (or  muscle)  a  cur- 
rent direct  from  the  battery  without  the  intervention  of  any 
induction-coil. 

Before  making  the  actual  experiment,  we  might  perhaps 
naturally  suppose  that  the  constant  current  would  act  as  a  stimulus 


CIIAr.   II.]  TIIH   CONTRACTILE   TISSUES.  79 

throughout  the  whole  time  during  which  it  was  apph'ed,  that,  so 
long  as  the  current  passed  along  the  nerve,  nervous  impulses 
would  be  generated  and  thus  the  muscle  thrown  into  something  at 
all  events  like  tetanus.  And  under  certain  conditions  this  docs 
take  place ;  occasionally  it  happens  that  at  the  moment  the 
current  is  thrown  into  the  nerve,  the  muscle  of  the  muscle-nerve 
preparation  falls  into  a  tetanus  which  is  continued  until  the  current 
is  shut  oft".  But  such  a  result  is  exceptional.  In  the  vast  majority 
of  cases  what  happens  is  as  follows.  At  the  moment  that  the 
circuit  is  made,  the  moment  that  the  current  is  thrown  into  the 
nerve,  a  single  spasm,  a  simple  contraction,  the  so-called  making 
contraction,  is  witnessed ;  but  after  this  has  passed  away  the 
muscle  remains  absolutely  quiescent  in  spite  of  the  current 
continuing  to  pass  through  the  nerve,  and  this  quiescence  is 
maintained  until  the  circuit  is  broken,  until  the  current  is 
shut  oft"  from  the  nerve,  when  another  simple  contraction, 
the  so-called  breaking  contraction,  is  observed.  The  mere  passage 
of  a  uniform  constant  current  of  uniform  intensity  through  a 
nerve  does  not  act  as  a  stimulus  generating  a  nervous  impulse ; 
such  an  impulse  is  only  set  up  when  the  current  either  falls  into 
or  is  shut  off  from  the  nen^e.  It  is  the  entrance  or  the  exit  of 
the  current,  and  not  the  continuance  of  the  current,  which  is  the 
stimulus. 

The  quiescence  of  the  nerve  and  muscle  during  the  passage  of 
the  current  is  however  dependent  on  the  current  remaining  uniform 
in  intensity  or  at  least  not  being  suddenly  increased  or  diminished. 
Any  sufficiently  sudden  and  large  increase  or  diminution  of  the 
intensity  of  the  current,  will  act  like  the  entrance  or  exit  of  a 
current,  and  by  generating  nervous  impulses  give  rise  to  contrac- 
tions. If  the  intensity  of  the  current  however  be  vary  slowly  and 
gradually  increased  or  diminished,  a  very  wide  range  of  intensity 
may  be  passed  through  without  any  contraction  being  seen.  It  is 
the  sudden  change  from  one  condition  to  another,  and  not  the 
condition  itself,  which  causes  the  nervous  impulse. 

In  many  cases,  both  a  'making'  and  a  'breaking'  contraction, 
each  a  simple  spasm,  are  observed,  and  this  is  perhaps  the 
commonest  event ;  but  under  conditions  which  will  be  discussed 
below  either  the  breaking  or  the  making  contraction  may  be 
absent,  i.e.  there  may  be  a  contraction  only  when  tlie  current  is 
thrown  into  the  nerve  or  only  when  it  is  shut  off  from  the  nerve. 

Under  ordinary  circumstances  the  contractions  witnessed  with 
the  constant  current  either  at  the  make  or  at  the  break,  are  of  the 
nature  of  a  *  simple '  contraction,  but,  as  has  already  been  said, 
the  application  of  the  current  may  give  rise  to  a  very  pronounced 


80  ELECTROTONUS.  [BOOK   I. 

tetanus.  Such  a  tetanus  is  seen  sometimes  when  the  current^is 
made,  lasting  during  the  appHcation  of  the  current,  sometimes 
when  the  current  is  broken,  lasting  some  time  after  the  current 
has  been  wholly  removed  from  the  nerve.  The  former  is  spoken 
of  as  a  'making,'  the  latter  as  a  'breaking'  tetanus.  But 
these  exceptional  results  of  the  constant  current  need  not  detain 
us  now. 

The  great  interest  attached  to  the  action  of  the  constant 
current  lies  in  the  fact,  that  duri7ig  the  passage  of  the  current,  in 
spite  of  the  absence  of  all  nervous  impulses  and  therefore  of  all 
muscular  contractions,  the  nerve  is  for  the  time  both  between  and 
on  each  side  of  the  electrodes  profoundly  modified  in  a  most 
peculiar  manner.  This  modification,  important  both  for  the  light 
it  throws  on  the  generation  of  nervous  impulses  and  for  its 
practical  applications,  is  known  under  the  name  of  electrotonus. 

Electrotonus.  The  marked  feature  of  the  electrotonic 
condition  is  that  the  nerve  though  apparently  quiescent  is  changed 
in  respect  to  its  irritability  ;  and  that  in  a  different  way  in  the 
neighbourhood  of  the  two  electrodes  respectively. 

Suppose  that  on  the  nerve  of  a  muscle-nerve  preparation  are 
placed  two  (non-polarizable)  electrodes  (Fig.  14,  a,  k)  connected 
with  a  battery  and  arranged  with  a  key  so  that  a  constant  current 


A. 


7t  a. 


Fig.  14.     Muscle-nerve  Preparations,  with  the  nerve  exposed  in  .4  to  a  descending  and 
in  B  to  an  ascending  constant  current. 

In  eacha  is  the  anode,  k  the  kathode  of  the  constant  current,    x  represents  the  spot 
where  the  induction-shocks  used  to  test  thp  irritability  of  the  nerve  are  sent  in. 


CHAl'.    Il.j  THE   CONTRACTILE  TISSUES.  8l 

can  at  pleasure  be  thrown  into  or  shut  off  from  tlie  nerve.  This 
constant  current,  whose  effects  we  are  about  to  study,  may  be 
called  the  'polarizing  current.'  I>et  a  be  the  positive  electrode 
or  anode,  and  k  the  negative  electrode  or  kathode,  both  placed  at 
some  distance  from  the  muscle,  and  also  with  a  certain  interval 
between  each  otlier.  ^  At  the  point  x  let  there  be  applied  a  pair 
of  electrodes  connected  with  an  induction-machine.  Let  the 
muscle  further  be  connected  with  a  lever,  so  that  its  contractions 
can  be  recorded,  and  their  amount  measured.  Before  the  polar- 
izing current  is  thrown  into  the  nerve,  let  a  single  induction-shock 
of  known  intensity  (a  weak  one  being  chosen,  or  at  least  not  one 
which  would  cause  in  the  muscle  a  maximum  contraction)  be 
thrown  in  at  x.  A  contraction  of  a  certain  amount  will  follow. 
That  contraction  may  be  taken  as  a  measure  of  the  irritability 
of  the  nerve  at  the  point  x.  Now  let  the  polarizing  current 
be  thrown  in,  and  let  the  direction  of  the  current  be  a  descending 
one,  with  the  kathode  or  negative  pole  nearest  the  muscle,  as 
in  Fig.  i^A.  If  while  the  current  is  passing,  the  same  induction- 
shock  as  before  be  sent  through  x,  the  contraction  which  results 
will  be  found  to  be  greater  than  on  the  former  occasion.  If 
the  polarizing  current  be  shut  off,  and  the  point  x  after  a  short 
interval  again  tested  with  the  same  induction-shock,  the  contraction 
will  be  no  longer  greater,  but  of  the  same  amount,  or  perhaps 
not  so  great,  as  at  first.  During  the  passage  of  the  polarizing 
current,  therefore,  the  irritability  of  the  nerve  at  the  point  x  has 
.  been  temporarily  increased,  since  the  same  shock  applied  to  it 
causes  a  greater  contraction  during  the  presence  than  in  the 
absence  of  the  current.  But  this  is  only  true  so  long  as  the 
polarizing  current  is  a  descending  one,  so  long  as  the  point  x  lies 
on  the  side  of  the  kathode.  On  the  other  hand,  if  the  polarizing 
current  had  been  an  ascending  one,  with  the  anode  or  positive  pole 
nearest  the  muscle,  as  in  Fig.  14  i?,  the  irritability  of  the  nerve  at 
X  would  have  been  found  to  be  diminished  instead  of  increased  by 
the  polarizing  current.  That  is  to  say,  when  a  constant  current  is 
applied  to  a  nerve,  the  irritability  of  the  nerve  between  the 
polarizing  electrodes  and  the  muscle  is,  during  the  passage  of  the 
current,  increased  when  the  kathode  is  nearest  the  muscle  (and  the 
polarizing  current  descending)  and  diminished  when  the  anode  is 
nearest  the  muscle  (and  the  polarizing  current  ascending).  The 
same  result,  i/nitatis  mutandis,  and  with  some  qualifications  to  be 
referred  to  directly,  would  be  gained  if  x  were  placed  not  between 
the  muscle  and  the  polarizing  current,  but  on  the  far  side  of  the 
latter.  Hence  it  may  be  stated  generally  that  during  the  passage 
of  a  constant  current  through  a  nerve  the  irritability  of  the  nerve 
F.  P.  6 


82 


ELECTROTONUS. 


[book  I. 


is  increased  in  the  region  of  the  kathode,  and  diminished  in  the 
region  of  the  anode.  The  changes  in  the  nerve  which  give  rise  to 
this  increase  of  irritabiUty  in  the  region  of  the  kathode  are  spoken 
of  as  kateledrotonus,  and  the  nerve  is  said  to  be  in  a  katelectro- 
tonic  condition.  Similarly  the  changes  in  the  region  of  the  anode 
are  spoken  of  as  aneledrotoiius,  and  the  nerve  is  said  to  be  in 
an  anelectrotonic  condition.  It  is  also  often  usual  to  speak  of 
the  katelectrotonic  increase,  and  anelectrotonic  decrease  of 
irritability. 

This  law  remains  true  whatever  be  the  mode  adopted  for  deter- 
mining the  irritability.  The  result  holds  good  not  only  with  a 
single  induction-shock,  but  also  with  a  tetanizing  interrupted 
current,  with  chemical  and  with  mechanical  stimuli.  The  increase 
and  decrease  of  irritability  are  most  marked  in  the  immediate 
neighbourhood  of  the  electrodes,  but  spread  for  a  considerable 
distance  in  either  direction  in  the  extrapolar  regions.  The  same 
modification  is  not  confined  to  the  extrapolar  region,  but  exists 
also  in  the  intrapolar  region.  In  the  intrapolar  region  there  must 
be  of  course  an  indifferent  point,  where  the  katelectrotonic  increase 
merges  into  the  anelectrotonic  decrease,  and  where  therefore  the 
irritability  is  unchanged.  When  the  polarizing  current  is  a  weak 
one,  this  indifferent  point  is  nearer  the  anode  than  the  kathode,  but 
as  the  polarizing  current  increases  in  intensity,  draws  nearer  and 
nearer  the  kathode  (see  Fig.  15). 


Fig.  15.    Diagram  Illustrating  the  Variations  of  Irritability  during  Electro- 
TONUs,  with  Polarizing  Currents  of  Increasing  Intensity.    (From  Pfliiger). 

The  anode  is  supposed  to  be  placed  at  A,  the  kathode  at  B  ;  AT5  is  consequently  the 
intrapolar  district.  In  each  of  the  three  curves,  the  portion  of  the  curve  below  the  base  line 
represents  diminished  irritability,  that  above,  increased  irritability,  y^  represents  the  effect 
of  a  weak  current ;  the  indifferent  point  x-^  is  near  the  anode  A.  In  j'2,  a  stronger  current, 
the  indifferent  point  jsTj  is  nearer  the  kathode  B,  the  diminution  of  irritability  in  aneiectrotonus 
and  the  increase  in  katelectrotonus  being  greater  than  in  y^  ;  the  effect  also  spreads  for  a 
greater  distance  along  the  extrapolar  regions  in  both  directions.  Inj/a  the  same  events  are 
seen  to  be  still  more  marked. 


lilt   CONTRACT] LK    TISSUtS.  8^ 

The  katclcctrotonic  increase  and  anclectrotonic  decrease  reach  a 
maximum  soon  after  tlic  making;  of  the  polirizing  current,  and  thence- 
forwari  gradually  diminish.  Tlie  two  efTects  however  are  not  cjuite 
parallel.  The  katelcctrotonic  increase  is  the  first  to  b;  developer!  ;  it 
r.ipidly  rises  to  a  maximum  and  somewhat  rapidly  declines.  The  an- 
clectrotonic decrease  is  not  manifest  at  first  ;  when  it  does  appear 
it  increases  slowly,  and  having  reached  a  maximum  diminishes  slowly 
:igain. 

When  the  polarizing  current  is  shut  oflf  there  is  a  rebound  at  both 
p.jles  ;  a  temporary  increase  of  irritability  in  the  anclectrotonic  and  a 
temporary  decrease  in  the  katelcctrotonic  regions. 

The  amount  of  increase  and  decrease  is  dependent  :  (i)  On  the 
strength  of  the  current,  the  stronger  current  up  to  a  certain  limit 
producing  the  greater  effect.  (2)  On  the  irritability  of  the  nerve, 
the  more  irritable,  better  conditioned  nerve  being  the  more  affected 
by  a  current  of  the  same  intensity. 

The  increase  or  decrease  of  irritability  applies  not  only  to  the 
origination  of  impulses,  but  also  to  their  propagation  or  conduction. 
At  least  anelectrotonus  offers  an  obstacle  to  the  passage  of  a 
nervous  impulse. 

These  variations  of  irritability  at  the  kathode  and  anodj  respec- 
tively must  be  the  result  of  molecular  changes,  brought  about  by 
the  action  of  the  constant  current.  They  are  interesting  because 
they  shew  that  the  generation  of  a  nervous  impulse  as  the  result  of 
the  making  or  breaking  of  a  constant  current  is  dependent  on  the 
change  of  a  nerve  from  its  normal  condition  into  either  katelectro- 
tonus  or  anelectrotonus,  or  back  agam  from  one  of  these  phases 
into  its  normal  condition.  And  certain  phenomena  which  will  be 
described  below  under  the  heading  of  the  '  law  of  contraction ' 
go  far  to  shew  that  a  nervous  impulse  is  generated  only  when  a 
nerve  passes  suddenly  from  a  normal  condition  into  the  phase  of 
katelectrotonus  (making  contraction)  or  returns  from  the  phase  of 
anelectrotonus  (breaking  contraction)  to  a  normal  condition,  in 
other  words,  when  it  passes  suddenly  from  a  phase  of  lower  to  a 
phase  of  higher  irritability. 

An  induction-shock  is  a  current  of  very  short  duration 
developed  very  suddenly  and  disappearing  more  gradually. 
Hence  when  it  falls  into  a  nerve,  the  nerve  undergoes  a  sudden 
transition  from  its  normal  condition  to  the  katelectrotonic  phase, 
and  consequently  a  nervous  impulse  giving  rise  to  a  contraction  is 
the  result.  The  return  from  the  anelectrotonic  phase  to  the 
normal  condition  is  more  gradual,  and  accordingly  no  nervous 
impulse  is  generated  and  no  contraction  is  witnessed.  We  might 
add  that  the  return  from  the  anclectrotonic  phase  to  the  normal 
condition  appears  from    a  number  of  considerations  to  be   less 

6 — 2 


84  LAW   OF   CONTRACTION.  [BOOK   I. 

effective  as  a  generator  of  nervous  impulses  than  the  change  from 
the  normal  condition  to  the  katelectrotonic  phase.  Hence  in  the 
induced  current  we  have  to  deal  with  a  '  making '  contraction 
only,  the  breaking  contraction  being  absent.  This  is  true  whether 
the  induced  current  be  produced  by  the  making  or  the  breaking 
of  a  constant  current. 

Law  of  Contraction.  At  the  making  of  a  constant  current,  then, 
there  is  set  up  a  condition  of  katelectrotonus  and  of  anelectrotonus  ; 
on  the  breaking  of  the  current  these  conditions,  with  more  or  less 
rebound,  disappear.  What  have  these  changes  to  do  with  the 
generation  of  nervous  impulses  ? 

It  has  already  been  stated  that  when  a  constant  current  is  applied 
to  a  nerve,  a  contraction  is  caused  in  the  muscle,  i  e.  a  nervous  impulse 
is  started  in  the  nerve,  either  at  the  make  or  at  the  break,  or  at  both. 
On  further  examination  it  is  found  that  the  occurrence  or  non-occurrence 
of  a  contraction  depends  on  the  direction  {i.e.  whether  descending 
with  the  kathode  nearest  the  muscle,  Fig.  14,  A,  or  ascending  with  the 
anode  nearest  the  muscle,  Fig.  14,  B}  and  the  intensity  of  the  cur- 
rent. The  results  have  been  formulated  in  the  following  '  law  of 
contraction.' 

Descending.  Ascending. 

Make     Break  Make     Break 

Very  Weak  C        —  —        — 

Weak  C        —  C         — 

Moderate      C         C  C  C  " 

Strong  C        —  —         C 

where  C  indicates  a  contraction.  This  law  becomes  intelligible  if  we 
suppose  that  nervous  impulses  are  originated  only  by  the  rise  of 
katelectrotonus,  and  by  the  fall  of  anelectrotonus,  and  not  at  all  by  the 
rise  of  anelectrotonus,  or  by  the  fall  of  katelectrotonus,  or  by  the 
steady  maintenance  of  either.  Remembering  that  in  katelectrotonus 
irritability  is  increased  and  in  anelectrotonus  diminished,  we  may 
formulate  the  law  as  follows  :  a  nervous  impulse  is  generated  at  any 
point  of  a  nerve  when  there  is  a  sudden  change  from  a  phase  of  lower 
to  one  of  higher  irritability,  as  from  the  normal  condition  to  katelec- 
trotonus, or  from  anelectrotonus  to  the  normal  condition.  We  must, 
however,  further  suppose  that  the  rise  of  katelectrotonus  more  readily 
gives  rise  to  an  impulse,  or  gives  rise  to  a  larger  impulse,  than  does 
the  fall  of  anelectrotonus,  and  that  the  condition  of  anelectrotonus, 
especially  when  pronounced,  is  an  obstacle  to  the  passage  towards  the 
muscle  of  impulses  originating  on  the  side  away  from  the  muscle. 
Thus  with  weak  currents  a  contraction  occurs  only  at  the  make,  at  the 
rise  of  katelectrotonus,  of  both  the  descending  and  ascending  currents. 
But  the  contraction  is  easier  to  get  with  the  descendmg  than  with  the 
ascending  current,  because  in  the  latter  the  impulse  started  at  the 
kathode  has  to  pass  through  an  anelectrotonic  region  before  it  can  arrive 
at  the  muscle,  and  hence  with  '  very  weak '  currents  we  get  a  contrac- 
tion with  the  make  of  the  descending  current  only.  With  a  moderate 
current,  as  for  instance  with  a  sinsrle  Daniell  acting:  as  the  source  of 


CHAP.    II.]  THE   CONTRACTILE   TISSUES.  8$ 

the  current,  there  is  a  contraction  Ijotli  at  the  make  and  at  the  break 
of  "botli  ascending  and  descending  cm  rc-nts  ;  tiie  fall  of  an  elcctrotonus 
here  is  able,  as  well  as  tlie  rise  of  katelectrotonus,  to  originate  a  ner- 
vous impulse.  Lastly,  \vhcn  the  current  is  very  strong,  as  that  for 
in-^tan.'c  of  two  or  more  Groves,  making  the  ascending  current  pro- 
duces no  contraction,  because  the  anelcctrotonus  round  the  anode  blocks 
the  iMi|)ulse  starting  from  the  kathode.  The  fall  of  anclectrotonus 
however  at  the  anode,  there  being  nothing  between  it  and  the  muscle, 
does  cause  a  contraction.  With  the  descending  current  the  rise  of 
katelectrotonus  produces  a  making  conlr.iction,  but  there  is  no  break- 
ing contraction  ;  tlic  absence  ot'  the  latter  may  l)c  accounted  for,  partly 
by  the  strong  current  depressing  the  irritability  and  especially  the 
conductivity  of  the  inlrapolar  nerve,  and  partly  perliaps  by  supposing 
that  the  rebound  on  the  disappearance  of  katelectrotonus  at  the 
kathode,  occurring  as  it  does  in  a  part  lying  between  the  anode  and 
the  muscle,  serves  to  block  the  downward  progress  of  the  impulse 
started  by  the  fall  ot'  anelcctrotonus  at  the  anode.  This  blocking  of 
nervous  impulses  by  the  defective  conduction  caused  in  anelcctrotonus, 
is  the  reason  why  in  testing  the  variations  of  irritability  in  anelcctrotonus 
and  katelectrotonus  it  is  preferable  to  apply  the  stimulus  between  the 
mus::le  and  the  polarizing  current. 

It  has  already  been  stated  that  in  many  cases  the  making  or  breaking 
of  a  constant  current  gives  rise  not  to  a  single  spasm  only  but  to  a 
pronounced  tetanus,  often  spoken  of  as  the  making  or  breakmg 
tetanus.  Of  these  two  the  most  common  is  the  breaking  tetanus,  or 
Ritter's  tetanus,  which  appears  when  a  strong  current  has  been  applied 
for  some  time  to  a  nerve.  It  is  developed  most  readily  and  lasts 
longest  after  the  application  of  an  ascending  current,  but  may  also 
make  its  appearance  with  a  descending  current.  When  it  manifests 
itself  it  may  be  at  once  diminished  or  suspended  altogether  by  applying 
the  same  current  in  the  same  direction.  It  is  increased  by  applying 
the  current  in  an  opposite  direction.  The  making  tetanus  is  seen  with 
currents  of  a  certain  intensity  only,  being  absent  with  those  of  less  or 
greater  strength.  Both  forms  arc  due  to  profound  electrolytic  changes 
in  the  nerve,  those  of  the  making  tetanus  being  of  a  katelectrotonic, 
and  those  of  the  breaking  tetanus  of  an  anelectrotonic  character. 

The  constant  current  applied  directly  to  a  muscle  from  which  the 
purely  ner\'ous  element  has  been  eliminated  by  urari  poisoning,  has 
effects  similar  to  and  yet  somewhat  different  from  those  which  it  has 
upon  a  nerve.  The  efficacy  of  the  rise  of  katelectrotonus  and  the  fall 
of  anelcctrotonus  respectively  in  producing  contraction  is  the  same  as 
in  a  nerve.  In  one  respect  the  muscle  is  more  striking,  and  offers  a 
support  of  the  hypothesis  mentioned  above.  The  making  contraction 
may  under  favourable  circumstances  be  seen  to  start  from  the  kathode 
and  the  breaking  contraction  from  the  anode.  Another  marked  difiicr- 
'  nee  between  muscle  and  nerve  is  that  in  muscle  the  current  must  act 
ior  a  much  longer  time  upon  the  tissue  before  it  can  call  forth  a  con- 
traction. This  is  what  we  might  e.xpect  from  the  more  sluggish  nature 
of  the  muscular  impulse-wave.  Hence  muscular  tissue  which  has  lost 
its  nervous  elements  or  does  not  {)ossess  them,  is  far  less  readily 
affected  by  the  almost  momentary  induction-shocks  than  are  nerves. 


36  THE   MUSCLE-NERVE   MACHINE.  [BOOK   I. 

During  the  passage  of  a  constant  current  the  muscle  is  thrown  into 
a  partial  tetanus,  which  however  may  be  sufficiently  weak  to  permit 
the  simple  make  and  break  contractions  to  be  readily  observed  \ 
Very  frequently  this  tetanus  changes  into  a  regular  rhythmic  pulsation 
if  the  intramuscular  nerves  be  intact. 


Sec.  4.     The  Muscle-Nerve  Preparation  as  a  Machine. 

The  facts  described  in  the  foregoing  sections  shew  that  a 
muscle  with  its  nerve  may  be  justly  regarded  as  a  machine  which, 
when  stimulated,  will  do  a  certain  amount  of  work.  But  the 
actual  amount  of  work  which  a  muscle-nerve  preparation  will  do 
is  found  to  depend  on  a  large  number  of  circumstances,  and  con- 
sequently to  vary  within  very  wide  limits.  These  variations  will 
be  largely  determined  by  the  condition  of  the  muscle  and  nerve  in 
respect  to  their  nutrition ;  in  other  words,  by  the  degree  of  irrita- 
biUty  manifested  by  the  muscle  or  by  the  nerve  or  by  both.  But 
quiet  apart  from  the  general  influences  affecting  its  nutrition  and 
thus  its  irritability,  a  muscle-nerve  preparation  is  affected  as  re- 
gards the  amount  of  its  work  by  a  variety  of  other  circumstances, 
which  we  may  briefly  consider  here,  reserving  to  a  succeeding 
section  the  study  of  variations  in  irritability. 

The  nature  and  7?iode  of  applicatioit  of  the  stimulus  as  affecting  the 
amount  and  character  of  the  coiitraction. 

Within  the  body,  the  stimuli  which  bring  about  natural  mus- 
cular contractions  are  nervous  impulses  proceeding  from  the 
central  nervous  system.  As  far  as  we  know,  these  natural  nervous 
impulses  are  identical  in  character  with  the  nervous  impulses  set 
going  in  the  course  of  the  nerve  by  artificial  stimuli.  Since  in  the 
majority  of  cases  natural  muscular  contractions  are  tetanic  in 
nature,  the  natural  nervous  impulses  occur,  not  singly,  but  repeated 
in  series,  the  interval  between  successive  impulses  -being  always 
about  one-nineteenth  of  a  second  (see  p.  56).  Variations  there- 
fore in  the  energy  and  extent  of  natural  muscular  contractions 
must  (apart  from  variations  in  the  irritability  of  the  muscles  or 
nerves)  depend  on  the  energy  of  the  individual  nervous  impulses 
as  they  leave  the  central  nervous  system,  and  not  on  any  cliange 
in  the  rapidity  of  their  sequence. 

A  mechanical  stimulus  in  the  shape  of  a  single  tap  or  blow, 
pinch  or  prick,  may  produce  a  single  spasm,  and  slight  taps 
repeated  regularly  and  rapidly  may  be  used  to  produce  a  tetanus. 

'  Cf.  Romanes,  yournal  of  Anat.  attd  Phys.,  X.  p.  70.7. 


CHAP.    II.]  THE   CONTRACTILE   TISSUES.  8/ 

As  a  rule,  however,  the  injury  inflicted  by  a  mechanical  stimulus 
destroys  the  irritability  of  the  spot  stimulaterl,  and  so  prevents  a 
repetition  of  the  spasms.  On  the  other  hand  even  a  momentary 
injury  may  produce  changes  leading  to  a  tetanus.  A  chemical 
stimulus  produces  an  irregular  tetanus,  as  does  also  the  sudden 
application  of  heat. 

The  constant  current  acts,  as  we  have  seen,  as  a  stimulus  only 
when  its  intensity  suddenly  rises  or  falls,  making  and  breaking  of 
the  circuit  being  extreme  cases  of  rise  and  fall.  If  the  rise  or  fall 
be  sufliciently  gradual  a  current  may,  while  still  passing  through  a 
nerve,  be  very  largely  increased  or  diminished  without  giving  rise 
to  any  contraction  ;  whereas  even  a  very  slight  sudden  rise  or  fall 
may  at  once  cause  one,  the  etil'ect  being  the  greater  the  more 
sudden  the  change.  This  influence  of  the  suddenness  of  the 
change  is  also  seen  in  the  case  of  single  induction-shocks;  the 
breaking  shock,  which  is  developed  much  more  rapidly  than  the 
making  slfock,  is  by  far  the  more  potent  of  the  two. 

It  is  worthy  of  notice,  as  a  matter  of  practical  importance, 
that  muscular  substance,  with  its  more  sluggish  impulse  of  stimu- 
lation (see  p.  68),  is  when  devoid  of  nerves  more  susceptible 
towards  the  more  slowly  acting  (break  and  make  of  the)  constant 
current  than  towards  the  momentary  induction-shock.  Hence 
muscles  which  by  degeneration  have  lost  their  nervous  supply 
respond  to  the  constant  current  much  more  readily  than  to  an 
induction-shock.  By  this  test  the  condition  of  the  nerves  in  the 
muscle  of  cases  of  paralysis  may  be  ascertained. 

In  order  that  a  galvanic  current  of  any  kind  may  call  forth  a 
contraction,  some  appreciable  length  of  nerve  must  be  placed 
between  the  electrodes.  If  the  current  simply  be  sent  transversely 
through  a  nerve,  little  or  no  contraction  takes  place. 

According  to  Tschirjew,^  however,  both  muscle  and  nerve  are 
irritable  in  a  transverse  direction ;  what  may  be  called  the  specific 
irritability,  being  in  the  case  of  muscle  not  at  all  less,  and  in  the  case 
of  nerve  only  slightly  less  in  a  transverse  than  in  a  longitudinal 
direction. 

With  the  same  strength  of  current,  the  longer  the  piece  of 
nerve  the  greater  the  contraction. 

This  when  the  constant  current  is  used  as  a  stimulus  is  said  to  be 
true  of  the  descending  but  not  of  the  ascending  current,  and  the  results 
are  more  constant  with  the  maknig  than  breaking  of  the  current.  =■ 

'  Archiv  f.  Ana',  u.  Physiol.,  1877,  p.  489. 

»  Willy,  Flliirer's   Archiv  v.    (iS72>,  275.     Cf.   Marcuse,    V^erh.  d.    Phys. 
Med.  Ges.  in  IViirzburg,  x.  (1877),  158. 


88  THE   MUSCLE-NERVE   MACHINE.  [BOOK   I. 

The  amount  of  the  contraction  is,  as  might  be  expected, 
dependent  on  the  strength  of  the  stimulus,  but  a  hmit  to  the 
increase  of  the  contraction  caused  by  augmenting  the  stimulus  is 
soon  reached.  Thus  if  the  nerve  of  a  muscle-nerve  preparation 
be  stimulated  at  intervals  by  currents  of  increasing  intensity, 
beginning  with  those  having  no  effect  at  all,  it  is  found  that  the 
effect,  as  measured  by  the  height  of  the  contraction,  rises  very 
rapidly  to  a  maximum,  beyond  which  it  remains  constant  so  long 
as  the  irritability  of  the  preparation  continues  unchanged. 

We  have  in  a  preceding  section  (p.  54)  discussed  at  length  the 
manner  in  which  a  stimulus  repeated  sufficiently  rapidly  produces 
a  complete  and  uniform  tetanus,  during  which  the  constituent 
single  contractions  cannot  be  recognized  either  by  the  appearance 
of  the  muscle  itself  or  by  any  features  in  the  curve  which  it  may 
be  made  to  describe,  though  the  '  muscular  sound  '  shews  that  the 
muscle  is  really  in  a  state  of  vibration.  If  the  frequency  of  the 
stimulus  be  reduced  the  tetanus  becomes  incomplete  and  a 
flickering  of  the  muscle  becomes  obvious,  and  upon  further 
reduction  of  the  frequency  the  flickering  gives  place  to  a  rhythmic 
series  of  single  contractions.  The  exact  frequency  of  repetition 
required  to  produce  complete  tetanus  varies  according  to  the 
condition  of  the  muscle  and  is  not  the  same  for  all  muscles,  being 
dependent  on  the  rapidity  with  which  the  muscle  executes  each 
single  contraction.  In  those  animals  which  possess  two  kinds  of 
skeletal  muscles,  red  and  pale,  the  red  muscles  (the  single  con^ 
tractions  of  which  are  slow  and  long-drawn)  are  thrown  into 
complete  tetanus  with  a  repetition  of  much  less  frequency  than 
that  required  for  the  pale  muscles.^ 

Kronecker  and  Stirling^  find  10  stimuli  per  sec.  quite  sufficient  to 
throw  the  red  muscles  of  the  rabbit  into  complete  tetanus,  while  the 
pale  muscles  require  at  least  20  stimuli  per  sec. 

When  the  stimulus  is  repeated  more  frequently  than  is  required  to 
bring  about  a  complete  tetanus  the  constituent  contractions  are  still 
proportionately  increased  in  frequency.  This  is  shewn  by  the  in- 
creased pitch  of  the  muscular  sound.  The  interesting  question  then 
arises,  How  far  can  the  increase  in  the  frequency  of  the  constituent 
contractions  be  carried  by  increasing  the  frequency  of  the  stimulus  ? 
But  this  question  obviously  involves  two  problems  :  (i)  How  far  can 
the  frequency  of  nervous  impulses  be  carried  ?  What  is  the  limit  to 
which  the  duration  of  a  stimulus  may  be  reduced  without  the  stimulus 
ceasing  to  evoke  a  nervous  impulse  ?  and  (2)  To  what  extent  may  the 
frequency  of  nervous  impulses  be  increased  without  the  muscle 
ceasing  to  respond  by  a  contraction  to  each  nervous  impulse  ?     One 

'  Ranvier,  Archives  de  Physiol.,  VI.  (1874),  p.  5. 

*  Arckiv  Anat.  u.  Physiol.,  1-878,  p.  i,  and  Journ.  Physiol.,  I.  (1878),  p.  384. 


CHAP.    II.]  THE   CONTRACTILE   TISSUES.  89 

would  naturally  suppose  that  there  is  a  limit  to  the  duration  of  a 
stimulus  (of  a  ^Mlvanic  current  for  instance),  necessary  to  efficiency, 
and  that  the  limit  would  vary  wiih  the  strength  of  the  stimulus,  the 
stronger  stimuli  remaining  effective  with  the  shorter  duration.  And 
the  experience  of  many  observers  confirms  this  view.  Kdnig'  came 
to  the  conclusion  that  a  galvanic  current  of  even  maximum  strength 
as  a  stimulus  must  last  at  least  about  0015  sec.  in  order  to  generate  a 
nervous  impulse.  And  Bernstein"  foun  1  that  when  induction-shocks 
of  submaxiuial  intensity  arc  thrown  suffi-iently  rapidly  (the  necessary 
rapidity  varying  with  the  strength  of  the  sliocks)  into  a  muscle-nerve 
preparation,  tetanus  of  the  muscle  fails  to  appear  ;  there  is  an  initial 
contraction  at  the  commencement  of  the  series  of  shocks,  and  after 
that  complete  re-it.  By  adequately  increasing  the  strength  of  the 
stimulus  however,  tetanus  might  always  be  brought  about.  The 
absence  of  tetanus  with  submaximal  stimulation  might  be  interpreted 
as  indicating  lh(^  failure  not  so  much  of  nervous  impulses  as  of  the 
conversion  of  the  nervous  into  the  muscular  impulse,  i.e.  the  molecular 
forerunner  in  the  muscle  of  the  visible  contraction.  Kronecker  ai>d 
Stirling^,  by  using  a  special  instrument  for  rapid  interruption,  the  so- 
called  tone-inductorium,  have  been  able  to  obtain  in  all  cases  a 
complete  tetanus  with  alternating  induction-shocxs,  even  when  repeated 
they  believe  as  frequently  as  22,000  times  a  second  ;  and  they  conclude 
that  '  the  upper  limit  of  the  frequency  of  electrical  stimulation  which 
can  throw  a  muscle  into  tetanus  lies  near  the  limit  where  variations  in 
the  current  can  no  longer  be  detected  by  the  help  of  other  physical 
rheoscopjs '  and  therefore  far  beyond  Kcinig's  limit. 

With  regard  to  the  second  question  the  following  important 
observation  is  worth  attention.  Helmholtz-'  has  shewn  that  when  an 
induction-shock  giving  a  maximum  contraction  is  followed  at  an 
interval  of  less  than  ^^^  sec.  by  a  second  shock  of  equal  strength,  no 
second  contraction  appears  at  all.  During  jjg  sec  subsequent  to  the 
first  shock  the  muscle  is  absolutely  devoid  of  irritability  ;  it  is  in  a 
'  refractory  phase  '  similar  to  but  mu.:h  shorter  than  that  which  is  so 
conspicuous  in  cardiac  muscles.  Hence  if  a  number  of  maximum 
induction-shocks  be  sent  into  a  muscle  or  nerve  at  intervals  of  a  little 
less  than  nio'^'^  sec.  half  the  shocks  sent  in  would  seem  to  be  without 
effect.  But  this  is  only  true  of  maximum  stimuli.  We  do  not  know 
where  to  place  a  similar  limit  to  subma.\imal  contractions. 

When  two  pairs  of  electrodes  are  placed  on  the  nerve  of  a 
long  and  a  perfectly  fresh  and  successful  nerve-preparation,  one 
near  to  the  cut  end,  and  tlu  otiier  nearer  the  muscle,  it  is  found 
that  the  same  stimulus  produces  a  greater  contraction  when  applied 
tlirough  the  former  pair  of  electrodes  than  through  the  latter. 

'    Wien.  Sitzungs-Berkh'e,  l.kii.  (1870). 

'  Nen'cn-  mid  Muskd-System,    1871.      Sec    also   Pl1u,'Cr's   Archiv,    XVIL 
(187S),  p.  121.  3  Op.  cit. 

*  Berlin.  Motiaisbenc/tt,  1854. 


90  THE   MUSCLE-NERVE   MACHINE.  [BOOK  I. 

Two  interpretations  of  this  result  are  possible.  Either  the  nerve 
at  the  part  farther  away  from  the  muscle  is  more  irritable,  i.e.  that 
the  stimulus  gives  rise  at  the  spot  stimulated  to  a  larger  nervous 
impulse ;  or  the  impulse  started  at  the  farther  electrodes  gathers 
strength,  like  an  avalanche,  in  its  progress  to  the  muscle.  The 
latter  view  has  been  strongly  urged  by  Pfluger,  and  is  generally 
known  under  the  name  of  the  '  avalanche  theory.'  As  far  as  we 
know,  however,  the  progress  of  the  negative  variation  along  a 
nerve  is  marked  by  no  such  increase.  It  is  probable  that  the 
larger  contraction  produced  by  stimulatioii  of  the  portions  of  the 
nerve  near  the  spinal  cord  is  due  to  the  stimulus  setting  free  a 
larger  impulse,  i.e.  to  this  part  of  the  nerve  being  more  irritable. 

The  effect  is  not  due  to  the  section  merely,  for  it  may  be  witnessed 
in  nerves  still  in  connection  with  the  spinal  cord.  Meidenhain'  states 
however  tliat  under  these  circumstances  the  diminution  of  the  effect  is 
not  gradual  from  the  central  to  the  peripheral  portions,  as  when  the 
nerve  is  cut;  on  the  contrary,  the  amount  of  contraction  is  at  first 
large,  then  becomes  smaller,  and  finally  increases  somewhat  again  as 
the  stimulation  is  carried  from  the  roots  of  the  nerves  to  the  muscular 
periphery. 

Hallsten  {Arch.  Anat.  Phys.,  1876,  242)  moreover  found  that  in  the 
case  of  sensory  nerves  also  the  effect  produced  was  greater  when  the 
stimulus  was  applied  to  the  more  central  than  when  it  was  applied  to 
the  more  peripheral  portions  of  the  nerve  ;  at  least  reflex  actions  were 
more  easily  excited. 

It  is  probable  that  the  irritability  of  the  nerve  may  vary  con- 
siderably at  different  points  along  its  course.  And  FieischP  states 
that  an  induction  shock  when  applied  as  an  ascending  current  has  a 
greater  effect  on  the  more  peripheral,  and  when  applied  as  a  descend- 
ing current  a  greater  effect  on  the  more  central,  portions  of  a  nerve. 


The  Influence  of  the  Load. 

It  might  be  imagined  that  a  muscle,  which,  when  loaded  with 
a  given  weight,  say  20  grammes,  and  stimulated  by  a  current  of  a 
given  intensity,  had  contracted  to  a  certain  extent,  would  only 
contract  to  half  that  extent  when  loaded  with  twice  the  weight 
(40  grammes)  and  stimulated  with  the  same  stimulus.  Such,  how- 
ever, is  not  the  case  \  the  height  to  which  the  weight  is  raised  may 
be  in  the  second  instance,  as  great,  or  even  greater,  than  in  the 
first.  That  is  to  say,  the  resistance  offered  to  the  contraction 
actually  increases  the  contraction,  the  tension  of  the  muscular 

*  Stud.  Physiol.  Instit.,  Bre'^laii,  il.  (1861). 

=  Wien.   Sitz.-Bericht,   Lxxii.    (1875),  Lxxiv.   (1876).      Compare  however 
Tiegel,  Pfliiger's  Archiv,  xiii.  (1876),  p.  598. 


CHAP,  II.]  THE   CONTRACTILE   TISSUES.  9I 

fibre  increases  the  facility  with  which  the  explosive  changes  result- 
ing in  a  contraction  take  place.  And  it  has  been  observed  by 
Hcidenhain'  that  tension  applied  to  a  muscle  increases  both  the 
cliemical  products  (carbonic  and  lactic  acid)  and  the  rise  of 
temperature  which  accompany  a  contraction.  There  is,  of  course, 
a  limit  to  this  favourable  action  of  the  resistance.  As  the  load 
continues  to  be  increased,  the  height  of  the  contraction  is  dimi- 
nished, and  at  last  a  point  is  reached  at  which  the  muscle  is 
unable  (even  when  the  stimulus  chosen  is  the  strongest  possible) 
to  lift  the  load  at  all. 

It  is  said  that  a  muscle,  loaded  beyond  its  power,  relaxes  and 
lengthens  when  stimul.ited  instead  of  shorteninj^,  in  consequence  of 
that  increase  of  extensibility  which  is  a  characteristic  of  the  contracted 
state.     The  occurrence  of  this  lengthening  is  however  doubtful. 

It  is  obvious  that  the  work  done  (height  to  which  the  load  is 
raised  multiplied  into  the  weight  of  the  load)  must  therefore  be 
largely  dependent  on  the  weight  itself.  Thus  there  is  a  certain 
weight  of  load  with  which  in  any  given  muscle,  stimulated  by  a 
given  stimulus,  the  most  work  will  be  done. 

Since  mere  tension  affects  the  changes  going  on  in  the  muscular 
fibres,  it  is  desirable  in  experiments  in  which  muscles  are  loaded, 
that  the  weight  should  not  bear  upon  the  lever  until  the  contraction 
actually  begins.  This  is  easily  managed  by  interposing  between  the 
end  of  the  muscle  and  the  weight  a  lever  with  a  support  so  arranged 
that,  before  contraction  takes  place,  the  weight  only  extends  the  muscle 
to  the  length  natural  to  it  during  rest  :  but  the  muscle  directly  it 
shortens  at  once  begins  to  pull  on  the  weight.  The  muscle  is  then  said 
to  be  after-loaded.'^ 

If  the  weight  be  determined  which  will  stop  a  contraction  when 
applied  directly  the  contraction  begins,  and  also  that  which  stops 
any  further  contraction  when  applied  at  a  moment  when  the  con- 
traction is  already  partly  accomplished,  it  will  be  found  that  the 
second  weight  is  much  less  than  the  first.  It  will  be  found,  in 
fact,  that  the  forces  which  produce  the  change  in  the  form  of  the 
muscle  are  at  their  maximum  at  the  beginning  of  the  shortening, 
and  thenceforwards  decline  until  they  become  nothing  when  tho 
shortening  is  complete. 

'  Mechanische  Leisiuug,  Wdrmeentwickdung  und  Stoffumsatz  bd  der  Musket- 
thaligknt      l.eipzijr,    1864. 

^  This  is  perhaps  the  best  equivalent  of  the  German  iiberlastet. 


92        IRRITABILITY   OF   MUSCLES   AND   NERVES.    [BgOK   I. 

Influence  of  the  Size  and  Form  of  the  Muscle. 

Since  all  known  muscular  fibres  are  much  shorter  than  the 
wave-length  of  a  contraction,  it  is  obvious  that  the  longer  the 
fibre,  the  greater  the  height  of  the  contraction  with  the  same 
stimulus.  Hence  in  a  muscle  of  parallel  fibres,  the  height  to 
which  the  load  is  raised  as  the  result  of  a  given  stimulus  applied 
to  its  nerve,  will  depend  on  the  length  of  the  fibres,  while  the 
weight  of  the  load  so  lifted  will  depend  on  the  number  of  the 
fibres,  since  the  load  is  distributed  among  them.  Of  two  muscles 
therefore  of  equal  length  (and  of  the  same  quality)  the  most  work 
will  be  done  by  that  which  has  the  greater  sectional  area  ;  and  of 
two  muscles  with  equal  sectional  areas,  the  most  work  will  be  done 
by  that  which  is  the  longer.  If  the  two  muscles  are  unequal  both 
in  length  and  sectional  area,  the  work  done  will  be  the  greater  in 
the  one  which  has  the  larger  bulk,  which  contains  the  greater 
number  of  cubic  units.  In  speaking  therefore  of  the  maximum  of 
work  which  can  be  done  by  a  muscle,  we  may  use  as  a  standard 
a  cubic  unit  of  bulk,  or,  the  specific  gravity  of  the  muscle  being 
the  same,  a  unit  of  weight. 

In  the  case  of  frog's  muscle,  the  maximum  of  work  which  can  be 
done  under  most  favourable  circumstances  has  been  estimated  by 
Fick '  to  vary  between  3  and  7  grammeters  for  i  grm.  of  muscle. 

The  weight  which  is  just  sufficient,  but  only  just  sufficient,  to  keep  a 
muscle,  when  stimulated,  from  actually  shortening,  may  be  taken  as 
the  measure  of  the  '  absolute  power'  of  the  muscle.  It  must  of  course 
be  taken  only  in  relation  to  the  sectional  area  of  the  muscle.  The 
absolute  power  of  a  square  centimetre  of  a  frog's  muscle  has  been  in 
this  way  estimated  at  about  2,800  to  3,coo  grms. :  of  a  square  centi- 
metre of  human  muscle  at  6,000  to  8,000  grms. 


Sec.  5.     The  Circumstances  which  determine  the  Degree 
OF  Irritability  of  Muscles  and  Nerves. 

A  muscle-nerve  preparation,  at  the  time  that  it  is  removed 
from  the  body,  possesses  a  certain  degree  of  irritability,  it  re- 
sponds by  a  contraction  of  a  certain  amount  to  a  stimulus  of  a 
certain  strength,  applied  to  the  nerve  or  to  the  muscle.  After  a 
while,  the  exact  period  depending  on  a  variety  of  circumstances^ 
the  same  stimulus  produces  a  smaller  contraction,  i.e.  the  irritability 
of  the  preparation  has  diminished.  In  other  words,  the  muscle 
or  nerve  or   both   have  becoine  partially  '  exhausted,'  and  the 

'  Untersuch.  ii.  Muskelarbeit,  Basel,  1867. 


CIIAT.    JI.J  THE   CONTRACTILE    TISSUES.  93 

exhaustion  sul)se(iucnlly  increases,  the  same  stimulus  producing 
smaller  c-.ontraclions  until  at  last  all  irritability  is  lost,  no  stimulus 
however  strong  producing  any  contraction  whether  applied  to  the 
nerve  or  directly  to  the  nmscle  ;  and  eventually  the  muscle,  as  we 
have  seen,  becomes  rigid.  The  jjrogress  of  this  exhaustion  is 
more  rapid  in  the  nerves  than  in  the  muscles ;  for  some  time  after 
the  nerve-trunk  has  ceased  to  respond  to  even  the  strongest 
stimulus,  contractions  may  be  obtained  by  applying  the  stimulus 
(.lirectly  to  the  muscle.  It  is  much  more  rapid  in  the  warm- 
blooded than  in  the  cold-blooded  animals.  The  muscles  and 
nerves  of  the  former  lose  their  irritability,  when  removed  from  the 
body,  after  a  period  varying  according  to  circumstances  from  a 
few  minutes  to  two  or  three  hours  ;  those  of  cold-blooded  animals 
(or  at  least  of  an  amphibian  or  a  reptile)  may  under  favour- 
able conditions  remain  irritable  for  two,  three,  or  even  more 
days. 

If  a  sharp  blow  widi  some  tliin  body  be  struck  across  a  muscle 
which  has  entered  into  the  later  stages  of  exhaustion,  a  wheal  lasting 
for  several  seconds  is  developed.  This  wheal  appears  to  be  a  con- 
traction wave  limited  to  the  part  struck,  and  disappearing  very  slowly, 
without  extending  to  the  neighbouring  muscular  substance.  It  has 
been  called  an  '  idiomusculai-'  contraction,  because  it  may  be  brought 
out  even  when  ordinary  stimuli  have  ceased  to  produce  any  effect.  It  may 
however  be  accompanied  at  its  beginning  by  an  ordinary  contraction. 
It  is  readily  produced  in  the  living  body  on  the  pectoral  and  other 
muscles  of  persons  suffering  from  phthisis  and  other  exhausting 
diseases. 

This  natural  exhaustion  and  diminution  of  irritability  in  muscles 
and  nerves  removed  from  the  body  may  be  modified  both  in  the 
case  of  the  muscle  and  of  the  nerve,  by  a  variety  of  circumstances. 
Similarly,  while  the  nerve  and  muscle  still  remain  in  the  body,  the 
irritability  of  the  one  or  of  the  other  may  be  modified  either  in  the 
way  of  increase  or  of  decrease,  by  various  events.  We  have 
already  seen  (p.  So)  how  the  constant  current  produces  the  varia- 
tions in  irritability  known  as  katelectrotonus  and  anelectrotonus. 
We  have  now  to  study  the  effect  of  more  general  influences,  of 
which  the  most  important  are,  severance  from  the  central  nervous 
system,  and  variations  in  temperature,  in  blood-supply,  and  in 
functional  activity. 

The  Effects  of  Se^rraiice  from  the  Central  Nervous  System. 

When  a  nerve,  such  for  instance  as  the  sciatic,  is  divided  in 
situ,  in  the   living  body,   there  is   first  of  all  observed  a  slight 


94  VARIATIONS   OF   IRRITABILITY.  [BOOK  I. 

increase  of  irritability,  noticeable  especially  near  the  cut  end  ;  but 
after  a  while  the  irritability  diminishes,  and  gradually  disappears. 
Both  the  slight  initial  increase  and  the  subsequent  decrease  begin 
at  the  cut  end  and  advance  centrifugally  towards  the  peripheral 
terminations.  This  centrifugal  feature  of  the  loss  of  irritability  is 
often  spoken  of  as  the  Ritter-Valli  law.  In  a  mammal  it  may  be 
two  or  three  days,  in  a  frog,  as  many,  or  even  more  weeks,  before 
irritability  has  disappeared  from  the  nerve-trunk.  It  is  maintained 
in  the  small  (and  especially  in  the  intramuscular)  branches  for 
still  longer  periods. 

A  similar  slight  temporary  increase  of  irritability  is  seen  to  follow 
the  section  of  a  nerve  even  when  removed  from  the  body.  In  the 
neighbourhood  of  the  section  the  nerve  is  for  a  while  more  irritable 
after  the  section  than  it  was  before. 

This  centrifugal  loss  of  irritability  is  the  forerunner  in  the 
peripheral  portion  of  the  divided  nerve  of  structural  changes 
which  proceed  in  a  similar  centrifugal  manner.  The  medulla 
suffers  changes  similar  to  those  seen  in  nerve-fibres  after  removal 
from  the  hody.  Its  double  contour  and  its  characteristic  indenta- 
tions become  more  marked,  it  breaks  up  into  small  irregular 
segments,  or  drops,  a  separation  apparently  taking  place  between 
its  proteid  and  its  fatty  constituents.  The  latter  are  soon  absorbed, 
but  the  former  remain  for  a  longer  time  within  the  sheath  of 
Schwann,  being  in  some  cases  scarcely,  if  at  all,  to  be  distinguished 
from  the  swollen  axis-cylinder.  Meanwhile  the  nuclei  of  the 
sheath  of  Schwann  divide  and  multiply  rapidly.  If  no  regenera- 
tion takes  place  the  whole  contents  of  the  sheath  are  gradually 
absorbed,  the  axis-cylinder  disappearing  last. 

In  the  central  portion  of  the  divided  nerve  similar  changes 
may  be  traced  as  far  only  as  the  next  node  of  Ranvier.  Beyond 
this  the  nerve  usually  remains  in  a  normal  condition. 

Regeneration,  when  it  occurs,  is  carried  out  by  the  peripheral 
growth  of  the  axis-cylinders  of  the  intact  central  portion.  When 
the  cut  ends  of  the  nerve  are  close  together  the  axis-cylinders 
growing  out  from  the  central  portion  run  into  and  between  the 
sheaths  of  Schwann  of  the  peripheral  portion ;  but  much  un- 
certainty still  exists  as  to  the  exact  parts  played  by  the  proliferated 
nuclei  of  the  sheath  of  Schwann,  the  proteid  remnants  of  the 
medulla,  and  the  old  axis-cylinders  of  the  peripheral  portion  in 
giving  rise  to  the  new  structures  of  the  regenerated  fibre. 

This  degeneration  may  be  observed  to  extend  down  to  the 
very  endings  of  the  nerve  in  the  muscle,  including  the  end-plates, 
but  does  not  affect  the  muscular  substance  itself.     The  muscle. 


CHAP.    II.]  Tllli   CONTRACTILE   TISSUES.  95 

though  it  has  lost  all  its  nervous  elements,  still  remains  irritable 
tdwards  stimuli  n|)j)lic(i  directly  to  itself;  an  additional  proof  of 
the  existence  of  an  independent  muscular  irritability.  As  was 
mentioned  before  (p.  87),  it  is  not  easily  stimulated  by  single 
induction-shocks  but  responds  readilv  to  the  make  or  break  of  a 
constant  current.  If  it  be  thus  artificially  stimulated  from  time 
to  time  it  will  remain  iiritable  for  a  very  considerable,  possibly 
for  an  indefinite  time  ;  but  if  it  be  not  thus  thrown  into  functional 
activity,  its  irritability  ultimately  disappears  and  its  substance 
undergoes  degeneration. 

The  Influence  of  Temperature, 

We  have  already  seen  (p.  43)  that  sudden  heat  applied  to  a 
limited  part  of  a  nerve  or  muscle,  as  when  the  nerve  or  muscle  is 
touched  with  a  hot  wire,  will  act  as  a  stimulus,  and  the  same 
might  be  said  of  cold  when  sufiiciendy  intense.  It  is  however 
much  more  difficult  to  generate  nervous  or  jnuscular  impulses  by 
exposing  a  whole  nerve  or  muscle  to  a  gradual  rise  of  temperature. 
Thus  according  to  most  observers  a  nerve  belonging  to  a  muscle* 
may  be  either  cooled  to  0°  C.  or  below,  or  heated  to  50°  or  even 
100°  C,  without  discharging  any  nervous  impulses,  as  shewn  by 
the  absence  of  contraction  in  the  a-ttached  muscle. 

The  contractions  moreover  may  be  absent  even  when  the  heating 
has  not  been  very  gradual.  Several  observers  however  have  found 
that  contractions  (of  an  irregular  flickering  tetanic  nature)  result  when 
a  nerve  is  heated  in  water  or  in  oil  or  in  a  moist  atmosphere  to  50° 
or  even  less.  It  has  been  suggested  that  the  contractions  in  these 
cases  arc  due  rather  to  spontaneous  impulses  (whose  discharge  was 
favoured  by  the  increased  molecular  activity  caused  by  the  rise  of 
temperature)  than  to  the  heat  acting  as  a  stimulus,  but  this  seems 
hardly  satisfactory.^ 

A  muscle  maybe  cooled  to  c°C.  or  below  without  any  contrac- 
tion being  caused  ;  but  when  it  is  heated  to  a  limit,  which  in  the 
case  of  frog's  muscles  is  about  45°,  of  mammalian  muscles  about 
50°,  a  sudden  change  takes  place :  the  muscle  falls,  at  the  limiting 
temperature,  into  a  rigor  mortis,  which  is  initiated  by  a  forcible 
contraction  or  at  least  shortening.  The  rigor  mortis  thus  brought 
about  by  heat  is  often  spoken  of  as  rigor  caloris. 

Moderate  waimth,  ex.  gr.  in  the  frog  an  increase  of  tempera- 
ture to  about  45°  C,  favours  both  muscular  and  nervous  irritability. 

*  The  action  of  cold  and  heat  on  sensor)'  nei*ves  will  be  considered  in  the 
later  portion  c.f  the  \\ork. 

'  Grlitzncr.  Pfliiger's  y/;r/;/-',  xvii.  (1S78),  p.  215.  Cf.  Lautcnbach,  Joum. 
Pliys.,  11.  (1879),  p.  I. 


96  VARIATIONS   OF   IRRITABILITY.  [BOOK   I. 

All  the  molecular  processes  are  hastened  and  facilitated :  the 
contraction  is  for  a  given  stimulus  greater  and  more  rapid,  i.e.  of 
shorter  duration,  and  nervous  impulses  are  generated  more  readily 
by  slight  stimuli.  Owing  to  the  quickening  of  the  chemical 
changes,  the  supply  of  new  material  may  prove  insufficient ;  hence 
muscles  and  nerves  removed  from  the  body  lose  their  irritability 
more  rapidly  at  a  high  than  at  a  low  temperature. 

The  gradual  application  of  cold  to  a  nerve,  especially  when 
the  temperature  is  thus  brought  near  to  o°,  slackens  all  the 
molecular  processes,  so  that  the  wave  of  nervous  impulse  is 
lessened  and  prolonged,  the  velocity  of  its  passage  being  much 
diminished,  from  28  m.  e.g.  to  i  m.  per  sec.  At  about  0°  the 
irritability  of  the  nerve  disappears  altogether. 

Whon  a  muscle  is  exposed  to  similar  cold,  ex,  gr.  to  a  tem- 
perature very  little  above  zero,  the  contractions  are  remarkably 
prolonged ;  they  are  diminished  in  extent  at  the  same  time,  but 
not  in  proportion  to  the  increase  of  their  duration.  Exposed  to 
a  temperature  of  zer<?  or  below,  muscles  soon  lose  their  irritability, 
without  however  undergoing  rigor  mortis.  After  an  exposure  of 
not  more  than  a  few  seconds  to  a  temperature  not  much  below 
zero,  they  may  be  restored,  by  gradual  warmth,  to  an  irritable 
condition,  even  though  they  may  appear  to  have  been  frozen. 
When  kept  frozen  however  for  some  few  minutes,  or  when  exposed 
for  a  less  time  to  temperatures  of  several  degrees  below  zero,  their 
irritability  is  permanently  destroyed.  When  thawed,  they  enter 
into  rigor  mortis  of  a  most  pronounced  character. 

The  Influence  of  Blood-Supply. 

When  a  muscle  still  within  the  body  is  deprived  by  any  means 
of  its  proper  blood-supply,  as  when  the  blood-vessels  going  to  it 
are  ligatured,  the  same  gradual  loss  of  irritability  and  final  ap- 
pearance of  rigor  mortis  are  observed  as  in  muscles  removed  out 
of  the  body.  Thus  if  the  abdominal  aorta  be  ligatured,  the 
muscles  of  the  lower  limbs  lose  their  irritability  and  finally  become 
rigid.  So  also  in  systemic  death,  when  the  blood-supply  to  the 
muscles  is  cut  off  by  the  cessation  of  the  circulation,  loss  of 
irritability  ensues,  and  rigor  mortis  eventually  follows.  In  a  human 
corpse  the  muscles  of  the  body  enter  into  rigor  mortis  in  a  fixed 
order  :  first  those  of  the  jaw  and  neck,  then  those  of  the  tnmk, 
next  those  of  the  arms,  and  lastly  those  of  the  legs.  The  rapidity 
with  which  rigor  mortis  comes  on  after  death  varies  considerably, 
being  determined  both  by  external  circumstances  and  by  the 
internal  conditions  of  the  body.     Thus  external  warmth  hastens 


CHAP.   II.]  THE   CONTRACTILIC   TI.SSUES.  97 

and  cold  retards  the  on.set.  After  great  muscular  exertion,  as  in 
hunted  animals,  and  when  death  closes  wasting  di-scases,  rigor 
mortis  in  most  cases  comes  on  rapidly.  As  a  general  rule  it  may 
be  said  that  the  later  it  is  in  making  its  appearance,  the  more 
pronounced  it  is,  and  the  longer  it  lasts  ;  but  there  are  many 
exceptions,  and  when  the  state  is  recognized  as  being  funda- 
mentally due  to  a  coagulation,  it  is  easy  to  understand  that  the 
amount  of  rigidity,  i.e.  the  amount  of  the  coagulum,  and  the 
rapidity  of  the  onset,  i.e.  the  quickness  with  which  coagulation 
takes  i)lace,  may  vary  independently.  The  rai)idity  of  onset  after 
muscular  exercise  and  wasting  disease  is  apparently  dependent  on 
an  excess  of  acid,  which  seems  to  be  favourable  to  the  coagulation 
of  the  muscle  plasma,  being  produced  under  those  circumstance;- 
in  the  muscle.  When  rigor  mortis  has  once  become  thoroughly 
established  in  a  muscle  through  deprivation  of  blood,  it  cannot  be 
removed  by  any  subsequent  supply  of  blood.  Thus  where  the 
abdominal  aorta  has  remained  ligatured  until  tlie  lower  limbs  have 
become  completely  rigid,  untying  the  ligature  will  not  restore  the 
muscles  to  an  irritable  condition  ;  it  simply  hastens  the  decom- 
position of  the  dead  tissues  by  supplying  them  with  oxygen  and, 
in  the  case  of  the  mammal,  with  warmth  also. 

.\  muscle  however  may  acquire  as  a  whole  a  certain  amount  of 
rigidity  on  account  of  some  of  the  fibres  becoming  rigid,  while  the 
remainder,  though  they  have  lost  their  irritability,  have  not  yet 
advanced  into  rigor  mortis.  At  such  a  juncture  a  renewal  of  the  blood- 
stream may  restore  the  irritability  of  those  fibres  which  were  not  yet 
rigid,  and  thus  appear  to  do  away  with  rigor  mortis  ;  yet  it  appears 
that  in  such  cases  the  fibres  which  have  actually  become  rigid  never 
regain  their  irritability,  but  undergo  degeneration.  It  is  stated  how- 
ever by  Preyer '  that  if  the  even  completely  rigid  muscles  of  the  frog 
be  washed  out  with  a  lo  p.  c.  sodium  chloride  solution  (which 
dissolves  myosin)  and  subsequently  injected  with  blood,  irritability 
will  be  restored.  ^ 

Mere  loss  of  irritability,  even  though  complete,  if  stopping 
short  of  the  actual  coagulation  of  the  muscle-substance,  may  be 
with  care  removed.  Thus  if  a  stream  of  blood  be  sent  artificially 
through  the  vessels  of  a  separated  (mammalian)  muscle,  the  irri- 
tability may  be  maintained  for  a  very  considerable  time.  On 
stopping  the  artificial  circulation,  the  irritability  diminishes  and  in 
time  entirely  disappears ;  if  however  the  stream  be  at  once 
resumed,  the  irritability  will  be  recovered.  By  regulating  the  flow, 
the  irritability  may  be  lowered  and  (up  to  a  certain  limit)  raised 
at  pleasure.     From  the  epoch  however  of  interference  with  the 

'   Centrbt.f.  ined.   IVisscfift.  1864,  p.  769. 
F.  P.  7 


98  VARIATIONS   OF   IRRITABILITY.  [BOOK   I. 

normal  blood-stream  there  is  a  gradual  diminution  in  the  responses 
to  stimuli,  and  ultimately  the  muscle  loses  all  its  irritability  and 
becomes  rigid,  however  well  the  artificial  circulation  be  kept  up. 
This  failure  is  probably  in  great  part  due  to  the  blood  sent  through 
the  tissue  not  being  in  a  perfectly  normal  condition  ;  but  we  have 
at  present  very  little  information  on  this  point.  Indeed  with 
respect  to  the  quality  of  blood  thus  essential  to  the  maintenance 
or  restoration  of  irritability,  our  knowledge  is  definite  with  regard 
to  one  factor  only,  viz.  the  oxygen.  If  blood  deprived  of  its 
oxygen  be  sent  through  a  muscle  removed  from  the  body,  irrita- 
bility, so  far  from  being  maintained,  seems  rather  to  have  its 
disappearance  hastened.  In  fact,  if  venous  blood  continue  to  be 
driven  through  the  muscle,  the  irritability  is  lost  even  more  rapidly 
than  in  the  entire  absence  of  blood.  It  would  seem  that  venous 
blood  is  more  injurious  than  none  at  all.  If  exhaustion  be  not 
carried  too  far,  the  muscle  may,  however,  be  revived  by  a  proper 
supply  of  oxygenated  blood. 

In  a  muscle  the  irritability  of  which  has  been  suspended  by  a 
current  of  venous  blood,  the  assumption  of  a  minute  fraction  of 
oxygen  is  sufficient  to  restore  irritability  to  such  an  extent  that  a  very 
distinct  amount  of  contraction  is  visible  on  the  application  of  stimuli. 
Much  more  than  this  must  be  taken  up  before  the  muscle  can  regain 
the  standard  at  which  it  was  previous  to  the  action  of  the  venous 
stream.' 

The  influence  of  blood-supply  cannot  be  so  satisfactorily 
studied  in  the  case  of  nerves  as  in  the  case  of  muscles  \  there  can 
however  be  little  doubt  that  the  effects  are  analogous. 


The  Influence  of  Functional  Activity. 

This  too  is  more  easily  studied  in  the  case  of  muscles  than  of 
nerves. 

When  a  muscle  within  the  body  is  unused,  it  wastes;  when 
used  it  (within  certain  limits)  grows.  Both  these  facts  shew  that 
the  nutrition  of  a  muscle  is  favourably  affected  by  its  functional 
activity. 

Part  of  this  may  be  an  indirect  effect  of  the  increased  blood-supply 
which  occurs  when  a  muscle  contracts.  When  a  nerve  going  to  a 
muscle  is  stimulated,  the  blood-vessels  of  the  muscle  dilate.  Hence 
at  the  time  of  the  contraction  more  blood  flows  through  the  muscle, 
and  this  increased  flow  continues -for  some  little  while  after  the 
contraction  of  the  muscle  has  ceased. 

'  Ludwig  and  Schmidt,  YmA-vix^s.  Arbeiten,  iJi68,  p.  i. 


CHAP.   II.]  THE  CONTRACTILE   TISSUES.  99 

A  muscle,  even  within  the  body,  after  prolonj:,'ed  action  is 
fatigued,  i.e.  a  stronger  stimukis  is  required  to  produce  the  same 
contraction  ;  in  other  words,  its  irritability  is  reduced  by  functional 
activity. 

The  fatigue  of  which,  after  prolonged  or  unusual  exertion,  we  arc 
conscious  in  our  own  bodies,  arises  partly  from  an  exhaustion  of  muscles, 
partly  from  an  exhaustion  of  motor  nerves,  but  chielly  from  an  ex- 
haustion of  the  central  nervous  system  concerned  in  the  production  of 
voluntary  impulse ;.  .'\  man  who  says  he  is  absolutely  exhausted  may 
under  excilenirnt  perform  a  very  large  amount  of  work  with  his  already 
wearied  muscles.  The  will  rarely  if  ever  calls  forth  the  greatest 
contractions  of  which  the  muscles  arc  capable. 

Absolute  (temporary)  exhaustion  of  the  muscles,  so  that  the 
strongest  stimuli  i^roducc  no  contraction,  may  be  produced  even 
•within  the  body  by  artificial  stimulation ;  recovery  takes  place  on 
rest.  Out  of  the  body  absolute  exhaustion  takes  place  readily. 
Here  also  recovery  may  take  place.  Whether  in  any  given  case  it 
does  occur  or  not,  is  determined  by  the  amount  of  contraction 
causing  the  exhaustion,  and  by  the  previous  condition  of  the 
muscle.  In  all  cases  recovery  is  hastened  by  renewal  (natural  or 
artificial)  of  the  blood-stream.  The  more  rapidly  the  contractions 
follow  each  other,  the  less  the  interval  between  any  two  con- 
tractions, the  more  rapid  the  exhaustion.  A  certain  number  of 
single  induction-shocks  repeated  rapidly,  say  every  second  or 
oftener,  bring  about  exhaustive  loss  of  irritability  more  rapidly 
than  the  same  number  of  shocks  repeated  less  rapidly,  for  instance 
every  5  or  lo  seconds.  Hence  tetanus  is  a  ready  means  of 
producing  exhaustion. 

There  are  reasons  for  thinking  that  for  each  muscle  it  may  be 
possible  to  choose  such  an  interval  between  successive  stimuli  of 
suitable  strength  as  shall  not  only  not  h:isten,  but  perhaps  even  retard, 
the  gradual  normal  exhaustion  following  upon  removal  from  the  body. 
In  other  words,  it  is  probable  that  the  exhaustion  caused  by  a  con- 
traction is  immediately  followed  by  a  reaction  favourable  to  the 
nutrition  of  the  mus  le ;  and  this  possibly  is  the  real  reason  why  a 
muscle  is  increased  by  use. 

When  a  muscle  is  subjected  to  a  prolonged  tetanus  the  course  of 
exhaustion,  as  indicated  by  the  varying  heights  to  which  the  load  is 
successively  raised  by  the  repeated  contractions,  is  at  first  very  slow, 
afterwards  more  rapid,  and  finally  slow  again. 

The  amount  of  the  load,  provided  this  be  not  too  great,  has  no 
marked  cfTcct  on  the  course  ot  exhaustion.  If  two  muscles  be  after- 
loaded,  one  with  a  heavy,  the  otiier  with  a  light,  weight,  and  stimulated 
at  the  same  intervals  with  the  same  stimulus,  the  course  of  exhaustion 

7—2 


100  VARIATIONS   OF   IRRITABILITY.  [BOOK   I. 

will  be  parallel  in  the  two  cases,  though  the  more  heavily  laden  muscle, 
responding  at  the  outset  with  smaller  contractions  than  the  more  highly 
laden  one,  will  be  the  first  to  enter  that  stage  of  exhaustion  at  which 
the  contractions  cease  to  be  visible  i.  The  above  is  probably  only  true 
for  weights  up  to  the  standard  which  is  most  favourable  for  the  muscles' 
doing  work  :  see  ante,  p.  90.  Weights  heavier  than  this  quicken  ex- 
haustion ;  and  the  mere  extension  caused  by  loading  with  a  heavy 
weight  (even  when  unaccompanied  by  a  contraction)  is  exhausting. 

Whether  there  be  a  third  factor,  i.e.  whether  muscles  for  instance 
are  governed  by  so-called  trophic  nerves  which  affect  their  nutrition 
directly  in  some  other  way  than  by  influencing  either  their  blood-supply 
or  activity,  must  at  present  be  left  undecided. 

Muscles  exhausted  by  prolonged  action  may  have  their  irritability 
temporarily  restored  by  passing  through  them  for  some  time  a  constant 
current. 

In  exhausted  muscles  the  elasticity  is  much  diminished  ;  the 
tired  muscle  returns  less  readily  to  its  natural  length  than  does  the 
fresh  one. 

The  exhaustion  due  to  contraction  maybe  the  result: — (i) 
Either  of  the  consumption  of  the  store  of  really  contractile 
material  present  in  the  muscle.  Or  (2)  of  the  accumulation  in 
the  tissue  of  the  products  of  the  act  of  contraction.  Or  (3)  of 
both  of  these  causes. 

The  restorative  influence  of  rest  may  be  explained  by 
supposing  that  during  the  repose,  either  the  internal  changes 
of  the  tissue  manufacture  new  explosive  material  out  of  the 
comparatively  raw  material  already  present  in  the  fibres,  or  the 
directly  hurtful  products  of  the  act  of  contraction  undergo  changes 
by  which  they  are  converted  into  comparatively  inert  bodies.  A 
stream  of  fresh  blood  may  exert  its  restorative  influence  not  only 
by  quickening  the  above  two  events,  but  also  by  carrying  off  the 
immediate  waste  products  while  at  the  same  time  it  brings  new 
raw  material.  It  is  not  known  to  what  extent  each  of  these  parts 
is  played.  That  the  products  of  contraction  are  exhausting  in 
their  effects,  is  shewn  by  the  fact  that  exhausted  muscles  are 
recovered  by  the  simple  injection  of  inert  saline  solutions  into 
their  blood-vessels  ;  and  that  such  bodies  as  lactic  acid  injected 
into  a  muscle  cause  rapid  exhaustion  ;  a  striking  instance  is  seen 
in  the  effect  of  dilute  alkalis  in  restoring  the  beat  of  the  exhausted 
frog's  heart.  One  important  element  brought  by  fresh  blood  is 
oxygen.  This,  as  we  have  seen,  is  not  necessary  for  the  carrying 
out  of  the  actual  contraction,  and  yet  is  essential  to  the  main- 
tenance of  irritability.     It  is  probably  of  use  as    what   may  be 

*  Kronecker,  Lud  wig's  Arbeiten,  1871. 


CHAP.    II. 


THE  CC)N'rkA(:TILl':  tissuks. 


lOl 


called  intra-iTioleruhir  oxygen  '  in  preparing  the  explosive  material 
whose  decomposition  gives  rise  to  the  carbonic  acid,  and  other 
products  of  contraction. 

It  is  stated  by  Kroncckcr"  that  oxygen,  not  in  the  form  of  oxyliacmo- 
globin,  but  adniinislcrcd  roughly  in  the  form  of  an  injection  of 
permanganate  of  potash,  restores  the  irritability  of  exhausted  muscle. 

After  prolonged  artificial  excitation  of  a  muscle  within  the  body  the 
exhaustion  is  accompanied  or  rather  followed  by  histological  changes 
of  the  nature  of  degeneration. 


Sec.  6.     A  further  Discussion  oh"  somr  points  in  the 
Physiology  of  Muscle  and  Nerve. 

The  Electrical  F/ienotnena  of  Muscle  and  Nerve. 

The  Natural  Currents.  The  Pre-existence  Theory.  .As  was 
stated  on  p.  64,  du  Bois-Reymond  and  those  with  him  believe  that 
electric  currents  naturally  exist  even  in  untouched,  perfectly  uninjured 
muscles  and  nerves  ;  and  their  view  is  generally  spoken  of  as  "The 
Pre-existence  Theory."  According  to  that  theory,  the  muscle  (or 
iverve)  is  made  up  of  electro-motive  particles  or  molecules  imbedded 


Fig.  i6.    Diagram  to  illustrate  du  Bois-Rey.mond's  Electro-motive  Molbculbs. 
Peripolar  Condition. 

in  an  indifferent  and  imperfectly  conducting  medium.  Each  molecule 
is  further  conceived  of  as  presenting  a  negative  surface  to  the  ends  or 
transverse  sections,  and  a  positive  surface  to  the  longitudinal  surface 
or  section  of  the  muscle  ;  the  molecule  in  fact  may  be  regarded  as  a 
minute  battery  whose  positive  and  negative  poles  arc  at  the  longi- 
tudinal and  transverse  surfaces  respectively.  For  reasons  which  will 
appear  presently  the  molecules  are  further  supposed  to  be  not  single 
but  double,  each  half-molecule  consisting,  as  shewn  in  Fig.  16,  of  a 
positive  and  negative  part,  and  the  two  positive  parts  of  the  two  halves 
being  placed  together  so  that  the  double  molecule  still  presents  a 
negative  surface  to  each  end  or  transverse  section  and  a  positive  surface 
to  the  longitudinal  surface  or  section  of  the  muicle. 

The    presence    of    the    (so-called    peripolar)    molecules   disposed 

'  Compare  the  section,  in  a  later  portion  of  tlic  work,  on  The   Respiratory 
Changes  in  the  Tis  ues. 
*  Ludwig's  Arbdlen,  1S71. 


102  THE   PRE-EXISTENCE   THEORY.  [BOOK  I. 

throughout  the  substance  of  the  muscle  will  give  rise  to  currents  in 
the  medium  by  which  they  are  all  surrounded.  Around  each  molecule 
will  stream  currents  circling  from  the  positive  middle  to  the  negative 
ends  ;  owing  to  the  imperfect  conductivity  of  the  medium  these  currents 
will  not  only  flow,  as  shewn  in  the  diagram,  in  the  immediate  neigh- 
Dourhood  of  each  molecule,  but  will  extend  in  more  or  less  concentric 
lines  at  some  distance  from  the  molecule.  Hence  when  the  elec- 
trodes of  a  galvanometer  ai'e  connected  with  two  points  of  the  surface 
of  the  muscle,  the  deflection  of  the  needle  will  indicate  a  surface  current 
which  is  a  resultant  of  the  numerous  currents  of  the  several  molecules. 
And  a  little  consideration  wili  shew  that  the  direction  and  intensity  of 
the  currents  passing  through  the  galvanometer  in  different  positions  of 
the  electrodes  will  be  such  as  is  described  on  p.  63  and  illustrated  by 
the  diagram,  Fig.  13.  It  need  hardly  be  added  that  the  hypothesis  of 
electro-motive  peripolar  molecules  is  applied  to  nerves  as  well  as  to 
muscles. 

Du  Bois-Reymond  was  led  to  conceive  of  these  molecules  as  being 
double  instead  of  single  in  order  that  he  might  explain  the  origin  of  the 
so-called  electrotonic  currents  which,  as  we  shall  presently  see,  are 
developed  when  a  nerve  is  subjected  to  the  action  of  a  constant  current. 
For  he  supposed  that  under  certain  circumstances  (among  these  the 
passage  into  the  nerve  of  a  constant  current)  each  half  of  each  molecule 
could  be  partially  or,  as  shewn  in  Fig.  17,  completely  reversed,  so  that 


Fig  17.    Diagram  illustrating  du  Bois-Reymond's   Molecules  in  their  Bipolar 

Condition. 

in  each  half-molecule  the  positive  surface  was  directed  to  one  end  and 
the  negative  surfacfe  to  the  other  end  of  the  piece  of  nerve.  The 
molecule  thus,  from  being  peripolar  becomes  bipolar,  and  the  currents 
discharged  by  each  molecule  into  the  surrounding  medium  have  all 
the  same  direction. 

In  order  to  explain  the  undoubted  fact  that  'natural'  currents  are 
either  absent  or  exceedingly  feeble  in  untouched  uninjured  muscles,  du 
Bois-Reymond  supposes  that  the  ends  of  the  muscle  in  contact  with 
the  tendons  are  composed  of  a  layer  or  region  in  which  all  the  molecules 
have  their  positive  instead  of  their  negative  surfaces  looking  to  the 
ends  of  the  muscle.  The  molecules  of  this  region,  which  he  calls  the 
parelectrofiomic  region,  may  be  looked  upon  as  bipolar,  and  the 
arrangement  shewn  in  Fig.  17  miy  be  taken  as  illustrating  the  con- 
dition of  the  molecules  in  this  parelectronomic  region.^     Obviously  the 

'  Since  in  the  figure  the  positive  sarfaces  of  the  molecules  looks  to  the  left- 
hand  side  of  the  page,  the  end  of  the  muscle,  of  which  they  may  be  supposed 
to  represent  parelectronomic  elements,  must  also  be  considered  as  directed  to 
the  left-hand  side  of  the  page. 


CHAr.    II.J  THE   CONTRACTILE   TISSUES.  103 

currents  which  the  clcctro-motivc  molecules  develop  in  this  region  are 
opposed  in  direction  to  those  originating  in  the  rest  of  the  muscle,  and 
hence  either  partially  or  wholly  conceal  the  existence  of  the  latter. 
The  development  of  this  parelcCtronomic  region  is  stated  by  du  Bois- 
Rcymond  to  be  greatly  assisted  by  cold,  but  Hermann,  who  of  course 
wholly  denies  the  existence  of  any  such  region,  hnds  no  electrical 
differences  in  frogs'  muscles  kept  in  a  warm  room  from  those  kept  in  an 
icc-cold  cellar,  though  when  currents  are  developed  they  are  increased 
by  an  elevation  of  temperature. 

It  is  obviously  reasonable  to  infer  that  if  this  view  of  du  Bois-Rey- 
mond's  be  correct,  if  natural  currents  do  exist  in  muscles  with 
untouched  natural  terminitions  but  exist  masked  by  the  parelcctro- 
nomic  region,  they  would  manifest  themselves  in  full  force  imme- 
diately, without  loss  of  time,  upon  the  removal  or  destruction  of  the 
parekcttonomic  region  ;  whereas  if  Hermann's  view  be  correct  that 
the  currents  do  not  pre-exist  but  are  developed  by  chemical  changes 
due  to  the  injury  (or  commencing  death)  of  the  ends  of  the  muscle,  it 
would  be  expected  that  a  measurable  interval  would  elapse  between, 
for  instance,  the  tearing  or  cutting  off  the  end  of  a  muscle  and  the 
appearance  of  the  muscle-currents  in  their  full  intensity.  And  Hermann 
has  attempted  to  shew  that  such  an  interval  does  exist.  P^or  this 
purpose  he  makes  use  of  the  fiill-rheotoftie,  an  instrument  the  nature  of 
which  may  be  explained  here,  as  it  is  applicable  for  other  purposes 
besides  the  one  in  question. 

A  weight  (Fig.  18)  is  let  fall  from  a  height  of  about  4  feet  in  a 
course  indicated  by  the  arrow  and  the  dotted  lines.  In  falling  it 
comes  in  contact  with  the  exposed  lower  tendinous  expansion  of  the 
gastrocnemius  muscle  M  stretched  over  the  ebonite  blojk  Qj  and 
tearing  this  off  presumably  removes  to  a  greater  or  less  extent  the 
parelectronomic  region  of  du  Bois.  The  muscle  itself  at  two  points 
^  and^'  is  connected  with  the  galvanometer  G,  but  in  the  circuit  are 
inserted  two  keys  j.^  and  j' which  are  so  arranged  that  the  weight  in 
falling  catches  a  projecting  part  of  x,  and  closes  the  galvanometer 
circuit  (by  pushing  the  opposite  end  of  x  against  the  metal  arc  2) ;  and 
then  opens  the  circuit  by  pushing  down  the  projecting  part  of  y. 

Thus  in  certain  definite  successive  times,  which  can  be  calculated 
from  the  rate  with  which  the  weight  falls,  the  tendinous  end  of  the 
muscle  is  torn  off,  the  galvanometer  circuit  is  closeu  so  that  any 
muscle  current  present  passes  into  the  galvanometer,  and  the  circuit 
is  again  opened.  Immediately  after  such  an  observation  has  been 
made  and  the  deflection  noted,  the  keys  are  replaced,  the  weight  is 
pgain  raised  and  again  let  fall,  and  the  deflection  again  noted  ;  during 
this  second  fall  the  muscle,  though  still  in  connection  with  the  gal- 
vanometer wires,  is  not  affected  by  the  weight.  The  first  deflection 
is  produced  by  the  current  which  is  present  in  the  muscle  an  extremely 
small  fraction  of  a  second  after  the  stripping  off  the  tendon,  the 
second  is  produced  by  the  current  present  in  the  muscle  a  certain 
number  of  seconds  later.  The  currents  pass  through  the  galvanometer 
for  the  same  time/,  viz.  that  taken  up  by  the  weight  in  falling  from  x  to 
/ ;  hence  then,  if  one  deflection  is  greater  than  the  other,  the  current 
producing  it  is  the  stronger  of  the  two  currents.     In  all  cases,  according 


I04 


THE  PRE-EXISTENCE  THEORY.  [BOOK   I. 


Fig.  i8.    A  Diagram  to  illustrate  the  Fall-Rheotome. 

The  explanation  of  most  of  the  figures  of  reference  is  given  in  the  text,  j,  the  space  com- 
prised between  the  two  first  dotted  horizontal  lines,  serves  as  a  measure  for  the  time  taken  in 
stripping  off  the  tendon,  v  similarly  serves  to  measure  the  time  elapsing  between  the 
beginning  of  the  stripping  off  the  tendon  and  the  closure  of  the  galvanometer  circuit,  e  is 
a  reversing  key  connected  with  a  compensator,  the  use  of  which  is  not  referred  to  in  the  text, 
for  brevity's  sake,    a  the  hook  by  which  the  gastrocnemius  is  fastened. 

to  Hermann,  the  second  deflection  is  stronger  than  the  first,  i.e.  in 
the  first  case,  the  muscle-current  has  not  reached  its  full  strength,  or 
in  other  words,  the  current  developes  after  the  injury,  and  is  not 
present,  in  full  force  a  measurable  time  after  the  removal  of  the 
parelectronomic  layer. 

The  argum.ent  based  on  this  is  perhaps  not  very  conclusive,  but  as 
far  as  it  goes  it  -is  adverse  to  the  pre-existence  theory. 

It  might  be  imagined  that  the  currents  which  may  be  observed, 
when  the  electrodes  connected  with  a  galvanometer  are  placed  in 
contact  with  various  points  on  the  surface  of  a  living  body  (human  or 
other,  indicate  the  pre-existence  of  muscle  currents  ;  but  it  is  im- 
possible to  prove  that  these  currents  are  anything  but  cutaneous 
currents  ;  and  indeed  in  fishes,  according  to  Hermann,  where 
cutaneous  currents  are  absent,  no  such  '  body '  currents  can  be 
witnessed. 

As  regards  the  pre-existence  of  a  current  in  nerves,  a  quite  similar 
contention  exists  ;  the  uninjured  nerve  in  the  body  is  isoelectric  ;  the 
proof  of  a  normal  current  here  is,  to  say  the  least,  no  stronger  than  in 
the  case  of  the  muscle. 

The  diagram,  Fig  13,  p.  63,  as  was  stated,  illustrates  the  currents 
observable  in  a  cylindrical  muscle  composed  of  parallel  fibres,  and 


CHAP.    II.]  THE   CONTRACTILE   TISSUES. 


105 


with  tolerably  rectangular  terminations.  In  muscles  not  having  this 
form,  the  direction  of  tiie  currents  is  different.  Thus  in  a  rhomb  cut 
from  a  muscle  with  i)arallcl  fibres  the  most  positive  portions  instead  of 
being  at  the  equator  ot'  the  longitudinal  surface  are  nearer  the  obtuse 
angles  ;  and  the  most  negative  points  instead  of  being  at  the  centres 
of  the  transverse  sections  arc  nearer  the  acute  angles.  In  the  frog's 
gastrocnemius,  in  which  the  fibres  have  a  characteristic  arrangement, 
the  directions  of  the  currents  differ  considerably  from  the  scheme  given 
for  regular  muscles.  The  currents  observed  agree  however  with  those 
theoretically  deduced  from  a  consideration  of  the  currents  of  a  rhomb 
of  muscle  and  of  the  arrangement  of  the  gastrocnemius  fibres. 

The  Currents  of  Action.  It  was  stated  above,  pp.  68 — 77,  that 
Bernstein  had  shewn  that  the  'negative  variation'  or  current  of 
action  passed  along  a  muscle  or  nerve  from  the  spot  stimulated  in  the 


Fic.  19.    A  Diagram  to  illustrate  Bernstein's  Differential  Rheotomk. 
The  expl.-1n.1t ion  of  the  figures  of  reference  is  given  in  the  text.     The  letter  /  referring  to 
the  pointer  which  strikes  the  wire  w,  is  att.iched  to  the  rod  only  in  the  position  jr.     Similarly 
the  references  /',  ^"  are  only  given  in  the  position  y. 

form  of  a  wave  travelling  in  the  nerve  at  the  same  rate  as  the  nervous 
impulse,  in  the  muscle  at  the  same  rate  as  the  contraction. 

The  principle  of  the  differential  rheotome  by  which  Bernstein  was 
enabled  to  establish  this  fact,  is  as  follows.     A  rod  r  (Fig.   19)  is 


106  CURRENTS   OF   ACTION.  [BOOK  I. 

made  to  rotate  with  a  definite  velocity  about  an  axis  a.  At  one  end 
of  the  rod  is  a  steel  pointer  p  passing  obliquely  downwards,  at  the 
opposite  end  are  two  other  steel  pointers  p' ,  p",  also  passing  obliquely 
downwards  and  connected  with  one  another.  As  the  rod  rotates  the 
pointer  p  comes  in  contact  at  one  part  of  its  course  with  a  stretched 

.  wire  w,  and  the  pointers  p',  p"  at  one  part  of  their  course  dip  into 
two  isolated  mercury  cups  ?n,  m'.  The  effect  of  p  coming  in  contact 
with  w  is  to  stimulate  the  nerve  n,  since  it  closes  the  primary  circuit 
B caw,  and  thus  causes  an  induced  current  in  the  secondary  coil  c'. 
The  effect  oi  p',  p"  dipping  into  ;«,  7n'  is  to  send  into  the  galvanometer 
any  nerve-current  present,  since  it  closes  the  circuit  jn ee  G in.  Any 
current  of  rest  present  in  the  nerve  is  compensated  by  an  arrange- 
ment not  shewn  in  the  figure,  so  that  in  the  non-stimulated  nerve,  no 
deflection  of  the  needle  follows  closure  of  the  galvanometer  circuit. 
It  will  be  seen  that  in  the  position  x  of  the  wire  w  the  contact  of 
p  with  w,  and  of  p' ,  p"  with  in,  in'  is  made  at  the  same  time, 
that  is,  the  nerve  is  stimulated  and  the  galvanometer  circuit  closed  at  the 
same  instant.  Accordingly  if  the  rod  r  be  made  to  rotate  rapidly, 
with  w  in  the  position  x,  the  nerve  will  be  stimulated,  and  the  gal- 
vanometer circuit  closed  at  the  same  instant,  a  number  of  times  in 
succession  corresponding  to  the  number  of  rotations.  When  this  is 
done,  it  is  found  that  no  deflection  of  the  galvanometer  needle  takes 
place,  though  if  the  galvanometer  circuit  be  kept  closed  by  connecting 
m,  in  without  the  aid  of  p'  p",  the  repeated  contact  of  p  with  w  as  r 
rotates  does  produce  a  most  distinct  deflection.  The  conclusion  from 
this  is  that  the  electric  change  in  the  nerve,  started  by  each  contact  of 
p  with  w,  has  not  had  time  to  affect  the  galvanometer  before  p',  p" 
have  left  m,  in',  but  has  passed  away  before  p,  p"  come  in  contact  with 
m,  m'  at  the  next  rotation  ;  in  other  words,  tliat  the  change  of  condition 
which  leads  to  the  current  is  not  established  instantaneously  in  the 
nerve,  but  takes  some  appreciable  time  to  pass  from  the  stimulated 
spot  to  the  electrodes  connected  with  the  galvanometer. 

If  now  the  position  of  the  wire  w  be  shifted  on  the  arc  A  a  short 
distance  towards  y,  then  p  will  touch  w  before  p',  p"  come  to  the 
mercury  cups  ;  that  is,  there  will  be  a  short  measurable  interval 
between  the  stimulation  of  the  nerve  and  the  closure  of  the  galvano- 
meter circuit.  Suppose  then  a  succession  of  experiments  are  made  in 
each  of  which  iv  is  moved  an  increasing  distance  towards  jk  ;  it  will 
be  found  that  at  a  certain  distance  from  x  a  slight  deflection  is 
obtained,  and  as  the  distance  from  x  increases  the  deflection  increases, 
goes  on  increasing,  reaches  a  maximum,  then  diminishes,  and  finally 
when  say  w  is  at_y  disappears  again.  Now  in  all  cases  the  deflection 
is  such  as  to  indicate  a  current  from  e'  through  the  galvanometer  to  e, 
that  is  as  w  is  moved  towards  j  the  first  effect  observed  is  that  e 
becomes  slightly  negative,  the  negativity  then  increases  up  to  a 
maximum,  and  afterwards  diminishes  until  once  more  e  is  in  the 
same  electric  condition  as  e'.  That  is  to  say,  when  a  nerve  is 
stimulated  at  any  point,  a  part  of  the  nerve  at  some  distance  from 
the  point  stimulated  does  not  become  negative  until  a  certain  time, 
dependent  on  the  distance  from  the  point  stimulated,  has  elapsed  ; 
further  the  negativity  is  developed  gradually  with  a  certain  rapidity, 


CHAP.    II.]  THF.   CONTRACTILE   TISSUES.  IO7 

and  having  reached  a  maximum  declines  and  disappears  ;  in  other 
words,  the  negativity  travels  along  the  nerve  from  the  spot  stimulated 
in  the  form  of  a  wave.  Obviou-ily  by  noting  the  position  of  iv  in  the 
various  experiments  and  the  rapidity  of  rotation  of  ;-,  the  rapidity 
with  which  this  condition  of  negativity  travels  down  the%nerve  to  e 
and  its  duration  there  can  be  calculated.  It  was  in  this  way  that 
IJernstcin"  obtained  the  results  quoted  at  the  beginning  of  this  section. 
The  same  method  maybe  applied  to  mus.?le  by  substituting  a  curarized 
muscle  for  the  nerve. 

Ihe  necessity  of  employing  a  series  of  rotations,  and  thus  of 
studying  the  effects  not  of  a  single  stimulus,  but  of  the  sum  of  a 
series,  arises  from  the  fact  that  though  the  current  of  action  developed 
by  a  single  induction  shock  may  be  shewn  by  a  suitable  galvanometer, 
the  indications  are  not  suflkiently  delicate  to  mark  the  very  beginning 
and  the  very  end  of  the  current,  i.e.  to  give  the  e.xact  limits  of  the 
wave. 

If  then,  as  seems  clearly  shewn  by  the  above,  each  point  of  the 
nerve  or  muscle  becomes  negative  during  the  nervous  or  muscular 
impulse,  several  difficulties  present  themselves.  Thus  it  is  obvious 
that  a  nervous  (or  muscular)  impulse,  started  say  by  a  single  induction 
shock,  must  give  rise  at  any  point  not  to  one  only  but  to  two  currents, 
and  those  in  opposite  directions.  For  as  the  wave  of  the  impulse 
travels   down   the  fibre  (Fig.   20)  in  the  direction    of   the  arrow,  a 

Fig.  so. 


becomes  negative  and  a  current  is  developed  which  passes  through 
the  galvanometer^  from  b  to  a.  Almost  immediately  afterwards  0 
becomes  negative,  while  the  negativity  of  a  diminishes  or  disappears. 
We  should  accordingly  expect  to  find  a  second  current  passing  through 
the  galvanometer  from  <i  to  d.  .And  practically  such  a  double  current 
was  observed  long  ago'  and  has  been  called  by  du  Bois-Rcymond  the 
'double  variation.'  Indeed  the  prominence  at  times  of  the  one  or  the 
other  current  in  the  hands  of  various  experimenters  gave  rise  to  a 
controversy  as  to  whether  the  variation  caused  by  a  single  induction 
shock  was  positive  or  negative  in  character. 

'   Untersiich.  it.  a.  Errc^uii^vorgan^  iin  Ncrven-  tind  Mitskelsysteme,  1871. 
*  In  all  llie  account  which  follows  the  direction  of  the  current  spoken  of  is 
to  be  supposed  to  be  that  of  the  current  throtigk  the  galvanometer, 
»  Mayer,  Archivf.  Anal.  u.  Phys.  1868,  p.  655, 


I08  CURRENTS   OF   ACTION.  "  [BOOK  I. 

But  if  such  a  double  current  is  developed  between  any  two  points, 
it  is  obvious  that  when  a  muscle  or  nerve  is  tetanized  and  wave  after 
wave  of  impulse  and  therefore  of  negativity  passes  over  both  points, 
the  current  from  a  to  i  of  one  impulse  will  neutralize  or  at  least  tend 
to  neutralize  the  current  from  d  to  a  of  the  succeeding  impulse.  We 
are  driven  to  suppose  that  the  current  which  is  observed  during  tetanus 
as  the  negative  variation  or  current  of  action  from  d  to  a,  is  able  to 
manifest  itself  because  at  each  impulse  it  is  greater  than  the  current 
from  a  to  6.  Such  a  difference  between  the  opposing  currents  might 
arise  either  from  the  wave  of  impulse  diminishing  along  its  whole 
progress,  or  from  its  diminishing  suddenly  at  the  end  of  the  fibre,  or 
from  both  causes  combined.  If  the  negativity  assumed  by  d  when 
the  impulse  reaches  it  is  less  than  the  negativity  assumed  by  a  when 
the  impulse  reaches  it,  the  current  from  a  to  d  will  be  less  than  that 
from  d  to  a  ;  and  this  will  be  true  whatever  the  position  of  a  and  d  on 
the  fibre. 

Bernstein  found  that  in  muscle  the  'negative  variation'  diminished 
in  its  course.  Du  Bois-Reymond  stated  that  this  was  true  of  exhausted 
muscle,  but  was  not  true  of  uninjured  muscle  for  a  short  time  after 
removal  from  the  body.  Hermann  finds  that  in  muscle  removed  from 
the  body  and  thus  deprived  of  its  blood  circulation  there  is  always  a 
gradual  diminution  of  the  current  of  action  as  it  travels  down  the  fibres, 
whether  the  muscle  be  urarized  and  stimulated  directly,  or  not  urarized 
and  stimulated  indirectly  by  means  of  its  nerve.  -In  the  latter  case 
two  currents  of  action  proceed  from  approximately  the  middle  of  the 
muscle  (the  region  of  the  end-plates)  towards  the  ends,  diminishing  as 
they  go.  He  found  that  the  diminution  was  greater  as  the  muscle 
became  more  exhausted,  in  this  confirming  du  Bois-Reymond.  Her- 
mann brings  forward  also  some  experiments  to  shew  that  the  dimi- 
nution is  equally  distributed  throughout  the  course  of  the  current,  so 
that  the  diminution  is  equal  for  equal  distances  of  muscle  traversed. 

Now  in  muscles  in  which  by  cutting  off  one  end  currents  of  rest 
have  become  conspicuous,  du  Bois-Reymond  has  shewn  that  the 
current  of  action  obtained  by  tetanizing  the  muscle  is  greater  than 
that  obtained  by  similarly  tetanizing  an  uninjured  muscle,  so  that  in 
the  former  case  either  the  current  of  action  is  in  itself  greater  or  the 
negativity  diminishes  more  rapidly  along  the  whole  or  in  some  part 
of  the  course  of  the  fibre  {i.e.  the  difference  between  the  currents  6  to 
a  and  a  to  d  becomes  more  marked  in  favour  of  that  from  d  to  a). 
By  comparing  with  the  help  of  the  fall-rheotome  the  amounts  of 
deflection  of  the  galvanometer  in  the  two  cases  when  single  induction 
shocks  are  sent  into  the  muscle,  Hermann  concludes  that  the  wave  is 
not  absolutely  less  in  the  uninjured  muscle,  so  that  the  greater  deflec- 
tion obtained  in  tetanizing  a  muscle  with  an  artificial  cross-section  must 
be  due  to  the  current  from  a  to  d  being  less  than  is  the  case  in  the 
uninjured  muscle.  This  may  in  part  be  due  to  a  greater  diminution 
of  the  stimulus  wave  as  it  travels,  but  is,  as  we  shall  see,  probably  in 
large  part  due  to  a  rapid  diminution  or  indeed  extinction  of  the  wave 
when  it  reaches  d. 

Hermann,  with  the  aid  of  the  differential-  and  fall-rheotome,  finds 
that  in  all  uninjured  muscle,  whether  stimulated  directly  or  indirectly, 


CHAP.   II.]  THE   CONTRACTILE   TISSUES.  IO9 

the  two  currents  from  b  io  a  and  from  a  to  b  may  be  observed  as 
described  above.  This  first  he  calls  ad-terminal^^  and  the  second 
ab-tenninal :  the  two  bcinj;  named  p/ia.^ic  currents.  The  former  he 
finds  always  greater  th m  the  latter.  In  a  muscle  with  an  artificial 
cross-section  he  finds  that  as  in  an  uninjured  muscle  two  currents  are 
developed  between  two  points,  provided  one  be  not  at  the  cross-section, 
as  from  b'  to  a'  and  from  a  to  b'  (Fifj.  20),  but  between  two  points,  one 
of.  which  is  at  the  section,  as  a  and  b,  only  one  current  is  observable, 
viz.  that  from  b  to  a,  i.e.  the  wave  disappears  at  b ;  the  end  of  the 
muscle,  for  some  reason  or  other,  does  not  become  more  negative. 
From  these  experiments  Hermann  concludes  that  in  uninjured  muscle, 
the  current  of  action  observed  by  the  ordinary  method  without  a 
rheotome  is  due  to  the  diminution  of  the  stimulus  wave  as  it  travels, 
but  that  the  current  of  action  similarly  observed  when  currents  of  rest 
are  present  has  an  additional  factor,  viz.  the  absence  of  any  power  of 
the  wave  to  atTect  the  end  of  the  fibres. 

Hcrmannfurther  states  that  when  two  moistened  threads  are  passed 
round  the  fore-arm' of  a  mm,  the  one  about  the  middle,  the  other  at 
the  wrist,  and  conne  ted  by  the  usual  electrodes  with  the  galvanometer, 
tetanizing  the  muscles  by  stimulating  the  nerves  in  the  upper  arm 
causes  no  deflection  of  the  galvanometer :  no  action  currents  are  in 
this  case  perceptible. 

(This  is  in  contradiction  to  the  result  of  the  classical  experiment  of 
du  Bois-Rcymond,"  in  which  the  inde.\  fingers  of  the  two  hands  being 
dipped  into  vessels  containing  salt  solution  and  connected  with  a 
galvanometer,  a  deflection  of  the  needle  takes  place  whenever  the 
muscles  of  the  one  or  the  other  arm  are  thrown  into  contraction  by 
voluntary  effort  ;  the  direction  of  the  deflection  indicates  the  develop- 
ment of  an  ascending  current  in  the  active  arm,  and  the  ascending 
current  thus  produced  is  regarded  as  the  resultant  of  the  '  negative 
variations '  or  currents  of  action  of  the  various  muscles  thrown  into 
contraction.  But  this  experiment,  though  long  looked  upon  as  a 
satisfactory  proof  of  a  'current  of  action'  or  'negative  variation,' 
is  regarded  by  Hermann  as  valueless  in  this  respect,  inasmuch  as  the 
current  observed  is  according  to  him  simply  a  cutaneous  current.) 

On  the  other  hand,  if  the  rheotome  ba  used  so  that  the  ad-  and 
ab-terminal  waves  present  can  be  separated  and  recognized,  the  two 
waves  are  found  to  be  present  but  to  be  of  equal  strength  ;  thus  in  the 
body  in  an  unyred  muscle  with  normal  circulation  the  wave  does  not 
diminish  in  its  course,  and  hence  the  two  waves,  the  ad-terminal  and 
ab-terminal,  compensate  one  another  and  cannot  be  detected  in  the 
ordinary  manner  of  looking  for  currents  of  action  in  tetanus.  The 
rapidity  of  transmission  of  the  wave  in  the  above  experiments  was 
from  10  to  13  metres  per  second. 

In  the  case  of  nerves,  since  the  rapidity  of  the  nervous  impulse  is 
much  greater  than  the  rapidity  of  the  stimulus  wave  of  muscle,  the 
separation  of  the  ad-  and  ab-terminal  current  is  naturally  more  difficult. 

'  Since  the  direction  of  the  cuiront  in  the  muscle  completing  the  circuit  would 
be  towards  the  end  of  the  fihre. 

»  Unlerstich,  ii.  thierischc  Electricitdt,  Bd.  II.,  Abth.  2,  p.  276  {1S60). 


no  CURRENTS  OF  ACTION.  [BOOK  1. 

But  Hermann  by  using  packets  of  the  sciatic  nerves  (frog's)  and 
cooling  them  down  to  o""  in  order  to  lessen  the  rapidity  of  the  nervous 
impulses,  has  obtained  results  analogous  to  those  just  described  in 
reference  to  muscle. 

Since  the  part  of  the  muscle  which  is  at  any  moment  stimulated 
becomes  negative,  if  the  whole  of  the  iminjured  muscle  from  end  to 
end  were  stimulated  equally  at  the  same  time,  every  part  would 
become  equally  negative,  and  no  current  would  occur.  Hermann 
finds  that  under  such  circumstances  no  current  does  occur.  This 
experiment  perhaps  requires  confirmation,  as  it  is  not  certain  that 
it  is  possible  by  the  method  given  to  equally  stimulate  all  parts  of  the 
muscle. 

To  recapitulate.  According  to  the  views  of  Hermann  and  his 
followers,  the  living  untouched  muscle  is  isoelectric  and  the  typical 
currents  of  rest  are  developed  in  consequence  of  the  ends  of  the 
muscle  dying,  and  therefore  becoming  negative.  To  the  experimental 
evidence  quoted  on  p.  65,  we  may  add  that,  according  to  Hermann, 
parts  of  other  tissues  besides  muscle  and  nerve  'become  on  dying 
negative  relatively  to  living  parts  of  the  same  tissue,  and  that  according 
to  Engelmann^,  although  the  section  of  a  skeletal  muscle  removed 
from  the  body,  unlike  the  section  of  cardiac  muscle,  remains  negative 
for  an  indefinite  tinne,  the  negativity  which  appears  at  the  cross-section 
of  a  muscle  divided  subcutaneously  disappears  after  a  while  in  con- 
sequence of  the  cut  surfaces  being  restored  to  a  living  condition  by  the 
help  of  the  blood-stream.  It  may  be  urged  as  a  difficulty  against 
Hermann's  view,  that  if  in  a  mus'^le  it  is  only  the  negativity  of  the 
cut  and  dying  portion  which  gives  rise  to  the  currents  of  rest,  we 
should  not  expect  the  current  from  the  equator  to  the  cross-section  to 
be  greater  than  one  from  a  point  nearer  the  cross-section,  seeing  that 
the  resistance  is  greater  in  the  former  case. 

According  to  the  same  school  the  current  of  action  is  due  to  the 
substance  of  the  muscle  which  is  at  any  moment  the  subject  of  an 
impulse  wave  becoming  at  that  time  negative  towards  the  rest  of  the 
muscle  ;  hence  as  the  wave  proceeds  along  the  fibres  ad-terminal  and 
ab-terminal  currents  of  necessity  make  their  appearance  as  successive 
points  of  the  muscle  or  nerve  substance  I'each  their  maximum  of 
negativity.  In  the  tetanus  of  an  uninjured  unexhausted  muscle  the 
ad-terrainal  and  ab-terminal  currents  neutralize  ea:h  other  and  no 
total  current  can  be  manifested  through  the  galvanometer.  In 
exhausted  but  otherwise  uninjured  muscle  the  negativity  of  the 
impulse  wave  diminishes  as  the  wave  proceeds.  Hence  the  ab- 
terminal  current  is  weaker  than  the  ad-terminal,  and  the  excess  of  the 
latter  makes  itself  manifest  as  the  so-called  negative  variation.  In  a 
muscle  with  an  artificial  cross-section  the  ad-terminal  current  and  so 
the  negative  variation  is  still  more  conspicuous  on  account  of  the  end 
of  the  fibre  not  being  affected  by  the  wave  at  all,  and  the  ab-terminal 
current  being  here,  therefore,  wholly  absent. 

Du  Bois-Reymond  on  the  other  hand  and  those  with  him,  regard 
the  currents  of  rest  as  due  to  the  electro-motive  molecules,  and  explain 

^  Pfliiger's  Archiv,  XV.  {1877),  p.  328. 


CHAP.    II.]  Tin-:   CONTRACTILE    TISSUES.  I  1»I 

the  al>scncc  of  currents  in  the  uninjured  muscle  by  the  presence  of 
the  parelectronomic  re<,Mon  or  layer.  They  regard  the  nc;(ativc 
variation  as  due  to  an  absolute  diminution  in  the  energy  of  the  mole- 
cules. In  the  case  of  uninjured  muscles  they  suppose  that  while  the 
energy,  both  of  the  ordinary  molecules  constituting  the  chief  substance 
of  the  muscle  and  of  the  molecules  constituting  the  parelectronomic 
region  and  giving  a  current  op])osed  in  direction  to  the  other,  is 
diminished,  the  diminution  of  the  latter  is  less  than  that  of  the  former, 
and  hence  a  negative  variation  can  make  its  appearance  in  a  muscle 
shewing  no  currents  of  rest.  In  a  muscle  with  an  artificial  cross- 
section  or  with  the  parelectronomic  region  otherwise  removed,  the 
negative  variation  of  the  natural  electric  molecules  occurs  without  any 
opposition  of  the  molecules  of  the  parelectronomic  region,  and  is  con- 
sequently greater  than  in  the  uninjured  muscle.  They  further  interpret 
the  double  current  (ab-tcrminal  and  ad-terminal)  seen  in  the  gastroc- 
nemius muscle  with  a  single  induction-shock,  as  due  to  a  difference  of 
time  in  the  development  of  the  negative  variation  in  the  parelectro- 
nomic regions  of  the  upper  and  of  the  lower  ends  of  the  muscle. 

Du  Bois-Reymond  found  that  in  tetanizing  a  muscle,  the  current  of 
rest  only  acquired  its  normal  strength  after  some  interval  ;  the 
negative  variation  did  not  at  once  disappear,  there  was  an  'after- 
action.' In  uninjured  muscle  this  'after-action'  he  found  to  be  con- 
siderable, amounting  to  as  much  as  one-half  or  two-thirds  of  the 
total  negative  variation  ;  in  muscles  with  artificial  transverse  sections 
it  was  much  less,  viz.  about  one-tenth.  He  explains  the  difference  by 
supposing  thnt  the  removal  of  the  end  of  the  muscle  does  away  with 
one  factor  of  the  after-action  ;  for  he  considers  that  there  are  two 
kinds  of  after-action  :  one,  the  i)iner  after-action,  affecting  the  whole 
of  the  muscle  substance,  the  other  or  terminal  after-action  concerning 
the  ends  of  the  muscle  fibres  only.  The  former  he  believes  to  be  due 
to  the  formation  of  lactic  acid  during  contraction,  the  electro-motive 
force  of  the  molecules  throughout  the  muscle  substance  being  thereby 
diminished.  The  latter  on  the  other  hand  he  considers  to  be  generated 
by  the  several  contraction-waves  as  they  reach  the  ends  of  the  fibres 
changing  some  of  the  peripolar  molecules  into  a  bipolar  condition, 
thereby  temporarily  increasing  the  parelectronomic  current.  In  a 
muscle  with  an  artificial  transverse  section,  in  which  no  parelectronomic 
current  is  present,  the  tendency  of  the  contraction-waves  to  establish 
such  a  current  by  the  formation  of  bipolar  molecules  at  the  ends  of  the 
fibres,  is  prevented  by  the  progressive  death  of  the  elements.  Du  Bois- 
Reymond  further  thinks  that  the  normal  presence  of  a  parelectronomic 
region  in  an  uninjured  muscle  within  the  body  is  in  reality  a  permanent 
terminal  after-action,  i.e.  contraction-waves  arriving  at  the  ends  of  the 
muscular  fibres  are  continually  tending  to  convert  the  peripolar  into 
bipolar  molecules.  Hermann  attributes  the  after-action  to  the  muscle 
plasma  not  being  able  under  the  circumstances  to  return  at  once  to 
a  condition  of  full  nutrition,  i.e.  to  its  normal  positive  state. 

It  is  we  venture  to  think  obvious  that  further  researches  are  needed 
before  either  the  one  view  or  the  other  can  be  regarded  as  established 
beyond  dispute. 


112  ELECTROTONIC   CURRENTS.  [BOOK   I. 

Electrotonic  Currents.  During  the  passage  of  a  constant  current 
through  a  nerve,  variations  in  the  electric  currents  of  the  nerve 
analogous  in  some  respects  to  the  variations  of  the  irritability  of  the 
nerve  may  be  witnessed.  Thus  if  a  constant  current  supplied  by  the 
battery  P  (Fig.  21)  be  applied  to  a  piece  of  nerve  by  means  of  two 
non-polarizable  electrodes  p,  p',  the  currents  obtainable  from  various 
points  of  the  nerve  will  be  different  during  the  passage  of  the 
polarizing  current  froin  those  which  were  manifest  before  or  after  the 
current  was  applied  ;  and,  moreover,  the  changes  in  the  nerve-currents 
produced  by  the  polarizing  current  will  not  be  the  same  in  the  neigh- 
bourhood of  the  anode  {p)  as  those  in  the  neighbourhood  of  the  kath- 
ode {p').  Thus  let  G  and  H  be  two  galvanometers  so  connected  with 
the  two  ends  of  the  nerve  as  to  obtain  good  and  clear  evidence  of  the 
natural  nerve-currents.  Before  the  polarizing  current  is  thrown  into 
the  nerve,  the  needle  of //will  occupy  a  position  indicating  the  passage 
of  a  current  of  a  certain  intensity  from  h  to  //  through  the  galvan- 
ometer (from  the  positive  longitudinal  surface  to  the  negative  cut  end 
of  the  nerve),  the  circuit  being  completed  by  a  current  in  the  nerve 
from  h'  to  h,  i.e.  the  current  will  flow  in  the  direction  of  the  arrow. 
Similarly  the  needle  of  G  will  by  its  deflection  indicate  the  existence 
of  a  current  flowing  from  g  to  g  through  the  galvanometer,  and  from 
g'  to  _^  through  the  nerve,  in  the  direction  of  the  arrow. 

At  the  instant  that  the  polarizing  current  is  thrown  into  the  nerve  at 
pp',  the  currents  at  gg",  hli'  will  suffer  a  negative  variation  corresponding 
to  the  nervous  impulse,  which,  at  the  making  of  the  polarizing  current, 
passes  in  both  directions  along  the  nerve,  and  may  cause  a  contraction 
in  the  attached  muscle.  The  negative  variation  is,  as  we  have  seen 
(p.  78),  of  extremely  short  duration,  it  is  over  and  gone  in  a  small 
fraction  of  a  second.  It  therefore  must  not  be  confounded  with  a 
permanent  effect  which,  in  the  case  we  are  dealing  with,  is  observed 
in  boih  galvanometers.  This  effect,  which  is  dependent  on  the 
direction  of  the  polarizing  current,  is  as  follows  :  Supposing  that  the 
polarizing  current  is  flowing  in  the  direction  of  the  arrow  in  the  figure, 
that  is,  passes  in  the  nerve  from  the  positive  electrode  or  anode  p  to 
the  negative  electrode  or  kathode  p',  it  is  found  that  the  current  through 
the  galvanometer  G  is  increased,  while  that  through  H  is  diminished. 
We  may  explain  this  result  by  saying  that  the  polarizing  current  has 
developed  in  the  nerve  outside  the  electrodes  a  new  current,  the 
'electrotonic'  current,  having  the  same  direction  as  itself,  which  adds 
to,  or  takes  away  from,  the  natural  nerve-current,  according  as  it  is 
flowing  in  the  same  or  in  an  opposite  direction. 

The  strength  of  the  electrotonic  current  is  dependent  on  the  strength 
of  the  polarizing  current,  and  on  the  length  of  the  intrapolar  region 
which  is  exposed  to  the  polarizing  current.  When  a  strong  polarizing 
current  is  used,  the  electromotive  force  of  the  electrotonic  current  may 
be  much  greater  than  that  of  the  natural  nerve-current.  The  exist- 
ence of  an  electrotonic  current  in  the  intrapolar  regions  between  the 
polarizing  electrodes  has  been  much  disputed,  some  observers  main- 
taining that  it  is  in  reality  absent  from  this  region,  and  confined  entirely 
to  the  extrapolar  districts,  while  others  regard  it  as  existing  in  the 


CHAP.   II.]  THE   CONTRACTILE   TISSUES. 


113 


intrapolar  region  as  well.  All  agree  that  it  spreads,  with  a  diminution 
in  intensity,  for  some  distance  along  the  extrapolar  districts  in  both 
directions. 

Wiicn  the  polarizing  current  is  broken  there  is  a  rebound  in  the 

P 

+ 


'M 


p  iBS »  ft 


-^  y 


// 


Fig.  21.    Di.vGRAM  illustrativo  Electrotonic  Curre.vts. 

P.  the  polarizing  battery,  with  k  a  key,  /  the  an  jdc,  and  /'  the  kathode.  At  the  left  end 
of  the  piece  of  nerve  the  natural  current  fl  .ws  ihr,>ugn  the  galvanometer  G  from  g  to^, 
in  the  directi  jn  •.•(  the  arr  ^wi;  its  direct.>in  therefore  i^  the  same  as  that  of  the  polarizing 
current ;  c  mseiuenily  it  appears  increased,  as  indicated  by  the  sign  +.  1  he  current  at 
the  other  end  of  the  piece  of  nerve,  from  h  to  /«'.  through  the  galvanometer  //,  fliws  in 
a  contrary  direction  to  the  polarizing  current;  it  consequently  appears  to  be  diminished, 
as  indicated  by  the  sign  -. 

N  B.  For  simplicity's  sake,  the  polarizing  current  is  here  supposed  to  be  thrown  in  at  the 
middle  of  a  piece  of  nerve,  .and  the  gal  van  .meter  placed  at  the  twj  ends,  i  )f  course  it  will 
be  iiiidersti  od  that  the  firmer  may  be  tiir  wn  in  anywhere,  and  the  latter  connected  with  any 
two  pairs  of  points  which  will  give  currents. 


opposite    direction,    the   natural    current    previously   diminished   or 
increased  being  for  a  brief  period  increased  or  diminished. 

The  strength  of  the  electrotonic  current  varies  with  the  irritability, 
or  vital  condition  of  the  nerve,  being  greater  with  the  more  irritable 
nerve  ;    and  a  dead  nerve  will  not   manifest   electrotonic   currents. 
F.   P.  8 


114  ELECTROTONIC   CURRENTS.  [BOOK   1. 

Moreover,  the  propagation  of  the  current  is  stopped  by  a  ligature,  or 
by  crushing  the  nerve. 

Lastly,  the  electrotonic  current,  like  the  natural  current,  suffers  a 
negative  variation  during  the  passage  of  a  nervous  impulsed 

The  application  of  the  constant  current  then  throws  a  nerve,  during 
its  passage,  into  a  peculiar  condition  characterized  by  the  appearance 
of  a  new  (electrotonic)  current.  This  we  may  speak  of  as  ■a.physual 
electrotonus  analogous  to  \.\\zX.  physiological &\itQ.\xoX.oxiw%  which  is  made 
known  by  variations  in  irritability.  And  the  one  set  of  phenomena 
are  in  some  respects  so  similar  to  the  other  that  it  seems  difficult  not 
to  suppose  that  they  are  fundamentally  connected.  Indeed  du  Bois- 
Reymond,  struck  by  the  differences  observable  between  the  effects  at 
the  kathode  and  those  at  the  anode,  irrespective  of  the  natural  currents, 
has  been  led  to  complete  the  analogy  of  the  physical  with  the  physio- 
logical electrotonus  by  speaking  of  a  katelectrotonic  current  and  an 
anelectrotonic  current.  The  katelectrotonic  current,  according  to  him, 
like  the  katelectrotonic  increase  of  irritability,  rises  very  rapidly  (almost 
immediately)  to  a  maximum  and  then  speedily  declines.  The  anelec- 
trotonic current,  like  the  anelectrotonic  decrease  of  irritability,  rises 
slowly  to  a  maximum  and  slowly  declines.  And  generally  the 
katelectrotonic  current  is  less  than  the  anelectrotonic.  There  are 
difficulties  in  the  way  of  estimating  the  force  exactly,  but  du  Bois- 
Reymond^  gives  as  an  instance  an  electromotive  force  of  "5  Daniell 
for  the  anelectrotonic  and  '05  Daniell  for  the  katelectrotonic  current. 

Great  difficulty  has  been  experienced  in  obtaining  evidence  of  the 
existence  in  muscles  of  electrotonic  currents  similar  to  those  observed 
in  nerves.  Hermann  ^  has  however  succeeded  in  satisfying  himself  of 
their  presence. 

The  two  schools  of  whose  views  we  have  so  often  spoken  naturally 
offer  totally  different  interpretations  of  the  nature  and  mode  of  origin 
of  the  electrotonic  current. 

Du  Bois-Reymond  and  those  with  him  explain  the  phenomena  by 
supposing  that  under  the  action  of  the  constant  current,  one  half  of 
each  electromotive  molecule  is  (partially  or  completely)  reversed  so 
that  every  half  molecule  has  its  positive  portion  directed  to  one  end  and' 
its  negative  portion  directed  to  the  other  end  of  the  nerve.  By  the 
action  of  the  constant  current,  in  fact,  each  molecule  from  being  peri- 
polar (Fig.  16)  has  become  bipolar  (Fig.  17),  and  the  currents 
discharged  by  the  molecule  into  its  surrounding  medium  have  all  the 
same  direction.  The  half  molecules  thus  (more  or  less)  reversed  by 
the  polarizing  current  are  those  the  currents  issuing  from  which  were 
previously  opposed  in  direction  to  itself  ;  hence  after  the  conversion 
from  the  peripolar  to  the  bipolar  condition,  the  currents  discharged  by 
the  several  molecules  have  the  same  direction  as  the  polarizing  current. 
In  other  words,  an  electrotonic  current  is  developed.  If  further  we 
suppose  that  each  (double)  molecule  is  capable  of  acting  on  its  fellows 
in  such  a  way  that  when,  as  in  the  normal  condition,  it  is  peripolar  it 

"  Bernstein,  A^xJiiv  Anat.  Phys.,  1866,  p.  596. 

^  Gesa?nL  Abhandl.,  II.  260. 

3  Die  Ergebnisse  Neuerer  Unters.  a.  d.  Gebict  d.  tlverisch.  Elect.,  1878. 


CHAP    U.]  THE   CONTRACTILE   TISSUES.  115 

helps  to  maintain  the  peripolar  condition  of  its  neij^hbours,  but  when 
it  becomes  bipolir  tenrls  to  render  them  bipolar  too,  the  influence 
diminishinj^  at  a  distance,  an  explanation  is  furnished  of  the  spreading 
of  the  electrotonic  current  along  both  extrapolar  regions. 

Hermann  and  his  followers,  rejecting  the  theory  of  electromotive 
molecules,  regard  the  electrotonic  current  as  due  to  the  escape  of  the 
polarizing  current  along  the  nerve  under  certain  peculiar  conditions. 
Mattcucci '  long  ago  shewed  that  phenomena  very  similar  to  those  of 
clectrotonus  might  be  produced  by  surrounding  a  metal  core  with  a 
moist  sheath  and  applying  a  constant  current  to  the  sheath.  Several 
writers  have  since  insisted  on  similar  experiments  as  demonstrating 
that  the  phenomena  of  electrotonus  arc  not  of  a  physiological  nature, 
but  they  were  always  met  with  the  valid  argument  that  the  electro- 
tonic current  varieil  with  the  irritability  of  the  nerve  and  was  stopped 
by  a  ligature  or  by  anything  which  destroyed  the  vital  continuity  of  the 
nerve.  The  currents,  simulating  electrotonic  currents,  which  Matteucci 
observed  appear  to  have  been  due  to  the  current  escaping  in  a  longi- 
tudinal direction,  in  consequence  of  the  resistance  offered  by  a  polari- 
zation taking  place  between  the  core  and  its  sheath.  When  no  such 
polarization  occurs,  when  for  instance  the  core  is  amalgamated  zinc 
and  the  sheath  a  layer  of  saturated  zinc  sulphate  solution,  the  escape 
of  the  current  in  a  longitudinal  direction  is  slight.  Under  the  influence 
of  polarization  set  up  between  the  core  and  the  sheath  the  escape  of 
the  current  in  longitudinal  loops  along  the  sheath  becomes  mote  and 
more  marked,  and  the  galvanometer  indicates  in  the  extrapolar  regions 
extending  to  some  distance  the  existence  of  currents,  having  the  same 
direction  as  the  constant  current  which  is  being  applied.  The  develop- 
ment of  these  currents  is  further  dependent  on  an  absolute  continuity 
(mere  contact  of  parts  is  insuftlcient)  of  the  core  and  the  sheath  respec- 
tively. -And  Hermann  contends  that  though  we  may  not  be  justified 
in  assuming  between  the  sarcolemma  of  a  muscle  and  the  muscle  sub- 
stance, or  between  the  primitive  sheath  of  a  nerve  fibre  and  its  con- 
tents, such  a  difference  of  conductivity  as  exists  between  the  core  and 
sheath  in  Matteucci' s  experiment,  yet  the  fact  of  tiie  electrical  resist- 
ance of  living  muscle  and  nerve  being  so  much  greater  in  a  transverse 
than  in  a  longitudinal  djre.-tion,  is  due  to  an  inner  polarization  taking 
place  between  the  muscle  or  nerve  substance  of  a  muscle  or  nerve  fibre 
and  its  respective  sheath,  and  hence  the  comparison  of  these  structures 
with  Matteucci's  experiment  is  valid.  Moreover  this  inner  polarization 
is  (in  the  muscle  wholly,  and  in  the  nerve  in  large  part)  dependent  on 
the  vital  condition  of  the  tissue.  Consequently  Matteucci's  experi- 
ment is  really  an  illustration  of  what  takes  place  in  a  living  nerve  (or 
muscle)  ;  the  electrotonic  current  is  simply  an  escape  of  the  polarizing 
current.  It  is  absent  or  insignificant  in  a  dead  nerve,  because  the 
inner  polarization,  whi  "h  determines  the  longitudinal  escape  of  the 
current,  is  a  function  of  the  living  state  ;  and  it  is  stopped  by  ligature 
or  crushing,  because  the  nervous  substance  of  the  fibres  is  thereby  con- 
verted into  a  dead  and  indifferent  substance,  and  the  functional 
continuity  of  the  nervous  core  thereby  broken. 

'   Compl.  Roid.,  i.vi.  (1863)  p.  760,  and  subsequent  papers. 

8—2 


Il6  ENERGY   OF   MLSCULAR   CONTRACTION.   [BOOK   I. 

He  further  offers  an  explanation  why  the  escape  of  the  current  under 
these  circumstances  leads  to  the  physiological  phenomena  of  katelec- 
trotonus  and  anelectrotonus,  but  on  this  point  we  must  refer  the  readers 
to  the  original  Memoirs, 

The  Etiergy  of  Muscle  and  Nerve,  and  the  nature  of  the  Chemical 

Changes. 

The  actual  amount  of  energy  developed  by  a  most  powerful  nervous 
impulse  is  exceedingly  slight,  and  hence  chemical  changes,  insignifi- 
cant in  amount,  may  be  the  cause  of  all  the  phenomena,  and  yet  re- 
main too  slight  to  be  readily  recognised.  The  muscular  contraction 
itself  is,  as  we  have  seen  (p.  60),  essentially  a  translocation  of  mole- 
cules. Whatever  be  the  exact  way  in  which  this  translocation  is 
effected,  it  is  fundamentally  the  result  of  a  chemical  change,  of  what 
we  have  already  seen  to  be  an  explosive  decomposition  of  certain  parts 
of  the  muscle-substance.  The  energy  which  is  expended  in  the 
mechanical  work  done  by  the  muscle  has  its  source  in  the  latent  energy 
of  the  muscle-substance  set  free  by  that  explosion.  Concerning  the 
nature  of  that  explosion  we  only  know  at  present  that  it  results  in  the 
production  of  carbonic  and  lactic  acids,  and  that  heat''  is  set  free  as 
well  as  the  specific  muscular  energy.  There  is  a  general  parallelism 
between  the  amount  of  decomposition  (the  quantity  of  carbonic  (and 
lactic)  acids  produced)  and  the  amount  of  energy  set  free.  The  greater 
the  development  of  carbonic  acid,  the  larger  is  the  contraction  and  the 
higher  the  temperature. 

It  has  not  been  possible  hitherto  to  draw  up  a  complete  equation 
between  the  latent  energy  of  the  material  and  the  two  forms  of  actual 
energy  set  free.  By  an  approximate  calculation  Helmholtz  has  arrived 
at  the  conclusion  that  in  the  human  body  one-fifth  of  the  energy  of  the 
material  goes  out  as  mechanical  work,  thus  contrasting  favourably  with 
the  steam-engine,  in  which  it  hardly  ever  amounts  to  more  than  one- 
tenth.     Fick3  ha,?  come  to  the  conclusion  that  the  proportion  of  energy 

'  The  views  of  du  Bois-Reymond  will  be  found  at  length  in  his  earlier  publi- 
cations, UnieTsuch.ii.thierische  Electriciidt,  1848-60,  and  in  the  later  articles 
republished  in  Gesammelte  Abhandlungen  z.  allgeineijun  Muskel-  zind  Ne'ven- 
Physik,  1875-77.  The  views  of  Hermann  will  be  found  in  his  Untersuch.  zur 
Physiol,  d.  Muskeln  ti.  Nerveti,  1867-68,  and  in  many  subsequent  papers  in 
Pfliiger's  Archiv :  viz.  Vol.  III.  (1870)  p.  15,  iv.  (1871)  p.  149,  Elfctromotor- 
ische  Erscheinungen  ;  v.  (1872)  p.  223,  vi.  (1872)  p.  312,  VVirkimg galvanisiher 
Strome ;  vi.  (1872)  p.  560,  GalvanischeVe7'.haltenu'dhrendderErregung;  vii. 
(1873)  p.  323,  Gesetz  der  Erregiwgsleitting ;  viii.  (1874)  p.  258,  Eleclrotoims , 
X.  {1875)  p.  215,  Polai'isation  und  Erregung ;  XII.  (1876)  p.  151,  Qtierstand 
wdhrendErregung ;  y.'\r .  (1877)  p.  2t,t„  Fall-Rheotom  ;  XVI.  (1878)  p.  191, 
p.  410,  Aciionsstro?n  der  Aluskeln ;  xix.  {1878)  p.  574,  Actionsstrbme  des 
Nerven.  A  rhtime  of  Hermann's  views  is  given  by  himself  in  a  small  pam- 
phlet &xv'C\\l^d.Die  Ergebnisse  neiierer  [Inters,  a.  d.  Gehitd.  thierisch.  Electricitdt, 
1878,  and  by  Dr.  Burdon-Sanderson  in  Journ.  Physiol,  i.  (1878)  p.  196. 

=  The  heat  given  out  by  muscles  will  be  further  discussed  in  Rook  II.  in 
connection  with  the  general  subject  of  Animal  Heat. 

3  Pfliiger's  Archiv,  XVI   (1877)  p.  58. 


CHAP.   11.1  I'^l'   CONTRACTlLh   TISSULS.  II7 

piven  out  as  licat  to  that  takinj^  on  the  form  of  work,  varies  according 
to  the  resistance  wliicjj  the  imiscle  has  to  overcome  ;  the  greater  the 
resistance  the  larger  is  the  portion  of  the  total  energy  set  free  which 
goes  to  the  work.  The  muscle  in  fact,  when  working  against  resistance 
docs  its  work  with  iacreased  economy.  Under  the  most  favourable 
conditions,  e  c^.  when  contra:ting  against  great  resistance,  the  energy 
of  the  work  may  (in  the  case  of  frog's  muscles  deprived  of  blood- 
supply)  amount  to  one-fourth  that  of  the  heat  given  out  ;  but  Fick 
believes  that  in  ordinary  circumstances  the  proportion  is  very  much 
less,  as  low  even  as  a  twenty-fifth.  The  muscle  in  fact  is  by  no  means 
more  economical  than  a  steam-engine  in  respect  to  the  conversion  of 
the  energy  of  chemical  action  into  mechanical  work. 

Nor  can  wc  at  present  say  thi'.t  it  has  been  experimentally  verified  in 
any  given  contra,  tion  that  the  mechanical  work  is  done  at  the  expense 
of  the  heat  which  would  be  otherwise  given  out.  Thus  if  of  two 
muscles  A  and  />,  A  be  not  loaded  and  />'  loaded  before  a  contraction 
and  unloaded  at  the  height  of  contraction,  it  is  obvious  that  A  does  no 
external  work,  for  the  muscle  returns  to  its  previous  condition,  while  B 
does  work,  the  more  so  the  heavier  the  load  and  the  more  frequently  it 
is  raised.  If  now  both  A  and  B  are  excited  by  the  same  stimulus  to 
equal  contractions,  the  temperature  of  .1  ought  to  rise  more  than  B, 
because  of  the  same  energy  set  free  in  each,  some  goes  out  as  work  in 
By  but  in  A  none  goes  out  as  work,  and  all  escapes  as  heat.  Experi- 
ment shews,  on  the  contrary,  that  B  is  the  warmer  of  the  two,  the 
reason  being  that  the  tension  caused  by  the  load  increases  all  the 
chemical  chmges  in  the  muscle  (as  shewn  by  the  increased  production 
of  carbonic  acid),  and  thus  increases  the  total  energy  set  free.  If  A 
and  />'  be  equally  loaded,  and  while  A  does  no  work,  the  load  remain- 
ing on  all  the  time,  the  load  of  B  is  removed  at  the  height  of  contrac- 
tion, it  is  then  found  that  y/  becomes  the  warmer  of  the  two.  This 
experiment  is  not  without  objection  ;  for  A  is  (immediately  after  the 
contraction)  stretched  by  its  load,  and  so  its  chemical  changes  still  in- 
crea?ed,  whereas  B  is  not ;  ani  Heidenhain  has  shewn  that  this  is 
sufificient  to  account  for  A  being  the  warmer. 

Of  the  exact  nature  of  the  chemical  changes  we  know  nothing.  As 
has  been  already  s:ated  (p.  75),  '.here  is  no  evidence  of  nitrogenous 
products  being  given  oil'  as  waste  ;  such  nitrogenous  crystalline  bodies 
as  are  present  in  mus:le,  kreatin,  &c.,  may  be  regarded  as  the  wear  and 
tear  of  the  machine,  and  not  as  products  of  the  material  consumed  in 
the  work.  Yet  it  is  hardly  consonant  .with  what  we  know  elsewhere,  to 
suppo-;e  that  the  contraction  of  a  muscular  fibre  has  for  its  essence  the 
decomposition  of  a  non-nitrogenous  substance  ;  and  we  may  suppose 
t'lat  the  explosion  does  involve  some  nitrogenous  products,  which  how- 
ever are  retained  within  the  tissue,  and  used  up  again.  Hermann,  in- 
sisting on  the  analogy  between  muscular  contraction  and  rigor  mortis, 
has  suggested  the  existence  of  a  hypothetical  inogeti  which  during  a 
contraction  splits  up  into  carbonic  ;'.cid,  lactic  acid,  and  a  nitrogenous 
body.  He  further  supposes  the  nitrogenous  body  to  be  myosin,  which 
however,  while  still  in  the  form  of  a  gelatinous  clot,  is  redissolved  and 
re  onvcrted  into  inogen.  But  the  fact  that  myosin  has  probably  ante- 
cedents like  those  of  fibrin,  an'l  is  not  formed  directly  as  a  product  of 


Il8        ENERGY   OF   MUSCULAR   CONTRACTION.        [BOOK   I. 

the  decomposition  of  a  more  complex  body,  and  especially  the  fact 
that  while  in  rigor  mortis  extensibility  is  diminished,  in  a  contraction 
it  is  increased,  seem  insuperable  objections  to  this  view.  It  may  be 
worth  while  to  point  out  that  during  even  the  most  complete  repose 
muscle  is  undergoing  chemical  changes,  which,  as  far  as  we  know,  are 
the  same  in  kind,  and  only  differ  in  degree  from  those  characteristic  of 
a  contraction.  Thus  carbonic  acid  is  constants  being  produced,  and 
probably  lactic  acid,  both  being  got  rid  of  as  they  form,  just  as  they  are 
got  rid  of  in  larger  quantities  during  the  repose  which  follows  contrac- 
tion. Supposing  the  existence  of  a  substance  which  sphts  up  into  these 
various  products,  and  which  we  may  speak  of  as  the  true  contractile 
material,  it  is  evident  that  this  material  being  thus  constantly  used  up, 
must  be  as  constantly  repaired.  Thus  a  stream  of  chemical  substances 
may  be  conceived  of  as  flowing  through  muscle,  the  raw  material 
brought  by  the  blood^  being  gradually  converted  into  true  contractile 
stuff,  the  breaking-down  again  of  which  is  gentle  and  gradual  so  long 
as  the  muscle  is  at  rest ;  when  a  contraction  takes  place,  the  decompo- 
sition is  excessive  and  violent.  When  rigor  mortis  sets  in,  the  whole 
remaining  contractile  material  is  decomposed.  It  has  been  already 
stated  that  according  to  Hermann  the  total  quantity  of  carbonic  and 
probably  of  lactic  acid  produced  after  removal  from  the  body  is  the 
same  whether  contraction  takes  place  or  no,  the  material  for  the  con- 
traction being  apparently  taken  away  from  that  destined  for  rigor 
mortis.  This  means  that  the  manufacture  of  true  contractile  material 
is  suddenly  arrested  immediately  on  the  cessation  of  the  blood-current, 
no  more  being  afterwards  formed.  Such  a  state  of  things  is  quite  con- 
trary to  our  general  physiological  experience,  and  there  are  other  facts 
which  render  it  doubtful.  Lastly,  it  may  be  mentioned  that  no  satis- 
factory explanation  can  be  given  of  the  connection  between  the  micro- 
scopic structure  of  a  striated  muscular  fibre  and  its  contraction. 
Striation  is  characteristic  of  muscles  whose  contraction  is  rapid,  but 
the  exact  purpose  of  the  striae  remains  as  yet  unknown. 

It  was  Haller^  who  laid  the  foundations  of  our  knowledge  of  the 
Physiology  of  Muscle  and  Nerve  by  establishing  the  doctrine  of 
muscular  and  nervous  irritability.  The  most  important  results  since 
that  time  have  been  those  gained  by  the  investigations  of  Weber^  on 
the  physical  changes  which  attend  a  mus:ular  contraction,  of  du  Bois- 
Reymond'^  on  the  electrical  phenomena  of  muscle  and  nerve,  of  Helm- 
holtzs  on  the  velocity  of  nervous,  impulses,  and  on  the  relative  duration 
of  the  several  phases  of  a  contraction,  of  Pfliiger"^  on  electrotonus,  of 
Kiihne'  on  the  chemistry  of  muscle,  and  of  Hermann^  on  the  respira- 
tion of  muscle  and  on  the  electrical  phenomena  of  muscle  and  nerve. 

'  Together  with  certain  nitrogenous  elements  still  remaining  in  the  muscle, 
iccording  to  the  view  explained  above. 
^  De  Part.  Co7-p.  Hum.  seniieniibus  et  irritabilibus,  1753. 
3  Muskelbewegung,  Wagner's  Hanawbrterbuck.  ^  Op.  cit. 

■  Miiller's  ^rf/z/w,  1850.     Berichte  Berlin  Acad.,  1854,  1864. 
^  Untersiich.  ii.  d.  Physiologic  des  Electrotonus,  1859. 
'  Protoplasma,  1864.  s  Qp  ^^ 


ClIAl'.    II.  I  TIIK    CON'TRACTILi:    TISSUKS.  I  IQ 

The  researches  of  otlier  and  more  recent  authors  arc  quoted  in  the 
previous  text. 

Sec.  7.     Unstkiated  Muscular  Tissue. 

Our  knowledge  of  the  ijlienonicna  of  these  structures  is  very 
imperfect,  since  (in  vertebrates)  they  do  not  exist  in  isolated 
masses,  like  the  striated  muscles,  but  occur  as  constituents  of 
complex  organs,  such  as  the  intestine,  ureter,  uterus,  &c.  They 
undergo  rigor  mortis  :  and  what  little  information  we  do  possess 
concerning  their  chemical  and  physical  features  leads  us  to  believe 
that  the  processes  whicli  take  place  in  them  are  fundamentally 
identical  with  those  occurring  in  striated  muscle,  the  two  differing 
in  degree  rather  than  in  kind.  When  stimulated,  they  contract. 
If  a  stimulus,  mechanical  or  electrical,  be  applied  to  the  intestine 
or  ureter  of  a  mammal,  a  circular  contraction  is  seen  to  take  place 
at  the  spot  stimulated.  The  contraction,  which  is  preceded  by  a 
very  long  latent  period,  lasts  a  very  considerable  time,  in  fact 
several  seconds,  after  which  relaxation  slowly  takes  place.  That 
is  to  say,  over  the  circularly  dispersed  fibres  of  the  intestine  (or 
ureter)  at  the  spot  in  question  there  has  passed  a  contraction-wave 
remarkable  for  its  long  latent  period  and  for  the  slowness  of  its 
development.  From  the  spot  so  directly  stimulated,  the  con- 
traction may  pass  as  a  wave  (with  a  length  of  i  cm.  and  a 
velocity  of  from  20  to  30  millimetres  a  second  in  the  ureter'), 
along  the  circular  coat  both  upwards  and  downwards.  The  longi- 
tudinal fibres  at  the  spot  stimulated  are  also  thrown  into  con- 
tractions of  altogether  similar  character,  and  a  wave  of  contraction 
may  also  travel  longitudinally  along  the  longitudinal  coat  both 
upwards  and  downwards.  It  is  evident  however  that  the  wave  of 
contraction  of  which  we  are  now  speaking  is  in  one  respect 
different  from  the  wave  of  contraction  treated  of  in  dealing  with 
striated  muscle.  In  the  latter  case  the  contraction-wave  was  one 
propagated  along  the  individual  fibre  ;  in  the  case  of  the  intestine 
or  ureter,  the  wave  is  one  which  is  projiagated  from  fibre  to  fibre, 
both  in  the  direction  of  the  fibres,  as  when  the  whole  circumference 
of  the  intestine  is  engaged  in  the  contraction,  or  when  the  wave 
travels  longitudinally  along  the  longitudinal  coat,  and  also  in  a 
direction  at  riglit  angles  to  the  axes  of  the  fibres,  as  when  the 
contraction-wave  travels  lengthways  along  the  circular  coat  of  the 
intestme,  or  when  it  passes  across  a  breadth  of  the  longitudinal 
coat.  In  addition  to  this  ditference,  however,  it  is  obvious  that 
a   contraction-wave  passing  along  even  a  single  unstriated  fibre 

'  Engelmann,  Pfliigcr's  ^^/r/n'r',  II.  (1S69),  243. 


120  CARDIAC   MUSCLES.  [BOOK   I. 

also  differs  from  that  passing  along  a  striated  fibre,  in  the  very 
great  length  both  of  its  latent  period  and  of  the  duration  of  its 
contraction. 

If  the  stimulus  be  severe  when  mecha.acal,  or  if  the  interrupted 
current  be  used  as  a  stimulus,  the  duration  of  contraction  may  be  still 
further  prolonged  ;  but  there  is  no  evidence  that  a  series  of  con- 
tractions are  fused  into  a  tetanus,  as  is  the  case  in  the  striated 
muscles. 

Like  the  skeletal  muscles,  whose  nervous  elements  have  been 
rendered  functionally  incapable  (p.  87),  unstriated  muscles  are  much 
more  sensitive  to  the  making  and  breaking  of  a  constant  current  than 
to  induction-shocks. 

The  unstriated  muscles  seem  to  be  remarkably  susceptible  to  the 
influences  of  temperature.  Thus  according  to  Horvath'  the  unstriated 
muscles  of  the  trachea  will  not  contract  at  a  temperature  below  12°  C, 
and  are  most  active  at  a  temperature  above  21°  C.  So  also  the 
movements  of  the  intestine  cease  at  a  temperature  below  19°  C. 

Waves  of  contraction  thus  passing  along  the  circular  and  longi- 
tudinal coats  of  the  intestine  give  rise  to  what  is  called  peristaltic 
action. 

In  striking  contradistinction  to  what  takes  place  in  the  striated 
muscles,  automatic  movements  are  exceedingly  common  in  struc- 
tures built  up  of  non-striated  muscles  ;  these  moreover  exhibit  a 
great  tendency  to  rhythmic  action.  Thus  the  peristaltic  action  of 
the  intestine  and  ureters,  and  the  corresponding  movements  of 
the  uterus,  are  at  once  rhythmic,  and  largely  automatic.  How 
far  the  automatism  and  the  rhythm  are  due  to  nervous  elements  is 
uncertain. 

According  to  Engelmann  '^  the  middle  and  part  of  the  upper  third 
of  the  ureter  in  the  rabbit  ^  contains  no  discoverable  nervous  ganglia, 
yet  this  portion  exhibits  automatic  rhythmic  contractions.  We  may 
suppose  that,  in  the  absence  of  an  adequate  nervous  arrangement,  the 
propagation  of  the  contraction  wave  is,  in  this  part  of  the  ureter, 
carried  on  by  the  simple  contact  of  the  adjacent  surface  of  the  fibres 
(which,  as  is  known,  possess  no  sarcolemma).  The  fibres,  by  their 
complete  contact,  may  be  spoken  of  as  heing  physiologically  contitmous 
with  each  other. 

Sec.  8.     Cardiac  Muscles. 

The  most  important  features  of  this  form  of  contractile  tissue 
will  be  studied,  when  we  come  to  deal  with  the  heart.  It  will  be 
seen  that  they  are  intermediate  between  ordinary  skeletal  and 
non  striated  muscles. 

*  Pfliiger's  Archiv,  XITI.  (1876),  508.  ^  Op.  cil. 

3  This  does  not  seen  to  hold  good  for  other  animals.  Cf.  Dog^iel,  Arch.f, 
micros.  Anat.,  xiv.  (1878),  p.  64. 


CHAT.    II.J  THE   CONTRACTILE   TISSUES.  121 


Sec.  9.     Cilia. 

Ciliary  movement  consists  in  the  rapid  flexion  (into  a  sickle  or 
hook-form)  of  the  cilium  and  its  less  rapid  return  to  its  previous 
straight  form.  The  diminished  velocity  of  the  return  leads  to  the 
force  of  the  ciliary  action  being  exerted  in  the  same  direction  as 
the  flexion.  The  cause  of  the  flexion  seems  to  be  the  contraction 
of  the  cilium,  and  that  of  the  return,  an  elastic  reaction. 

Various  attempts  to  explain  the  movement  by  the  presence  of 
special  mechanisms  at  the  base  of  the  cilia  have  hitherto  failed. 
Some  authors  have  attributed  the  movement  to  a  protoplasmic  con- 
traction of  the  cell  itself,  the  cilium  acting  merely  as  a  minute  elastic 
rod  ;  and  some  such  view  as  this  is  supported  by  the  fact  that  no 
movement  has  ever  been  observed  in  an  isolated  cilium.  It  is  difficult 
however  to  understand  how  the  peculiar  sici^le-like  flexion  of  the 
cilium  can  be  brought  about  unless  the  contractile  material  is  continued 
up  into  the  cilium  itself." 

Ciliary  movement  appears  therefore  to  differ  from  ordinary 
muscular  contraction  chiefly  in  the  size  of  the  apparatus  con- 
cerned. The  movement  is  exceedingly  rapid  :  thus  Engelmann' 
has  estimated  that  in  the  frog  the  flexions  are  repeated  at  least 
twelve  times  in  a  second.  The  movement  in  fact  is  too  rapid  to 
be  visible  ;  it  can  only  be  seen  at  a  time  when  exhaustion  and 
coming  death  have  begun  to  retard  the  action ;  thus  Engelmann 
found  that  he  vvas  first  able  to  count  them  when  their  rapidity 
declined  to  eight  in  a  second.  The  tail  of  a  spermatozoon  is 
practically  a  single  cilium. 

In  the  vertebrate  animal,  cilia  are  as  far  as  we  know  wholly 
independent  of  the  nervous  system,  and  their  movement  is 
probably  ceaseless.  In  such  animals  however  as  Infusoria,  Hy- 
drozoa,  tScc.  a  ciliary  tract  may  often  be  seen  to  stop  and  go  on 
again,  to  move  fast  or  slow,  according  to  the  needs  of  the  economy, 
and,  as  it  almost  seems,  according  to  the  will  of  the  animal. 
Observations  with  galvanic  currents,  constant  and  interruptetl,  have 
not  led  to  any  satisfactory  results,  and,  as  far  as  we  know  at 
})resent,  ciliary  action  is  most  aff'ected  by  changes  of  temperature 
and  chemical  media.  Moderate  heat  quickens  the  movements,  but 
a  rise  of  temperature  beyond  a  certain  limit  (about  40°  C.  in  the 
case  of  the  pharyngeal  membrane  of  the  frog 3)  becomes  injurious  ; 
cold  retards.  Very  dilute  alkalis  are  favourable,  acids  are  in- 
jurious.     An  excess  of  carbonic  acid  or  an  absence  of  oxygen 

'  Cf.  Nus<baum,  Archh> f.  micro    Anat.,  XIV.  (1877)  p.  390. 

'  Uiber  die  F>immerbrMegnn^,  p.  22  (<.S6S). 

3  Engelmann,  Onderzotk.  Utrecht.  PhysioL  Lab.,  3''«  Keeks,  V.  (iS78)p.  44. 


122  MIGRATING   CELLS.  [BOOK  I. 

diminishes  or  arrests  the  movements,  either  temporarily  or  per- 
manently, according  to  the  length  of  the  exposure.  Chloroform 
or  ether  in  slight  doses  diminishes  or  suspends  the  action  tem- 
porarily, in  excess  kills  and  disorganises  the  cells. 

Sec.  io.     Migrating  Cells. 

We  have  already  (p.  42)  urged  the  view  that  an  amoeboid 
movement  of  a  white  corpuscle  is  essentially  a  form  of  contraction. 

All  the  circumstances  which  affect  muscular  contraction,  heat, 
absence  or  presence  of  oxygen  and  carbonic  acid,  &c.,  also  affect 
protoplasmic  movements.  The  white  corpuscles,  like  muscular 
fibres,  suffer  rigor  mortis,  in  which  state  they  become  spherical. 

The  complete  analogy  between  muscular  fibre  and  white  corpuscle 
is  rendered  difficult  by  the  fact  that  complete  rest  of  the  corpuscle  and 
universal  contraction  of  the  corpuscle  both  result  in  the  maintenance 
of  the  same  spherical  form.  The  movement  of  a  white  corpuscle  is 
dependent  on  a  contraction  of  soiiu  part.  If  the  whole  corpuscle 
suffers  the  change  which  occurring  in  any  part  would  lead  to  a  move- 
ment in  that  part,  no  outward  visible  change  takes  place,  just  as  a  set 
of  carefully  balanced  muscles  would  remain  as  motionless  during 
contraction  as  during  rest. 


CHAPTER   III. 


THE   FUNDAMENTAL   PROPERTIES   OF 
NERVOUS   TISSUES. 

In  its  simplest,  and  probably  earliest  form,  a  nerve  is  nothing 
more  than  a  thin  strand  of  irritable  protoplasm,  forming  the  means 
of  vital  communication  between  a  sensitive  ectodermic  cell 
exposed  to  extrinsic  accidents,  and  a  muscular,  highly  contractile 


Fig.  22.    Diagram  to  illustrate  the  Simplest  Fokms  of  a  Nervous  Svste.m. 

A.  An  ectoderm  cell  e.  c.  with  its  muscular  process  »«/. ,  as  in  Hydra. 

S    The  ectoderm  cell  e.  c.  is  connected  with  the  muscle  cell  m.  c.  by  means  of  the  primary 

motor  nerve  nt.n. 
C.  The  differentiated  sensitive  cell  s.c.  is  connected  by  means  of  the  sensory  nerve  i.n.  with 

the  central  cell  c.c,  which  is  again  connected  by  means  of  the  motor  nerve  m.n.  with  llie 

muscle  cell  tn-c. 


124  SENSORY   AND   MOTOR   NERVES,  [BOOK    I 

cell  (or  a  muscular  process  of  the  same  cell)  buried  at  some 
distance  from  the  surface  of  the  body,  and  thus  less  susceptible 
to  external  influences.  (Fig.  22,  A,  B.)  If  in  Hydra,  we  imagine 
the  junction  of  the  ectodermic  muscular  process  with  the  body  of 
its  cell  to  be  drawn  out  into  a  thin  thread  (as  is  said  to  be  the 
case  in  some  other  Hydrozoa),  we  should  have  just  such  a 
primary  nerve.  Since  there  would  be  no  need  for  such  a  means 
of  communication  to  be  contractile  and  capable  of  itself  changing 
in  form,  but  on  the  other  hand  an  advantage  in  its  remaining 
immobile,  and  in  its  dimensions  being  reduced  as  much  as 
possible  consistent  with  the  maintenance  of  irritability,  the 
primary  nerve  would  in  the  process  of  development  lose  the 
property  of  contractility  in  proportion  as  it  became  more  irritable, 
z.e.  more  apt  in  the  propagation  of  the  waves  of  disturbance 
arising  in  the  ectodermic  cell. 

We  have  already  seen  that  automatism,  t'.e.  the  power  of 
initiating  disturbances  or  vital  impulses,  independent  of  any 
immediate  disturbing  event  or  stimulus  from  without,  is  one  of  the 
fundamental  properties  of  protoplasm.  In  simpler  but  less  exact 
language,  such  a  mass  of  protoplasm  as  an  amoeba,  though 
susceptible  in  the  highest  degree  to  influences  from  without,  'has 
a  will  of  its  own ; '  it  executes  movements  which  cannot  be 
explained  by  reference  to  any  changes  in  surrounding  circum- 
stances at  the  time  being,  A  hydra  has  also  a  will  of  its  own ; 
and  seeing  that  all  the  constituent  cells  (beyond  the  distinction 
into  ectoderm  and  endoderm)  are  alike,  we  have  no  reason  for 
thinking  that  the  will  resides  in  one  cell  more  than  in  another,  but 
are  led  to  infer  that  the  protoplasm  of  each  of  the  cells  (of  the 
ectoderm  at  least)  is  automatic,  the  will  of  the  individual  being 
the  co-ordinated  wills  of  the  component  cells.  In  both  Hydra 
and  Amoeba  the  processes  concerned  in  automatic  or  spontaneous 
impulses,  though  in  origin  independent  of,  are  subject  to  and 
largely  modified  by,  influences  proceeding  from  without.  Indeed 
the  great  value  of  automatic  processes  in  a  living  body  depends 
on  the  automatism  being  affected  by  external  influences,  and  on 
the  simple  effects  of  stimulation  being  profoundly  modified  by 
automatic  action. 

The  next  step  of  development  beyond  Hydra,  is  evidently  to 
differentiate  the  single  (ectodermic)  cell  into  two  cells,  of  which 
one,  by  division  of  labour,  confines  itself  chiefly  to  the  simple 
development  of  impulses  as  the  result  of  stimulation,  leaving  to 
the  other  the  task  of  automatic  action,  and  the  more  complex 
transformation  of  the  impulses  generated  in  itself.  The  latter, 
which  we  may  call  the  eminently  automatic  cell  (though  much  of 


CHAP.   III.]      PROPERTIES   OF   NERVOUS   TISSUES.  1 25 

the  work  which  it  has  to  do  is  of  the  kind  we  shall  presently 
speak  of  as  reflex  action),  will  naturally  be  withdrawn  from  the 
surface  of  the  body,  while  the  other,  which  we  may  call  the 
eminently  sensitive  coll,  will  still  retain  its  superficial  position,  so 
that  it  may  most  readily  be  afiected  by  all  changes  in  the  world 
without,  Fig.  22  C.  And  just  as  a  primary  fiiotor  nerve  arises  as 
a  retained  thread  of  communication  between  a  sensitive  cell  and 
its  muscular  process,  so  a  primary  sensory  nerve  may  be  conceived 
of  as  arising  as  a  thread  of  communication  between  an  eminently 
sensitive  cell  and  its  twin  the  eminently  automatic  or  central  cell. 
By  this  arrangement  the  sensitive  cell,  relieved  of  the  heavy 
burden  of  spontaneous  action,  is  enabled  to  devote  itself  with 
greater  vigour  to  the  reception  of  external  influences ;  while  the 
automatic  cell,  no  longer  hampered  by  the  physical  necessities  of 
being  which  are  imposed  on  the  superficial  cell,  exposed  as  this  is 
to  every  wind  and  wave,  but  secure  in  its  internal  retreat,  is  able 
with  similar  increased  energy,  to  devote  itself  either  to  the 
production  of  spontaneous  impulses,  or  to  profoundly  modifying 
the  impulses  which  it  receives  from  the  sensitive  cell.  Naturally 
the  muscular  process  or  muscular  fibre  would  on  the  splitting  of 
the  original  single  cell  remain  in  connection  with  the  more 
eminently  automatic.  We  thus  arrive  at  that  triple  fundamental 
arrangement  of  a  nervous  system,  in  its  simplest  form,  viz.  a 
sensitive  cell  on  the  surface  of  the  body  connected  by  means  of  a 
sensory  nerve  with  the  internal  automatic  central  nervous  cell, 
which  in  turn  is  connected  by  means  of  a  motor  nerve  with  the 
muscular  fibre-cell. 

We  have  already  seen  that  the  physiology  of  the  motor  nerve 
cannot  without  inconvenience  be  separated  from  that  of  the 
muscular  fibre.  In  the  same  way  the  physiology  of  the  sensory 
nerve  cannot  well  be  separated  from  those  modifications  of 
superficial  sensitive  cells  which  constitute  the  organs  of  sense. 
We  may  add  that  the  special  physiology  of  the  central  nervous 
cells  can  only  profitably  be  studied  in  connection  with  the  sensory 
organs.  In  the  present  chapter,  therefore,  we  purpose  to  confine 
ourselves  to  the  consideration  of  the  simplest  and  most  general 
properties  of  the  central  nervous  cells. 

These  are  arranged  in  the  vertebrate  body  in  two  great  systems  : 
the  cerebro-spinal  axis,  and  the  various  ganglia  scattered  over  the 
body ;  w-e  shall  deal  with  such  properties  only  as  are  more  or 
less  common  to  the  two  systems.  W'q  may  premise  that  as  far 
as  our  knowledge  at  present  goes,  the  processes  which  are  con- 
cerned in  the  propagation  of  nervous  impulses  along  a  sensory 
nerve  trunk  are  identical  with  those  which  take  place  in  a  motor 


126  SENSORY   AND   MOTOR   NERVES.  [BOOK   I. 

nerve-trunk.  The  phenomena  of  the  natural  nerve-current,  of 
the  negative  variation  during  the  passage  of  an  impulse  and  of 
electrotonus  (and  these  facts  mark  out,  as  we  have  seen,  the 
limits  of  our  information  on  this  matter),  are  exactly  the  same, 
whether  the  piece  of  nerve-trunk  experimented  on  be  a  mixed 
nerve-trunk,  or  an  almost  purely  motor,  or  an  almost  purely 
sensory  nerve-trunk,  or  an  anterior  or  posterior  nerve-root,  or  the 
special  sensory  nerve  of  a  particular  sense,  such  as  the  optic 
nerve.  In  both  sensory  and  motor  nerves  the  changes  .accom- 
panying a  nervous  impulse  are  transmitted  equally  well  in  both 
directions. 

We  seem  justified  in  concluding  that  the  events  which  occur  in 
a  sensory  nerve  when  it  is  an  instrument  of  sensation,  differ  from 
those  which  take  place  in  a  motor  nerve  when  that  is  an  instru- 
ment of  movement,  only  so  far  as  the  sensory  impulses  are 
generated  by  particular  processes  which  bear  the  stamp  of  the 
sensory  cell  in  which  they  originated,  while  the  motor  impulses 
are  generated  by  particular  processes  which  bear  the  stamp  of  the 
central  nervous  cells  in  which  they  in  turn  originated.  All 
sensory  impulses  appear  to  be  tetanic  in  nature,  i.e.  to  be 
composed  of  a  series  of  constituent  simple  impulses ;  and  it  is 
probable  that  while  the  motor  impulses  which  proceed  from  the 
central  nervous  system  to  the  muscles  are  composed  of  simple 
impulses  repeated  with  the  same  rapidity,  and  thus  giving  rise  to 
the  same  muscular  note  (p.  57),  the  sensory  impulses  which 
proceed  from  the  peripheral  sense  organs  to  the  central  nervous 
system  vary  exceedingly  as  to  the  way  in  which  their  constituent 
simple  impulses  are  combined.  It  is  indeed  possible  that  the 
complex  sensory  impulses  which  give  rise,  for  instance,  to  sight 
and  touch  respectively,  may  differ  only  in  the  wave-length,  so  to 
speak,  of  their  constituent  simple  impulses,  much  in  the  same 
way  as  red  light  differs  from  blue  light. 

In  the  scheme  sketched  out  above,  the  same  central  nervous 
cell  is  supposed  to  be  engaged  at  once,  both  in  originating  auto- 
matic actions  and  in  modifying  sensory  impulses  {i.e.  impulses 
proceding  from  the  superficial  sensitive  cells)  previous  to  these  being 
passed  on  to  the  muscular  fibre.  It  is  evident  that,  where  two  or 
more  central  nervous  cells  occur  together,  a  further  differentiation 
would  be  of  advantage  :  a  differentiation  into  cells  which,  though 
still  susceptible  of  being  influenced  from  without,  should  be  more 
especially  restricted  to  automatic  action,  and  into  cells  which 
should  forego  their  automatism  for  the  sake  of  being  more  efficient 
in  modifying  sensory  impulses,  with  a  view  of  transmitting  them 
into    motor    impulses,    and    so    of   giving   rise   to   appropriate 


CHAP.    III.]      PROPERTIKS   OF    NERVOUS   TISSUES.  \2^ 

movements.  We  thus  gain  the  funtlamental  and  primary  differen- 
tiation of  the  work  of  a  central  nervous  system  into  automatic 
and  into  rellex  operations.  These  are  very  clearly  manifested  by 
the  brain  and  spinal  cord,  and  probably  also,  though  this  is  less 
certain,  by  the  sporadic  ganglia. 

Automatic  actions.  In  the  vertebrate  animal  the  highest 
form  of  automatism,  individual  volition,  with  which  conscious 
intelligence  is  associated,  is  a  function  of  certain  parts  of  the 
brain.  There  are  evidences  of  the  existence  in  the  brain  of  other 
forms  of  automatism.  All  these  will  be  considered  in  detail 
hereafter. 

In  the  spinal  cord  separated  from  the  brain  by  section  of  the 
medulla  oblongata,  it  becomes  difficult  to  draw  a  line  between 
purely  automatic  and  reflex  actions.  Thus,  when  we  come  to  deal 
with  respiration,  we  shall  see  that  while  there  can  be  no  doubt  that 
the  muscular  respiratory  apparatus  is  kept  at  work  by  impulses 
proceeding,  in  a  rhythmic  manner,  from  a  group  of  nerve  cells,  or 
respiratory  nervous  centre,  in  the  medulla  oblongata,  it  is  an  open 
question  whether  those  impulses,  whose  generation  is  certainly 
modified  by  centripetal  impulses  passing  to  the  centre  along 
various  nerves,  are  absolutely  automatic :  i.e.  whether  they  can 
continue  to  make  their  appearance  when  no  influences  whatever 
from  without  are  brought  to  bear  upon  the  centre.  Similar  doubts 
hover  round  other  automatic  functions  of  the  spinal  cord.  We 
shall  see  hereafter  reasons  for  speaking  of  the  existence  in  the 
medulla  oblongata  of  a  vaso-moior  centre,  that  is  of  a  group  of 
nerve-cells,  whence  impulses  habitually  proceed  along  the  so-called 
vaso-motor  nerves  to  the  muscular  coats  of  the  small  arteries,  and 
keep  these  vessels  in  a  state  of  semi-contraction  or  tone.  Here 
too  it  is  doubtful  whether  these  motor  or  efferent  impulses  can  be 
generated  in  the  a"bsence  of  all  sensory  or  afferent  impulses.  The 
posterior  lymphatic  hearts  of  the  frog  are  connected  by  the  small 
tenth  pair  of  spinal  nerves  with  the  grey  matter  of  the  termination 
of  the  si)inal  cord,  in  such  a  manner  that  destruction  of  that  part 
of  the  spinal  cord  or  section  of  the  tenth  nerves  apparently  puts 
an  L-nd  to  the  rhythmic  pulsations  of  the  lymphatic  hearts.  Here 
it  would  seem  as  if  rhythmic  impulses  were  automatically  generated 
in  the  lower  end  of  the  cord,  and  proceeded  along  the  efterent 
nerves  to  the  hearts,  thus  determining  their  rhythmic  pulsations. 
But  if  it  be  true,  as  asserted,  that  the  rhythmic  pulsations, 
though  arrested  for  a  time  by  severance  of  the  nerves,  or  destruc- 
tion of  the  lower  end  of  the  cord,  are  after  a  while  resumed,  then 
these,    too,    can   be   no   longer   counted    among   the    automatic 


128  AUTOMATIC   ACTIONS.  [BOOK   I. 

phenomena  of  the  cord.  And  so  in  other  instances  which  we 
shall  meet  with  in  the  course  of  this  book.  The  existence  of  auto- 
matism, then,  even  of  this  comparatively  simple  character,  is  at  least 
doubtful.  That  all  higher  automatism  comparable  at  least  to  that 
of  the  cerebral  hemispheres  is  absent,  may  be  regarded  as  certain. 

In  the  sporadic  ganglia  the  evidence  of  automatic  action  seems 
more  clear,  and  yet  is  by  no  means  absolutely  decisive.  The  beat 
of  the  heart  is  a  typical  automatic  action  :  and,  since  the  heart 
will  continue  to  beat  for  some  time  when  isolated  from  the  rest  of 
the  body  (that  of  a  cold-blooded  animal  continuing  to  beat  for 
hours,  or  even  days),  its  automatism  must  lie  in  its  own  structures. 
When,  however,  we  come  to  discuss  the  beat  of  the  heart  in 
detail,  we  shall  find  that  it  is  still  an  open  question  whether  the 
automatism  is  confined  to  the  ganglia  (either  of  the  sinus  venosus, 
auricles,  or  auriculo-ventricular  boundary),  or  shared  in  by  the 
muscular  tissue  :  whether,  in  fact,  the  automatism  is  a  muscular 
automatism  like  that  of  a  ciliated  cell,  or  the  automatism  of  a 
differentiated  nerve-cell.  And  yet  the  heart  is  the  case  where  the 
automatism  of  the  gangha  seems  clearest. 

The  peristaltic  contractions  of  the  alimentary  canal  are  auto- 
matic movements;  we  cannot  speak  of  them  as  being  simply 
excited  by  the  presence  of  food  in  the  canal,  any  more  than  we 
can  say  that  the  beat  of  the  heart  is  caused  by  the  presence  of 
blood  in  its  cavities.  When  absent  they  may  be  set  agoing,  and 
when  present  may  be  stopped  without  any  change  in  the  contents 
of  the  canal.  They  may,  of  course,  be  influenced  by  the  contents, 
just  as  the  beat  of  the  heart  is  influenced  by  the  quantity  of  blood 
in  its  cavities.  Throughout  the  intestines  are  found  the  nerve 
plexus  of  Auerbach  and  that  of  Meissner ;  to  each  or  both  of 
these  the  automatism  of  the  peristaltic  movements  has  been 
referred.  Yet  in  the  ureter,  whose  peristaltic  waves  of  contraction 
closely  resemble  that  of  the  intestine,  automatism  is  evident  in 
the  middle  third  of  its  length  even  when  completely  isolated  ;  in 
which  region  (in  the  rabbit  at  least),  according  to  Engelmann', 
ganglia,  and  indeed  nerve-cells,  are  entirely  absent. 

Thus,  while  in  the  spinal  cord  there  is  doubt  whether  purely 
automatic,  as  stringently  distinguished  from  reflex,  actions  take 
place,  in  the  case  of  the  sporadic  ganglia  the  uncertainty  is  whether 
the  clearly  automatic  movements  of  the  organs  with  which  the 
ganglia  are  associated  are  due  to  the  nerve-cells  of  the  ganglia,  or 
to  the  muscular  tissue  itself. 

Reflex  Actions. — The  spinal  cord  offers  the  best  and  most 

'  Pfliiger's  Archiv  (1869)  II.  243. 


CHAP.    Ill]      PROPERTIES   OF   NERVOUS   TISSUES.  1 29 

numerous  examples  of  reflex  action.  In  fact,  reflex  action  may 
be  said  to  be,  par  excellence,  the  function  of  the  spinal  cord  ;  and 
the  grey  matter  of  the  spinal  cord  may  be  broadly  considered  as 
a  multitude  of  reflex  centres.  We  have  here  to  consider  the  cord 
merely  in  its  general  aspects  ;  and  must  postpone  the  special  con- 
sideration of  the  particular  forms  of  reflex  action  which  it  exhibits, 
as  tliey  come  before  us  in  various  connections,  or  until  we  have  to 
deal  with  it  as  part  of  the  great  central  nervous  machinery. 

In  its  simplest  form  a  reflex  action  is  as  follows.  All  the  ma- 
chinery it  demands  is  [a)  a  sentient  surface  (external  or  internal), 
connected  by  {h)  a  sensory,  or — to  adopt  the  more  geneml  and 
better  term — afferent  nerve,  with  (c)  a  central  nerve-cell  or  group 
of  connected  nerve-cells,  which  is  in  relation  by  means  of  {d)  a 
motor,  or  efferent,  nerve  or  nerves,  with  {e)  a  muscle,  or  muscles, 
or  some  other  irritable  tissue-elements,  capable  of  responding  by 
some  change  in  tlieir  condition,  to  the  advent  of  efferent  impulses. 
The  afferent  impulses  started  in  a,  passing  along  b,  reach  the 
centre  c,  are  there  transmuted  into  efferent  impulses,  which,  passing 
along  d,  finally  reach  e,  and  there  produce  a  cognisable  effect. 
The  essence  of  a  reflex  action  consists  in  the  transmutation,  by 
means  of  the  irritable  protoplasm  of  a  nerve-cell,  of  afferent  into 
efferent  impulses.  As  an  approach  to  a  knowledge  of  the  nature 
of  that  transmutation,  we  may  lay  down  the  following  propositions. 

T/ie  iuiinbe)\  intensity,  character  and  distribution  of  the  efferent 
impulses  is  determined  chiefiy  by  the  events  which  take  place  in  the 
protoplasm  of  the  reflex  centre.  It  is  not  that  the  afferent  impulse 
is  simply  reflected  in  the  nerve-cell,  and  so  becomes  with  but  little 
change  an  efferent  impulse.  On  the  contrary,  an  afferent  impulse 
passing  along  a  single  sensory  fibre  may  give  rise  to  efferent  im- 
pulses passing  along  many  motor  nerves,  and  call  forth  the  most 
complex  movements.  An  instance  of  this  disproportion  of  the 
afferent  and  efferent  impulses  is  seen  in  the  case  where  the  con- 
tact with  the  glottis  of  a  foreign  body  so  insignificant  as  a  hair 
causes  a  violent  fit  of  coughing.  Under  such  circumstances  a 
slight  contact  with  the  mucous  membrane,  such  as  could  not 
possibly  give  rise  to  anything  more  than  few  and  feeble  impulses, 
may  cause  the  discharge  of  so  many  efferent  impulses  along  so 
many  motor  nerves,  that  not  only  all  the  respiratory  muscles,  but 
almost  all  the  muscles  of  the  body,  are  brought  into  action. 
Similar  though  less  striking  instances  of  how  incommensurate  are 
afferent  and  efterent  impulses  may  be  seen  in  reflex  actions.  In 
fact,  the  afferent  impulse  when  it  reaches  the  protoplasm  of  the 
nerve  produces  there  a  series  of  changes,  of  explosive  disturb- 
ances, which,  except  that  the  nerve-cell  does  not  in  aiiv  way 
F.  P.  9 


130 


REFLEX  ACTIONS.  [BOOK   I. 


change  its  form,  may  be  likened  to  the  explosive  changes  in  a 
muscle  on  the  arrival  of  an  impulse  along  its  motor  nerve*. 
The  changes  in  a  nerve-cell  during  reflex  action,  we  might  say 
during  its  activity,  far  more  closely  resemble  the  changes  during 
a  muscular  contraction  than  those  which  accompany  the  passage 
along  a  nerve  of  either  an  afferent  or  efferent  impulse.  The 
simple  passage  along  a  nerve  is  accompanied  by  little  expenditure 
of  energy ;  it  neither  gains  nor  loses  force  to  any  great  extent  as 
it  progresses.  The  transmutation  in  a  nerve-cell  is  most  probably 
(though  the  direct  proofs  are  perhaps  wanting)  accompanied 
by  a  large  expenditure  of  energy,  and  a  simple  nervous  impulse 
in  suffering  this  transmutation  in  a  central  nervous  organ  may 
accumulate  in  intensity  to  a  very  remarkable  extent,  as  in  the 
case  of  strychnia  poisoning. 

The  nature  of  the  efferent  itnpulses  is,  however,  determined  also  by 
the  nature  of  the  afferent  impulses.  The  nerve-centre  remaining  in 
the  same  condition,  the  stronger  or  more  numerous  impulses  will 
give  rise  to  the  more  forcible  or  more  comprehensive  movements. 
Thus  if  the  flank  of  a  brainless  frog  be  very  lightly  touched,  the 
only  reflex  movement  which  is  visible  is  a  slight  twitching  of  the 
muscles  lying  immediately  underneath  the  spot  of  skin  stimu- 
lated. If  the  stimulus  be  increased,  the  movements  will  spread 
to  the  hind-leg  of  the  same  side,  which  frequently  will  execute  a 
movement  calculated  to  push  or  wipe  away  the  stimulus.  By 
forcibly  pinching  the  same  spot  of  skin,  or  otherwise  increasing  the 
stimulus,  the  resulting  movements  may  be  led  to  embrace  the  fore- 
leg of  the  same  side,  then  the  opposite  side,  and  finally,  almost 
all  the  muscles  of  the  body.  In  other  words,  the  disturbance  set 
going  in  the  central  nerve-cells,  confined  when  the  stimulus  is 
slight  to  a  few  nerve-cells  and  to  a  few  nerve-fibres,  overflows, 
so  to  speak,  when  the  stimulus  is  increased,  on  to  a  number  of 
adjoining  and  (we  must  conclude)  connected  cells,  and  thus  throws 
impulses  into  a  large  and  larger  number  of  efferent  nerves. 

Certain  relations  may  be  observed  between  the  sentient  spot  stimu- 
lated and  the  resulting  movement.  In  the  simplest  cases  of  reflex 
action  this  relation  is  merely  that  the  muscles  thrown  into  action 
are  those  governed  by  a  motor  nerve  which  is  the  fellow  of  the 
sensory  nerve,  the  stimulation  of  which  calls  forth  the  movement. 
In  the  more  complex  reflex  actions  of  the  brainless  frog,  and 
in  other  cases,  the  relation  is  of  such  a  kind  that  the  resulting 
movement  bears  an  adaptation  to  the  stimulus ;  the  foot  is  with- 
drawn from  the  stimulus,  or  the  movement  is  calculated  to  push 

*  The  question  as  to  how  far  these  processes  in  the  central  cells  are  connected 
\h  the  developmeni  of  consciousness  is  here  purposely  passed  over. 


CHAP.    III.]      PROPERTIES   OF   NERVOUS   TISSUES.  13I 

or  wipe  away  the  stimulus.  In  other  words,  a  certain  purpose  is 
evident  in  the  reflex  action; 

Thus  in  all  cases,  e.xcept  perhaps  the  very  simplest,  the  move- 
ments called  forth  by  a  rerlcx  action  are  exceedingly  complex, 
com|)ared  with  those  which  result  from  the  direct  stimulation  of  a 
motor  trunk.  When  the  peripheral  stump  of  a  divided  sciatic 
neivc  is  stimulated  with  the  interrupted  current,  the  muscles  of 
the  leg  are  at  once  thrown  into  tetanus,  continue  in  the  same  rigid 
condition  during  the  passage  of  the  current,  and  relax  immediately 
on  the  current  being  shut  off.  When  the  same  current  is  applied 
for  a  second  only,  to  the  skin  of  the  flank  of  a  brainless  frog,  the 
leg  is  drawn  up  and  the  foot  rapidly  swept  over  the  spot  irritated, 
as  if  to  wipe  away  tlie  irritation  ;  but  this  movement  is  a  complex 
one,  requiring  the  contraction  of  particular  muscles  in  a  definite 
sequence,  with  a  carefully  adjusted  proportion  between  the 
amounts  of  contraction  of  the  individual  muscles.  And  this  com- 
plex movement,  this  balanced  and  arranged  series  of  contractions, 
may  be  repeated  more  than  once  as  the  result  of  a  single  stimula- 
tion of  the  skin.  When  a  deep  breath  is  caused  by  a  dash  of  cold 
water,  the  same  co-ordinated  and  carefully  arranged  series  of  con- 
tractions is  also  seen  to  result,  as  part  of  a  reflex  action,  from  a 
simple  stimulus.     And  many  more  examples  might  be  given. 

In  such  cases  as  these,  part  of  the  complexity  may  be  due  to 
the  fact  that  the  stimulus  is  applied  to  terminal  sensory  organs 
and  not  directly  to  a  nerve-trunk.  As  we  shall  see  in  speaking  of 
the  senses,  the  impulses  which  are  generated  by  the  ap]jlication  of 
a  stimulus  to  a  sensory  organ  are  more  complex  than  those  which 
result  from  the  direct  stimulation  of  a  sensory  nerve-trunk.  Never- 
theless, reflex  actions  of  great  if  not  of  equal  complexity  may  be 
induced  by  stimuli  applied  directly  to  a  nerve-trunk.  We  are 
therefore  obliged  to  conclude  that  in  a  reflex  action,  the  processes 
which  are  originated  in  the  central  nerve-cells  by  the  arrival  of 
simple  impulses  along  aft'erent  nerves  may  be  highly  complex  ; 
and  that  it  is  the  constitution  and  condition  of  the  nerve-cells 
which  determine  the  complexity  and  character  of  the  movements 
which  are  effected.  In  other  words,  the  central  nerve-cells  con- 
cerned in  reflex  actions  are  to  be  regarded  as  constituting  a  sort 
of  molecular  machinery,  tiie  character  of  the  resulting  movements 
being  determined  by  the  nature  of  the  machinery  set  going  and  its 
condition  at  tlie  time  being,  the  character  and  amount  of  the  afferent 
impulses  determining  exactly  what  parts  of  and  how  far  the  central 
machinery  is  thrown  into  action. 

Actions  of  Sporadic  Ganglia.     Seeing  that  in  the  spinal 

9—2 


132  SPORADIC   GANGLIA.  [BOOK  I. 

cord,  the  nerve-cells  undoubtedly  are  the  central  structures  con- 
cerned in  the  production  of  reflex  action,  it  is  only  natural  to 
infer  that  the  nerve-cells  of  the  sporadic  ganglia  possess  similar 
functions.  Yet  the  evidence  of  this  is  at  present  of  very  limited 
extent.  With  regard  to  the  ganglia  on  the  posterior  roots  of  the 
spinal  nerves,  all  the  evidence  goes  to  shew  that  these  possess  no 
power  whatever  of  reflex  action.  Of  the  larger  ganglia  visible  to 
the  naked  eye,  such  as  the  ciliary  otic,  &c.,  we  have  indications  of 
reflex  action  in  one  only,  viz.  the  submaxillary,  and  these  indica- 
tions are,  as  we  shall  see  in  treating  of  the  salivary  glands,  dis- 
puted. We  have  no  exact  proof  that  the  ganglia  of  the  sympa- 
thetic chain,  or  of  the  larger  sympathetic  plexuses,  are  capable  of 
executing  reflex  actions. 

In  fact,  in  searching  for  reflex  actions  in  ganglia,  we  are  reduced 
to  the  small  microscopic  groups  of  cells  buried  in  the  midst  of  the 
tissues  to  which  they  belong,  such  as  the  ganglia  of  the  heart,  of 
the  intestine,  the  bladder,  &c.  When  a  quiescent  frog's  heart  is 
stimulated  by  touching  its  surface,  a  beat  takes  place.  This  beat 
is,  as  we  shall  see,  a  complex,  co-ordinated  movement,  very  simi- 
lar to  a  reflex  action  brought  about  by  means  of  the  spinal  cord ; 
and  in  its  production  it  is  probable  that  the  cardiac  ganglia  are  in 
some  way  concerned.  When  a  quiescent  intestine  is  touched  or 
otherwise  stimulated,  peristaldc  action  is  set  up.  Here  again  the 
ganglia  present  in  the  intestinal  walls  may  be  supposed  to  play  a 
part;  but  this  movement  is  much  more  simple  than  the  beat  of 
the  heart,  and  as  regards  it,  and  more  especially  as  regards  the 
similar  peristaltic  action  of  the  ureter,  it  becomes  difficult  to  dis- 
tinguish betwe^'n  a  movement  governed  by  ganglia,  and  one  pro- 
duced by  direct  stimulation  of  the  muscular  fibres.  We  have 
seen  that  the  great  distinction  between  a  reflex  action  and  a 
movement  caused  by  direct  stimulation  of  a  nerve  or  of  a  muscle 
lies  in  the  greater  complexity  of  the  former;  and  we  may  readily 
imagine,  that  by  continued  simplification  of  the  central  nervous 
machinery,  the  two  might  in  the  end  become  so  much  alike  as  to 
be  almost  indistinguishable. 

In  the  vertebrate  animal  then  the  chief  seat  of  reflex  action  is 
the  spinal  cord  and  brain.  We  say  '  and  brain '  because,  as  we 
shall  see  later  on,  the  brain,  in  addition  to  its  automatism,  is  as 
busy  a  field  of  reflex  action  as  the  spinal  cord. 

Inhibition.  In  speaking  of  reflex  action,  we  took  it  for 
granted  that  the  spinal  cord  was,  at  the  moment  of  the  arrival  of 
the  afferent  impulses  at  the  central  nerve-cells,  in  a  quiescent  state  ; 
tliat  the  nerve  cells  themselves  were  not  engaged  in  any  automatic 


CHAP.    III.]      PROPERTIES   OF   NERVOUS   TISSUES.  1 33 

action.  We  were  justified  in  doing  so,  because  as  far  as  the 
muscles  2;enerally  of  the  body  are  concerned,  the  spinal  corfl  is  in 
a  brainless  frog  perfectly  quiescent;  an  afierent  impulse  reaching 
an  ordinary  nerve-cell  of  the  spinal  cord  does  not  find  it  pre- 
occupied in  any  other  business.  But  what  happens  when  afferent 
impulses  reach  a  nerve-cell  or  a  gioup  of  nerve-cells  already 
engaged  in  automatic  action  ? 

We  have  already  referred  to  an  automatic  respiratory  centre 
in  the  medulla  oblong.ita.  We  may  here  premise,  what  we  shall 
shew  more  in  detail  hereafter,  that  the  pneumogastric  nerve  is 
peculiarly  associated  as  an  afferent  nerve  with  this  respiratory 
centre.  Now  it  tlie  central  end  of  tlie  divided  pneumogastric  be 
stimulated  at  the  time  when  the  respiratory  centre  is  engaged  in 
its  accustomed  rhytlimic  action,  sending  oi.'.t  comple.x  co  ordinated 
impulses  of  inspiration  (and  of  exj)iration)  at  regular  intervals, 
one  of  two  things  may  happen,  the  choice  of  events  being 
determined  by  circumstances  which  need  not  be  considered 
here. 

The  most  sti iking  event,  and  the  one  which  interests  us  now, 
is  that  the  respiratory  rhythm  is  slowed  or  stopped  altogether. 
That  is  to  say,  that  afferent  impulses  which,  under  ordinary 
conditions,  would,  on  reaching  a  quiescent  nervous  centre,  give 
rise  to  movement,  may,  under  certain  conditions,  when  brought 
to  bear  on  an  already  active  automatic  nervous  centre,  check  or 
stop  movement  by  interfering  with  the  i)roduction  of  efferent 
impulses  in  .tliat  centre.  This  stopping  or  checking  an  already 
present  action  is  spoken  of  as  an  '  inhibition  ; '  and  the  effect  of 
the  pneumogastric  in  this  way  on  the  respiratory  centre  is  spoken 
of  as  '  the  inhibitory -action  of  the  pneumogastric  on  the  respiratory 
centre.' 

The  other  event  is  that  the  respiratory  rhythm  is  accelerated. 
We  shall  hereafter  discuss  the  explanation  of  the  two  events. 
We  may  however  premise  that  according  to  one  view  the  pneumo- 
gastric contains  among  its  afferent  fibres  two  sets,  which  are  either 
of  a  different  nature  from  each  other,  or  are  so  differently  con- 
nected with  the  respiratory  centre,  that  impulses  arriving  along 
one  stop,  while  those  arriving  along  the  other  quicken,  the  action 
of  that  centre.  Hence,  the  one  set  are  called  '  inhibitory,'  the 
other  *  accelerating '  or  '  augmenting '  fibres.  But  we  are  concerned 
at  present  only  with  the  fact  t.iat  the  stimulation  of  a  nerve  may 
produce  inhibitory  or  augmentative  etTects. 

Similarly  the  vaso-motor  centre  in  the  medulla  may,  by 
impulses  arriving  along  various  afferent  tracts,  be  inhibited,  during 
which    the    muscular   walls   of  various   arteries   are    relaxed  ;    or 


134  INHIBITION.  [book    I. 

augmented,  whereby  the  tonic  contraction  of  various  arteries 
is  increased. 

The  most  striking  instance  of  inhibition  is  offered  by  the 
heart.  If  when  the  heart  is  beating  well  and  regularly,  the 
pneumogastric  be  divided,  and  the  peripheral  portion  be  stimulated 
even  for  a  very  short  time  with  an  interrupted  current,  the  heart 
is  immediately  brought  to  a  standstill.  Its  beats  are  arrested,  it 
lies  perfectly  Haccid  and  motionless,  and  it  is  not  till  after  some 
little  time  that  it  recommences  its  beat.  Here  again  it  is  usually 
said  that  the  pneumogastric  contains  efferent  cardio-inhibitory 
fibres,  impulses  passing  along  which  from  the  medulla  stop  the 
automatic  actions  of  the  cardiac  ganglia  ;  the  respiratory  inhibitory 
fibres  of  the  same  nerve  are  afferent,  i.e.  impulses  pass  along  them 
up  to  the  medulla. 

Though  inhibition  is  most  clearly  seen  in  the  case  of  automatic 
actions,  other  actions  may  be  similarly  inhibited.  Thus,  as  we 
shall  see  later  on,  the  reflex  actions  of  the  spinal  cord  may,  by 
appropriate  means,  be  inhibited. 

To  sum  up,  then,  the  most  fundamental  properties  of  nervous 
tissues. 

Nerve-fibres  are  concerned  in  the  propagation  only,  not  in  the 
origination  or  transformation,  of  nervous  impulses.  As  far  as  is  at 
present  known,  impulses  are  propagated  in  the  same  manner  along 
both  sensory  and  motor  nerves.  Sensory  impulses  differ  from 
motor  impulses  inasmuch  as  the  former  are  generated  in  sensory 
organs  and  pass  up  to  the  central  nervous  cells,  while  the  latter 
pass  from  the  central  nervous  cells  to  the  muscles  or  to  some 
other  peripheral  organs. 

The  operations  of  the  nerve-cells  are  either  automatic  or 
reflex.  In  both  an  automatic  and  a  reflex  action,  the  diversity 
and  the  co-ordination  of  the  impulses  is  determined  by  the 
condition  of  the  nerve-cells.  During  the  passage  of  an  impulse 
along  a  nerve-fibre,  there  is  no  augmentation  of  energy  ;  in  passing 
through  a  nerve-cell,  the  augmentation  may  be,  and  generally  is, 
most  considerable. 

When  afierent  impulses  reach  a  centre  already  in  action,  the 
activity  of  that  centre  may,  according  to  circumstances,  be  either 
depressed  or  exalted,  may  be  'inhibited'  or  'augmented.' 

The  sketch  of  the  evolution  of  a  nervous  system  given  at  the 
beginning  of  this  chapter  is  based  on  the  observations  of  Kleiuenberg' 

*  Hydra,  Leipzig,  1872. 


CHAP.    Ill]      PROPERTIES   OF    NERVOUS   TISSUES.  1 35 

and  the  subsequent  results  of  Eimcr,'  O.  and  R.  Hertwig,'  and  Romanes.' 
The  view  expressed  as  to  the  original  continuity  of  muscle  and  nerve  is 
supported  by  the  now  well  recognised  fact  that  in  skeletal  muscles  the 
axis-cylinder  of  the  motor  nerve  not  only  pierces  the  sarcolemma,  but 
comes  into  close  contact  with  the  contractile  substance  ;  and  this  truth 
we  owe  largely  to  Kiihne.* 

'  Zoologische  Untersuch.,   1874.     Archiv  f.   micro.    Atml.,    XIV.  (1877)  p. 

394- 

'  Das  Nerven-Sy  stem  und  die  StnnesOrgane  der  Mcdnscn,  1878. 

3  Phil.   Trans.  1S76,  p.  269,  1877,  p.  659. 

♦  Archiv  f.  Anat.  und  Phys.,  1859,  p.  564.  Uebcr  d.  peripherischen 
Endorgane  der  motorischen  Xerven,  1862,  and  subsequent  papers  in  Virchow's 
Archiv,  Dde.  24,  27,  28  and  29.  Doycre  undoubtedly  had  previously  (1840) 
seen  tlie  continuity  of  the  motor  nerve-fibre  with  the  sarcolemma-les-^  muscular 
filM-e  in  invertebrates  (tardigrades),  and  Wagner  (1847)  had  expressed  a  belief 
that  in  vertebrates  al-o  the  motor  nerve-fibre  ends  in  the  muscular  filire.  Vet 
we  owe  to  Kiihne  the  first  definite  proof  that  both  in  vertebrates  and  in  inver- 
tebrates the  muscular  fibres  of  which  p. assess  a  sarcolemma,  the  axis-cylinder 
pierces  the  sarcolemma.  We  are  indebted  to  him  also  for  the  discovery  of  the 
mode  of  termination  of  the  axis-cylinder  in  the  muscular  fibres  of  amphibia, 
a^  well  as  for  a  correct  appreciation  of  the  structure  and  position  within  the 
sarcolemma  of  the  end-plate  or  essential  part  of  the  nerve-eminence  (nerven- 
hiigel)  discovered  in  other  vertebrates  by  Kouget,  Krause,  and  Engelmann. 


CHAPTER   IV. 

THE   VASCULAR   MECHANISM. 

In  order  that  the  blood  may  be  a  satisfactory  medium  of  com- 
munication between  all  the  tissues  of  the  body,  two  things  are 
necessary.  In  the  first  place,  there  must  be  through  all  parts  of 
the  body  a  flow  of  blood,  of  a  certain  rapidity  and  general 
constancy.  In  the  second  place,  this  flow  must  be  susceptible 
of  both  general  and  local  modifications.  In  order  that  any  tissue 
or  organ  may  readily  adapt  itself  to  changes  of  circumstances 
(action,  repose,  &c.),  it  is  of  advantage  that  the  quantity  of  blood 
passing  to  it  should  be  not  absolutely  constant,  but  capable  of 
variation.  In  order  that  the  material  equilibrium  of  the  body 
may  be  maintained  as  exactly  as  possible,  it  is  desirable  that  the 
loading  of  the  blood  with  substances  proceeding  from  the  un- 
wonted activity  of  any  one  tissue,  should  be  accompanied  by  a 
greater  flow  of  blood  through  some  excretory  or  metabolic  tissue 
by  which  these  substances  may  be  removed.  Similarly  it  is  of 
advantage  to  the  body  that  the  general  flow  of  blood  should  in 
some  circumstances  be  more  energetic,  and  in  others  less  so,  than 
normal. 

The  first  of  these  conditions  is  dependent  on  the  mechanical 
and  physical  properties  of  the  vascular  mechanism ;  and  the 
problems  connected  with  it  are  almost  exclusively  mechanical  or 
physical  problems.  The  second  of  these  conditions  depends  on 
the  intervention  of  the  nervous  system ;  and  the  problems 
connected  with  it  are  essentially  physiological  problems. 

I.     The  Physical  Phenomena  of  the  Circulation. 

The  apparatus  concerned  in  the  Maintenance  of  the 
Normal  Flow  is  as  follows  : 

I.  The  heart,  beating  rhythmically  by  virtue  of  its  con- 
tractility and  intrinsic  mechanisms,  and  at  each  beat  discharging 


CHAP.    IV.]  TlIK   VASCULAR    MECHANISM.  I37 

a  certain  quantity  of  blood  into  the  aorta.     [For  simplicity's  sake 
we  omit  for  the  i)resent  the  piihiionary  circuhilion.] 

2.  The  arteries,  highly  elastic  throughout,  with  a  circular 
muscular  element  increasing  in  relative  importance  as  the  arteries 
diminish  in  size..  It  must  not  be  forgotten  that  the  muscular 
element  is  also  elastic. 

When  an  artery  divides,  the  united  sectional  area  of  the 
branches  is,  as  a  rule,  larger  than  I  lie  sectional  area  of  the  stem. 
Thus  the  collective  capacity  of  the  arteries  is  continually  (and 
rapidly)  increasing  from  the  heart  towards  the  capillaries.  If  all 
the  arterial  branches  were  fused  touether,  they  would  form  a 
funnel,  with  its  apex  at  the  aorta.  The  united  sectional  area  of 
the  capillaries  has  been  calculated  by  Vierordt  to  amount  to 
several  (eight  ?)  hundred  times  that  of  the  aorta. 

3.  The  capillaries,  channels  of  exceedingly  small  but  variable 
size.  Their  walls  are  elastic  (as  shewn  by  their  behaviour  during 
the  passage  of  blood-corpuscles  through  them),  exceedingly  thin 
and  ])<-rmcable.  They  are  permeable  both  in  the  sense  of  allow- 
ing fluids  to  pass  through  them  by  osmosis,  and  also  in  the  sense 
of  allowing  white  and  red  corpuscles  to  traverse  them.  The 
small  arteries  and  veins,  which  gradually  pass  into  and  from  the 
capillaries  properly  so  called,  are  similarly  permeable,  the  more 
so,  the  smaller  they  are.  ' 

4.  The  veins,  less  elastic  than  the  arteries,  and  with  a  very 
variable  muscular  element.  The  united  sectional  area  of  the  veins 
diminishes  from  the  capillaries  to  tiie  heart,  thus  resembling  the 
arteries  ;  but  the  united  sectional  area  of  the  vence  cavje  at  their 
embouchment  into  the  right  auricle  is  greater  than  that  of  the 
aorta  at  its  origin.  (The  proportion  is  nearly  two  to  one.)  The 
total  capacity  of  the  veins  is  similarly  much  greater  than  that  of 
the  arteries.  The  veins  alone  can  hold  the  total  mass  of  blood 
which  in  life  is  distributed  over  both  arteries  and  veins.  Indeed 
nearly  the  whole  blood  is  capable  of  being  received  by  what  is 
merely  a  part  of  the  venous  system,  viz.  the  vena  ])orl?e  and  its 
branches.  Such  veins  as  are  for  various  reasons  liable  to  a  reflux 
of  blood  from  the  heart  towards  the  capillaries,  are  provided  with 
valves. 

Sec.  1.     Main  General  Facts  of  the  Circulation. 
I.      The  Capillary  Circulation. 

If  the  web  of  a  frog's  foot  be  examined  with  a  microscope, 
the  blood,  as  judged  of  by  the  movements  of  the  corpuscles,  is 
seen  to  be  passing  in  a  continuous  stream  from  the  small  arteries 


138  THE   CAPILLARY   CIRCULATION.  [BOOK   I. 

through  the  capillaries  to  the  veins.  The  velocity  is  greater  in  the 
arteries  than  in  the  veins,  and  greater  in  both,  than  in  the 
capillaries.  In  the  arteries  faint  pulsations,  synchronous  with  the 
heart's  beat;  are  occasionally  visible ;  and  not  unfrequently 
variations  in  velocity  and  in  the  distribution  of  the  blood,  due  to 
causes  which  will  be  hereafter  discussed,  are  witnessed  from  time 
to  time. 

The  flow  through  the  smaller  capillaries  is  very  variable. 
Sometimes  the  corpuscles  are  seen  passing  through  the  channel 
(which  when  collapsed  may  have  a  diameter  smaller  than  the  short 
axis  of  a  red  corpuscle)  in  single  file  with  great  regularity  at  a 
velocity  of  about  -57  mm.  in  a  second.  (In  the  human  retina  the 
velocity  is  75  mm.  per  sec.  according  to  Vierordt.)  At  other 
times,  the  corpuscles  which  pass  along  a  given  capillary  may  be 
few  and  far  between.  Sometimes  the  corpuscle  may  remain 
stationary  at  the  entrance  into  a  capillary,  the  channel  itself  being 
for  some  little  distance  entirely  free  from  corpuscles.  Any  one  of 
these  conditions  readily  passes  into  another,  and,  especially  with  a 
somewhat  feeble  circulation,  instances  of  all  of  them  may  be  seen 
in  the  same  field  of  the  microscope.  It  is  only  in  the  case  of  a 
very  full  circulation  that  all  the  capillaries  can  be  seen  equally 
filled  with  corpuscles.  The  long  oval  red  corpuscle  moves  with 
its  long  axis  parallel  to  the  stream,  frequently  rotating  on  its  long 
axis  and  sometimes  on  its  short  axis.  The  flexibility  and  elas- 
ticity of  a  corpuscle  are  well  seen  when  it  is  being  driven  into  a 
capillary  narrower  than  itself,  or  when  it  becomes  temporarily 
lodged  at  the  angle  between  two  diverging  channels.  The  small 
mammalian  corpuscles  rotate  largely  as  they  are  driven  along. 

In  the  larger  capillaries,  and  especially  in  the  small  arteries 
and  veins  which  permit  the  passage  of  several  corpuscles  abreast,- 
it  is  observed  that  the  red  corpuscles  run  in  the  middle  of  the 
channel,  forming  a  coloured  core,  between  which  and  the  sides  of 
the  vessel  all  round  is  a  layer,  containing  no  red  corpuscles.  In 
this  layer,  the  so-called  '  inert  layer,'  especially  in  that  of  the 
veins,  are  frequently  seen  white  corpuscles,  sometimes  clinging  to 
the  sides  of  the  vessel,  sometimes  rolhng  slowly  along,  and  in 
general  moving  irregularly,  and  often  in  jerks.  This  division  into 
an  inert  layer  and  an  axial  stream  is  due  to  the  fact  that  in  any 
stream  passing  through  a  closed  channel  the  friction  is  greatest 
at  the  immediate  sides,  and  diminishes  towards  the  axis.  The 
corpuscles  pass  where  the  friction  is  least,  in  the  axis.  A  quite 
similar  axial  core  is  seen  when  any  fine  particles  are  driven  in  a 
stream  of  fluid  through  a  narrow  tube.  The  phenomena  cease 
with  the  flow  of  the  fluid.     Tlie  presence  of  the  white  corpuscles 


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CHAP.^JV.]  THi:    VASCULAR    MECHANISM.  139 

in  the  inert  layer  is  said  to  be  due  to  their  being  s[)ecifically  hghter 
than  the  red  corpuscles.  When  fine  particles  of  two  kintis,  one 
lighter  than  the  other,  are  driven  through  a  narrow  tube,  the 
heavier  particles  flow  in  the  axis  and  the  lighter  in  the  more 
peripheral  portions  of  the  stream.  The  white  corpuscles  however 
are  distinctly  more  adhe.si\e  than  the  red,  as  is  seen  by  the 
manner  in  which  they  become  fixed  to  the  glass  slide  and  cover- 
slip  when  a  drop  of  blood  is  mounted  for  microscopical  examina- 
tion ;  and  by  reason  of  this  adhesiveness  they  may  become 
temporarily  attached  to  the  walls  of  the  vessel,  and  consequently 
appear  in  the  inert  layer.  The  resistance  to  the  flow  of  blood 
thus  caused  by  the  friction  generated  in  so  many  minute  passages, 
is  one  of  the  most  important  physical  facts  in  the  capillary  cir- 
culation. In  the  large  arteries  the  friction  is  small ;  it  increases 
as  they  divide,  and  receives  a  ver}'  great  addition  in  the  minute 
arteries  and  capillaries.  It  need  perhaps  hardly  be  said  that  this 
peripheral  friction  not  only  opposes  the  flow  of  blood  through  the 
capillaries  themselves,  but,  working  backwards  along  the  whole  ar- 
terial system,  has  to  be  met  by  the  heart  at  each  systole  of  the 
ventricle. 

2 .     TJu  Flow  in  the  Arteries. 

When  an  artery  is  severed,  the  flow  from  the  proximal 
section  is  not  equable,  but  comes  in  jets,  which  correspond  to  the 
heart-beats,  though  the  flow  does  not  cease  between  the  jets. 
The  blood  is  ejected  with  considerable  force ;  thus,  in  Dr. 
Stephen  Hales'*  experiments,  when  the  crural  artery  of  a  mare 
was  severed,  the  jet,  even  after  much  loss  of  blood,  rose  to  the 
height  of  two  feet.  The  larger  the  artery  and  the  nearer  to  the 
heart,  the  greater  the  force  with  which  the  blood  issues,  and  the 
more  marked  the  intermittence  of  the  flow.  The  flow  from  the 
distal  section  may  be  very  slight,  or  may  take  place  with  con- 
siderable force  and  marked  intermittence,  according  to  the 
amount  of  collateral  communication. 

Arterial  pressure.  If,  while  the  blood  is  flowing  normally 
along  a  large  artery,  e.g.  the  carotid,  a  mercury  (or  other)  mano- 
meter. Fig.  23,  bo  connected  with  a  hole  in  the  side  of  the  artery, 
so  that  there  is  free  communication  between  the  interior  of  the 
arter)-  and  the  proximal  (descending)  limb  of  the  manometer,  the 
following  facts  are  observed. 

Immediately  that  communication  is  established  between  the 
interior  of  the  artery  and  the  manometer,  blood  rushes  from  the 

*  Statical  Essays,  Vol.  11.  p.  2  (1732). 


I40  ARTERIAL   PRESSURE.  [BOOK  I. 

former  into  the  latter,  driving  some  of  the  mercury  from  the 
descending  limb  into  the  ascending  linvb,  and  thus -causing  the 
level  of  the  mercury  in  tlie  ascending  limb  to  rise  rapidly.  This 
rise  is  marked  by  jerks  corresponding  with  the  heart-beats. 
Having  reached  a  certain  level,  the  mercury  ceases  to  rise  any 
more.  It  does  not,  however,  remain  absolutely  at  rest,  but  under- 
goes oscillations  ;  it  keeps  rising  and  falling.  '  Each  rise,  which  is 
very  slight  compared  with  the  total  height  to  which  the  mercury 
has  risen,  has  the  same  rhythm  as  the  systole  of  the  ventricle. 
Similarly,  each  fall  corresponds  with  the  diastole. 

If  a  float,  swimming  on  the  top  of  the  mercury  in  the  ascend- 
ing limb  of  the  manometer,  and  bearing  a  brush  or  other  marker, 
be  brought  to  bear  on  a  travelling  surface,  some  such  tracing  as 
that   represented   in   Fig.    24  will   be  described.      Each  of  the 


Fig.  24.    Tracing  of  Arterial  Pressure  with  a  Mercury  Manometer. 

The  smaller  curves  p p  are  the  pulse-curves.     The  space  from  r  to  r  embraces  a  respiratory 

undulation. 

smaller  curves  (/,/)  corresponds  to  a  heart-beat,  the  rise  corre- 
sponding to  the  systole  and  the  fall  to  the  diastole  of  the  ventricle. 
The  larger  undulations  {r,  r)  in  the  tracing,  which  are  respiratory 
in  origin,  will  be  discussed  hereafter.  This  observation  teaches 
us  that  the  blood,  as  it  is  passing  along  the  carotid  artery,  is 
capable  of  supporting  a  column  of  mercury  of  a  certain  height 
(measured  by  the  difference  of  level  between  the  mercury  in  the 
descending  limb,  and  that  in  the  ascending  limb,  of  the  mano- 
meter), when  the  mercury  is  placed  in  direct  communication  with 
the  side  of  the  stream  of  blood.  In  other  words,  the  blood,  as  it 
passes  through  the  artery,  exerts  a  lateral  pressure  on  the  sides 
of  the  artery,  equal  to  so  many  millimetres  of  mercury.  In  this 
lateral  pressure  we  have  further  to  distinguish  between  the  slighter 
oscillations  corresponding  with  the  heart-beats,  and  a  mean  pressure 
above  and  below  which  the  oscillations  range.  A  similar  mean 
pressure  with  similar  oscillations  is  found,  when  any  artery  of 
the  body  is  examined  in  the  same  way.  In  all  arteries  the  blood 
exerts  a  certain  pressure  on  the  walls  of  the  vessels  which  contain 


CHAP.   IV.]  THE   VASCULAR    MECHANISM.  I4I 

it.  This  is  generally  spoken  of  as  arterial  pressure,  and  the 
pressure  in  the  aorta  of  any  animal  is  usually  spoken  of  as  its 
blood- pressure. 

Description  of  Experiment.  The  carotid,  or  other  vessel,  is  laid 
bare,  clamped  in  two  pla.cs  and  divided  between  the  clamps.  Into 
the  cut  eirls  is  inserted  a  hollow  T  piece  of  the  same  bore  as  the 
artery,  the  cross  portion  forming  the  continuation  of  the  artery.  The 
vcrtic:ti  portion  is  connected  by  nu-ans  of  a  non  elastic  flexible  tube 
with  t"ie  des.ending  limb  of  the  manometer.  In  order  to  avoid  loss  of 
blood,  fluid  is  injecteil  into  the  flexible  tube  until  the  mercury  in  the 
manometer  stands  a  very  little  below  what  may  be  beforehand  guessed 
at  as  the  probable  mean  pressure.  The  fluid  chosen  is  a  saturated 
solution  of  sodium  carbonate,  with  a  view  to  hinder  the  coagulation  of 
the  blood  in  tlie  tube.  When  the  clamps  are  removed  from  the  artery 
the  blood  ru-;hes  through  the  cross  of  the  [—  pie^e.  Some  passes  into 
the  side  limb  of  t'^e  |—  piece  and  continues  to  do  so  until  the  mean 
pressure  is  quite  reached.  Thenceforward  there  is  no  more  esjape  ; 
but  the  pressure  continues  in  the  interior  of  the  cross  of  the  |—  pie:e, 
is  transmitted  along  the  conne.ting  tube  to  the  manometer,  and  the 
mercury  continues  to  stand  at  a  height  indicative  of  the  mean  pressure 
with  oscilhitions  corresponding  to  the  heart's  beats.  Practically  the 
use  of  the  |—  piece  is  found  inconvenient.  Accordingly  the  general 
custom  is  to  ligature  the  artery,  to  place  a  clamp  on  the  vessel  on  the 
proximal  side  of  the  ligature,  and  to  introduce  a  straight  cannula, 
Fig.  23,  connected  with  the  manometer,  between  the  ligature  and  the 
clamp.  In  this  casj,  on  loosing  the  clamp,  the  whole  column  of  blood 
in  the  artery  is  brought  to  bear  on  the  manometer,  ;ind  the  tracings 
taken  illustrate  the  lateral  pressure  not  of  the  artery  but  of  the  vessel 
(aorta  (S:c.  as  the  case  may  be)  of  which  it  is  itself  a  branch. 

Tracings  of  the  movements  of  the  column  of  mercury  in  the  mano- 
meter may  be  taken  either  on  a  smoked  surl'ace  of  a  revolving  cylinder 
(Fig.  i),  or  by  means  of  a  brush  and  ink  on  a  continuous  roll  of  paper, 
ai  in  the  more  complj.x  k\mograi)li  (Fig.  26). 

In  such  a  mercury  manometer,  the  inertia  of  the  mer:ur>'  obscures 
m.my  of  the  features  of  the  minor  curves  caused  by  the  heart-beats. 
When  therefore  these,  rather  than  variations  in  the  mean  pressure, 
are  being  studied  it  is  advisiijle  to  have  recourse  to  the  spring  mano- 
meter (Fig  25),  introduce  1  by  Pick.  In  using  this  instrument,  the 
tube  /,  Fig.  23,  is  connected  with  the  tube  c,  Fig.  25. 

The  average  prcssine  of  the  blood  in  the  same  body  is 
greatest  in  the  largest  arteries,  and  diminishes  as  the  arteries  get 
less ;  but  the  fall  is  a  very  gradual  one  until  the  smalL-st  arteries 
are  reached,  in  which  it  l)econics  very  rapid.  In  the  carotid  of 
the  horse,  the  mean  arterial  pressure  varies  from  150  to  200  mm. 
of  mercury  ;  of  the  dog  from  100  to  175  ;  of  the  rabbit  from  50  to 
90.     In  the  carotid  of  man  it  jjrobably  amounts  to  150  or  200. 

Since  in  all  arteries  the  blood  is  pressing  on  the  arterial  walls 


142 


ARTERIAL   PRESSURE. 


[BOLK   I. 


with  some  considerable  force,  all  the  arteries  must  be  in  a  state  of 
permanent  distension,  so  long  as  blood  is  flowing  through  them 
from  the  heart.  When  the  blood-current  is  cut  off,  as  by  a  ligature, 
this  expansion  or  distension  disappears. 


re.  23.    Diagram  illustrating  Kick's  Spring  Manometer. 

This  consists  essentially  of  a  hollow  flattened  german-silver  tube  a,  curved  in  the  form  of 
an  incomplete  circle.  The  lower  open  end  b,  firmly  fastened  to  the  stand  5,  is  connected  with 
a  tube  c,  bearing  a  stop-cock.  To  the  upper  closed  end  is  attached  a  light  upright  rod  d 
connected  with  the  writing  lever  /. 

Through  the  tube  c  the  hollow  curved  spring  is  filled  with  alcohol,  and  the  stop-cock 
closed.  The  tube  c  is  then  connected  with  the  artery  by  means  of  a  non-elastic  flexible  (leaden) 
tube  filled  with  sodium  carbonate  solution.  On  opening  the  stop-cock  the  variations  of  pres- 
sure of  the  blood  in  the  artery  are  communicated  to  the  fluid  in  the  hollow  curved  spring  ;  at 
each  increase  of  pressure  the  spring  expands,  and  the  movements  of  the  free  end  are  trans- 
ferred by  d  to  the  writing  lever  /.  The  instrument  as  generally  sent  out  also  bears  an 
arrangement  (not  shewn  in  ihe  diagram),  by  which  the  point  of  the  lever  describes  a  straight 
instead  of  a  curved  line.  The  spring  manometer  is  e.xtremely  useful  where  it  is  desirable  to 
investigate  closely  the  variations  in  the  form  of  the  pressure-curve.  In  order  to  measure  the 
amount  of  variation,  the  instrument  must  be  experimentally  graduated. 

Not  only  is  there  a  permanent  expansion  corresponding  to  the 
mean  pressure,  but  just  as  the  mercury  in  the  manometer  rises 
above  the  level  of  mean  pressure  at  each  systole  of  the  heart,  and 
falls  below  it  at  each  diastole,  so  at  any  spot  in  the  artery  there  is 


CllAi).   IV.J  THE    VASCULAR    MECHANISM. 


'43 


for  each  heart-beat  a  temporary  expansion  succeeded  by  a 
temporary  contraction,  tlie  diameter  of  the  artery  in  its  temjiorary 
expansions  and  contractions  oscillating,  in  correspondence  with  the 
oscillations  of  the  manometer,  beyond  and  within  the  diameter  of 
permanent  expansion.  These  temporary  expansions  constitute 
what  is  called  the  pulse,  and  will  be  discussed  more  fully  hereafter 


Fig.  26.     Large  Kymogsaih  \vi  1 11  coNTraous  roll  of  pafek. 

The  clock-worV  m.achinery.  some  of  ihe  details  of  which  are  seen,  unrolls  ihe  paper  from 
the  roll  C.  cairies  it  smoo'.hly  over  ihe  cj'lindcr  H,  ani  then  winds  it  i-.p  into  the  roll  A. 

1  wo  electromagnetic  markers  are  seen  in  the  position  in  which  they  record  their  move- 
ments  on  the  paper  .-is  it  travels  over  B.  T  he  manomeier.  or  any  other  recording  instrtiment 
used,  can  be  fixed  either  in  liie  notch  immediately  in  front  of  B  or  in  any  other  position  that 
may  be  desired. 

The  velocity  of  the  flow.  When  even  a  small  artery  is 
severed  a  considerable  quantity  of  blood  escapes  from  the 
proximal  cut  end  in  a  very  short  space  of  time.  That  is  to  say, 
the  blood  moves  in  the  arteries  from  the  heart  to  the  capillaries, 
with  a  very  consideral)le  velocity.  By  various  methods,  this 
velocity  of  the  blood-current  has  been  measured  at  different  farts 
of  the  arterial  system  ,  the  results,  owing  to  imperfections  in  the 
methods  employed,  cannot  be  re;;arded  as  satisfactorily  exact,  but 
may  be  accepted  as  approximatively  true.  The  velocity  of  the 
arterial  stream  is  greatest  in  the  largest  arteries,  and  diminishes 


144  THE   VELOCITY   OF   THE   FLOW.  [BOOK   I. 

from  the  heart  to  the  capillaries,  far i passu  with  the  increase,  so  to 
speak,  of  the  widih  of  the  bed,  i.e.  with  the  increase  of  the  united 
sectional  area. 

Methods.  The  Hsemadromometer  of  Volkmann.  An  artery,  e.g. 
a  carotid,  is  clamped  in  two  places,  and  divided  between  the  clamps. 
Two  cannulse,  of  a  bore  as  neaiiy  equal  as  possible  to  that  of  the 
artery,  or  of  a  known  bore,  are  inserced  in  the  two  ends.  The  two 
cannulae  are  connected  by  means  of  two  stop-cocks,  which  work 
together,  with  the  two  ends  of  a  long  glass  tube,  bent  m  the  bhape  of 
a  U,  and  filled  with  water,  or  with  a  coloured  innocuous  fluid.  The 
clamps  on  the  artery  being  released,  a  turn  of  the  stop-cocks  permits 
the  blood  to  enter  the  proximal  end  of  the  long  (J  tube,  along  which 
it  courses,  driving  the  fluid  out  into  the  artery  through  the  distal  end. 
Attached  to  the  tube  is  a  graduated  scale,  by  means  of  which  the 
velocity  with  which  the  blood  flows  along  the  tube  may  be  read  off. 
Even  supposing  the  cannulse  to  be  of  the  same  bore  as  the  artery,  it  is 
evident  that  the  conditions  of  the  flow  through  the  tube  are  such  as 
will  only  admit  of  the  result  thus  gained  being  considered  as  an 
approximative  estimation  of  the  real  velocity  in  the  artery  itself 

The  Rheometer  (Stromuhr)  of  Ludwig.  This  consists  of  two  glass 
bulbs  A  and  B,  Fig.  27,  communicating  above  with  each  other  and 


Fig.  27.    Diagrammatic  Representation  of  Lodwig's  Stromuhr. 

with  the  common  tube  C  by  which  they  can  be  filled.  Their  lower 
ends  are  fixed  in  the  metal  disc  D,  which  can  be  made  to  I'otate, 
through  two  right  angles,  round  the  lower  disc  E.  In  the  upper  disc 
are  two  holes  a  and  b  continuous  with  A  and  B  respectively,  and  in 
t'le  lower  disc  are  two  similar  holes  a'  and  b' ,  similarly  continuous  with 
the  tubes  //and  G.  Hence,  in  the  position  of  the  discs  shewn  in  the 
figure,  the  tube  G  is  continuous  through  the  two  di=cs  with  the  bulb  ^4 
and  the  tube  //with  the  bulb  B.  On  turning  the  disc  D  through  two 
right  angles  the  tube  G  beromes  continuous  with  B  instead  of  A.,  and 
the  tube  H  with  A  instead  of  B.  There  is  a  further  arrangement, 
omitted  from  the  figure  for  the  sake  of  simplicity,  by  which  when  the 


CHAl'.    IV.]  THE   VASCULAR    MECHANISM.  I45 

disc  D  is  turned  through  one  instead  of  two  right  angles  from  either 
of  the  above  positions,  G  becomes  directly  continuous  with  //,  both 
being  completely  shut  off  from  the  bulbs. 

The  ends  ot  the  tubes  //  and  G  arc  made  to  fit  exactly  into  two 
cannula:  inserted  into  the  two  cut  ends  of  the  artery  about  to  be 
experimented  upon,  and  having  a  bore  as  nearly  equal  as  possible  to 
that  of  the  artery. 

The  method  of  experimenting  is  as  follows.  The  disc  D,  being 
placed  in  the  intermediate  position,  so  that  a  and  b  are  both  cut  off 
from  a'  and  b\  the  bulb  A  is  filled  with  pure  olive  oil  up  to  the  mark 
X,  and  the  bulb  B,  the  rest  of  A^  and  the  junction  C,  with  dehbrmatcd 
blood  ;  and  C  is  then  clamped.  The  tubes  H  and  G  are  also  filled 
with  dehbrinatcd  blood,  and  G  is  inserted  into  the  cannula  of  the 
central,  //  into  that  of  the  peripheral,  end  of  the  artery.  On  removing 
the  clamps  from  the  artery  the  blood  flows  through  G  to  H,  and  so 
back  into  the  artery.  The  observation  now  begins  by  turning  the  disc 
D  into  the  position  shewn  in  the  figure  ;  the  blood  then  flows  into  Ay 
driving  the  oil  there  contained  out  before  it  into  the  bulb  B,  in  the 
direction  of  the  arrow,  the  dehbrinated  blood  previously  prcseiit  in  B 
passing  by  H  into  the  artery,  and  so  into  the  system.  At  the  moment 
that  the  blood  is  seen  to  rise  to  the  mark  x,  ihc  disc  D  is  with  all 
possible  rapidity  turned  through  two  right  angles  ;  and  thus  the  bulb 
B,  now  largely  liilcd  with  oil,  placed  in  communication  with  G.  The 
blood-stream  now  drives  the  oil  back  into  A,  and  the  new  blood  in  A 
through  //  into  the  artery.  As  soon  as  the  oil  has  wholly  returned  to 
its  original  position,  the  disc  is  again  turned  round,  and  A  once  more 
placed  in  communication  with  G,  and  the  oil  once  more  driven  from  A 
to  B.  And  this  is  repeated  several  times,  indeed  generally  until  the 
clotting  of  the  blood  or  the  admixture  of  the  oil  with  the  blood  puts 
an  end  to  the  experiment.  Thus  the  flow  of  blood  is  used  to  fill 
alternately  with  blood  or  oil  the  space  of  the  bulb  A,  whose  cavity  as 
fur  as  the  mark  x  has  been  exactly  measured  ;  hence  if  the  number  of 
times  in  any  given  time  the  disc  D  has  to  be  turned  round  be  known, 
the  number  of  times  A  has  been  tilled  ij  also  known,  and  thus  the 
quantity  of  blood  which  has  passed  in  that  time  through  the  cannula 
connected  with  the  tube  G  is  directly  measured.  For  insttmce,  sup- 
posing that  the  quantity  held  by  the  bulb  A  when  filled  up  to  the  mark 
x  is  5  C.C.,  and  supposing  that  from  tlie  moment  of  allowing  the  first 
5  c.c.  of  blood  to  begin  to  enter  the  tube  to  the  moment  when  the 
t  scape  of  the  last  5  c.c.  from  the  artery  into  the  tube  was  complete, 
too  seconds  had  elapsed,  during  which  time  5  c.c.  had  been  received 
10  times  into  the  tube  from  the  artery  (all  but  the  last  5  c.c.  being 
remrncd  into  the  distal  portion  of  the  artery),  obviously  "5  c  c.  of 
blood  had  flowed  from  the  proximal  section  of  the  arter\  in  one  second. 
Hence  supposing  that  the  diameter  of  the  cannula  (and  of  the  artery, 
they  beng  the  same)  were  2  mm.,  with  a  sectional  area  therefore  of 
3'14  square  mm.,  an  outflow  through  the  section  of  "5  c.c.  or  500  c.mm. 
in  a  second  would  give  (■j°^)>  a  velocity  of  about  159  mm.  in  a 
second. 

The  Hncmatachometcr  of  Vicrordt  is  constructed  on  the  principle 
of  measuring  the  velocity  of  the  current  by  observing  the  amount  of 
F.  P.  '  10 


146  THE   VELOCITY   OF   THE   FLOW.  [BOOK  L 

deviation  undergone  by  a  pendulum,  the  free  end  of  which  hangs 
loosely  in  the  stream.  A  square  or  rectangular  chamber,  one  side  of 
which  is  of  glass  and  marked  with  a  graduated  scale  in  the  form  of  an 
arc  of  a  circle,  is  connected  by  means  of  two  short  tubes  with  the  two 
cut  ends  of  an  artery  ;  the  blood  consequently  flows  from  the  proximal 
(central)  portion  of  the  artery  through  the  chamber  into  the  distal 
portion  of  the  artery.  Within  the  chamber  and  suspended  from  its 
roof  is  a  short  pendulum,  which  when  the  blood-stream  is  cut  off  from 
the  chamber  hangs  motionless  in  a  vertical  position,  but  when  the 
blood  is  allowed  to  flow  through  the  chamber,  is  driven  by  the  force 
of  the  current  out  of  its  position  of  rest.  The  pendulum  is  so  placed 
that  a  ^marker  attached  to  its  free  end  travels  close  to  the  inner  surface 
of  the  glass  side  along  the  arc  of  the  graduated  side.  Hence  the 
amount  of  deviation  from  a  vertical  position  may  easily  be  read  off 
on  the  scale  from  the  outside.  The  graduation  of  the  scale  having 
been  carried  out  by  experimenting  with  streams  of  known  velocity,  the 
velocity  can  at  once  be  calculated  from  the  amount  of  deviation. 

An  instrument  based  on  the  same  principle  has  been  invented  by 
Chauveau  and  improved  by  Lortet.  In  this  the  part  which  corresponds 
to  the  pendulum  in  Vierordt's  instrument  is  prolonged  outside  the 
chamber,  and  thus  the  portion  within  the  chamber  is  made  to  form  the 
short  arm  of  a  lever,  the  fulcrum  of  which  is  at  the  point  where  the 
wall  of  the  chamber  is  traversed  and  the  long  arm  of  which  projects 
outside.  A  somewhat  wide  tube,  the  wall  of  which  is  at  one  point 
composed  of  an  india-rubber  membrane,  is  introduced  between  the 
two  cut  ends  of  an  artery.  A  long  light  lever  pierces  the  india- 
rubber  membrane.  The  short  expanded  arm  of  this  lever  projecting 
within  the  tube  is  moved  on  its  fulcrum  in  the  india-rubber  ring  by  the 
current  of  blood  passing  through  the  tube,  the  greater  the  velocity  of 
the  current,  the  larger  being  the  excursion  of  the  lever.  The  move- 
ments of  the  short  arm  give  rise  to  corresponding  movements  in  the 
opposite  direction  of  the  long  arm  outside  the  tube,  and  these,  by 
means  of  a  marker  attached  to  the  end  of  the  long  arm,  may  be  directly 
inscribed  on  a  recording  surface.  This  instrument  is  very  well  adapted 
for  observing  changes  in  the  velocity  of  the  flow.  In  determining 
actual  velocities,  for  which  purpose  it  has  to  be  experimentally 
graduated,  it  is  not  so  useful. 

In  the  horse,  Volkmann  found  the  velocity  of  the  stream  to  be 
in  the  carotid  artery  about  300  mm.,  in  the  maxillary  artery 
165  mm.,  and  in  the  metatarsal  artery  56  ram.  in  the  second. 
Chauveau  determined  the  velocity  in  the  carotid  of  the  horse  to 
vary  from  520  to  150  mm.  per  sec.  at  each  beat  of  the  heart, 
flowing  at  the  former  rate  during  the  height  of  each  pulse-expan- 
sion, and  at  the  latter  in  the  interval  between  each  two  beats. 
Ludwig  and  Dogiel  found  the  velocity  in  the  dog  and  in  the 
rabbit  to  vary  within  very  wide  limits,  not  only  in  different  arteries, 
but  in  the  same  artery  under  different  circumstances.  Thus  while 
in  the  carotid  of  the  rabbit  it  may  be  said  to  vary  from  100  to  200 


CIIAl'.    IV.J         THE   VASCULAR    MECHANISM.  147 

mm.  per  sec,  and  in  the  carotid  of  the  dog  from  200  to  500  mm. 
per  sec,  both  these  limits  were  frequently  passed, 

3.      The  Fhmi  in  the   Veins. 

When  a  vein  is  severed,  the  (low  from  the  distal  cut  end  (/'.  e. 
the  end  nearest  the  capillaries)  is  continuous,  the  blood  is  ejected 
with  comparatively  little  force,  and  with  slight  velocity. 

Wiicn  a  vein  is  connected  with  a  manometer,  the  lateral  pres 
sure  is  found  to  be  very  small ;  it  is  greater  in  the  veins  farther 
from  the  heart  than  in  those  nearer  the  heart.  In  the  immediate 
neighbourhood  of  the  heart  the  pressure  may  (during  the  inspira- 
tory movenient)  become  negative,  i.e.  when  the  manometer  is 
brought  into  connection  with  the  interior  of  the  vein,  the  mercury 
in  the  distal  limb  falls,  instead  of,  as  in  the  case  of  the  artery, 
rising. 

In  the  brachial  vein  of  the  sheep  Jacobson  found  the  mean  pressure 
to  be  4  mm.  of  mercury,  in  a  branch  of  the  same  9  mm.  In  the 
crural  it  was  11  "4  mm.  In  the  subclavian  the  mean  pressure  was 
negative,  viz.  —  'i  mm.,  becoming  —  i  mm.  during  inspiration,  —  3 
mm.  or  —  5  mm.  during  a  strong  inspiration,  and  changing  to  positive 
during  e.vpiration. 

The  level  of  mercury  in  the  manometer,  except  in  the  case  of 
certain  veins,  subject  to  influences,  which  will  be.  discussed  here- 
after, remains  constant.  The  pulse  oscillations,  so  striking  in  the 
arteries,  are  absent  in  the  veins.  In  the  small  veins  the  velocity 
of  the  current,  measured  in  the  same  way  as  the  arteries,  is  very 
slight.  It  increases  in  the  larger  veins,  corresponding  to  the 
diminution  of  the  area  of  '  the  bed ' ;  it  is  about  200  mm.  per.  sec. 
in  the  jugular  vein  of  the  dog. 

Thus  the  flow  in  the  veins  presents  strong  contrasts  with  that 
in  the  arteries.  In  the  arteries,  even  in  the  smallest  branches, 
there  is  a  considerable  mean  pressure.  In  the  veins,  even  in  the 
small  veins  where  it  is  largest,  the  mean  pressure  is  very  slight. 
In  other  words,  there  is  always  a  difference  of  pressure  tending  to 
make  the  blood  flow  continuously  from  the  arteries  into  the  vems. 
A  pulse  is  present  in  the  arteries,  but,  with  certain  exceptions, 
absent  in  the  veins.  The  velocity  of  the  stream  of  blood  in  the 
arteries  is  considerable  ;  in  the  small  veins  it  is  much  less,  but  it 
increases  in  the  larger  trunks  ;  for  in  both  arteries  and  veins  it 
corresponds  with  the  area  of  the  bed,  diminishing  in  the  former 
from  the  heart  to  the  cai)illaries,  and  increasing  in  the  latter  from 
the  capillaries  to  the  heart. 

10 — 2 


148  '    INTERMITTENT   FLOW.  [BOOK   I. 

Hydraulic  Principles  of  the  Circulation. 

All  the  above  phenomena  are  the  simple  results  of  an  inter- 
mittent force  (Uke  that  of  the  systole  of  the  ventricle)  working  in 
a  closed  circuit  of  branching  elastic  tubes,  so  arranged  that  while 
the  individual  tubes  first  diminish  (from'  the  heart  to  the  capillaries) 
and  then  increase  (from  the  capillaries  to  the  heart),  the  area  of 
the  bed  first  increases  and  then  diminishes,  the  tubes  together  thus 
formmg  two  cones  placed  base  to  base  at  the  capillaries,  with  their 
apices  converging  to  the  heart.  To  this  it  must  be  added  that  the 
friction  in  the  small  arteries  or  capillaries,  at  the  junction  of  the 
bases  of  the  cones,  offers  a  very  great  resistance  to  the  flow  of  the 
blood  through  them.  It  is  this  peripheral  resistance  (in  the 
minute  arteries  and  capillaries,  for  the  resistance  offered  by  the 
friction  in  the  larger  vessels  may,  when  compared  with  this,  be 
practically  neglected),  reacting  through  the  elastic  walls  of  the 
arteries  upon  the  intermittent  force  of  the  heart,  which  gives  the 
circulation  of  the  blood  its  peculiar  features. 

Circumstances    determining  the    character   of    the 

flow.  When  fluid  is  driven  by  an  intermittent  force,  as  by  a 
pump,  through  a  perfectly  rigid  tube  (or  system  of  tubes),  at  each 
stroke  of  the  pump  there  escapes  from  the  distal  end  of  the 
system  just  as  much  fluid  as  enters  it  at  the  proximal  'end.  The 
escape  moreovej:  takes  place  at  the  same  time  as  the  entrance, 
since  the  time  taken  up  by  the  transmission  of  the  shock  is  so 
small,  that  it  may  be  neglected.  This  result  remains  the  same 
when  any  resistance  to  the  flow  is  introduced  into  the  system. 
The  force  of  the  pump  remaining  the  same,  the  introduction  of 
the  resistance  undoubtedly  lessens  the  quantity  issuing  at  the 
distal  end  at  each  stroke,  but  it  does  so  simply  by  lessening  the 
quantity  entering  at  the  proximal  end  ;  the  income  and  outgo 
remain  equal  to  each  other,  and  occur  at  almost  the  same  time. 
And  what  is  true  of  the  two  ends,  is  also  true  of  any  part  of  the 
course  of  the  system,  so  far,  at  all  events,  as  the  following  propo- 
sition is  concerned,  that  in  a  system  of  rigid  tubes,  either  with 
or  without  an  intercalated  resistance,  the  flow  caused  by  an 
intermittent  force  is,  in  every  part  of  the  tubes,  intermittent 
synchronously  with  that  force. 

In  a  system  of  elastic  tubes  in  which  there  is  little  resistance  to 
the  progress  of  the  fluid,  the  flow  caused  by  an  intermittent  force 
is  also  intermittent.  The  outgo  being  nearly  as  easy  as  the  income, 
the  elasticity  of  the  walls  of  the  tubes  is  scarcely  at  all  called  into 
play.     These  behave  prnctically  like  rigid  tubes.     When,  however, 


CHAP.   IV.]  THE   VASCULAR    MECHANISM.  149 

sufficient  resistance  is  introduced  into  any  part  of  the  course,  the 
fluid,  being  unable  to  pass  by  the  resistance  as  rapidly  as  it  enters 
the  system  from  the  pump,  tends  to  accumulate  on  ih.e  proximal 
side  of  the  resistance.  This  it  is  able  to  do  by  expanding  the 
elastic  walls  of  the  tubes.  At  each  stroke  of  the  pump  a  certain 
quantity  of  fluid  enters  the  system  at  the  proximal  end.  Of  this 
only  a  fraction  can  pass  through  the  resistance  during  the  stroke. 
At  the  moment  when  the  stroke  ceases,  the  rest  still  remains  on 
the  proximal  side  of  the  resistance,  the  elastic  tubes  having  ex- 
panded to  receive  it.  During  the  interval  between  this  and  the 
next  stroke,  the  distended  elastic  tubes,  striving  to  return  to  their 
natural  undistended  condition,  press  on  this  extra  quantity  of  fluid 
which  they  contain  and  tend  to  drive  it  i)ast  the  resistance.  Thus 
in  the  rigid  system  (and  in  the  elastic  system  without  resistance) 
there  issues,  from  the  distal  end  of  the  system,  at  each  stroke  just 
as  much  fluid  as  enters  it  at  the  proximal  end,  while  between  the 
strokes  there  is  perfect  quiet.  In  the  elastic  system  with  resist- 
ance, on  the  contrary,  the  quantity  which  passes  the  resistance  is 
only  a  fraction  of  that  which  enters  the  system  from  the  pump, 
the  remainder,  or  a  portion  of  the  remainder  continuing  to  pass 
during  the  interval  between  the.  strokes.  In  the  former  case,  the 
system  is  no  fuller  at  the  end  of  the  stroke  than  at  the  beginning  ; 
in  the  latter  case  there  is  an  accumulation  of  fluid  l)et\veen  the 
pump  and  the  resistance,  and  a  corresponding  distension  of  that 
part  of  the  system,  at  the  close  of  each  stroke — an  accumulation 
and  distension,  however,  which  go  on  diminishing  until  the  next 
stroke  conies.  The  amount  of  fluid  thus  remaining  after  the 
stroke  will  depend  on  the  amount  of  resistance  in  relation  to  the 
force  of  the  stroke,  and  on  the  distensibility  of  the  tubes ;  and 
the  amount  which  passes  the  resistance  before  the  next  stroke  will 
depend  on  the  degree  of  elastic  reaction  of  which  the  tubes  are 
capable.  Thus  if  the  resistance  be  very  considerable  in  relation 
to  the  force  of  the  stroke,  and  the  tubes  very  distensible,  only  a 
small  portion  of  the  fluid  will  pass  the  resistance,  the  greater  part 
remaining  lodged  between  the  pump  and  the  resistance.  If  the 
elastic  reaction  be  great,  the  large  portion  of  this  will  be  passed 
on  through  the  resistance  before  the  next  stroke  comes.  In  other 
words,  the  greater  the  resistance  (in  relation  to  the  force  of  the 
stroke),  and  the  greater  the  elastic  force  brought  into  play,  the  less 
intermittent,  the  more  nearly  continuous,  will  be  the  flow  on  the 
far  side  of  the  resistance. 

If  the  first  stroke  be  succeeded  by  a  second  stroke  before  its 
quantity  of  fluid  has  all  passed  by  the  resistance,  there  will  be  an 
additional  accumulation  of  fluid  on  the  near  side  of  the  resistance, 


I50  OVERFULL   ARTERIES.  [BOOK   I. 

an  additional  distension  of  the  tubes,  an  additional  strain  on  their 
elastic  powers,  and,  in  consequence,  the  flow  between  this  second 
stroke  and  the  third  will  be  even  more  marked  than  that  between 
the  first  and  the  second,  though  all  three  strokes  were  of  the  same 
force,  the  addition  being  due  to  the  extra  amount  of  elastic  force 
called  into  play.  In  fact,  it  is  evident  that,  if  there  be  a  sufficient 
store  of  elastic  power  to  fall  back  upon,  by  continually  repeating 
the  strokes  a  state  of  things  will  be  at  last  arrived  at,  in  which  the 
elastic  force,  called  into  play  by  the  continually  increasing  dis- 
tension of  the  tubes  on  the  near  side  of  the  resistance,  will  be 
sufficient  to  drive  through -the  resistance,  in  the  interval  between 
each  two  strokes,  just  as  much  fluid  as  enters  the  near  end  of  the 
system  at  each  stroke.  In  other  words,  the  elastic  reaction  of  the 
walls  of  the  tubes  will  have  converted  the  intermittent  into  a 
continuous  flow.  The  flow  on  the  far  side  of  the  resistance  is  in 
this  case  not  the  direct  result  of  the  strokes  of  the  pump.  All 
the  force  of  the  pump  is  spent,  first  in  getting  up,  and  afterwards 
in  keeping  up,  the  over-distension  of  the  tubes  on  the  near  side  of 
the  resistance  ;  it  is  the  over-distended  tubes  which  are  the  cause 
of  the  continuous  flow,  by  emptying  themselves  into  the  far  side 
of  the  resistance,  at  such  a  rate,  that  they  discharge  through  the 
resistance  during  a  stroke  and  in  the  succeeding  interval  just  as 
much  as  they  receive  from  the  pump  by  the  stroke  itself 

This  ia  exactl/  what  takes  place  in  the  vascular  system.  The 
friction  in  the  minute  arteries  and  capillaries  presents  a  consider- 
able resistance  to  the  flow  of  blood  through  them  into  the  small 
veins.  In  consequence  of  this  resistance,  the  force  of  the  heart's 
beat  is  spent  in  maintaining  the  whole  of  the  arterial  system  in  a 
state  of  over-distension,  as  indicated  by  the  arterial  pressure.  The 
over-distended  arterial  system  is,  by  the  agency  of  its  elastic  walls, 
continually  emptying  itself  by  overflowing  through  the  capillaries 
into  the  venous  system,  overflowing  at  such  a  rate,  that  just  as 
much  blood  passes  from  the  arteries  to  the  veins  during  each 
systole  and  its  succeeding  diastole  as  enters  the  aorta  at  each 
systole. 

It  cannot  be  too  much  insisted  upon  that  the  whole  arterial 
system  is  overfull.  This  is  what  is  meant  by  the  high  arterial 
pressure.  On  the  other  hand,  the  veins  are  much  less  full.  This 
is  shewn  by  the  low  venous  pressure.  The  overfull  arteries  are 
continually  striving  to  pass  their  surplus  in  a  continuous  stream 
through  the  capillaries  into  the  veins,  so  as  to' bring  both  venous 
and  arterial  pressure  to  the  same  level.  As  continually  the  heart 
by  its  beat  is  keeping  the  arteries  overfull,  and  thus  maintaining 
the  difference  between  the  arterial  and  venous  pressure,  and  thus 


CTIAP.    IV.]         THE   VASCULAR    MECHANISM.  15I 

preserving  the  steady  capillary  stream.  When  the  heart  ceases  to 
beat,  the  arteries  do  succeed  in  emptying  their  surplus  into  the 
veins,  and  when  the  pressure  on  both  sides  of  the  capillaries  is 
thus  equalized,  the  flow  through  the  capillaries  ceases. 

In  the  facts  just  discussed,  it  makes  no*  essential  difference 
whether  the  outflow  on  the  far  side  of  the  resistance  be  an  open 
one,  or  whether,  as  is  the  case  in  the  vascular  system,  the  fluid  be 
returned  to  the  pump,  provided  only  that  the  resistance  offered 
to  that  return  be  sufficiently  small.  We  shall  see,  in  speaking  of 
the  heart,  that  so  far  from  there  being  any  resistance  to  the  flow  of 
blood  from  the  great  veins  into  the  auricle,  the  flow  is  favoured  by 
a  variety  of  circumstances.  We  have  seen  moreover  that,  besides 
the  very  sudden  decrease  in  the  immediate  neighbourhood  of  the 
capillaries,  there  is  in  passing  along  the  whole  vascular  system  from 
the  aorta  to  the  vcnce  cavce  a  gradual  f;ill  of  pressure.  A  little 
consideration  shews  that  this  must  be  the  case.  After  what  has 
been  said  it  is  obvious  that  the  movement  of  the  blood  may  be 
compared  to  that  of  a  body  of  fluid,  driven  by  pressure  from  the 
ventricle  through  the  vessels  to  its  outflow  .in  the  auricle.  Were 
the  pressure  a  continuous  one,  and  were  there  no  capillary  resistance, 
there  would  be  a  gradual  fall  of  pressure,  from  the  part  farthest 
from  the  outfall,  vi/,  the  aorta,  to  the  part  nearest  the  outfall,  viz, 
the  vena2  cavae.  The  introduction  of  the  capillary  resistance  and 
its  attendant  phenomena  gives  rise  to  the  feature  of  a  very  sudden 
and  marked  fall  in  the  capillary  region,  but  leaves  untouched  the 
gradual  character  of  the  fall  in  the  rest  of  the  course,  from  the 
aorta  to  the  minute  arteries,  and  from  the  minute  veins  to  the 
venae  cavce. 

To  recapitulate  :  there  are  three  chief  factors  in  the  mechanics 
of  the  circulation,  (i)  the  force  and  frequency  of  the  heart-beat, 
(2)  the  peripheral  resistance,  (3)  the  elasticity  of  the  arterial  walls. 
These  three  factors,  in  order  to  produce  a  normal  circulation,  must 
be  in  a  certain  relation  to  each  other,  A  disturbance  of  these 
relations  brings  about  abnormal  conditions.  Thus,  if  the  capillary 
resistance  be  reduced  beyond  certain  limits,  while  the  force  and 
frequency  of  the  heart  remain  the  same,  so  much  blood  passes 
through  the  capillaries  at  each  stroke  of  the  heart  that  there  is 
not  suflicient  left  behind  to  distend  the  arteries,  and  bring  their 
elasticity  into  play.  In  this  case  the  intermittence  of  the  arterial 
flow  is  continued  on  into  the  veins.  An  instance  of  this  is  seen  in 
the  experiments  on  the  submaxillary  gland,  where  sometimes  the 
capillary  resistance  in  the  gland  is  so  much  lowered,  that  the  blood 
in  the  veins  of  the  gland  pulsates'.     A   like  result  occurs  when, 

'  See  Book  i.  cap.  i.  sec.  2,  on  the  Secielion  of  the  Digestive  Juices. 


152  THE  VELOCITY   OF   THE   FLOW.  [BOOK  1. 

the  capillary  resistance  remaining  the  same,  the  force  or  frequency 
of  the  heart's  beat  is  lowered.  Thus  the  beats  may  be  so  feeble 
that  at  each,  stroke  no  more  blood,  or  but  little  more,  enters  the 
arterial  system  than  can  pass  through  the  capillaries  before  the 
next  stroke  ;  or  so  infrequent  that  the  whole  quantity  sent  on  by  a 
stroke  has  time  to  escape  before  the  next  stroke  comes.  If,  while 
the  heart's  beat  and  the  resistance  remain  the  same,  the  elasticity 
of  the  arterial  walls  be  reduced,  the  arteries  will  be  unable  to 
expand  sufficiently  to  retain  the  surplus  of  each  stroke  or  to  exert 
sufificient  elastic  reaction  to  carry  forward  the  stream  between  the 
strokes ;  and  in  consequence  more  or  less  intermittence  will 
become  manifest. 

Marey'  states  that  when  fluid  is  driven  through  two  tubes  of  equal 
calibre,  one  elastic  and  the  other  rigid,  with  equal  force  and  like  inter- 
mittence, the  outflow  through  the  elastic  tube  is  greater  than  through 
the  rigid  tube.  This  he  attributes  to  the  fact  that  in  the  rigid  tube  all 
the  friction  falls  in  the  period  of  the  stroke,  when  the  velocity  of  the 
stream  is  greatest,  and  is  therefore  greater  than  in  the  elastic  tube 
where  it  is  distributed  as  well  over  the  interval  between  the  strokes. 
Under  this  view,  the  afrangements  of  the  vascular  system  are  useful, 
not  only  in  causing  the  flow  through  the  capillaries  to  be  continuous, 
and  therefore  best  adapted  for  carrying  on  the  interchange  between 
the  tissues  and  the  blood,  but  also  in  providing  that  the  flow  should  be 
as  large  as  possible. 

Circumstances  determining  the  velocity  of  the  flow. 

We  have  seen  that  the  velocity  of  the  blood-stream  diminishes 
from  the  aorta  to  the  capillaries,  and  increases  from  the  capillaries 
to  the  great  veins.  Thus  in  the  dog  the  velocity  in  the  great 
arteries  may  be  stated  at  from  300  to  500  mm.,  in  the  capillaries 
at  less  than  i  mm.  ("5  to  "75  mm.),  and  in  the  large  veins  at  about 
200  mm.  in  a  sec.  In  fact,  the  greater  part  of  the  time  of  the 
circuit  is  taken  up  in  the  capillary  region.  An  iron  salt,  injected 
into  the  jugular  vein  of  one  side  of  the  neck  of  a  horse,  makes  its 
appearance  in  the  blood  of  the  jugular  vein  of  the  other  side  in 
about  30  seconds. 

Hering's  mean  result  in  the  horse  was  27"6  sees.  In  the  dog 
Vierordt  found  it  to  be  I5'2  sees,;  in  the  rabbit  7  sees. 

Without  laying  too  much  stress  on  this  experiment,  it  may  be 
taken  as  a  fair  indication  of  the  time  in  which  the  whole  circuit  may 
be  completed.  It  takes  about  the  same  time  (see  p.  138)  to  pass 
through  about  20  mm.  of  capillaries.  Hence,  if  any  corpuscle  had 
in  its  circuit  to  pass  throtigh  10  mm.  of  capillaries,  half  the  whole 
time  of  its  journey  would  be  spent  in  the  narrow  channels  of  the 

'  Ann.  d,  Sci.  Nat.  (iv.)  viii.  p.  329. 


CHAT.    IV.J         THE   VASCULAR    MECHANISM.  1 53 

capillaries.  Since,  however,  the  average  length  of  a  capillary  is 
about  "5  mm.,  about  one  second  is  spent  in  the  capillaries.  Inas- 
much as  the  purposes  served  by  the  blood  are  chiefly  carried  out 
in  the  capillaries,  it  is  obviously  of  advantage  that  its  stay  in  them 
should  bo  prolonged. 

T\\c/<er/iianc'nt  variationsin  the  velocityof  the  stream  are  directly 
dependent  on  the  area  of  the  '  bed.'  When  a  fluid  is  flriven  by  a 
uniform  pressure  through  a  narrow  tube  with  an  enlargement  in  the 
middle,  the  velocity  of  the  stream  diminishes  in  the  enlargement, 
but  increases  again  when  the  tube  once  more  narrows.  So  a  river 
slackens  speed  in  a  broad,  but  rushes  on  rapidly  again  when  the 
banks  close  in.  Exactly  in  the  same  way  the  velocity  of  the  blood- 
stream slackens  from  the  aorta  to  the  capillaries  corresponding  with 
the  increased  total  bed,  but  hurries  on  again  as  the  numerous  veins 
are  gathered  into  the  smaller  bed  of  the  vence  cavce.  Tiie  loss  of 
velocity  in  the  capillaries,  as  compared  with  the  arteries,  is  not  due 
to  there  being  so  much  more  friction  in  the  narrow  channels  of  the 
former  than  in  the  wide  canals  of  the  latter.  For  the  peripheral 
resistance  caused  by  the  friction  in  the  capiHaries  and  small  arteries 
is  an  obstacle  not  only  to  the  flow  of  blood  through  these  small 
vessels  where  the  resistance  is  actually  generated,  but  also  to  the 
escape  of  the  blood  from  the  large  into  the  small  arteries,  and 
indeed  from  the  heart  into  the  large  arteries.  It  exerts  its  influence 
along  the  whole  arterial  tract.  And  it  is  obvious  that  if  it  were 
this  peripheral  resistance  which  checked  the  flow  in  the  capillaries, 
there  could  be  no  recovery  of  velocity  along  the  venous  tract.  The 
rapidity  of  the  flow  in  arteries,  capillaries,  and  veins,  is  in  each 
case  determined  by  the  total  sectional  area  of  the  channels.  There 
is,  however,  a  loss  of  velocity  on  the  whole  course.  .-Xt  each 
stroke  as  much  blood  enters  the  right  auricle  as  issues  from  the 
left  ventricle  ;  but  the  sectional  area  of  the  venae  cavce  is  greater 
than  that  of  the  aorta,  so  that  even  if  the  auricle  were  filled  in 
exactly  the  same  time  as  the  ventricle  is  emptied,  the  blood  must 
pass  more  rapidly  through  the  narrow  aorta  than  through  the  broad 
venre  cavse,  in  order  that  the  same  quantity  of  blood  should  pass 
each  in  the  same  time.  The  diastole  of  the  auricle,  however,  is 
distinctly  longer  than  the  systole  of  the  ventricle  ;  the  time  during 
which  the  auricle  is  being  filled  is  greater  than  that  during  which 
the  ventricle  is  being  em|)tied,  and  hence  the  velocityof  the  venous 
flow  into  the  auricle  must  be  still  less  than  that  of  the  arterial 
blood  in  the  commencing  aorta. 

The  icmpora7y  variations  of  the  velocity  of  the  stream  in  any 
given  channel,  and  these  we  have  already  (p.  147)  seen  to  be  very 
considerable  in  the  case  of  the  arteries  at  least,  are  dependent  on 


154  "^HE   HEART.  [BOOK  I. 

a  variety  of  circumstances.  In  a  tube  of  constant  calibre,  the 
velocity  with  which  fluid  flows  from  one  point  to  another,  for 
instance  from  the  point  a  to  the  point  b,  will  be  in  main  dependent 
on  the  difii'erence  between  the  pressures  existing  at  a  and  b.  The 
lower  the  pressure  at  b  as  compared  with  a  the  greater  the  rapidity 
with  which  the  fluid  flows  from  a  to  b.  And  temporary  variations 
of  pressures  form  undoubtedly  the  main  cause  of  the  temporary 
variations  observable  in  the  velocity  of  the  arterial  flow.  Thus 
with  each  systole  of  the  ventricle  there  is  an  increase  of  velocity 
in  the  whole  arterial  flow  followed  by  a  diminution  during  the 
diastole.  So  also  if  the  peripheral  resistance  in  the  minute  arteries 
into  which  a  larger  artery  divides  be  suddenly  lowered  (by  the 
action  of  vaso-motor  nerves,  in  a  manner  which  we  shall  presently 
discuss),  without  the  calibre  of  the  larger  artery  itself  being  changed, 
the  pressure  on  the  distal  (peripheral)  side  of  the  artery  may  be 
much  diminished,  while  the  pressure  on  the  proximal  (cardiac) 
side  remains  at  first  unaltered ;  and  this  would  necessarily  cause 
an  increase  in  the  rapidity  of  the  stream  through  that  artery.  But, 
as  we  shall  see  later  on,  from  the  complications  of  the  vascular 
machinery  such  problems  as  these  become  very  intricate  ;  and 
the  results  of  observations  on  variations  in  arterial  velocity  are 
not  altogether  intelligible.  It  has  been  suggested  that  varying 
conditions  of  the  blood,  by  aff'ecting  the  amount  of  adhesion 
between  the  blood  and  the  walls  of  the  vessels,  may  be  an 
important  factor  in  determining  the  variations  in  the  velocity  of 
the  stream^ 

Sec.  2.     The  Heart. 

The  heart  is  a  pump,  the  motive  power  of  which  is  supplied 
by  the  contraction  of  its  muscular  fibres.  Its  action  consequently 
presents  problems  which  are  pardy  mechanical,  and  partly  vital. 
Regarded  as  a  pump,  its  effects  are  determined  by  the  frequency 
of  the  beats,  by  the  force  of  each  beat,  by  the  character  of  each 
beat — whether,  for  instance,  slow  and  lingering,  or  sudden  and 
sharp — and  by  the  quantity  of  fluid  ejected  at  each  beat.  Hence, 
with  a  given  frequency,  force,  and  character  of  beat,  and  a  given 
quantity  ejected  at  each  beat,  the  problems  which  have  to  be  dealt 
with  are  for  the  most  part  mechanical.  The  vital  problems  are 
chiefly  connected  with  the  causes  which  determine  the  frequency, 
force,  and  character  of  the  beat.  The  quantity  ejected  at  each 
beat  is  governed  more  by  the  state  of  the  rest  of  the  bod}',  than 
by  that  of  the  heart  itself. 

'  Ludwig  and  Dogiel,  Ludwig's  Arbeiten,  1867.     Cf.  also  Ewald,  Archiv  f, 
Anat.  u.  Phys.,  1877,  p.  208. 


CHAP.    IV.J         THE   VASCULAR    MECHANISM.  I55 

The  Phenomena  of  the  Normal  Beat. 

The  visible  movements.  When  the  chest  of  a  mammal 
is  opened  and  artificial  respiration  kept  up,  a  complete  beat  of 
the  whole  heart,  or  cardiac  cycle,  may  be  observed  to  take  place 
as  follows. 

The  great  veins,  inferior  and  superior  venae  cavae  and  pul- 
monary veins,  are  seen,  while  full  of  blood,  to  contract  in  the 
neiglibourhood  of  the  heart :  the  contraction  runs  in  a  peristaltic 
wave  towards  the  auricles,  increasing  in  intensity  as  it  goes. 
Arrived  at  tlie  auricles,  which  are  then  full  of  blood,  the  wave 
suddenly  spreads,  at  a  rate  too  rapid  to  be  fairly  judged  by  the 
eye,  over  the  whole  of  those  organs,  which  accordingly  contract 
with  a  sudden  sharp  systole.  In  the  systole,  the  walls  of  the 
auricles  press  towards  the  auriculo-vontricular  orifices,  and  the 
auricular  appendages  are  drawn  inwards,  becoming  smaller  and 
paler.  During  the  auricular  systole,  the  ventricles  may  be  seen  to 
become  more  and  more  turgid.  Then  follows,  as  it  were  imme- 
diately, the  ventricular  systole,  during  which  the  ventricles  become 
shorter  and  thicker.  Held  between  the  fingers  they  are  felt  to 
become  tense  and  hard.  As  the  systole  progresses,  the  aorta  and 
pulmonary  arteries  are  seen  to  expand  and  elongate,  and  the  heart 
to  twist  slightly  on  its  long  axis,  so  that,  while  the  base  is  fixed  by 
the  great  arteries,  the  apex  moves  from  the  left  and  behind 
towards  the  front  and  right ;  hence  more  of  the  left  ventricle 
becomes  displayed.  As  the  systole  gives  way  to  the  succeeding 
pause  or  diastole,  the  ventricles  flatten  and  elongate,  the  aorta  and 
pulmonary  artery  contract  and  shorten,  the  heart  turns  back 
towards  the  left,  and  thus  the  cycle  is  completed. 

More  exact  observation  shews,  as  regards  the  change  of  form 
of  the  ventricular  portion,  that  this,  during  diastole,  has  somewhat 
the  shape  of  a  flattened  cone,  with  an  ellipse,  having  its  long 
diameter  from  right  to  left,  as  a  base,  but  during  the  systole 
becomes  a  shorter,  more  reguLar,  cone,  with  a  circle  for  its  base, 
having  lessened  chiefly  in  its  longitudinal  and  right-to-left 
diameters,  and  slightly  only  in  its  antero-posterior  diameter. 
Accor(Hng  to  Kurschner',  the  circumference  of  the  base  of  the 
ventricle  is  absolutely  increased  during  the  systole;  a  tape  placed 
round  the  base  becomes  tense  at  the  commencement  of  the 
systole,  while  the  cavity  is  still  lull  of  blood. 

When  the  chest  is  opened,  the  heart  is  deprived  of  its  natural 
supports ;  and  consequently,  under  such  circumstances,  its  change 
of  position  during  the  systole  cannot  be  properly  studied.  For  it 
•  Wagner's  Handworterbuch,  Art.  Herzthdiigkeit. 


156  MOVEMENTS   OF   THE   HEART.  [BOOK   I. 

must  be  remembered  that  the  heart,  closely  covered  by  the  peri 
cardium,  lies  immediately  under  the  sternum  and  ribs,  there  being 
between  them  nothing  more  than  a  small  amount  of  mediastinal 
connective  tissue,  and  rests  on  the  slope  of  the  diaphragm  below, 
with  the  lungs  on  either  side.  If,  in  the  unopened  chest  of  a 
rabbit  or  dog,  three  needles  be  inserted  through  the  chest-wall  so 
that  their  points  are  plunged  into  the  substance  of  the  ventricle, 
one  (B)  at  the  base,  close  to  the  auricles,  another  (A)  through  the 
apex,  and  a  third  (M)  at  about  the  middle  of  the  ventricle,  all 
three  needles  will  be  observed  to  move  at  each  beat  of  the  heart. 
The  head  of  B  will  move  suddenly  upwards,  shewing  that  the 
point  of  the  needle  plunged  into  the  ventricle  moves  downwards, 
whereas  A  will  only  quiver,  and  move  neither  distinctly  upwards 
nor  downwards.  M  will  move  upwards  (and  therefore  its  point 
downwards),  but  not  to  the  same  extent  as  B.  The  nearer  to  B, 
M  is,  the  more  it  moves  :  the  nearer  to  A,  the  less.  Thus,  while 
during  the  beat,  the  base  (B)  moves  downwards  as  the  result  of 
the  contraction  (and  longitudinal  shortening)  of  the  ventricle,  the 
apex  (A)  does  not  change  its  place,  the  shortening  of  the  ventricle 
itself  being  compensated  by  the  lengthening  of  the  great  arteries. 
The  middle  of  the  ventricle  moves  downwards  more  than  the  apex, 
but  less  than  the  extreme  base.  After  the  death  of  the  animal, 
the  needles,  if  properly  inserted  at  first,  perpendicular  to  the  chest, 
will  be  found  with  all  their  heads  directed  downwards,  indicating 
that  the  whole  ventricle  has  been  drawn  up  by  the  contraction  of 
the  empty  aorta  and  pulmonary  artery. 

Cardiac  Impulse.  If  the  hand  be  placed  on  the  chest,  a 
shock  or  impulse  will  be  felt  at  each  beat,  and  on  examination 
this  impulse,  'cardiac  impulse,'  will  be  found  to  be  synchronous 
with  the  systole  of  the  ventricle.  In  man,  the  cardiac  impulse 
may  be  most  distinctly  felt  in  the  fifth  costal  interspace,  about  an 
inch  below  and  a  Uttle  to  the  median  side  of  the  left  nipple.  The 
same  impulse  may  be  felt  in  an  animal  by  making  an  incision 
through  the  diaphragm  from  the  abdomen,  and  placing  the  finger 
between  the  chest-wall  and  the  apex.  It^then  can  be  distinctly 
recognized  as  the  result  of  the  hardening  of  the  ventricle  during 
the  systole.  And  the  impulse  which  is  felt  on  the  outside  of  the 
chest  is  the  same  hardening  of  tfie  stationary  portion  of  the 
ventricle  in  contact  with  the  chest-wall,  transmitted  through  the 
chest-wall  to  the  finger.  In  its  flaccid  state,  during  diastole,  the 
apex  is  (in  a  standing  position  at  least)  here  in  contact  with  the 
chest-wall,  lying  between  it  and  the  tolerably  resistant  diaphragm. 
During  the  systole,  while  occupying,  as  we  have  seen,  the  same 


CHAP.    IV.]        TIIK   VASCULAR    MECHANISM.  157 

position,  it  suddenly  grows  tense  and  hard.  The  ventricles,  in 
executing  their  systole,  have  to  contract  against  resistance.  They 
have  to  produce  wiiiiin  their  cavities,  tensions  greater  tlian  those 
in  the  aorta  and  pulmonary  arteries,  respectively.  This  is,  in 
fact,  the  object  of  tho  systole.  Hence,  during  the  swift  systole, 
the  ventricular  portion  of  the  heart  becomes  suddenly  tense,  just 
as  a  bladder  full  of  fluid  would  become  tense  and  hard  when 
forcibly  squeezed.  The  sudden  onset  of  this  hardness  gives  an 
impulse  or  shock  both  to  the  chest-wall  and  to  the  diaphragm, 
which  may  be  felt  readily  both  on  the  chest- wall,  and  also  through 
the  diajjhragm  when  the  abdomen  is  opened,  and  the  finger 
inserted.  If  the  modification  of  the  sphygmograph  (see  section 
on  Pulse),  called  the  cardiograph,  be  placed  on  the  spot  where 
the  iminilse  is  felt  most  strongly,  the  lever  is  seen  to  be  raised 
during  the  systole  of  the  ventricles,  and  to  fall  again  as  the 
systole  passes  away,  very  much  as  if  it  were  placed  on  the  heart 
directly.  A  tracing  may  thus  be  obtained  (Fig.  28),  of  which  we 
shall  have  to  speak  more  fully  immediately.  If  the  button  of  the 
le\cr  be  placed,  not  on  the  exact  spot  of  the  impulse,  but  at  a 
little  distance  from  it,  the  lever  will  be  depressed  during  the  systole. 
While  at  the  spot  of  impulse  itself  the  contact  of  the  ventricle  is 
increased  during  systole,  away  from  the  spot  the  ventricle  retires 
from  the  chest- wall  (by  the  diminution  of  its  right-to-left  diameter), 
and  hence,  by  tiie  mediastinal  attachments  of  the  pericardium, 
draws  the  chest-wall  after  it. 

Endo-cardiac  pressure.  In  order  to  study  more  fully  the 
changes  going  on  in  tiie  heart  during  the  cardiac  cycle,  it  becomes 
necessary  to  know  something  of  what  is  taking  place  in  the 
interior  of  the  cavities  of  the  heart.  Chauveau  and  Marey',  by 
introducing  into  the  right  auricle  and  ventricle  respectively  of  the 
horse,  tlirough  the  jugular  vein,  small  elastic  bags,  each  com- 
municating with  a  recording  tambour,  were  enabled  to  take 
simultaneous  tracings  of  all  the  changes  of  pressure  occurring  in 
the  two  cavities.  These  results"are  embodied  in  Fig.  28,  of  which 
the  upper  curve  represents  the  changes  of  pressure  in  the  auricle, 
the  middle  curve  the  changes  of  pressure  in  the  ventricle,  and  the 
lower  curve  the  cardiographic  tracing  of  the  cardiac  implilse.  All 
these  curves  were  taken  simultaneously  on  the  same  recording 
surface. 

Method.  A  tube  of  appropri  Uc  curvature  is  furnished  witli  two 
small  clastic  bags,  one  at  the  extreme  end  and  the  other  at  such  a 
distance  that  when  the  former  is  within  the  cavity  of  the  ventricle  the 

'   Marcy,  Cirrulation  dtt  Sau^. 


158 


ENDO-CARDIAC   PRESSURE. 


[BOOK  I. 


Fig.  28.  Tracing  of  the  Variations  of  Pressure  in  the  right  Auricle  and  Ven 
TRicLE,  AND  OF  THE  Cardiac  IMPULSE  IN  THE  HoRSE.  (After  Marey.)  To  be  read 
from  left  to  right'. 

The  upper  curve  represents  the  variation  of  pressure  within  the  auricle,  the  middle  curve 
the  variations  of  pressure  within  the  ventricle  ;  these  two  therefore  illustrate  changes  taking 
place  in  the  interior  of  the  heart.  The  lower  curve  represents  the  variations  of  pressure  trans- 
mitted to  a  lever  outside  the  chest  and  constituting  the  cardiac  impulse.  A  complete  cardiac 
cycle,  beginning  at  the  close  of  the  ventricular  systole,  is  comprised  between  the  thick  vertical 
lines  I.  and  II.  The  thin  vertical  lines  represent  tenths  of  a  second,  a,  the  gradual  filling  of 
the  auricle  and  ventricle  ;  b,  the  auricular  sysfole  ;  c,  the  ventricular  systole  ;  d,  oscillations  of 
pressure,  interpreted  by  Marey  as  caused  by  vibrations  of  the  auriculo-ventricular  valves ;  * 
probably  marks  the  closing  of  the  semilunar  valves. 

latter  is  in  the  cavity  of  the  auricle.  Each  bag  (Fig.  29  A)  communi- 
cates by  a  separate  air-tight  tube  with  an  air-tight  tambour  (Fig.  29  B) 
on  which  a  lever  rests  so  that  any  pressure  on  either  bag  is  communi- 
cated to  the  cavity  of  its  respective  tambour,  the  lever  of  which  is  raised 
in  proportion.  The  writing  points  of  all  three  levers  are  brought  to 
bear  on  the  same  recording  surface  exactly  underneath  each  other. 
The  tube  is  carefully  introduced  through  the  right  jugular  vein  into 
the  right  side  of  the  heart  until  the  lower  (ventricular)  bag  is  fairly  in 
the  cavity  of  the  right  ventricle,  and  consequently  the  upper  (auricular) 
bag  in  the  cavity  of  the  right  auricle.  Changes  of  pressure  in  either 
cavity  then  cause  movements  of  the  corresponding  lever.  When  the 
pressure  is  increased  for  instance  in  the  auricle,  the  auricular  lever  is 
raised  and  describes  on  the  recording  surface,  an  ascending  curve  ; 

*  It  must  be  remembered  that  the  curves  in  the  diagram  are  intended  merely 
to  illustrate  the  variations  of  pressure  occurring  at  difterent  times  in  the  same 
chamber,  or  to  shew  what  changes  in  the  one  chamber  are  coincident  in  point 
of  time  with  changes  in  the  other.  They  in  no  way  indicate  the  ainount  oj 
pressure  in  the  auricle  as  compared  with  that  in  the  ventricle. 


CHAP.    IV. 


Till?  VASCULAR    MKCHANISM. 


'59 


wlicn  the  pressure  is  taken  off  the  curve  descends  ;  and  so  also  with 
tlic  ventricle. 

A  complete  cardiac  cycle  is  comprised  between  the  vertical 
lines  I  and  II,  Fig.  28.  The  recording  surface  was  travelling  at 
such  a  rate  that  the  intervals  between  any  two  of  the  thin  vertical 
lines  corresponds  to  one-tenth  of  a  second.  Hence  in  this  case 
the  whole  cardiac  cycle  occupied  about  Yof'"'s  of  a  second.  Any 
point  in  the  cycle  might  of  course  be  taken  as  its  commencement. 
In  the  figure,  the  cycle  is  supposed  to  begin  shortly  after  the  end 
of  the  ventricular  systole,  and  the  beginning  of  the  diastole. 


Fig.  29.    Marey's  Tambour,  with  Cardiac  Sound. 

The  n;r.i5;n^i"!ff  fj.'^'^'^''"'n^°""1-  ^""^  ?^  "'"^7^.  "^ed  for  exploration  of  the  left  ventricle. 

worL-'^^V.^  n-       '""''""'''  ?'  '^^  '"'', '"  °f  ''""  india-rubber  stretched  over  an  open  frame- 

^vUv  whir"hT    7'"'^'?"'  ^^°r  ""''  '"■"'°*-     '^'"=  '°"e  tube  i  senes  to  introduce  it  into  the 
cavity  which  it  is  desired  to  explore. 

inAi^'^.J.^^^l"'^""''-      1^"  """",'  ^hambcrw  is  covered  in  .in  .-lir-tight  ni.inner  with  the 
india-rubber  <:.  bearing  a  thin  metal  plate  ,«'  to  which  is  att.-iched  the  lever  /  moving  on  the 

"rcivitv  nf  rh":  Jl^l^'u'^^^l  '"^  ■  t"''"  I"  =°""«=^'  'h-^  in=<=rior  of  the  tambour  ti.hcr  with 
nected  wK V^n        ^  ^  °''  V'^  '''">'  "',''"  "^"y-     Supposing  ih.at  the  tube  /  were  con- 

^?m  of  t  le  lever  wriTr  ""=*^^.""  "  V°' '4  ""'^'^  'h^  roof  of  the  tambour  to  rise  and  the 
point  ol  the  lever  would  be  proportionately  niiscd. 

On  examining  the  throe  curves  we  see,  at  a,  a  steady  rise  of 
the  auncular,  accompanied  by  similar  gradual  ascents  of  the 
ventricular  and  also  of  the  cardiograi)h  lever.  These  may  be 
interpreted  as  indicating  that  the  blood  is  pouring  from  the  great 


l6o  ENDO-CARDIAC   PRESSURE.  [BOOK   I. 

veins  into  the  auricle,  increasing  the  pressure  there,  and  at  the 
same  time  passing  on  into  the  ventricle,-  increasing  also  the 
internal  pressure  there,  a',  and  also  by  distending  the  ventricle, 
causing  it  to  press  somewhat  on  the  chest-wall  and  thus  to  raise 
the  cardiograph  lever,  a  .  This  continues  for  about  yV^^is  of  a 
second,  and  is  then  followed  by  the  sudden  rise  of  auricular 
pressure  b  due  to  the  auricular  systole,  followed  by  a  sudden  fall 
as  the  blood  escapes  into  the  ventricle.  The  sudden  entrance  of 
blood  into  the  ventricle  causes  a  sudden  increase  of  the  pressure 
in  the  ventricle  as  indicated  by  the  ventricular  lever  b',  and  a 
sudden  increase  in  the  pressure  on  the  chest-wall  b" .  The 
auricular  systole  is  followed  immediately  by  the  sudden  strong 
ventricular  systole  c' ,  the  pressure  rising  very  abruptly.  Owing  to 
the  presence  of  the  tricuspid  valves,  this  increase  of  pressure  is 
kept  off  the  auricle  altogether ;  but  the  chest-wall,  as  shewn  by  the 
tracing  at  c,  feels  the  sudden  increase  of  the  pressure  of  the 
ventricle  against  it.  The  ventricular  pressure  lasts  for  some  time, 
gradually  declining,  and  then  suddenly  falls.  This  may  be 
interpreted  as  indicating  that  the  systole  rapidly  reaches  a 
maximum,  maintains  that  maximum  with  a  slight  decline  only  for 
some  little  time,  and  then  suddenly  ceases.  The  oscillations 
during  the  maximum,  as  seen  at  d\  and  also  manifest  in  the 
auricular  curve,  and  in  the  impulse  curve  at  d'\  are  interpreted  by 
Marey  as  due  to  vibrations  of  the  tricuspid  valves,  but  their 
causation  is  at  present  by  no  means  clear.  At  the  end  of  the 
ventricular  systole,  the  descent  of  the  lever  is  broken  by  a  slight 
rise  at  e ,  visible  also  in  the  auricle  at  e,  and  even  in  the  impulse 
curve  at  e".  This  is  interpreted  by  Marey  as  indicating  the 
closure  of  the  semilunar  valves.  After  this  slight  rise,  the 
ventricular  curve  and  the  impulse  curve  fall  to  their  lowest  points, 
while  the  auricle  is  already  beginning  to  fill ;  and  the  cardiac  cycle 
begins  anew. 

Thus  of  the  whole  period  of  a  beat,  the  largest  fraction  is  that 
of  the  diastole,  or  'passive  interval,'  i.e.  of  the  interval  between 
the  end  of  the  ventricular  and  the  commencement  of  the  auricular 
systole.  The  next  largest  is  that  of  the  ventricular  systole,  and 
the  smallest  that  of  the  auricular  systole.  The  duration  of  the 
diastole  is  usually  given  as  4  of  the  whole  period,  that  of  the 
whole  systole  being  f ,  of  which  far  the  greatest  part  is  taken  up 
by  the  ventricle  ;  but  in  these  measurements  the  systole  is  sup- 
posed to  end  with  the  cessation  of  the  ventricle's  contraction  and 
not  to  include  its  relaxation.  Bonders  found  the  ventricular 
systole,  as  determined  by  the  time  elapsing  between  the  com- 
mencement of  the  first  and  of  the  second  sounds,  and  therefore 


CHAP.    IV.]         THE   VASCULAR    MECHANISM.  l6l 

including  the  relaxation  as  well  as  the  contraction  of  the 
ventricular  fibres,  to  occupy  on  the  average  •301  to  '327  sec,  or 
40  to  46  p.c.  of  the  whole  period.  1  .andois '  gives  the  following 
measurements,  the  whole  cycle  lasting  ri3o  sec. 

Mean  Duratii  n  of  auricular  systole  to  begin- 
ning of  ventricular  sy^iole    '177  sec.     "V 

Me.m  Durat  on  of  veniricular  c  ntraciion  ...   "192    .,^     |     '451  sec.  =  systole  of  the  heart  as 


Mean  iturali-n  ■  f  mainnnante  of    c  ntrac-  |     [  usually  understood. 


>IcanT)vrr.ui"nfVo!u  beginning  orreVaxallo^  "(  346    ..     =  systole  of  ^%^mricle^ as 

t  >  closure  of  semilunar  valve "072    ,,  /  ""  ""^''  ""   ""^ 

Mean   Duration  of  closure  o.'  valves  to  be- 


ginning  of  p..use -200.,        (     '^79..     =  diastole  of    ihe  heart 

Mean  Durat.un  .f  remainder  of  cycle 407    „       )  ^  "^"^^'^  ""J^^'o*^*^- 

I '130 

The  proportions  however  are  not  fixed,  but  vary  somewhat. 
Practically  speaking,  there  is  no  interval  between  the  auricular  and 
ventricular  systole,  the  latter  being  separated  from  the  former  by  a 
fraction  of  time  which  is  almost  inap])reciable. 

Although  the  instrument  of  Cliauveau  and  Marey  may  be 
experimentally  graduated  and  thus  used  to  measure  the  amount  of 
pressure  in  the  several  cavities  of  the  heart,  more  exact  results 
may  be  gained  by  passing  through  the  jugular  vein  into  the  right 
auricle  and  thence  into  the  right  ventricle,  or  through  the  carotid 
artery  into  the  left  ventricle,  a  tube  opened  at  the  end  introduced 
into  the  heart  and  connected  at  the  other  end  with  a  manometer. 
Variations  of  pressure  in  the  cardiac  cavities  are  thus  transmitted 
directly  to  the  mercury  column  of  the  manometer  in  the  same 
way  as  those  of  an  artery  when  arterial  pressure  is  measured. 
Further,  by  using  maximum  and  minimum  manometers,  the  maxi- 
mum and  minimum  pressures  of  the  several  cavities  may  be 
determined.  In  this  way  in  the  dog  a  maximum  pressure  has  been 
observed  in  the  left  ventricle  of  about  140  mm.  (mercuiy),  in  the 
right  ventricle  of  about  60  mm.,  and  in  the  right  auricle  of  about 
20  mm.  During  the  diastole,  or  rather  immediately  after  the 
systole,  the  pressure  in  the  two  ventricles  and  even  in  the  auricle 
may  become  negative,  i.e.  sink  below  the  pressure  of  the  atmo- 
sphere. In  the  left  ventricle  (of  the  dog)  a  minimum  pressure 
varying  from  —  52  to  —  20  mm.  may  be  reachetl,  the  nnnimum 
ol<he  right  ventricle  being  from  —  17  to  —  16  mm.,  and  of  the 
right  auricle  from  —  12  to  —  7  mm.^  Part  of  tliis  diminution  of 
pressure  in  the  cardiac  cavities  may  be  due,  as  will  be  explained 
in  a  later  part  of  this  work,  to  the  aspiration  of  the  thorax  in  the 

'  C/>f.  nicJ.  Wiss.  1866,  p.  179. 

'  These  numbers  are  to  be  con>iclercd  merely  as  instances  which  have  been 
ob.^crved,  and  not  as  averages  drawn  from  a  large  number  of  ra^es. 

F.  \\  II 


1 62 


ENDO-CARDIAC   PRESSURE. 


[book  I. 


respiratory  movements.  But  even  when  the  thorax  is  opened,  and 
artificial  respiration  kept  up,  under  which  circumstances  no  such 
aspiration  takes  place,  the  pressure  in  the  left  ventricle  may  sink 
as  low  as  —  24  mm.  The  occurrence  of  so  marked  a  negative 
pressure  in  the  ventricular  cavities  shews  that  these  cavities,  but 
especially  the  left,  exert  a  considerable  suction  power  during 
diastole.  The  heart  in  fact  appears  to  act  not  only  as  a  force- 
pump  but  also  as  a  suction-pump,  thereby  aiding  to  refill  itself 
with  blood  at  each  stroke  ;  the  suction  of  the  left  ventricle  besides 
greatly  assisting  the  circulation  through  the  lungs. 

The  results  given  above  are  those  of  Goltz  and  Gaule'.  The 
principle  of  their  maximum  manometer,  Fig.  30,  consists  in  the 
introduction  into  the  tube  leading  from  the  heart  to  the  mercury  column, 


Fig.  30.  The  Maximum  Manometer  of  Goltz  and  Gaule. 
At  «  a  connection  is  made  with  the  tube  leading  to  the  heart.  When  the  screw  damp  k  is 
closed,  the  valve  v  comes  into  action,  and  the  instrument,  in  the  position  of  the  valve  shewn 
in  the_  figure,  is  a  maximum  manometer.  By  reversing  the  direction  of  v  it  is  converted  in'o 
a  minimum  manometer.  When  k  is  opened,  the  variations  of  pressure  are  conveyed  along  a, 
and  the  instrument  then  acts  like  an  ordinary  manometer. 

of  a  (modified  cup-and-ball)  valve,  opening,  like  the  aortic  semilunar 
valves,  easily  from  the  heart,  but  closing  firmly  when  fluid  attempts  to 
return  to  the  heart.  By  reversing  the  direction  of  the  valve,  the 
manometer  is  converted  from  a  maximum  into  a  minimum.     When  an 

'  Pfliiger's  Archiv,  xvil.  (1878)  p.  loo. 


CHAT.    IV.]  THE   VASCULAR    MKCIIAXISM.  163 

ordinary  manometer  is  connected  with  a  ventricular  cavity,  the  move- 
ments of  the  mercury  do  not  follow  exactly  the  rapid  variations  of 
pressure  of  the  cavity,  and  the  heif,^ht  of  the  column  fails  to  indicate 
both  the  highest  and  the  lowest  pressures.  Hence,  as  Fick'  observed, 
especially  with  rapidly  bcaiing  hearts  the  pressure  in  the  ventricle  may 
appear  to  be  less  than  that  in  the  aorta.  Thus  in  Fig.  31,  when  the 
tube  is  slipped  at  b  from  the  aorta  into  the  left  ventricle,  und  the 
manometer  at  the  same  time  converted  from  a  maximum  into  an 
ordinary  manometer,  the  curve  of  the  ventricular  pressure  falls  below 


Fic.  31.    Curve  of  Pressure  in  Aorta   and   Left  Ventricle  of   the  Dog.  taken 
WITH  THE  Manometer  of  Goltz  and  Gaule.     (To  be  read  from  left  to  right.) 

Before  a.  ihe  manometer  is  working-as  an  ordina'-\'  manometer  c  nnected  with  the  aorta,  and 
the  curve  shews  both  the  heart-beats  and  the  respiraiory  curves,  the  latter  str  ngly  marked. 
At  a  the  manometer  is  made  maximum  by  clamping  k  (Kig.  30),  and  the  curve  then 
shews  the  straight  l.ne  of  the  maximum  aortic  pressure.  At  b  the  tube  c  f  the  manometer  is 
slipped  I'own  into  the  left  ventricle,  and  at  the  same  lime  convcr.?d  into  an  ordinary  mano- 
meter by  opening:  k  ;  the  hcart-btais,  marked  on  the  respiratory  curves,  are  seen  at  a  level 
lower  than  '.ha;  uf  the  aor;ic  pressure.  But  when  at  c  the  nianonuter  is  changed  back  again 
into  a  maxinm  n  manometer  the  pressure  rises  at  each  heart -heat  until  a  maximum  is  reached, 
which  is  .as  high,  ani  in  this  case,  probably  on  account  ot^  the  heart  beating  more  strongly, 
very  distinctly  higher  than  the  aortic  ma.ximum. 

that  of  the  aorta.  As  soon  however  as  the  manometer  is  converted, 
as  at  c,  into  a  maximum  manometer,  it  becomes  evident  that  the 
maximum  pressure  in  the  left  ventricle  is  as  high  (in  the  figure  slightly 
higher)  as  that  in  the  aorta.  Goltz  ani  Gaule  regard  the  negative 
pressure  of  diastole  as  due  to  the  elasticity  of  the  ventri-iilar  walls, 
by  virtue  of  which  these  structures,  pressed  closely  in  contact  during 
the  latter  part  of  the  systole,  spring  asunder  with  con>idcrablc  energy 
when  the  relaxation  of  the  muscular  fibres  begins  ;  Briicke  however 

•  ArbcHcn  a.  d.  physio'og.  Laborator.  d.  W'ui-zburger  Hochschule,  I.ief.  II. 
(1S73)  p.  '83- 

I  I  —2 


164  THE   VALVES   OF   THE   HEART.  [BOOK   1. 

has  given  another  explanation  of  the  dilation  of  the  ventricular  cavities, 
see  p.  165.  Marey^  had  previously,  by  a  graduation  of  the  instrument 
described  above,  determined  the  pressure  in  the  horse  to  be  in  the  left' 
ventricle  about  200  mm.,  in  the  right  ventricle  only  about  25  mm., 
while  that  of  the  right  auricle  he  estimated  at  not  more  than  2  or  3 
mm.  He  too  believed  the  pressure  in  both  ventricles  to  become 
negative  after  systole,  especially  in  the  case  of  the  left  side.  Fick^ 
had  also  by  introducing  a  tube  in  the  several  cavities  of  the  heait  and 
making  use  of  his  spring  manometer  (see  Fig.  25,  p.  142)  arrived  at 
results  which  agree  with  those  of  Goltz  and  Gaule  in  so  f;tr  as  the 
ventricular  cavities  are  concerned.  He  found  in  the  dog  the  pressure 
to  be  in  the  right  ventricle  from  20  to  40  mm.,  in  the  left  ventricle 
about  140  mm.  According  to  him,  however,  the  pressure  in  the 
right  auricle  is  nearly  constant,  varying  not  more  than  2  mm.  from 
the  base  line  of  atmospheric  pressure,  and  remaining  for  the  most 
part  slightly  below.  This  Fick  gives  as  a  support  to  the  view  held 
by  him  that  the  proper  function  of  the  auricles  is  to  equalize  and 
keep  constant  the  pressure  at  the  entrance  of  the  great  veins  into 
the  heart. 

The  Mechanism  of  the    Valves. 

The  auriculo-ventricular  valves  present  no  difficulty.  As 
the  blood  is  being  driven  by  the  auricular  systole  into  the  ventricle, 
a  reflux  current  is  set  up,  by  which  the  blood,  passing  along  the 
sides  of  the  ventricle,  gets  between  them  and  the  flaps  of  the 
valve  (whether  tricuspid  or  mitral).  As  the  pressure  of  the 
auricular  systole  diminishes,  the  same  reflux  current  floats  the  flaps 
up,  until  at  the  extreme  end  of  the  systole  thev  meet,  and  thus  the 
orifice  is  at  once  and  firmly  closed,  at  the  very  beginning  of  the 
ventricular  beat.  The  increasing  intraventricular  pressure  serves 
only  to  render  the  valve  more  and  more  tense,  and  in  consequence 
more  secure,  the  chordae  tendineae  and  the  contraction  of  the 
papillary  muscles  (simultaneous  with  that  of  the  rest  of  the  ven- 
tricular walls)  preventing  the  valve  from"  being  inverted  into  the 
auricle,  and  indeed  keeping  the  valvular  sheet  convex  to  the 
ventricular  cavity,  by  which  means  the  complete  emptying  of  the 
ventricle  is  more  fully  effected.  Since  the  same  papillary  muscle 
is  in  many  cases  connected  by  chordae  with  the  adjacent  edges  of 
two  flaps,  its  contraction  also  serves  to  keep  these  flaps  in  more 
complete  apposition.  Moreover  the  extreme  borders  of  the  valves, 
outside  the  attachments  of  the  chordae,  are  excessively  thin,  so 
"that  when  the  valve  is  closed,  these  thin  portions  are  pressed  flat 
together  back  to  back ;  hence  while  the  tougher  central  parts  of 
the  valves  bear  the  force  of  the  ventricular  systole,  the  opposed 

'  Op.  cit.  =  Op.  cit. 


CHAF.    IV.]  THE   VASCULAR    MECHANISM.  16$ 

thin   membranous  edges,  pressed  togethtr   by   the   blood,   more 
completely  secure  the  closure  of  the  orifice. 

The  semilunar  valves  are,  during  the  ventricular  systole, 
pressed  outward;  towards  the  arterial  walls,  and  thus  offer  no 
obstacle  to  the  escape  of  blood  from  the  cavities  of  the  ventricles. 
As  the  ventricular  systole  diminishes,  a  reflux  current  partially  fills 
the  pockets,  and  tends  to  carry  their  free  margins  towards  the 
middle  of  the  tube.  Upon  the  sudden  close  of  the  systole,  the 
elastic  rebound  of  the  arterial  walls  causes  a  sudden  current  back- 
wards, which,  filling  and  distending  the  pockets,  causes  their  free 
margins  to  come  into  complete  and  firm  contact,  and  thus  entirely 
blocks  the  way.  The  corpora  Arantii  meet  in  the  centre,  and  the 
thin  membranous  festoons  or  lunulce  are  brought  into  exact  ap- 
position. As  in  the  tricuspid  valves,  so  here,  while  the  pressure 
of  the  blood  is  borne  by  the  tougher  bodies  of  the  several  valves, 
each  two  thin  adjacent  lunulse,  pressed  together  by  tl>€  blood 
acting  on  both  sides  of  them,  are  kept  in  complete  contact,  without 
any  strain  being  put  upon  them  ;  in  this  way  the  orifice  is  closed 
in  a  most  efficient  manner. 

An  ingenious  view  has  been  put  fonvard  by  Brucke'  concerning 
the  action  of  the  semilunar  valves.  He  maintains  that  during  the  ven- 
tricular systole,  the  flaps  are  pressed  back  flat  against  the  arterial  walls, 
and  in  the  case  of  the  aorta  completely  cover  up  the  orifices  of  the 
coronary  arteries  ;  hence  the  flow  of  blood  from  the  aorta  into  the 
coronary  arteries  can  take  place  only  during  the  ventricular  diastole  or 
at  the  very  beginning  of  the  systole,  and  not  at  all  during  the  systole 
itself  The  object  of  this,  he  argues,  is  twofold.  In  the  first  place,  the 
muscular  tissue  of  the  ventricle  is  not  burdened  with  blood  at  the 
moment  that  it  is  undergoing  contraction,  but  receives  its  nutritive 
supply  during  the  phase  of  relaxation  ;  hence  the  whole  force  of  the 
contrnction  of  tlie  ventricular  fibres  is  spent  on  the  contents  of  the 
cavity,  and  none  is  wasted  in  compression  of  the  intra-muscular  blood- 
vessels. In  the  second  place,  the  effect  of  the  flow,  at  the  close  of 
the  systole,  into  the  previously  emptied  coronary  arteries,  is  to  unfold, 
so  to  speak,  the  collapsed  cavities  of  the  ventricles  very  much  in  the 
same  way  as  the  collapsed  cavity  of  a  double-walled  ball  may  be  rein- 
stated by  the  forcible  injection  of  fluid  into  the  space  between  the  two 
walls.  Through  this  particukir  behaviour  of  the  v;ilves,  in  fact,  the 
heart,  as  an  atter-eflect  of  the  systole,  dilates  its  own  ventricles  ;  hence 
the  mechanism  has  been  called  by  Briicke  a  'self-regulating 
mechanism.'    , 

Briicke's  view  has  however  been  much  disputed.  In  the  first  place, 
we  know  that  the  flow  of  blood  from  an  ordinary  skeletal  musde, 
though  it  may  suffer  a  brief  initial  check  (probably  from  compression 

*   IVien.  Sitz.-Bcrichlc,  1854  ;  and  Dcr  Vtrschluss  d.  KtanzschlagOdern. 


1 66  THE  VALVES  OF  THE  HEART.      [BOOK  I. 

of  the  larger  veins),  is  increased  and  not  diminished  by  a  tetanic  con- 
traction of  the  muscle,  the  increase  being  visible  while  the  contraction 
is  still  at  its  height  ^.  Corresponding  to  this  last  increased  flow  from 
the  veins  there  must  be  an  increased  flow  into  the  arteries.  And  in 
certain  dispositions  of  the  blood-vessels  and  muscular  fibres  (as  when 
a  vessel  is  surrounded  by  fibres  running  lengthways  parallel  to  itself), 
the  increased  thickening  of  the  fibres  will  tend  not  to  compress  but  to 
dilate  the  vessel.  The  advantage  to  the  muscular  tissue  therefore  of 
the  closure  of  the  coronary  arteries  seems  at  least  doubtful.  In  the 
second  place,  it  has  been  urged  that,  in  point  of  fact,  the  mouths  of  the 
coronary  arteries  are  not  covered  by  the  valves.  .Briicke  replies  that 
they  may  appear  uncovered  during  dissection  after  death,  but  are 
actually  covered  during  life.  He  moreover  brings  forward  an  experi- 
ment on  a  pig's  heart  removed  from  the  body,  in  which  a  stream  of 
water  sent  through  the  pulmonary  veins  and  auricle  into  the  left  ven- 
tricle issues  through  the  open  aorta,  without  a  drop  of  it  appearing  at 
the  cut  end  of  an  open  coronary  artery,  if  the  aorta  be  maintained  in  a 
proper  position,  and  all  vibration  and  jar  be  avoided  ;  and  argues  that 
it  is  the  closure  of  the  orifices  by  the  valves  which  prevents  the  flow, 
because  any  shake  sufficient  to  d'evelope  a  backward  current  in  the 
aorta,  and  thus  to  lift  up  the  valves,  at  once  gives  rise  to  a  flow.  If 
however,  as  has  been  stated,  the  experiment  will  succeed  equally  well 
in  the  absence  of  the  valves,  and  will  not  succeed  if  the  free  exit  of  fluid 
from  the  end  of  the  aorti  be  hindered  though  the  valves  be  intact,  the 
absence  of  a  flow  through  the  coronary  artery  must  be  due  to  a  defi- 
ciency of  pressure  in  the  aorta  and  not  to  any  action  of  the  valves. 
The  undoubted  fact  that  blood  flows  from  a  wounded  coronary  artery 
in  jerks  corresponding  to  the  systole  and  not  to  the  diastole,  Briicke 
meets  with  the  observation  that  the  coronary  arteries  must  share  just 
previous  to  the  closure  of  the  valves  in  that  increased  pressure  in  the 
aorta  which  is  the  cause  of  the  closure  of  the  valves,  and  that  the 
higher  pressure  thus  gained  at  the  beginning  of  the  systole  is  main- 
tained during  the  systole  by  the  obstruction  to  the  outward  flow  arising 
from  the  contracting  fibres  compressing  the  small  vessels ;  while  the 
empty  condition  of  the  small  branches  of  the  coronary  arteries  and  of 
the  veins  at  the  commencement  of  the  diastole,  must  diminish  the  pres- 
sure in  the  main  coronary  arteries  themselves  during  diastole,  and  so 
prevent  a  diastolic  spurt  from  a  wound  in  them.  This  however  is 
hardly  satisfactory,  since  as  regards  the  systole,  as  has  been  urged 
above,  an  obstruction  of  the  flow  from  compression  by  the  muscular  fibres 
is  at  least  doubtful  ,and  as  regards  the  diastole  the  supposed  empty 
condition  of  the  coronary  vessels  can  produce  an  effect  only  at  the  very 
beginning  of  the  diastole.  On  the  other  hand,  Ceradini  ^,  who  observed 
the  condition  of  the  valves  in  an  excised  heart  by  looking  down 
through  a  wide  glass  tube  inserted  into  the  aorta,  is  of  opinion  that 
during  the  systole  the  valves  are  not  applied  close  to  the  arterial  wall, 
but  float  in  an  intermediate  position  of  equilibrium,  maintained  by 
reflux   currents,   their   orifice   taking  on  the  form   of  an   equilateral 

'  Gaskell,  Ludwig's  Arbeiten,  1876  ;  and  yourn.  Anat.  and  Phys.  XI.  360. 
*  Der  Mechanismw  der  halbmondfdrmigen  Herzklappen.     Leipzig,  1872. 


ClIAF.   IV.]  Till-:    VASCULAR   MECHANISM.  167 

triangle  with  curved  sides.  The  same  reflux  currents  gradually  (hut  of 
course  rapidly)  close  the  orifice  as  the  fon  c  of  the  systole  diminishes, 
and  the  effect  of  the  elastic  rebound  is  simply  to  render  the  closure  tense 
and  firm.  Thus,  argues  Ceradini,  no  regurgitation  of  fluid  from  the 
aorta  into  the  ventricle  at  the  end  of  the  systole  and  the  beginning  of 
the  diastole  is  possible,  and  a  hurtful  waste,  which  on  Briicke's 
hypothesis  seems  unavoidable,  is  averted. 

The  passage  of  the  blood  through  the  heart  takes 
place  as  follows.  The  right  auricle  during  its  diastole,  by  the 
relaxation  of  its  muscular  fibres,  and  by  the  fact  that  all  pressure 
from  the  ventricle  is  removed  by  the  tension  of  the  tricuspid 
valves,  offers  but  little  resistance  to  the  ingress  of  blood  from  the 
veins.  On  the  other  hand,  the  blood  in  the  trunks,  both  superior 
and  inferior  vena  cava,  is  under  a  certain  though  low  pressure, 
augmented  in  the  case  of  the  superior  vena  cava  by  gravity,  and 
in  consequence  flows  into  the  empty  auricle.  At  each  inspiration, 
this  flow  is  favoured  by  the  negative  pressure  in  the  heart  and 
great  vessels  caused  by  the  respiratory  movements.  Before  this 
has  gone  on  very  long,  the  diastole  of  the  ventricle  begins,  its 
cavity  sudtlenly  dilates,  the  pressure  in  that  cavity  becomes 
negative,  drawing  the  blood  into  it,  the  flaps  of  the  tricuspid  valve 
fall  back,  and  blood  for  some  little  time  flows  in  an  unbroken 
stream  from  the  venre  cavge  into  the  ventricle.  In  a  short  time, 
however,  before  much  blood  has  had  time  to  enter  the  ventricle, 
the  auricle  is  full,  and  forthwith  its  sharp  sudden  systole  takes 
place.  Partly  by  reason  of  the  onward  pressure  in  the  veins, 
which  increases  rapidly  from  the  heart  towards  the  capillaries, 
partly  from  the  presence  of  valves  in  the  venous  trunks  and  at  the 
mouth  of  the  inferior  vena  cava,  but  still  more  from  the  fact  that 
the  systole  begins  at  the  great  veins  themselves  and  spreads  thence 
over  the  auricle,  the  force  of  the  auricular  contraction  is  spent  in 
driving  the  blood,  not  back  into  the  veins,  but  into  the  ventricle, 
where  the  pressure  is  still  exceedingly  low. 

Whether  there  is  any  backward  flow  at  all  into  the  veins,  or  even 
an  interruption  to  the  forward  flow,  or  whether  by  the  progressive 
character  of  the  systole  the  flow  of  blood  continuci,  so  to  speak,  to 
follow  up  the  systole  without  break  so  that  the  stream  from  the  veins 
into  the  auricle  is  really  continuous,  is  at  present  doubtful ;  though  a 
slight  positive  wave  of  pressure  synchronous  with  the  auricular  systole, 
travcllmg  backward  along  the  veins,  has  been  observed  at  least  in 
cases  where  the  heart  is  beating  vigorously.  The  question  of  a 
negative  venous  pulse,  i.e.  the  transmission  backwards  of  the  negative 
pressure  of  the  right  cardi  ic  cavities,  will  be  considered  later  on. 

The  ventricle  thus  being  filled,  the  play  of  the  tricuspid  valves 
described  above  comes  into  action,  the  auricular  systole  is  followed 


l68  THE   SOUNDS    OF   THE    HEART.  [BOOK   I. 

by  that  of  the  ventricle,  and  the  pressure  witliin  the  ventricle,  cut 
off  from  the  auricle  by  the  tricuspid  valves,  is  brought  to  bear 
entirely  on  the  conns  arteriosus  and  the  pulmonary  semilunar 
valves.  As  soon  as  by  the  rapidly  increasing  force  of  the  ven- 
tricular contraction,  the  pressure  within  the  ventricle  becomes 
greater  than  that  in  the  pulmonary  artery,  the  semilunar  valves 
open,  and  the  still  increasing  systole  discharges  the  contents  of  the 
ventricle  into  that  vessel.  But  as  the  systole  passes  off,  the 
pressure  in  the  artery  becomes  greater  than  that  in  the  cavity  of 
the  ventricle,  and  a  rebound  of  the  blood  takes  place.  The  first 
act  of  this  rebound  however  is,  as  we  have  seen,  firmly  to  close 
the  semilunar  valves,  and  thus  to  shut  off  the  over-distended 
artery  from  the  now  empty,  or  nearly  empty,  ventricle. 

During  the  whole  of  this  time  the  left  side  has  with  still 
greater  energy  been  executing  the  same  manoeuvre.  At  the  same 
time  that  the  venae  cavse  are  filling  the  right  auricle,  the  pulmonary 
veins  are  filling  the  left  auricle.  At  the  same  time  that  the  right 
auricle  is  contracting,  the  left  auricle  is  contracting  too.  The 
systole  of  the  left  ventricle  is  synchronous  with  that  of  the  right 
ventricle,  but  executed  with  greater  force  ;  and  the  flow  of  blood 
is  guided  on  the  left  side  by  the  mitral  and  aortic  valves  in  the 
same  way  that  it  is  on  the  right  by  the  tricuspid  valves  and  those 
of  the  pulmonary  artery. 

The  Sounds  of  the  Heart. 

When  the  ear  is  applied  to  the  chest,  either  directly  or  by 
means  of  a  stethoscope,  two  sounds  are  heard,  the  first  a  com- 
paratively long  dull  booming  sound,  the  second  a  short  sharp 
sudden  one.  Between  the  first  and  second  sounds,  the  interval  of 
time  is  very  short,  too  short  to  be  measurable,  but  between  the 
second  and  the  succeeding  first  sound  there  is  a  distinct  pause. 
The  sounds  have  been  likened  to  the  pronunciation  of  the  syllables 
lubb,  diip,  so  that  the  cardiac  cycle,  as  far  as  the  sounds  are 
concerned,  might  be  represented  by : — lubb,  diip,  pause.  The 
relative  duration  of  the  sounds,  and  of  the  pause,  as  well  as  their 
relations  in  point  of  time  to  the  changes  taking  place  in  the  heart, 
are  shewn  in  the  following  diagram.     Fig.  32. 

The  second  short  sharp  sound  presents  no  difficulties.  It 
is  coincident  in  point  of  time  with  the  closure  of  the  semilunar 
valves,  and  is  heard  to  the  best,  advantage  over  the  second  right 
costal  cartilage  close  to  its  junction  with  the  sternum,  i.e.  at  the 
point  where  the  aortic  arch  comes  nearest  to  the  surface.  Its 
characters  are  such  as  would  belong  to  a  sound  generated  by  the 


CHAP.    IV.]  TIIK    VASCUl-.\k    MK(HANISM. 


169 


sudden  tension  of  valves  like  the  semilunar  valves.  It  is  obscured 
and  altered,  replaced  by  '  nuirinur.s  '  when  the  semilunar  vabes 
are  affected  by  disease,  the  idteration  being  niobt  manifest  to  the 
ear  at  the  above-mentioned  spot  when  the  aortic  valves  are 
affected.     When  the  aortic  valves  are  hooked  up  by  means  of  a 


Fig.  32.     DiAGRAM.MATic  Represemtation  of  the  Movements  and  Sounds  o»  the 
Heart  during  a  Cardiac  Period.    (After  Dr.  Sharpey.) 

The  ventricular  systole,  which  is  here  used  to  denote  the  action  of  the  ventricle  up  to  the 
closure  of  the  semilunar  valves,  is  represented  as  occupying  about  45  p.c.  and  the  two  sound) 
together  as  rather  more  than  half,  of  the  whole  period  ;  but  the  diagram  is  intended  to  shew 
merely  the  general  relations  of  the  var.ous  events,  and  not  to  serve  as  a  means  of 
measurement. 

wire  introduced  down  the  arteries,  the  second  sound  is  obliterated 
and  replaced  by  a  murmur.  These  facts  prove  that  the  second 
sound  is  due  to  the  sudden  tension  of  the  aortic  (and  pulmonary) 
semilunar  valves. 

The  first  sound,  longer,  duller,  and  of  a  more  'booming'  char- 
acter than  the  second,  heard  with  greatest  distinctness  at  the  spot 
where  the  cardiac  impulse  is  felt,  i)resents  many  difficulties  in  the  way 
of  a  complete  explanation.  It  is  heard  distinctly  when  the  chest- 
v.-alls  are  removed.  The  cardiac  impulse  therefore  can  have  little 
or  nothing  to  do  with  it.  In  point  of  time,  and  in  the  position  in 
which  it  may  be  heard  to  the  greatest  advantage  (at  the  spot  of  the 
cardiac  impulse  where  the  ventricles  come  nearest  to  the  surtace), 
it  corresponds  to  the  closure  of  the  auriculo-ventricular  valves. 
In  point  of  character  it  is  not  such  a  sound  as  one  would  expect 
from  the  vibration   of  membranous  structures,   but  has,  on   the 


I/O  THE   SOUNDS   OF   THE   HEART.  [BOOK   I. 

contrary,  many  of  the  characters  of  a  muscular  sound.  In  favour 
of  its  being  a  valvular  sound,  may  be  urged  the  fact  that  it  is 
obscured,  altered,  replaced  by  murmurs,  when  the  tricuspid  or 
mitral  valves  are  diseased  ;  and  Halford  ^  found  that  clamping  the 
great  veins  stopped  the  sound  though  the  beat  continued.  On  the 
other  hand,  Ludwig  and  Dogiel  ^  heard  the  sound  distinctly  in  a 
bloodless  dog's  heart,  in  which  there  was  no  fluid  to  render  the 
valves  tense  and  set  them  vibrating.  But  there  is  a  grea^  difficulty 
in  regarding  it  as  a  muscular  sound,  for  a  muscular  sound  is  the 
result  of  a  tetanic  contraction,  the  height  of  the  note  produced 
varying  with  the  number  per  second  of  the  simple  contractions 
which  go  to  make  up  the  tetanus.  A  simple  contraction  or 
spasm  cannot  possibly  produce  a  musical  sound,  such  as  is  the 
cardiac  sound.  The  beat  of  the  heart  is  a  comparatively  slow  long- 
continued  single  spasm,  and  not  a  tetanic  contraction.  In  its  long 
latent  period,  and  in  all  its  characters,  the  heart's  beat  bears  the 
stamp  of  being  a  single  spasm.  If  so  it  cannot  give  rise  to  a  note ; 
and  the  attempt  to  solve  the  difficulty  by  supposing  that,  though 
the  contraction  of  each  cardiac  fibre  is  simple,  there  is  a  sequence 
of  these  simple  contractions  over  the  whole  heart  in  consequence 
of  the  several  fibres  not  contracting  at  the  same  time,  and 
that  this  sequence  generates  the  sound,  does  not  appear  very 
satisfactory. 

When  the  nerve  of  the  rheoscopic  muscle-nerve  preparation  (p.  66) 
is  placed  over  the  heart,  each  beat  of  the  heart  (ventricle  or  auricle) 
is  followed  by  a  single  spasm,  not  by  tetanus,  of  the  rheoscopic 
muscle.  By  properly  disposing  the  nerve  of  the  preparation  a  con- 
traction corresponding  to  the  systole  of  the  auricle  followed  rapidly  by 
a  second  corresponaing  to  the  systole  of  the  ventricle  may  be  obtained, 
but  in  each  case  the  contraction  in  the  leg  is  simple  and  not  tetanic. 
This  result  is  consistent  with  the  view  that  the  systole  is  a  simple 
spasm,  but  cannot  be  regarded  as  a  proof  that  it  is  such.  For  it  is 
not  every  tetanus  in  a  muscle  which  will  give  a  secondary  tetanus  in 
the  rheoscopic  muscle.  When  the  tetanus  in  a  muscle  is  induced  by 
the  ordinary  interrupted  current  applied  directly  to  the  nerve  of  the 
muscle,  the  tetanus  in  the  rheoscopic  muscle  appears  without  difficulty  ; 
but  where  the  tetanus  is  produced  by  a  constant  current,  the  so-called 
breaking  or  making  tetanus  (p.  79),  the  rheoscopic  muscle  responds  by 
a  single  (initial)  spasm  instead  of  a  tetanus.  The  pronounced  tetanus 
of  strychnia  similarly  gives  rise  to  a  simple  initial  spasm  and  not  to  a 
tetanus  of  the  rheoscopic  muscle,  and  the  same  feature  is  characteristic 
of  the  natural  respiratory  contractions  of  the  diaphragm  and  probably 
of  all  voluntary  contractions.^ 

'  Action  and  Sounds  of  the  Heart      London,  i860. 

^  Ludwig's  Arbeiteti,  Jahrg.  1868. 

3  Hering  u.  Friedrich,   Wien.  Siizungs-Berichtc,  LXXII.  (1875). 


CUAl'.    IV. J  THE   VASCULAR    MIXIIANISM.  I/I 

Moreover,  in  cases  of  hypertropliy,  where  the  muscular  element 
and  action  is  increased,  the  sound,  so  far  from  being  increased,  is 
nni)aired.  Hence,  the  first  sound,  whether  it  be  regarded  as  the 
result  of  the  vibration  of  the  auriculo-ventricular  valves,  acted  upon 
by,  and  in  turn  acting  on,  columns  of  blood,  or  as  a  muscular  sound, 
presents  great  difficulties.  No  other  cause,  in  the  least  satisfactory, 
has  been  suggested  ;  and  the  difficulties  are  rather  increased  than 
met  by  supposing  that  the  sound  is  at  once  both  valvular  and 
muscular  in  origin. 

The    Work  done. 

We  can  measure  with  exactness  the  intraventricular  pressure, 
the  length  of  each  systole,  and  the  number  of  times  the  systole  is 
repeated  in  a  given  period,  but  perhaps  the  most  important  factor 
of  all  in  the  determination  of  the  work  of  the  vascular  mechanism, 
the  quantity  ejected  from  the  ventricle  into  the  aorta  at  each  systole, 
cannot  be  accurately  determined  ;  we  are  obliged  to  fall  back  on 
calculations  having  many  sources  of  error.  The  mean  result  of 
these  calculations  gives  about  i8o  grms.  (6  oz.)  as  the  quantity  of 
blood  which  is  driven  from  each  ventricle  at  each  systole  in  a  full- 
grown  man  of  average  size  and  weight.  It  is  evident  that  exactly 
the  same  quantity  must  issue  at  a  beat  from  each  ventricle  ;  Tor  if 
the  right  ventricle  at  each  beat  gave  out  rather  less  than  the  left, 
after  a  certain  number  of  beats  the  whole  of  the  blood  would  be 
gathered  in  the  systemic  circulation.  Similarly,  if  the  left  ventricle 
gave  out  less  than  the  right,  all  the  blood  would  soon  be  crowded 
into  the  lungs.  The  fact  that  the  pressure  in  the  right  ventricle  is 
so  much  less  than  that  in  the  left  (30  or  40  mm.  as  compared  with 
200  mm.  of  mercury),  is  due,  not  to  differences  in  the  quantity 
of  blood  in  the  cavities,  but  to  the  fact  that  the  peripheral  resistance 
which  has  to  be  overcome  in  the  lungs  is  so  much  less  than  that 
in  the  rest  of  ihj  body. 

Various  methods  have  been  adopted  for  calculating  the  average 
amount  of  blood  ejected  at  each  ventricular  systole.  It  has  been 
calculated  from  tlie  capacity  of  the  recently  removed  and  as  yet  not 
rijjid  ventricle,  filled  with  blood  under  a  pressure  equal  to  the  calcu- 
lated average  pressure  in  the  ventricle.  This  method  of  course  pre- 
supposes that  the  whole  contents  of  the  ventricle  are  ejected  at  each 
systole.  Volkinann '  measured  the  sectional  area  of  the  aorta,  and 
taking  an  average  velocity  of  the  blood  in  the  aorta  (a  very  uncertain 
datum),  calculated  the  quantity  of  blood  which  must  pass  through  the 
sectional  area  in  a  given  time.  The  number  of  beats  in  that  time  then 
gave  him  the  quantity  flowing  through  the   area  and   consequently 

'  Hdmodyuamik,  p.  206. 


1/2  VARIATIONS   IN    THE    HEART'S    BEAT.      [BOOK   I. 

ejected  from  the  heart  at  each  beat.  The  mean  of  many  experiments 
on  different  animals  came  out  ■0025  p.  c.  of  the  body  weight,  which 
in  a  man  of  75  kilos  would  be  i87'5  grms.  Vierordt  measured  the 
mean  velocity  and  the  sectional  area  in  the  carotid,  and  thence,  from 
a  measurement  of  the  sectional  area  of  the  aorta,  and  from  a  calcu- 
lation of  the  blood's  mean  velocity  in  it,  based  on  the  supposition  that 
the  mean  velocity  in  an  artery  was  inversely  as  its  sectional  area, 
arrived  at  the  quantity  flowing  through  the  aorti;  sectional  area  in  a 
given  time,  and  thus  at  the  quantity  passing  at  each  beat.  Both  these 
calculations  are  vitiated  by  the  fact  that  the  variations  of  velocity  in 
the  aorta  are  so  great,  that  any  mean  has  really  but  little  positive 
value. 

Fick^by  means  of  calculations  based  partly  on  the  data  gained 
by  observing  the  in:rease  of  the  volume  of  the  whole  arm  at  each 
cardiac  systole,  arrived  at  results  much  less  than  either  of  the  above. 
In  one  case  he  estimated  the  quantity  ejected  from  the  heart  at  each 
beat  at  53  grm.,  and  in  a  second  case  at  77  grm. 

It  must  be  remembered  that  though  it  is  of  advantage  to  speak 
of  an  average  quantity  ejected  at  each  stroke,  it  is  more  than 
probable  that  that  quantity  may  vary  within  very  wide  lijrnits. 
Taking,  however,  180  grms.  as  the  quantity,  in  man,  ejected  at 
each  stroke  at  a  pressure  of  250  mm.^  of  mercury  which  is 
equivalent  to  3 "21  metres  of  blood,  this  means  that  the  left 
ventricle  is  capable  at  its  systole  of  lifting  180  grms.  3*2 1  m.  high, 
i.e.  it  does  578  gram-metres  of  work  at  each  beat.  Supposing  the 
heart  to  beat  72  times  a  minute,  this  would  give  for  the  day's  work 
of  the  left  ventricle,  nearly  60,000  kilogram -metres  ;  calculating 
the  work  of  the  right  ventricle  at  one-fourth  that  of  the  left,  the 
work  of  the  whole  heart  would  amount  to  75,000  kilogram-metres. 
A  calculation  of  more  practical  value  is  the  following.  Taking 
the  quantity  of  blood  as  ^3  of  the  body  weight,  the  blood  of  a 
man  weighing  75  kilos  would  be  about  5,760  grms.  If  180  grms. 
left  the  ventricle  at  each  beat,  a  quantity  equivalent  to  the  whole 
blood  would  pass  through  the  heart  in  32  beats,  i.e.  in  less  than 
half  a  minute. 

Variations  in  the  Heart" s  beat. 

These  are  for  the  most  part  in  reality  vital  phenomena,  i.e. 
brought  about  by  events  depending  on  changes  in  the  vital, 
properties  of  some  or  other  of  the  tissues  of  the  body.  It  will 
be  convenient,  however,  briefly  to  review  them  here,  though  the 
discussion  of  their  causation  must  be  deferred  to  its  appropriate 
place. 

'   Untcrsuch.  physiol.  Lab.  Zurich.  Hochschule,  Hft.  I.  p.  51  (1869). 
"  A  high  estimate  is  pnrpo  ely  taken  here. 


CIIAl'.    I\.j  TllK    VASCULAR    .M  KCll  ANISM.  1/3 

The  frequency  of  the  heart,  i.e.  the  number  of  beats  in  any 
given  time,  may  vary.  The  average  rate  of  the  human  pulse  or 
heart-beat  is  72  a  minute.  It  iscjuickerin  children  than  in  adults, 
but  (juickens  a;^ain  a  little  in  advanced  age.  It  is  quicker  in  the 
adult  female  than  in  the  adult  male,  in  persons  of  short  stature 
than  in  tall  people.  It  is  increased  by  exertion,  and  thus  is  quicker 
in  a  standing  than  in  a  sitting,  and  in  a  sitting  than  in  a  lying 
posture.  It  is  quickened  by  meals,  and  while  varying  thus  from 
time  to  time  during  the  day,  is  on  the  whole  quicker  in  the  evening 
than  in  early  morning.  It  is  said  to  be  on  the  whole  quicker  in 
summer  than  in  winter.  Even  independently  of  muscular  exertion 
it  seems  to  be  quickened  by  great  altitudes.  Its  rate  is  profoundly 
influenced  by  mental  conditions. 

The  length  of  the  systole  may  vary,  though  as  a  general 
and  broad  rule  it  may  be  stated  that  a  frequent  differs  from  an 
infrequent  pulse  chiefly  by  the  length  of  the  diastole. 

Bonders  found  the  length  of  the  systole  as  measured  by  the 
interval  between  the  first  and  se-:ond  sounds  to  be  for  ordinary  pulses 
remarkably  constant  in  different  persons,  varying  not  more  than  from 
•327  to  '301  sec.,  and  being  therefore  relatively  to  the  whole  cardiac 
period  less  in  slow  than  in  quick  pulses. 

The  force  of  the  beat  may  vary  ;  the  ventricular  systole 
may  be  weak  or  strong. 

When  the  rate  of  beat  is  suddenly  increased  there  is  a  tendency  for 
the  individual  beats  to  be  diminished  in  force,  and  on  the  other  hand 
to  be  increased  in  force  when  the  rate  is  diminished.  But  there  is  no 
necessary  connection  between  rate  and  strength ;  both  a  frequent 
and  an  infrequent  pulse  may  be  either  weak  or  strong. 

The  character  of  the  beat  may  vary  :  the  systole  may  be 
sudden  and  sharp,  rapiiUy  reaching  a  maximum  and  rapidly 
declining,  or  slow  and  lengthened,  reaching  its  maximum  only 
after  some  time  and  declining  very  gradually  ;  the  latter  being  the 
slow  pulse  {pulsus  tardus)  as  distinguished  from  the  infrequent 
])ulse  (/>u/sus  rarus).  The  pulse  is  also  sometimes  spoken  of  as 
being  slapping,  and  sometimes  as  heaving. 

The  rhythm  may  be  intermiltent  or  irregular.  Thus  in  an 
intermittent  i)ulse,  a  beat  may  be  so  to  speak  dropped  :  the  hiatus 
occurring  either  regularly  or  irregularly.  In  an  irregular  rhythm 
succeeding  beats  may  differ  in  length,  force,  or  character. 

Sec.  3.    The  Pulse. 

When  the  finger  is  placed  on  an  artery,  such  as  the  radial,  an 
intermittent   pressure  on   the   finger,  coming  and  going  with  the 


174  THE   PULSE.  [BOOK   I. 

beat  of  the  heart,  is  felt.  When  a  Hght  lever  such  as  that  of  the 
sphygraograph  is  placed  on  the  artery,  the  lever  is  raised  at  each 
beat,  falling  between.  The  pressure  on  the  finger,  and  the  raising 
of  the  lever,  are  expressions  of  the  expansion  of  the  elastic  artery, 
cf  the  temporary  additional  distension  which  the  artery  undergoes 
at  each  systole  of  the  ventricle.  This  intermittent  expansion  is 
called  the  pulse  ;  it  corresponds  exactly  to  the  intermittent  outflow 
of  blood  from  a  severed  artery,  being  present  in  the  arteries  only, 
and  except  under  particular  circumstances,  absent  from  the  veins 
and  capillaries.  The  expansion  is  frequently  visible  to  the  eye, 
and  in  some  cases,  as  where  an  artery  has  a  bend,  may  cause  a 
certain  amount  of  locomotion  of  the  vessel. 

All  the  more  important  phenomena  of  the  pulse  may  be 
witnessed  on  an  artificial  scheme. 

If  two  levers  be  placed  on  the  arterial  tubes  of  an  artificial  * 
scheme,  one  near  to  the  pump,  and  the  other  near  to  the 
peripheral  resistance,  with  a  considerable  length  of  tubing  between 
them,  and  both  levers  be  made  to  write  on  a  recording  surface, 
one  immediately  below  the  other,  so  that  their  curves  can  be 
more  easily  compared,  the  following  facts  may  be  observed,  when 
the  pump  is  set  to  work  regularly. 

I.  With  each  stroke  of  the  pump,  each  lever  (Fig.  ^3,  I. 
and  II.)  rises  to  a  maximum,  la,  2a,  and  then  falls  again,  thus 
describing  a  curve, — the  pulse-curve^.  This  shews  that  the 
expansion  of  the  tubing  passes  the  point  on  which  the  lever  rests 
in  the  form  of  a  wave.  At  one  moment  the  lever  is  quiet :  the 
tube  beneath  it  is  simply  distended  to  the  normal  permanent 
amount  indicative  of  the  mean  arterial  pressure ;  at  the  next 
moment  the  pulse  expansion  reaches  the  lever,  and  the  lever  begins 
to  rise,  and  continues  to  do  so  until  the  top  of  the  wave  reaches 
it,  after  which  it  falls  again  until  it  is  once  more  at  rest,  the  wave 
having  completely  passed  by. 

The  rise  of  each  lever  is  somewhat  sudden,  but  the  fall  is 
more  gradual,  and  is  generally  marked  with  some  irregularities. 
The  suddenness  of  the  rise  is  due  to  the  suddenness  with  which 
the  sharp  stroke  of  the  pump  expands  the  tube ;  the  fall  is  more 
gradual  because  the  elastic  reaction  of  the  walls,  whereby  the  tube 

'  By  this  is  simply  meant  a  system  of  tubes,  along  which  fluid  can  be  driven 
by  a  pump  worked  at  regular  intervals.  In  the  course  of  the  tubes  a  (variable) 
resistance  is  introduced  in  imitation  of  the  capillary  resistance.  The  tubes  on 
the  proximal  side  of  the  resistance  consequently  represent  arteries  ;  those  on 
the  distal  side,  veins. 

'''■  Cf.  Marey,  Trav.  d.  Lab.  I.  (1875)  p.  100. 


CHAP.   IV 


Tllli   VASCULAR    MLCll ANISM. 


175 


returns  to  its  former  condition  after  the  expanding  power  of  the 
pump  has  ceased,  is  gradual  in  its  action. 

2.     The  size  and  form  of  each  curve  depends  in  part  on  the 


«,yV\AAAAAAAAAA/\AAA/ 


Fic.  33.  Pulsc-curvcs  described  by  a  scries  of  sphygmographic  levers  placed  at  intervals 
of  20  cm.  from  each  other  aloriR  aa  clasiic  lube  into  which  fluid  is  forced  by  the  sudden 
stroke  of  a  pump.  The  pulsc-wavc  is  travelling  from  left  10  right,  as  indicated  by  the  arrows 
over  the  primary  (a)  and  secondary  (*,  c)  puKc-waves.  The  dotted  veriical  lines  drawn  (rom 
the  summit  of  the  several  primary  waves  to  the  tuning-forlc  curve  below,  each  complete 
vibration  of  which  occupies  -^  sec.,  allow  the  time  to  be  measured  which  is  t.iken  up  by  the 
wave  in  parsing  .-.lonp  20  cm.  of  the  tubing.  1  he  waves  a  are  waves  rejjfctfd  from  the  closed 
distal  end  of  the  tubing  ;  this  is  indicated  by  the  direction  r  f  the  arrows.  It  will  be  observed 
that  in  the  more  distant  lever  VI  the  reflected  wave,  having  but  a  slight  distance  to  travel, 
becomes  fused  with  the  primary  wave.     (From  Marey.) 


176  •       THE   PULSE.  [book   I. 

amount  of  pressure  exerted  by  the  levers  on  the  tube.  If  the 
levers  only  just  touch  the  tube  in  its  expanded  state,  the  rise  in 
each  will  be  insignificant.  If  on  the  other  hand  they  be  pressed 
down  too  firmly,  the  tube  beneath  will  not  be  able  to  expand 
as  it  otherwise  would,  and  the  rise  of  the  levers  will  be  pro- 
portionately diminished.  There  is  a  certain  pressure,  depending 
on  the  expansive  power  of  the  tubing,  at  which  the  tracings  are 
best  marked. 

3.  If  the  points  of  the  two  levers  be  placed  exactly  one  under 
the  other  on  the  recording  surface,  it  is  obvious  that,  the  levers 
being  alike  except  for  th-eir  position  on  the  tube,  any  diiference 
in  time  between  the  movements  of  the  two  levers  will  be  shewn 
by  an  interval  between  the  beginnings  of  the  curves  they  describe, 
if  the  recording  surface  be  made  to  travel  sufficiently  rapidly. 

If  the  movements  of  the  two  levers  be  thus  compared,  it  will 
be  seen  that  the  far  lever  (Fig.  33,  II.)  commences  later  than  the 
near  one  (Fig.  33,  I.) ;  the  fardier  apart  the  two  levers  are,  the 
greater  is  the  interval  in  time  between  their  curves.  Compare 
the  series  I.  to  VI.  (Fig.  33).  This  means  that  the  wave  of 
expansion,  the  pulse-wave,  takes  some  time  to  travel  along  the 
tube.  By  exact  measurement  it  would  similarly  be  found  that  the 
rise  of  the  near  lever  began  some  fraction  of  a  second  after  the 
stroke  of  the  pump. 

This  travelling  of  the  expansion-wave,  or  pulse-wave,  must  be 
carefully  distinguished  from  the  propagation  of  the  shock  given  by 
the  stroke  of  the  pump.  When  a  long  glass  (or  other  rigid)  tube 
filled  with  water  is  smartly  tapped  at  one  end,  the  blow  is  imme- 
diately felt  as  a  shock  at  the  other  end.  The  transmission  of  this 
shock,  if  carefully  measured,  would  be  found  to  be  exceedingly 
rapid ;  compared  with  the  pulse-wave  now  under  consideration,  it 
would  be  practically  instantaneous.  When  fluid  is  driven  by  the 
strokes  of  a  pump  along  a  rigid  tube,  a  similar  shock,  travelling 
equally  rapidly,  may  be  readily  felt,  and  might  be  registered  with 
a  lever.  When  however  the  tube  along  which  the  fluid  is  being 
pumped  is  elastic,  the  force  of  the  pump  is  so  much  taken  up  in 
expanding  the  tube,  that  the  shock  is  reduced  to  very  small 
dimensions.  It  becomes  so  slight,  that  it  makes  no  impression 
on  such  levers  as  are  used  to  register  the  expansion- wave. 

The  velocity  with  which  the  pulse-wave  travels  depends  chiefly 
on  the  amount  of  rigidity  possessed  by  the  tubing.  The  more 
extensible  (with  corresponding  elastic  reaction)  the  tube,  the 
slower  is  the  wave  ;  the  more  rigid  the  tube  becomes,  the  faster 
the  wave  travels.     According  to  Bonders  the  size  of  the  tube  has 


CHAl'.    IV.J  Tllli    VASCULAR    MECHANISM.  1/7 

no  marked  influence  ;  but  Moens'  finds  it  to  be  less  in  the  wider 
tubes.  According  to  Marey  the  initial  velocity,  the  steepness  of 
the  wave,  has  an  influence  on  its  rate  of  progress.  In  the  human 
body  the  wave  has  been  estimated  to  travel  at  a  rate  of  9  to  ro 
metres  (Weber  9*240;  Garrod  9 — 108,  or  according  to  Landois 
5  to  6  metres)  a  second'.  It  probably  varies  very  considerably. 
According  to  all  observers  the  velocity  of  the  wave  in  passing  from 
the  groin  to  the  foot  is  greater  than  that  in  passing  from  the  axilla 
to  the  wrist  (6743  mm.  against  5772).  This  is  probably  due  to 
the  fact  that  the  femoral  artery  with  its  branches  is  more  rigid  than 
the  a.xillary. 

Since  with  increase  of  mean  tension,  the  arteries  become  more  and 
more  rigid,  it  would  be  e.>cpected  that  the  velocity  would  increase  with 
the  mean  tension  ;  and  Moens'',  in  opposition  to  Weber's  earlier  results, 
finds  that  it  does. 

4.  When  two  curves  taken  at  different  distances  from  the 
pump  are  compared  with  each  other,  the  far  curve  will  be  found 
to  be  shallower,  with  a  less  sudden  rise,  and  with  a  more  rounded 
summit  than  the  near  curve  :  compare  5a  with  la.  Fig.  33.  In 
other  words,  the  pulse-wave  as  it  travels  onward  becomes  dimi- 
nished and  flattened  out.  If  a  series  of  levers,  otherwise  alike, 
were  placed  at  intervals  on  a  piece  of  tubing  sufficiently  long  to 
convert  the  intermittent  stream  into  a  continuous  flow,  the  pulse- 
wave  might  be  observed  to  gradually  flatten  out  and  grow  loss 
until  it  ceased  to  be  visible. 

Care  must  be  taken  not  to  confound  the  progression  of  the 
pulse-wave  with  the  progression  of  the  fluid  itself.  The  pulse- 
wave  travels  over  the  moving  blood  somewhat  as  a  rapidly  moving 
natural  wave  travels  along  a  sluggishly  flowing  river,  the  velocity 
of  the  pulse-wave  being  9  metres  per  sec,  while  that  of  the 
current  of  blood  is  not  more  than  -5  metre  per  sec.  even  in  the 
large  arteries,  and  diminishes  rapidly  in  the  smaller  ones. 

Taking  the  duration  of  the  systole  of  the  ventricle  as  j*fj  of  a 
second,  it  is  evident  that  the  pulse-wave  started  by  any  one  systole, 
if  it  travels  at  9  m.  per  sec,  will  d(fL>fr  the  end  of  the  systole  have 
reached  a  point  -^^  of  9  m.  =3 '6  m.  distant  from  the  ventricle. 
In  other  words,  the  wave-length  of  the  pulse-wave  is  much  longer 
than  the  whole  of  the  arterial  system,  so  that  the  beginning  of 
each  wave  has  become  lost  in  the  small  arteries  and  capillaries 
some  time  before  the  end  of  it  has  finally  left  the  ventricle. 

The  general  causation  of  the  pulse  may  then  be  summed  up 
somewhat    as    follows.      The  systole  of  the   ventricle  drives   a 

»  Dii  Puhcume.     Leiden,  1878.  »  Op.  cit. 

F.  P.  12 


1/8  THE   PULSK.  [book   I. 

quantity  of  fluid  into  the  already  full  aorta.  The  portion  of  the 
aorta  next  to  the  heart  expands  to  receive  it,  thus  giving  rise  to 
the  sudden  upstroke  of  the  pulse-curve.  The  systole  over,  the 
aortic  walls,  by  virtue  of  their  elasticity,  tend  to  return  to  their 
former  calibre,  and  the  aortic  valves  being  closed,  this  elastic  force 
is  spent  in  driving  the  blood  onward.  -The  elastic  recoil  being 
slower  than  the  initial  expansion,  the  down-stroke  of  the  pulse- 
curve  is  more  gradual  than  the  up-stroke.  Of  this  portion  of  the 
aorta,  which  actually  receives  the  blood  ejected  from  the  heart, 
the  part  immediately  adjacent  to  the  semilunar  valves  begins  to 
expand  first,  and  the  expansion  travels  thence  on  to  the  end  of 
this  portion.  In  the  same  way  it  travels  on  from  this  portion 
through  all  the  succeeding  portions  of  the  arterial  system.  For 
the  total  expansion  required  to  make  room  for  the  new  quantity 
of  blood  cannot  be  provided  by  that  portion  alone  of  the  aorta 
into  which  the  blood  is  actually  received  ;  it  is  supplied  by  the 
whole  arterial  system ;  the  old  quantity  of  blood  which  is  replaced 
by  the  new  in  this  portion  has  to  find  room  for  itseM"  in  the  rest  of 
the  arterial  space.  As  tlie  expansion  travels  onward,  however, 
the  increase  of  pressure  which  each  portion  transmits  to  the  suc- 
ceeding portion  will  be  less  than  that  which  it  received  from  the 
precedmg  portion,  for  the  whole  increase  of  pressure  due  to  the 
systole  of  the  ventricle  has  to  be  distributed  over  the  whole  of  the 
arterial  system,  and  a  fraction  of  it  must  therefore  be  left  behind 
at  each  stage  of  its  progress ;  that  is  to  say,  the  expansion  is 
continually  growing  less,  as  the  pulse  travels  from  the  heart  to  the 
capillaries ;  hence  the  diminished  height  of  the  pulse-curve  in  the 
more  distant  arteries,  and  its  disappearance  in  the  capillaries. 

Secondary  Waves.  In  the  natural  pulse- curve  the  fun- 
damental wave  is  seen  to  be  marked  by  two  or  more  secondary 
waves  imposed  upon  it.  These  secondary  waves  vary  much  ac- 
cording to  circumstances,  and  are  consequently  of  interest,  as 
throwing  light  on  the  condition  of  the  vascular  system. 

In  an  artificial  scheme,  two  kinds  of  secondary  waves  are  seen. 

I.  Waves  of  oscillation.  When  a  moderate  quantity  of  fluid 
is  injected  into  the  tube  at  each  stroke,  one,  two,  or  more  secondary 
waves  are  seen  to  follow  the  primary  one.  They  are  the  more 
marked,  the  more  sudden  the  stroke,  the  more  extensible  (and 
elaS'tic)  the  tubing,  and  the  less  the  pressure  in  it.  When  the  pump 
is  a  pump  without  valves,  they  form  a  regular  decreasing  series, 
succeeding  the  primary  wave,  and  travelling  at  the  same  velocity 
as  it  (Fig.  33,  I.  II.  III.  b,  c),  but  becoming  sooner  obliterated 

These  waves  are  due  to  the  inertia  of  the  elastic  walls,  and  of 


ClIAl'.    IV.]  Tllli    VASCULAR    MECHANISM.  1/9 

the  contained  lliiid,  and  so  correspond  to  the  secondary  oscilla- 
tions of  the  mercury  in  a  manometer.  If  the  tube  be  filled  with 
air  instead  of  water,  they  are  almost  entirely  absent.  If  mercury 
be  employed  instead  of  water,  they  become  very  conspicuous. 

When  the  quantity  of  fluid  injected  is  large  compared  with  the 
calibre  of  the  tubing,  the,  secondary  waves  may  be  seen  on  tiie 
descending  line  of  the  primary  wave. 

2.  Reflected  waves.  When  the  tube  of  the  artificial  scheme 
bearing  two  levers  is  blocked  just  beyond  the  far  lever,  the 
primary  wave  is  seen  to  be  accompanied  by  a  second  wave,  which 
at  the  far  lever  is  seen  close  to,  and  often  fused  into,  the  primary 
wave  (Fig.  33,  VI.  a'),  but  at  the  near  lever  is  at  some  distance 
from  it  (Fig.  ;^t^,  I.  a'),  being  the  fariher  from  it,  the  longer  the 
interval  between  the  lever  and  the  block  in  the  tube.  This  second 
wave  is  evidently  the  primary  wave  reflected  at  the  block  :ind 
travelling  backwards  towards  the  pump.  It  thus  of  course  passes 
the  far  lever  before  the  near  one.  The  secondary  waves  of 
oscillation  may  be  similarly  reflected. 

Of  the  secondary  waves  on  the  natural  pulse-curve,  two  deserve 
special  notice. 

The  first  and  most  important  is  the  dicrotic  wave,  occurring 
towards  the  end  of  the  descent.  This  is  always  more  or  less 
marked  in  every  pulse ;  it  may  be  witnessed  in  the  aorta  as  well  as 
in  other  arteries  (Fig.  34,  a  to  e,  C).  Sometimes  it  is  so  slight  as 
to  be  hardly  discernible.  Sometimes  it  is  so  marked  as  to  give  rise 
to  the  appearance  of  a  double  pulse,  hence  the  name  (Fig.  34, 

It  is  more  pointed  in  the  aorta,  and  in  the  larger  arteries  near  to 
the  heart,  than  in  the  more  distant  and  smaller  ones  ;  its  summit  in- 
deed rounds  off  more  rapidly  than  docs  that  of  the  primary  one.  The 
interval  between  »he  primary  and  dicrotic  rises  of  the  pulse-curve  is 
longer  in  the  more  distant  arteries',  and  longer  even  in  the  more  distant 
parts  of  the  same  artery".  It  diminishes  as  the  mean  tension 
increases. 3 

The  conditions  which  favour  the  prominence  of  the  dicrotic 
wave  are  chiefly: — (i)  A  sudden  strong  ventricular  systole.  (2) 
Low  tension.  Hence  dicrotism,  not  previously  well  marked,  may 
be  brought  on  at  once  by  diminution  of  the  peripheral  resistance 
by  section  of  the  vaso-motor  nerves  (see  Sec.  5).  (3)  Extensibility 
(with  elastic  reaction)  of  the  arterial  walls.  Hence  dicrotism  is 
not  well  seen  in  arteries  rigid  from  disease.  It  may  be  well  marked 
in  one  artery  and  yet  very  slight  in  another. 

'  Landois,  o/>.  at.  ■  Moens,  of>.  cit.  '  Moen.s,  op.  cit, 

12 — 2 


i8o 


Fig-  34  "■• 


THE  PULSE.  [BOOK  I. 

Fig.  34  * 


..    SPKVGMOGK.PK   TK.cxNG  KKOM   THE    ASCKKDiHG    AOKXA   (AneuHsmal    dilation). 

Amplified  40  times.  _ 

In  this   and   the   succeeding   pulse-curves,  B   indicates    the   predicrotic   wave,    C 
dicrotic  wave  . 

are  not  intended  for  careful  comparison. 

b     From  carotid  artery  of  a  healthy  man  (set.  26),  amplified  30  times 
Fig.  34^.  ^'''■^'^■ 


c     From  the  radial  artery  of  the  same  person  as  34  b.     Pressure  4  02.     Amplified 

90  times,  as  are  also  the  succeeding  curves. 

(Where  not  otherwise  indicated  this  is  the  amplificauon  of  all  the  pulse-curves.) 

d.     From  radial  artery  of  a  healthy  man  less  athletic  than  34  "?•      Pressure  3  ox. 

Fig,  34  e. 


e.    From  Thk  dorsalis  pedis  of  tke  same  person  as  b  and  c.    Pressure  3  oz. 
Fig.  34/  ^'°    34  ^-^ 


V 


/  Tracing   of   pulse   Ftn.LV    dicrotic;     ffedk-rotic    wave   also   bHE-.VN.     Pressure 

-'■  o  oz.     (?  Typhoid  Fever.) 

e  Pui  se  fully  dicrotic,  and  dicrotic  wave  very  large.     Pressure  i  oz.    (Typhoid 

*■  Fever.) 

»  For  this  and  the  succeeding  pulse-curves  I  am  indebted  to  the  great  kindness 
of  Dr.  Galabin. 


CHAP.    IV.]  THE   VASCULAR   MECHANISM. 

Fig.  34  A.  Fig.  34  k. 


181 


h.      PuusB    WITH    VKRV    LARGE    PREDicROTic   WAVE.      Pressure    4    02.       (Acute    Albu* 

minuria.) 

k.       HVPBRDICROTIC     POLSK,   THE     DICROTIC   WAVE    BECOMING     LOST     OV     THE    SUCCEEDING 

BEAT.  Pressure  J  oz.     After  hxmorrhage  in  typhoid  fever. 

Can  we  explain  the  dicrotic  wave  by  shewing  that  it  is  either  a 
wave  of  oscillation,  or  a  reflected  wave?  That  the  dicrotic  wave 
is  not  one  reflected  from  the  periphery  is  clearly  shewn  by  the  fact 
that  its  distance  from  the  summit  of  the  primary  curve  is  either 
greater  or  at  least  is  not  regularly  less  at  points  of  the  arteries 
nearer  the  capillaries  than  at  points  farther  from  them.  This 
feature  indeed  shews  that  the  dicrotic  wave  cannot  be  in  any  way 
a  retrograde  wave.  Again,  the  more  the  primary  wave  is  obliter- 
ated by  the  elastic  action  of  the  arterial  walls,  the  less  should  be 
the  reflected  wave.  Hence  dicrotism  should  diminish  with  in- 
creased extensibility  and  elastic  reaction  of  the  walls.  The  reverse 
is  the  case.  Besides,  the  multitudinous  peripheral  division  of  the 
arterial  system  would  render  one  large  peripherally  reflected 
wave  impossible. 

On  the  other  hand,  all  the  conditions  which  favour  dicrotism, 
also  favour  the  occurrence  of  waves  of  oscillation.  If  Fig.  33  I. 
be  compared  with  Fig.  34  c,  the  similarity  between  the  wave  of 
oscillation  b  in  the  one  case  and  the  dicrotic  wave  C  in  the  other 
is  very  striking.  And  we  shall  probably  not  go  far  wrong  if  we 
regard  the  dicrotic  wave  as  in  the  main  a  wave  of  oscillation. 
There  is  however  evidence  that  it  is  not  a  simple  wave  of  os- 
cillation but  one  of  mixed  character,  the  movement  of  oscillation 
being  reinforced  by  a  wave  of  expansion  arising  from  the  closure 
of  the  aortic  valves. 

It  has  been  questioned  whether  waves  of  oscillation,  so  manifest  in 
an  artificial  scheme,  do  occur  to  any  extent  in  the  arteries  of  the  body, 
surrounded  as  these  are  by  tissues  which  it  is  argued  must  tend  to  act 
as  dampers  towards  any  oscillations  due  to  inertia.  But  there  is  no 
positive  evidence  of  the  e.\i-tcn:e  of  any  such  marked  damping  a.  tion, 
and  the  remarkable  similarity  between  the  tracings  obtained  by  means 
of  exposed  tubes  and  those  given  by  arteries  in  siiit  is  sufiicient 
evidence  that  in  this  respect  the  two  behave  alike. 

That  however  the  dicrotic  wave  is  not  simply  due  to  the  inertia  of 


1 82  THE   PULSE.  [BOOK   I. 

the  vessels  but  mixed  in  character,  is  shewn  by  its  peculiar  features. 
In  simple  waves  of  oscillation,  such  as  those  shewn  in  Fig.  33  I.,  the 
first  wave  of  oscillation  is  the  largest,  the  succeeding  ones  diminishing 
in  size.  Now  the  dicrotic  wave,  though  undoubtedly  the  most  promi- 
nent and  in  many  cases  the  only  observable  secondary  wave,  is  not  the 
first  secondary  wave.  It  is  frequently  preceded  by  the  so-called 
'  predicrotic '  wave,  which,  sometimes  (Fig.  34  h)  of  considerable  size, 
is  probably  also  a  wave  of  oscillation.  If  both  these  are  waves  of 
oscillation,  there  must  be  causes  at  work  tending  to  diminish  the  first 
(predicrotic)  or  to  exaggerate  the  second  (dicrotic).  And  there  is  an 
event  which  readily  suggests  itself  as  likely  to  reinforce  the  later 
occurring  wave  of  oscillation,  viz.  the  closure  of  the  aortic  valves. 
At  the  close  of  the  ventricular  systole  the  pressure  in  the  aorta  be- 
comes higher  than  that  in  the  ventricle  itself,  and  the  blood  in  conse- 
quence tends  to  flow  back  towards  the  ventricle.  Thus  the  pressure 
in  the  aorta  having  reached  its  maximum  begins  to  fall  by  reason  of 
the  backward  as  well  as  of  the  forward  flow  of  the  blood.  But  the 
closure  of  the  semilunar  valves  gives  a  check  to  this  falk  A  new  wave 
of  expansion  starting  from  the  valves  is  propagated  along  the  aorta  and 
great  arteries  in  sequence  to  the  main  primary  wave.  If  we  suppose 
this  wave,  due  to  the  closure  of  the  aortic  valves,  to  coincide  with  a 
wave  of  oscillation,  the  prominence  of  the  latter  as  the  dicrotic  wave 
becomes  intelligible.  This  view  is  supported  by  the  fact  that  insuffi- 
ciency in  the  working  of  the  semilunar  valves,  the  so-called  aortic 
regurgitation,  materially  interferes  with  the  development  of  the  dicrotic 
wave.  That  the  wave  in  question  should  wholly  disappear  under  these 
circumstances,  is  not  to  be  expected,  seeing  on  the  one  hand  that  it  is 
partly  a  wave  of  oscillation,  and  on  the  other  that  the  valves  need  not 
be  perfectly  closed  in  order  that  a  secondary  wave  of  expansion  maybe 
started  at  the  end  of  the  systole.  Such  a  wave  would  be  originated  by 
any  obstacle  to  the  return  of  blood  into  the  ventricle,  and  such  an 
obstacle  must  exist  with  even  the  most  imperfect  valves,  or  otherwise 
the  circulation  would  soon  come  to  an  end. 

Burdon-Sanderson  however  denies  that  the  aortic  valves  act  as 
above  explained  in  producing  the  dicrotic  wave,  basing  his  opinion  on 
the  grounds  :  1st,  That  not  only  may  the  dicrotic  wave  be  produced, 
but  that  a  tracing  presenting  all  the  graphical  characters  of  the 
radial  pulse  tracing  may  be  obtained  on  an  artificial  scheme  in  the 
absence  of  any  valves  corresponding  to  the  aortic  valves  ;  2nd,  That 
the  form  of  a  tracing  taken  at  any  point  of  an  artificial  scheme  may  be 
modified  at  pleasure,  and  any  natural  pulse  tracing  imitated  by  intro- 
ducing changes  into  the  distal  portion  of  the  scheme  while  the  portion 
corresponding  to  the  heart  remains  absolutely  the  same.  The  view  he 
takes  is  somewhat  as  follows.  If  ^  be  a  point  in  the  arterial  system 
and  B  a  more  distal  point,  the  maximum  expansion  of  B  will  take 
place  somewhat  later  than  the  maximum  expansion  of  A  ;  when  B  is 
at  its  maximum  of  expansion,  A  will  be  already  declining.  As  the 
elastic  reaction  of  B  sets  in  it  exerts  a  pressure  not  only  forwards  but 
backwards,  so  that  the  decline  of  exj^nsion  in  B  may  be  regarded  as 
giving  rise  to  a  wave  of  expansion  travelling  forwards,  and  to  a  wave 
of  expansion  travelling  backwards,  the  latter  reaching  A  during  the 


CHAP.    IV. 1  Tilt:    VASCUI,.\R    MKCIIAMSM.  183 

decline  of  expansion  at  that  point,  and  therefore  givini;  rise  in  A  to  a 
secondary  expansion.  This  secondaryexpansion  due  to  the  action  of 
the  artery  at  the  single  point  B  is  ot  course  small  ;  but  what  is  true  of 
/}  is  also  true  of  all  the  points  distal  to  A.  Consequently  the  artery  at 
the  point  A  is,  durin^j  the  decline  of  its  primary  expansion,  subject 
10  a  secondary  expansion  caused  by  the  elastic  reaction  of  all  the 
arteries  in  front  of,  i.e.  more  distal  than,  itself.  The  dicrotic  wave  at 
any  ^'iven  point  is  in  fact  a  secondary  expansion  brought  about  by  the 
combined  elastic  reaction  of  the  more  distal  portions  of  the  system. 

Moens  '  compares  the  dicrotic  wave  to  the  waves,  which  he  calls 
'waves  of  closure,'  seen  when  the  flow  of  fluid  through  a  tube  is 
suddenly  checked,  and  looks  upon  it  as  simply  a  wave  generated  by 
the  reflux  of  blood  against  the  closed  aortip  valves. 

Mosso"  while  admitting  the  dicrotic  wave  to  be  a  wave  of  oscillation, 
affirms,  in  opposition  to  most  other  observers,  that  it  is  diminished  by 
a  diminution  of  tension,  being  lessened  or  even  abolished  when  the 
artery  dilutes. 

The  other  secondary  wave  worthy  of  notice,  the  so-called  predi- 
crotic  wave.  Fig.  34  /i,  V>.  is  much  more  variable  than  the  dicrotic. 
Its  mode  of  origin  is  obscure,  but  it  is  probably  a  wave  of 
oscillation. 

Sometimes,  though  rarely,  the  dicrotic  wave  is  followed  by  still 
another  wave,  which  seems  to  be  simply  a  wave  of  oscillation.  The 
pulse  is  then  said  to  be  '  tricrotic' 

In  some  instances  the  predicrotic  wave  appears  to  be  broken  into 
two,  and  it  becomes  often  very  difficult  to  distinguish  those  secondary 
waves  of  the  pulse-curve  which  are  really  due  to  events  taking  place 
in  the  artery  from  those  which  have  their  origin  (through  inertia  in  the 
spring,  &c.)  in  the  instrument  itself  3.  It  is  worthy  of  notice  that  the 
summit  of  the  curve  of  intra-ventricular  pressure,  Fig.  28,  is  also 
marked  by  one  or  more  secondary  waves,  bearing  a  considerable  re- 
semblance to  the  predicrotic  wave.  In  the  curves  obtained  by 
Landois-',  by  allowing  the  blood  from  the  end  of  a  divided  artery  to 
spurt  out  on  to  a  recording  surface,  there  is  no  trace  of  a  predicrotic 
wave  though  the  dicrotic  wave  is  exceedingly  well  marked. 

The  pulse  then  is  the  expression  of  two  sets  of  conditions : 
one  pertaining  to  the  heart,  and  the  other  to  the  arterial  system. 
The  arterial  conditions  remaining  the  same,  the  characters  of  the 
pulse  may  be  modified  by  changes  taking  place  in  the  beat  of  the 
heart ;  and  again,  the  boat  of  the  heart  remaining  the  same,  the 
l>ulse  may  be  motlified  by  changes  taking  place  in  tlie  arterial  walls. 
Hence   the  diagnostic    value    of   tiie    pulse-characters.     It  must 

'  Op.  cil.  »   Variazioiii  Lorali  del  Toho,  1878. 

■*  Compare  Galahin,  Jourti.  of  Anal,  and  F/iys   Vol.  Vlii.  p.  i,  also  Vol.  X. 
p.  297- 
*  riliiger's  Anhir,  IX.  (1874)  7r. 


1 84     VITAL  PHENOMENA  OF  THE  CIRCULATION.     [BOOK  I. 

however  be  remembered  that  arterial  changes  may  be  accompanied 
by  compensating  cardiac  changes,  to  such  an  extent,  that  the  same 
features  of  the  pulse  may  obtain  under  totally  diverse  conditions, 
provided  that  these  conditions  affect  both  factors  in  compensating 
directions. 

Venous  Pulse.  Under  certain  circumstances  the  pulse  may  be 
carried  on  from  the  arteries  through  the  capillaries  into  the  veins. 
Thus  when  the  salivary  gland  is  actively  secreting,  the  blood  may  issue 
from  the  gland  through  the  veins  in  a  rapid  pulsating  stream.  This  as 
will  be  explained  hereafter  is  due  to  a  dilation  of  the  arteries.  Such 
exceptional  cases  do  not  militate  against  the  general  assertion  made 
on  p.  174  that  the  pulse  is  absent  from  the  veins. 

If,  as  was  stated  on  p.  161,  the  pressure  in  the  right  ventricle  and 
auricle  becomes  negative  at  the  beginning  of  the  diastole  of  the  ven- 
tricle, we  should  expect  to  find  that  a  wave  of  diminished  pressure 
travelled  backwards  from  the  heart,  along  the  great  veins  ;  and  many 
authors  have  insisted  on  the  existence  of  such  a  '  negative  pulse  '  even 
in  health.  Thus  Mosso  '  gives  tracings  of  the  pressure  curves  of  the 
jugular  and  other  veins  which  are  marked  by  depressions  corresponding 
to  the  elevations  of  the  arterial  pressure  curves. 

Variations  of  pressure  in  the  great  veins  due  to  the  respiratory 
movements  are  sometimes  spoken  of  as  a  venous  pulse  ;  the  nature  of 
these  variations  will  be  explained  in  treating  of  respiration. 

II.     The  Vital  Phenomena  of  the  Circulation. 

So  far  the  facts  with  which  we  have  had  to  deal,  with  the  ex- 
ception of  the  heart's  beat  itself,  have  been  simply  physical  facts. 
All  the  essential  phenomena  which  we  have  studied  may  be 
reproduced  on  a  dead  model.  Such  an  unvarying  mechanical 
vascular  system  would  however  be  useless  to  a  living  body  whose 
actions  were  at  all  complicated.  The  prominent  feature  of  a  living 
mechanism  is  the  power  of  adapting  itself  to  changes  in  its  internal 
and  external  circumstances.  In  such  a  system  as  we  have  sketched 
above  there  would  be  but  scanty  power  of  adaptation.  The  well- 
constructed  machine  might  work  with  beautiful  regularity  ;  but  its 
regularity  would  be  its  destruction.  The  same  quantity  of  blood 
would  always  flow  in  the  same  steady  stream  through  each  and 
every  tissue  and  organ,  irrespective  of  local  and  general  wants. 
The  brain  and  ihe  stomach,  whether  at  work  and  needing  much, 
or  at  rest  and  needing  little,  would  receive  their  ration  of  blood, 
allotted  with  a  pernicious  monotony.  Just  the  same  amount  of 
blood  would  pass  through  the  skin  on  the  hottest  as  on  the  coldest 
day      The  canon  of  the  life  of  every  part  of  the  whole  period  of 

*  Archivio p.  I.  Scien.  Med.  II.  (1878)  p.  401. 


CUM'.    IV.]  THE   VASCUL.\R    MECllA.MSM.  185 

its  existence  would   be  furnished   by  the  inborn  diameter  of  its 
blood-vessels,  and  by  the  unvarying  motive  power  of  the  heart. 

Such  a  rip;id  system  however  does  not  exist  in  actual  living 
beings.  The  vascular  mechanism  in  all  animals  which  possess  one 
is  cai)CLble  of  local  and  general  modifications,  adapting  it  to  local 
and  general  changes  of  circumstances.  These  modifications  fall 
into  two  great  classes  : 

1.  Changes  in  the  heart's  beat.  These,  being  central,  have  of 
course  a  general  effect. 

2.  Changes  in  tlie  peripheral  resistance,  due  to  variations  in 
the  calibre  of  the  minute  arteries,  brought  about  by  the  agency  of 
their  contractile  muscular  coats.     These  changes  may  be  either  • 
local  or  general. 

To  these  may  be  added  as  subsidiary  modifying  events  : 

3.  Changes  in  the  peripheral  resistance  of  the  capillaries  due 
to  alterations  in  the  adhesiveness  of  the  capillary  walls  or  to  other 
influences  arising  out  of  the  as  yet  obscure  relations  existing 
between  the  blood  within  and  the  tissue  without  the  thin  permeable 
capillary  walls,  and  depending  on  the  vital  conditions  of  the  one 
or  of  the  other.  Such  changes  causing  an  increase  of  peripheral 
resistance  are  seen  to  a  marked  degree  in  inflammation. 

4.  Changes  in  the  quantity  of  blood  in  circulation. 

The  two  first  and  chief  classes  of  events  (and  probably  the 
third)  are  directly  under  the  dominion  of  the  nervous  system.  It 
is  by  means  of  the  nervous  system  that  the  heart's  beat  and  the 
calibre  of  the  minute  arteries  are  brought  into  relation  with  each 
other,  and  with  almost  every  part  of  tiie  body.  It  is  by  means 
of  the  nervous  system  acting  either  on  the  heart,  or  on  the  small 
arteries,  or  on  both,  that  a  change  of  circumstances  affecting 
either  the  whole  or  a  part  of  the  body  is  met  by  compensating  or 
regulative  changes  in  the  flow  of  blood.  It  is  by  means  of  the 
nervous  system  that  an  organ  has  a  more  full  supply  of  blood  when 
at  work  than  when  at  rest,  that  the  stream  of  blood  through  the 
skin  rises  and  ebbs  with  the  rise  and  fall  of  the  temperature  of  the 
air,  that  the  work  of  the  heart  is  tempered  to  meet  the  strain  of 
overfull  arteries,  and  that  the  arterial  gates  open  and  shut  as  the 
force  of  the  central  pump  waxes  and  wanes.  Each  of  these  vital 
factors  of  the  circulation  must  therefore  be  considered  in  con- 
nection with  those  parts  of  the  nervous  system  which  are  concerned 
in  their  action. 


1 86  THE   BEAT   OF   THE   HEART.  [BOOK  I. 

Sec.  4.     Changes  in  the  Beat  of  the  Heart. 

We  have  already  discussed  the  more  purely  mechanical  pheno- 
mena of  the  heart.  We  have  therefore  in  the  present  section  only 
to  inquire  into  the  nature  and  working  of  the  mechanism  by  which 
the  beat  of  the  heart  is  maintained,  varied,  and  regulated. 

When  a  frog's  ventricle  which  has  ceased  to  beat  spontaneously 
is  stimulated  by  touching  it  with  a  blunt  needle,  a  beat  is  fre- 
quently called  forth ;  this  artificial  beat  differs  in  no  obvious 
characters  from  a  natural  beat.  The  latent  period  of  such  an 
artificial  beat  is  remarkably  long,  the  length  varying  within  very 
wide  limits.  Thus  the  cardiac  contraction  is  more  like  that  of  an 
unstriated  than  of  a  striated  muscle.  The  beat  is  in  fact  a  modified 
*  or  peculiar  form  of  peristaltic  contraction.  In  the  hearts  of  some 
animals,  the  ventricle  forms  a  straight  tube  ;  and  in  these  the 
peristaltic  character  of  the  beat  is  obvious ;  but  in  a  twisted  tube 
like  that  of  the  vertebrate  ventricle,  ordinary  peristaltic  action  would 
be  impotent  to  drive  the  blood  onward,  and  is  accordingly  so  far 
modified  that  the  peristaltic  character  of  the  beat  is  recognised 
only  when  the  action  of  the  heart  becomes  slow  and  feeble. 

The  cardiac,  like  the  skeletal  muscular  fibre,  after  a  con- 
traction returns  by  relaxation  to  its  previous  shape,  and  the  whole 
ventricle  (or  whole  heart)  regains  after  a  beat  the  form  natural  to 
its  quiescent  state.  This  diastolic  expansion,  though  increased  by, 
is  not  dependent  on,  the  influx  of  fluid  into  the  cavities  of  the 
heart.  Thus  the  cavity  of  the;  empty  quiescent  mammalian  left 
ventricle,  though  smaller  than  when  it  is  distended  with  blood  as 
in  its  normal  action,  is  larger  than  when  it  is  in  systole  or  when 
rigor  mortis  has  set  in  ;  moreover  if  its  dimensions  be  artificially 
lessened,  as  when  it  is  squeezed  with  the  hand,  it  returns  by  aii 
elastic  reaction  to  its  former  volume  when  the  pressure  is  removed. 
It  is  by  this  elastic  expansion  that  the  negative  pressure  during 
diastole  (p.  162)  is  probably  brought  about. 

One  great  feature  of  the  cardiac  beat  produced,  by  artificial 
stimulation  is  seen  in  the  absence  of  any  relationship  between  the 
strength  of  the  stimulus  employed  to  produce  a  beat  and  the  amount 
of  contraction  evoked.  The  beat  with  which  a  heart  responds  to  a 
stimulus,  e.g.  a  single  induction  shock,  is,  if  there  be  any  response  at 
all,  equally  large  when  a  feeble  as  when  a  strong  stimulus  is  used, 
though  the  strength  of  the  beat  evoked  either  by  a  strong  or  a  weak 
stimulus  may  vary  considerably  within  even  a  very  short  period  of 
time. 

When  a  second  induction  shock  is  sent  in  at  a  certain  interval  after 
the  first,  the  beat  due  to  the  second  shock  is  often  larger  than  the  first, 
the  beneficial  effects  of  a  contraction  (see  p.  99)  being  even  still  more 


CIIAI'.    IV.  1  TIIK    VASCULAR    MlJ  HA.NISM.  1 87 

manifest  in  the  licart  than  in  an  ordinary  skeletal  muscle.     Frequently 
by  successive  shock-;  of  equal  intensity  a  'staircase'  of  beats  of  suc- 
cessively increasing,'  amplitu^le  may  be  produced. 
►  When  a  second  induction  sho-k  follows  upon  the  first  too  rapidly, 

it  is  apparently  without  effect  ;  no  second  beat  is  produced.  So  also 
when  a  scrici  of  rapidly  repeated  induction  shocks  are  sent  in,  a 
certain  number  of  thc;n  are  thus  'ineffectual  *  ;  the  application  of  the 
ordinary  interrupted  current  gives  rise  not  to  a  tetanus  but  to  a  rhythmic 
series  of  beats.  The  'refractory  period,'  which  is  so 'brief  in  the 
skeletal  muscle  (see  p.  89),  is  very  prolonged  in  the  cardiac  muscle. 
So  also  in  a  spnnt meously  beating  heart,  induction  shocks  sent  in  at 
a  certain  phase  of  a  cardiac  cycle,  ^.^i.--.  the  commencement  of  the 
systole,  are  ineffectual,  though  they  produce  forced  beats  when  sent 
in  at  the  other' phases  of  the  cycle'. 

The  elasticity  of  the  cardiac  walls  is  in  a  healthy  condition,  like 
that  of  a  skeletal  muscle,  very  perfect.  It  is  however  soon  interfered 
with  by  unptTftct  nutrition;  and  a  'contraction  remainder'  (p.  60) 
under  certain  circumstances  is  readily  developed^ 

Under  the  influences  of  certain  poisons,  veratrin,  digitalin,  &c.,  the 
length  of  the  beat  is  enormously  prolonged,  and  the  ventricle  eventually 
thrown  into  a  remarkable  contracted  condition,  the  exact  nature  of 
which  is  perhaps  not  thoroughly  understood,  though  it  is  believed  by 
many  to  be  due  to  a  deficiency  of  elastic  reaction  3. 

Nervous  mechanism  of  the  Beat.  The  beat  of  the 
heart  is  an  automatic  a£tion ;  the  muscular  contractions  which 
constitute  the  beat  are  caused  by  impulses  which  arise  sponta- 
neously in  the  heart  itself. 

The  heart  of  a  frog  (or  of  a  turtle  or  fish,  &c.)  will  continue 
to  beat  for  hours,  or  under  favourable  circumstances  for  days, 
after  removal  from  the  body.  'I'he  beat  goes  on  even  after  the 
cavities  have  been  cleared  of  blood,  and"^  indeed  when  they  are 
almost  empty  of  all  fluid.  The  beats  are  more  vigorous,  and  last 
longer,  when  tlie  heart  is  removed  by  incisions  which  leave  the 
sums  venosus  still  attached  to  the  auricles.  The  excised  heart 
does  liowever,  though  for  a  shorter  time  and  not  so  readily,  con- 
tinue to  beat  spontaneously  when  removed  by  an  incision  carried 
through  the  auricles  so  that  a  portion  or  even  the  whole  of  the 
auricles  together  with  the  sinus  venosus  is  left  behind  in  the 
body.  In  this  case  the  parts  left  behind  are  seen  also  to  go  on 
beating  by  them.selves. 

If  in  an  excised  heart  the  ventricle  be  divided  from  the 
auricles,  both   ventricle  and  auricle    will   go   on    beating.     Each 

'  C f.  Bnvdilch,  Ludwij^'s  Arbiitni,  1S71  ;  .-ind  Marey,  Travaux  du  Laboiat, 
n.  (1S76)  p.  63. 

'  l<oy,  Journ.  Physiol.  I,  (1878)  p.  452. 

^  Schmiedcbcrg,  I.udwi.('s  Ftitgiibc,  (1S74)  p.  222. 


l88  CARDIAC   INHIBITION.  [BOOK  I. 

moiety  has  then  an  independent  rhythm.  If  the  spontaneously- 
beating  auricle  be  bisected  longitudinally,  each  lateral  half  will  go 
on  beating  spontaneously.  Each  lateral  half  may  be  still  further 
divided,  and  yet  the  pieces  will  under  favourable  circumstances  go 
on  pulsating.  The  ventricle  will  go  on  beating  when  bisected  lon- 
gitudinally ;  but  if  it  be  cut  across  transversely,  the  lower  half 
remains  motionless,  while  the  upper  goes  on  pulsating.  The 
power  of  spontaneous  pulsation  is  limited  to  the  extreme  base,  for 
if  the  transverse  incision  be  carried  only  at  a  little  distance  from 
the  auriculo-ventricular  groove  all  power  of  spontaneous  pulsation 
is  lost  in  the  lower  part.  When  these  several  parts  of  the  heart 
are  examined,  it  is  found  that  in  all  of  those  which  beat  spon- 
taneously ganglia  are  present,  while  from  the  ventricle  except  at 
the  extreme  base  ganglia  are  absent.  There  are  ganglia  in  the 
sinus,  ganglia  in  the  auricular  septum  and  walls,  ganglia  in  the 
auriculo-ventricular  groove,  but  none  have  been  found  in  the  mass 
of  the  ventricle  itself.  From  these  facts  the  conclusion  is  drawn 
that  the  spontaneous  pulsations  in  the  heart  are  in  some  way 
associated  with,  and  due  to  the  action  of,  the  ganglia  scattered  in 
its  substance.  Of  these  ganglia  those  in  the  sinus  seem  more 
potent  than  those  in  other  parts  of  the  heart. 

The  exact  manner  in  which  these  gangha  act  is  still  obscure.  The 
vigour  of  the  rhythmic  contractions,  and  the  time  they  continue  to  go 
on  is  so  much  greater  in  the  case  of  the  heart  retaining  the  sinus 
venosus  than  in  that  from  which  it  has  been  removed,  that  many  regard 
the  beats  of  the  former  only  as  really  automatic.  They  look  upon  the 
beats  of  the  latter,  though  repeated  rhythmically,  and  that  for  even  a 
long  series,  to  be  the  result  of  some  stimulation  or  other.  They  accor- 
dingly speak  of  the  sinus  ganglia  as  being  automatic,  and  of  the  rest  as 
being  of  reflex  or  other  function. 

Though  the  portion  comprising  the  lower  two-thirds  of  the  ventricle 
remains  after  separation  from  the  basal  third  permanently  quiescent,  it 
may  be  thrown  into  rhythmic  contractions,  indistinguishable  in  their 
character  from  normal  beats,  by  the  application  of  the  constant  current. 
It  will  also  give  apparendy  spontaneous  rhythmic  beats,  when  supplied, 
according  to  the  Leipzig  method,  with  rabbit's  serum  or  dilute  rabbit's 
blood'.  For  this  purpose,  a  tube,  completely  divided  by  a  longitudinal 
partition  into  two  canals,  is  introduced  into  the  cavity  of  the  ventricle, 
and  the  latter  securely  ligatured  round  the  tube  at  the  junction  of  the 
upper  and  middle  thirds.  Fluid  introduced  through  one  canal  at  a  low 
pressure  distends  the  ventricle,  and  when  a  beat  takes  place,  is  driven 
out  through  the  other  canal.  Fed  in  this  way  with  rabbit's  (or  sheep's, 
&c.)  serum  or  blood,  almost  any  part  of  the  ventricle  may  be  made  after 
a  period  of  rest  to  execute  what  are  apparently  spontaneous  rhythmic 

^  Merunowicz,  Lud wig's  Arbeiten,  1875,  p,  132.  Compare  however  Bern- 
stein, Cetitralbt.  f.  med.  Wiss.  1876,  385,  435.  Bov/ditch,  Jourru  Physiol.  I, 
(1878)  p.  104. 


CHAP.    IV.  1  THE    VASCULAR    .MECHANISM.  189 

pufsations.  If  it  be  urged  that  the  serum  or  blood  is  a  stimulus  which 
provokes  contractions,  there  still  remains  the  difficulty,  why  the  con- 
tinued stimulus  produces  not  a  continued  contraction,  but  a  rhythmic 
pulsation.  Moreover,  in  the  case  of  the  rhythmic  beats  evoked  by  the 
con-.tant  current,  the  current  cannot  during  its  passage  be  regarded  aa 
a  stimulus  in  the  ordinary  sense  of  the  word. 

The  beat  of  the  mammalian  heart  cannot  be  studied  in  th>; 
same  way  as  that  of  the  frog,  for  the  former  ceases  to  beat  almost 
immediately  after  removal  from  the  boiiy ;  but  all  the  facts  which 
have  hitherto  been  observed  go  to  prove  that  the  heart  of  a  warm 
blooded  animal  is  governed  by  a  nervous  mechanism  similar  to 
that  which  has  just  been  described. 

Just  as  the  two  auricles  of  the  frog's  heart  beat  synchronous!) 
under  all  circumstances  (excepting  actual  separation),  so  also  the 
two  ventricles  of  the  mammalian  heart  act  completely  as  one.  A 
want  of  synchronism  in  the  two  ventricles,  though  it  has  been 
called  in  to  explain  certain  pathological  phenomena,  has  not  been 
observed  experimentally. 

The  o.currence  of  two  cardiac  impulses  to  one  arterial  pulse,  /.  e.  an 
intt.rminence  of  the  arterial  pulse  unaccompanied  by  a  cardiac  inter- 
mittence,  which  has  sometimes  suggested  the  idea  of  a  want  of  syn- 
chronism in  the  two  ventricles,  leading  to  a  double  cardiac  impulse, 
may  be  otherwise  explained.  In  such  a  cise,  of  the  two  contractions 
of  the  ventricle  one  is  so  wenk  that  it  fails  to  throw  into  the  arterial 
system  enough  blood  to  give  rise  to  a  pulse-wave. 

Inhibition  of  the  Beat.  The  beat  of  the  heart  may  be 
stopped  or  checked,  /.  c.  may  be  inhibited  by  efferent  impulses 
descending  the  vagus  nerve. 

If  while  the  beats  of  the  heart  of  a  frog  or  rabbit  are  being 
carefully  registered  (Fig.  35)  an  interrupted  current  of  moderate 
strength  be  sent  through  one  of  the  vagi,  the  heart  is  seen  to  stop 
beating.  It  remains  for  a  time  in  diastole,  perfectly  motionless 
and  flaccid.  If  the  duration  of  the  current  be  short  and  the 
strength  of  the  current  great,  the  stand  till  may  continue  after  the 
current  has  been  shut  off;  the  beats  when  they  reappear  are 
generally  at  first  feeble  and  infrequent,  but  soon  reach  or  even  go 
beyond  their  previous  vigour  and  frequency.  A  wholly  similar 
inhibition  may  be  setjn  in  the  mammal ;  and  indeed  in  man  : 
Czermak,  by  pressing  his  vagus  against  a  small  osseous  tumour  in 
his  neck,  and  tlius  mechanically  stimulating  the  nerve,  was  able  to 
stop  at  will  the  beating  of  his  own  heart;  it  need  hardly  be  added 
that  such  an  experiment  is  a  dangerous  one. 

The  effect  is  not  produced  instantaneously  ;  if  on  the  curve  the 
point  be  exactly  marked  as  at  a   (F:g.   35)  where  the  current  i3 


190 


CARDIAC   INHIBITION. 


[BOOK   I. 


6  a 


MMMMm.^^ 


mm^ 


Fig.  35.    Inhibition  of  Frog's  Heart  by  stimulation  of  the  Vagus. 

The  contractions  of  the  ventricle  are  registered  by  means  of  a  simple  lever,  so  that  each  rise 
of  the  lever  corresponds  to  a  beat.  The  interrupted  current  was  thrown  in  at  a,  and  shut  off 
at  b.  It  will  be  seen  that  one  beat  occurred  afi.er  a,  and  that  the  pause  continued  for  some 
time  after  b.     To  be  read  from  right  to  left. 

made,  it  will  frequently  be  found  that  one  beat  at  least  occurs  after 
the  current  has  passed  into  the  nerve.  In  other  words,  the  inhibi- 
tory action  of  the  vagus  has  a  long  latent  period  :  this  has  been 
estimated  by  Bonders  to  last  in  the  rabbit  •16  sec.  The  inhibitory 
effect  is  at  a  maximum  soon  after  the  moment  of  application  of 
the  current,  and  diminishes  gradually  onward ;  so  much  so  is  this 
the  case  that  when  the  current  is  applied  for  more  than  a  very 
short  time  the  heart  recommences  beating  before  the  current  is 
removed.  The  effect,  especially  with  weak  currents,  is  much  more 
in  the  direction  of  prolonging  the  diastole,  than  of  diminishing 
the  extent  of  the  systole.  Hence  with  weak  currents,  no  actual 
stoppage  takes  place,  but  the  pauses  between  the  beats  are  much 
prolonged,  especially  at  the  beginning  of  the  action  of  the  current, 
and  the  pulse  thereby  rendered  slow.  During  the  standstill,  direct 
stimulation  of  the  heart,  as  by  touching  the  auricle  or  ventricle, 
will  produce  a  single  beat ;  though  spontaneous  pulsations  are 
absent,  the  irritability  of  the  muscular  fibres  is  not  destroyed. 

The  stimulus  need  not  be  an  interrupted  current ;  mechanical 
and  chemical  stimulation  of  the  vagus  also  produces  inhibition, 
though  less  readily. 

After  atropin,  even  in  a  minute  dose,  has  been  injected  into  the 
blood,  stimulation  of  the  vagus  even  with  thfe  most  powerful  cur- 
rents produces  no  inhibition  whatever.  The  heart  continues  to 
beat  as  if  nothing  were  happenmg  ;  atropin  in  some  way  or 
other  does  away  with  the  normal  inhibitory  action  of  the  vagus. 

The  above  facts  shew  that  the  events  which  are  at  the  bottom  of 
vagus  inhibition  are  complex.  The  following  considerations  render 
this  still  more  evident. 


CIIAl"     IV.]  Till';    VASCULAR    MECHANISM.  I9I 

A  single  induction  shock  rarely  produces  an  efTect  which  can  be 
measured  ;  but  a  series  of  shocks  repeated  at  intervals  (the  interval 
may  b^  ccjual  to  or  even  greater  than  the  length  of  a  whole  cardiac 
cycle)  produces  very  mnked  inhibition. 

If  one  application  of  the  current  be  rapidly  followed  by  a  second 
application  of  the  same  current,  the  effects  arc  very  markedly  less. 
This  seems  to  be  due  partly  to  exhaustion  of  the  vagus  fibres  but  also 
to  something  which  has  taken  pla  -c  in  the  heart  itself,  for  a  stimulation 
of  one  vagus,  immediately  following  a  stimulation  of  the  other,  at  least 
when  prolonged,  is  diminished  in  effect'. 

The  stimulus  may  be  applied  at  any  part  of  the  course  of  either 
vagus  (though  it  frequently  happens  in  the  frog  that  one  vagus  is  more 
efficient  than  the  other)  ;  but  perhaps  the  most  marked  effects  are  pro- 
duced, when  the  electrodes  are  placed  on  the  boundary-line  between 
the  sinus  venosus  and  the  auricles. 

In  slight  urari  poisoning,  the  inhibitory  action  of  the  vagus  is  still 
present  ;  in  the  profounder  stages  it  disappears,  but  even  then  inhibition 
may  be  obtained  by  applying  the  electrodes  to  the  sinus. 

In  order  to  explain  this  result  it  has  been  supposed  that  the  in- 
hibitory fibres  of  the  vagus  terminate  in  an  inhibitory  meclianism 
(probably  ganglionic  in  nature),  seated  in  the  heart  itself,  and  that  the 
urari,  while  in  large  doses  it  may  paralyse  the  terminal  fibres  of  the 
vagus,  leaves  this  inhibitory  mechanism  intact  and  capable  of  being 
thrown  into  activity  by  a  stimulus  applied  directly  to  the  sinus.  After 
atropin  has  been  given,  inhibition  cannot  be  brought  by  stimulation 
either  of  the  vagus  fibres  or  of  the  sinus,  or  indeed  of  any  part  of  the 
heart.  Hence  it  is  inferred  that  atropin,  unlike  urari,  paralyses  this 
intrinsic  inhibitory  mechanism  itself. 

After  the  application  of  muscarin  or  jaborandi,  the  heart  stops 
beating,  and  remains  in  diastole  in  perfect  standstill.  Its  appearance 
is  then  exactly  that  of  a  heart  inhibited  by  profound  and  lasting  vagus 
stimulation.  This  eftect  is  not  hindered  by  urari.  The  application 
however  of  a  small  dose  of  atropin  at  once  restores  the  beat.  These 
facts  are  interpreted  as  meaning  that  muscarin  (or  jaborandi)  stimu- 
lates or  excites  the  inhibitory  apparatus  spoken  of  above,  which  atropin 
paralyses  or  places  ]iors  lie  covibat.  It  is  doubtful  whether  the  stand- 
still produced  by  musL\arin  after  it  has  been  put  on  one  side  by  atropin, 
can  be  brought  back  again  by  further  doses  of  muscarin.  In  the  case 
of  jaborandi  it  can.  When  jaborandi  is  carefully  applied  to  the  ven- 
tricle externally,  the  ventricle  may  be  brought  to  a  standstill,  while  the 
auri -les  continue  to  go  on  beating  as  usual ^ 

Nicotin,  when  given,  first  slows  the  heart  even  to  a  standstill  ;  but 
after  a  while  the  beats  recover  their  usual  rhythm.  Stimulation  of  the 
vagus  is  then  found  to  have  no  effect  ;  muscarin  however  at  once 
produces  a  standstill,  which  in  turn  may  be  removed  by  atropin. 
The  initial  slowing  effect  is  absent  if  atropin  or  urari  be  previously 
given  These  facts  are  interpreted  as  shewing  that  nicotin  first  excites 
the  terminal  fibres  of  the  vagus,  producing  inhibitory  effects,  but  that 

»  Cf.  Gamgce  and  Priestley,  Journ.  Physiol.  I.  (1878)  p.  39. 
■  Langley,  Jjuni.  Anat.  .K.  (1875)  1S7. 


192  CARDIAC   INHIBITION.  [BOOK   I. 

this  excitement  ends  in  an  exhaustion  of  these  fibres.  The  action  of 
the  drug  however  is  hmited  to  the  terminal  fibres  of  the  vagus,  and 
does  not  bear  on  the  intrinsic  inhibitory  apparatus,  with  which  these 
fibres  are  connected  ;  hence  while,  after  nicotin  poisoning,  stimulation 
of  the  trunk  of  the  vagus  is  ineffectual,  a  small  dose  of  muscarin, 
which  acts  directly  on  the  apparatus  itself,  produces  standstill. 

According  to  Nuel^  stimulation  of  the  vagus  while  it  producfes  in 
the  ventricle  simply  lengthening  of  the  diastole,  without  change  in 
the  force  of  the  systole,  has  a  marked  effect  on  the  force  of  the  systole 
of  the  auricle.  Roy^  finds  direct  stimulation  of  the  auricle  to  bring 
about,  according  to  the  spot  stimulated,  sometimes  slowing  sometimes 
quickening  of  the  beat,  with  increase  or  with  decrease  of  force. 

If  a  ligature  be  drawn  tightly  round  the  junction  of  the  sinus 
venosus  with  the  auricles,  or  if  the  auricles  be  separated  from  the  sinus 
by  an  incision  carried  along  the  boundary-fine  between  the  two,  a 
standstill  is  produced  closely  resembling  a  very  prolonged  vagus  inhi- 
bition. The  quies:ence  thus  induced  may  last  an  indefinite  time.  This 
experiment  we  owe  10  Stannius^.  During  the  standstill,  a  pulsation 
may  be  induced  by  a  stiinulus  applied  directly  to  the  heart,  a  whole 
series  of  beats  being  evoked  when  a  mechanical  stimuius,  such  as  the 
prick  of  a  needle  is  applied  over  the  seat  of  Bidder's  ganglia  at  the 
junction  of  the  auricles  with  the  ventricles,  or  to  the  ganglia  in  the 
auricles  and  in  the  bulbus* ;  and  when  the  ventricle  is  separated  by 
an  incision  from  the  auricles,  the  former  will  recommence  beating, 
while  the  latter  remain  as  quiescent  as  before.  A  rhythmic  beat  may 
also  be  induced  during  the  standstill  by  applying  the  constant  current, 
during  the  action  of  M'hich  there  is  a  great  tendency  for  the  ventricle 
to  beat  before  the  auricles. 

Two  interpretations  have  been  offered  of  this  standstill.  It  has 
been  suggested  that  the  ligature  or  section  stimulates  the  endings  of 
the  vagus,  and  so  produces  inhibition.  This  is  disproved  by  the  fact 
that  the  standstill  appears  equally  well,  whether  atropin  have  been 
previously  given  or  not.  According  to  the  other  view,  the  really  auto- 
matic movements  of  the  heart  depend  on  the  ganglia  in  the  sinus,  the 
pulsations  which  appear  in  the  isolated  ventricle  or  auricles  being  in 
reality  reflex  pulsations,  or  pulsations  caused  by  some  stimulus  not 
really  automatic,  and  therefore  not  so  lasting  ;  or,  if  there  be  an  auto- 
matic apparatus  in  ventricle  or  auricle,  it  is  kept  in  check  by  the  action 
of  the  inhibitory  apparatus  spoken  of  above,  and  only  makes  its  pre- 
sence felt  on  some  stimulus  bemg  applied.  This  view  again  is  disproved 
by  the  fact  that  if  the  sinus  be  gradually  separated  from  the  auricles,  no 
standstill  takes  place.     The  whole  subject  needs  further  elucidation. 

Reflex  Inhibition.  This  inhibitory  action  of  the  vagus 
may  be  brought  about  by  reflex  action.  If  the  abdomen  of  a  frog 
be  laid  bare,  and  the  intestine  be  struck  sharply,  as  with  the  handle 

»  Pfluger's  Arc/iiv,  IX.  (1874)  p.  83.     ^  yotcrn.  Physiol.  I.  \,\2,-]2,)  p.  452. 
3  Mliller's  Archiv,  1852,  p.  85. 

*  Munk,  Verharidl.  Berl.  physiol.  Gesell.  x&vo-cttdin  Airhivf.  Anat.u.  Fhys., 
1878,  p.  569- 


CHAl'.    IV. J  THE   VASCULAR    MECHANISM.  Iy3 

of  a  scalpel,  the  lieart  will  stand  still  in  diastole  with  all  the  pheno- 
mena of  vagus  inhibition.  If  the  ncn'i  fncsenierici  or  the  connec- 
tions of  these  nerves  with  the  sympathetic  chain  be  stimulated 
with  the  interrupted  current,  cardiac  inhibition  is  similarly  pro- 
duced. If  in  these  two  experiments  both  vagi  are  divided,  or  the 
medulla  oblongata  destroyed,  inhibition  is  not  produced,  however 
much  either  the  intestine  or  the  mesenteric  nerves  be  stimulated. 
This  shews  that  the  phenomena  are  caused  by  impulses  ascending 
along  the  mesenteric  nerves  to  the  medulla,  and  so  aft'ecting  a  por- 
tion of  that  organ  as  to  give  rise  by  reflex  action  to  impulses  which 
descend  the  vagi  as  inhibitory  impulses.  The  portion  of  the 
medulla  thus  mediating  between  the  afferent  and  efferent  impulses 
may  be  spoken  of  as  the  cardio-inhibitory  centre. 

If  the  peritoneal  surface  of  the  intestine  be  inflamed,  very 
gentle  stimulation  of  the, inflamed  surface  will  produce  marked 
inhibition  ;  and  in  general  the  alimentary  tract  seems  in  closer 
'  connection  with  the  cardio-inhibitory  centre  than  other  parts  of 
the  body;  but  apparently  stimuli  if  sufficiently  powerful  will  through 
reflex  action  produce  inhibition  from  whatever  part  of  the  body 
they  may  come.  Thus  crushing  a  frog's  foot  will  stop  the  heart. 
In  ourselves  the  fainting  from  emotion  or  from  severe  pain  is  the 
result  of  a  reflex  inh'b.tion  of  the  heart,  the  afferent  impulses  in 
the  one  case  at  least,  and  probably  in  both  cases,  reaching  the 
medulla  from  the  brain. 

Direct  stimulation  of  the  centre  itself,  such  as  occurs  during 
the  destruction  of  or  results  from  injury  to  the  medulla,  of  course 
produces  inhibition  ;  and  inhibition  through  one  vagus  may  be 
brought  about  by  stimulation  of  the  central  end  of  the  other. 

Thus  by  nervous  links,  the  regulative  action  of  the  inhibitory 
mechanism  is  brought  into  more  or  less  close  communion  with  all 
parts  of  the  body. 

The  question  naturally  arises.  Has  this  cardio-inhibitory  centre  any 
constant  automatic  action  ? 

In  the  dog,  and  also,  though  to  a  far  less  extent,  in  the  rabbit,  sec- 
tion of  both  vagi  is  followed  by  a  quickening  of  the  heart's  beat. 
This  result  may  be  interpreted  as  shewing  that  the  centre  in  the 
medulla  exercises  a  permanent  restraining  influence  on  the  heart ;  that 
organ  in  fact  being  habitually  curbed.  (The  argument  that  the  effects 
of  an  artificial  stimulation  of  the  vagus  soon  wear  off,  and  that  there- 
fore a  permanent  stimulation  of  the  vagi,  leading  to  permanent  in- 
hibitory action,  would  be  inipo>sible,  may  be  met  by  the  suj;gestion 
that  the  effects  of  natural  stimulation  need  not  necessarily  wear  otT. ) 
If  however,  previous  to  the  section  of  the  vagi,  afferent  impulses  to 
the  centre  in  the  medulla  are  cut  off  by  the  section  of  the  spinal  coid 
below  the  medulla,  and  by  division  of  the  cervical  sympathetic  chain, 
F.  l>.  13 


194  ACCELERATOR   NERVES.  [BOOK   I. 

110  acceleration  follows  the  division  of  the  vagi.  This  would  shew 
that  the  action  of  the  medulla  in  this  matter  is  purely  reflex  and  not 
automatic.  Such  an  experiment,  however,  introduces  many  sources  of 
error  ;  and  perhaps,  the  question  itself  is  at  bottom  a  barren  one. 
Granting,  however,  the  existence  of  a  centre  in  the  medulla,  which 
either  automatically  or  otherwise  is  in  permanent  action,  it  is  obviously 
open  to  us  to  speak  of  reflex  inhibition  as  being  brought  about  by  in- 
fluences which  augment  the  action  of  that  centre.  But  we  have  seen 
that  active  nervous  centres  are  subject,  not  only  to  augmentative,  but 
also  to  inhibitory  influences.  Hence  the  cardio-inhibitory  centre  might 
itself  be  inhibited  by  impulses  reaching  it  from  various  quarters.  In 
other  words,  the  beat  of  the  heart  might  be  quickened  by  a  lessening 
of  the  normal  action  of  its  inhibitory  centre  in  the  medulla.  It  is  in 
fact  probable,  that  many  cases  of  quickening  of  the  heart's  beat  are 
produced  in  this  way  ;  though  the  matter  requires  further  investigation. 

Accelerator  nerves.  The  heart's  beat  may  in  the  mammal  be 
quickened,  even  after  division  of  both  vagi,  by  direct  stimulation  of 
the  cervical  spinal  cord.  The  efifects  produced,  however,  are  very 
complex,  and  led,  on  their  first  being  made  known,  to  much  discussion, 
one  outcome  of  which  was  the  discovery  of  certain  nerves  of  a  very 
peculiar  character,  which  pass  from  the  cervical  spinal  cord,  frequently 
along  the  nerve  accompanying  the  vertebral  artery,  and  reach  the 
heart  through  the  last  cervical  and  first  thoracic  ganglia  :  these  have 
been  called  the  'accelerator  nerves.'  Their  course  is  different  in  the 
rabbit  and  in  the  dog,  see  Figs.  36  and  37,  and  indeed  varies  even  in 
the  same  kind  of  animal.  Stimulation  of  these  nerves  with  the  inter- 
rupted current  causes  a  quickening  of  the  heart's  beat,  in  which  what 
is  gained  in  rate  is  lost  in  force,  for  the  blood-pressure  is  not  necessarily 
increased,  but  may  remain  the  same,  or  even  be  diminished.  Not 
only  is  the  latent  period  of  the  action  of  these  nerves  considerable, 
but  it  moreover  takes  a  very  long  time,  as  much  as  10  seconds,  even 
with  maximal  stimulation,  before  the  maximum  of  acceleration  is 
reached  (the  acceleration  often  continuing  after  the  stimulus  has  been 
removed)  and  the  decline  back  to  the  normal  pulse-rate  is  still  slower. 
Stimulation  for  even  a  second  may  thus  produce  an  acceleration  lasting 
a  considerable  time.  These  accelerator  nerves  seem '  to  be  unaffected 
by  the  various  poisons,  including  urari,  which  act  upon  the  vagus  and 
other  parts  of  the  nervous  system  of  the  heart,  and  are  effective  in  the 
midst  of  profound  asphyxia.  Their  influence  is  closely  dependent  on 
temperature  ;  at  low  temperatures  their  influence  is  slight,  and  long  in 
making  its  appearance  ;  as  the  temperature  rises  their  action  becomes 
more  speedily  developed  and  more  powerfuk  They  are  not  to  be 
considered  as  antagonistic  to  the  vagi  ;  for  if  during  maximum  stimu- 
lation of  the  accelerator  nerves  the  vagus  be  stimulated,  even  with 
minimum  currents,  inhibition  is  produced  with  the  same  readiness  as  if 
these  were  not  acting^     The  period  of  inhibition  however  is  followed 

'  Schmiedeberg,  Ludwig's  Arbdten,   187 1. 

^  Baxt.  Die  Siellung  dcs  N.   vagus  zuni  N.  accelerans,  Ludwig's  Arbeiten 
1875. 


CMAP.    IV.J  THE   VASCULAR   MliCIIAXISM,  I95 

by  a  period  of  acceleration  similtxr  to  that  produced  by  the  action  of 
the  accelerator  alone,  the  vagus  action  appearing  simply  to  suspend, 
during  its  continuance,  the  manifestation  of  the  accelerator  action  but 
not  to  annul  it.  We  know  at  present  little  concerning  the  share  which 
these  nerves  take  in  the  natural  action  of  the  econo.ny.  If,  as  later 
researches  of  Haxt'  would  seem  to  shew,  their  accelerating  effect  is 


si/ni.t^r. 


Fig.  36.    The  la«:t  cervical  antj  first  thoracic  Ganglia  in  the  Rabbit.  (Left  side.) 
(Somewhat  diagrammatic,  many  of  the  various  branches  being  omitted.) 

Trach.  Trachex  Ca.  carotid  artery,  sb.  subclavian  artery.  «.  Vaz-  the  vagus  trunk. 
n.  rec.  the  recurrent  laryngeal,  sym  the  cervical  sympathetic  nerve  ending  in  the  inferior 
cervical  ganglion,  g-l.  cern.  inf.  Two  roots  of  the  ganglion  are  shewn,  ritd..  the  lower  of 
the  two  accompanying  the  vertebral  artery,  A.  vert.,  being  the  one  generally  possessing 
accelerator  properties.  s;l.  thor.  fir.  the  first  thoracic  ganglion.  Its  two  branches  communi- 
cating with  the  cervical  ganglion  surround  the  subclavi.an  ar  ery  forming  the  annuhis  of 
Vieussens.  sym.  thor.  the  thoracic  sympathe'.ic  ch.ain.  «.  tiefi.  depressor  nerve  Thi-i  is 
joined  in  its  c  nirse  by  a  branch  from  the  lower  cervical  ganglion,  there  being  a  small  g.anglion 
at  their  junction,  from  which  prorced  necvc-s  to  form  a  plexus  over  the  arch  of  the  aorta.  It 
IS  this  branch  from  the  lower  cervical  ganglion  which  possesses  accelerator  properties — hence 
the  course  of  the  accelerator  fibres  is  indic.ited  in  the  figure  by  the  arrows. 

characterized  not  only  by  a  diminution  of  the  diastole  but  also  by  an 
actual  shortening  of  the  cardiac  systole,  it  is  obvioui  that  the  quickening 
of  the  heart's  beat  produced  by  their  action  is  something  quite  dilfcrcnt 
from  the  quickening  indirectly  brought  about  by  a  diminution  of  the 
activity  of  the  cardio-inhibitory  centre.     Haxt  compares  their  action 


Archivf.  Atiat.  u.  P/iys.  187S,  p.  121. 


13—2 


196 


ACCELERATOR   NERVES. 


[BOOK   I. 


to  that  of  heat  directly  influencing  the  cardiac  tissues  ;  and  the  com- 
parison is  certainly  a  suggestive  one. 

Many  observers  have  obtained  an  acceleration  of  the  heart's  beats 
upon  stimulation,  under  certain  circumstances,  of  the  trunk  of  the 
vagus.  And  Schiff^  maintains  that  the  accelerator  nerves  described 
above  come  from  the  vagus  and  not  from  the  spinal  cord. 


r.  ^yjit. 


gtth.pr 


sym.-^rac. 


Fig.  37.     The  last  cervical  and  first  thoracic  Ganglia  in  the  Dog. 

The  cardiac  nerves  of  the  Dog.     The  figure  is  largely  diagrammatic,  and  represents  the 

left  side. 

V.  sym.  the  united  vagus  and  cervical  sympathetic  nerves,  gl.  cerv.  i.  the  inferior 
cervical  ganglion.  n.  v.  the  continuation  of  the  trunk  of  the  vagus,  ann.  V.  the  two 
branches  forming  the  annulus  of  Vieussens  round  the  subclavian  artery,  art.  sulci.,  and 
joining^/,  th.  pr.,  the  first  thoracic  or  stellate  ganglion  ('he  branch  running  in  front  of  the 
artery  is  considered  by  Schmiedeberg  to  be  an  especial  channel  of  accelerator  fibres),  sym. 
thorac.  the  .sympathetic  trunk  in  the  thorax,  r.  vert,  communicating  branches  from  the  cer- 
vical nerves  running  alongside  the  vertebral  artery,  the  rami  vertebrales.  71  7'ec.  the  recurrent 
laryngeal,  n.  c.  cardiac  branches  from  the  lower  cervical  ganglion,  accelerator  nerves  of 
Schmiedeberg  71'.  c' .  cardiac  branches  from  the  first  thoracic  ganglion,  accelerator  nerves  of 
Cyon._  71" .  c" .  cardiac  branch  from  recurrent  nerve.  r.  7-ec.  branch  from  lower  cervical 
ganglion  .to  the  recurrent  nerve,  often  containing  accelerator  fibres. 

The  beat  of  the  heart  may  also  be  modified  by  influences  bear- 
ing directly  on  the  nutrition  of  the  heart.  The  tissues  of  the 
heart,  like  all  other  tissues,  need  an  adequate  supply  of  blood  of 
a  proper  quality ;  if  the  blood  vary  in  quality  or  quantity  the  beat 
of  the  heart  is  correspondingly  afifected.     The  excised  frog's  heart, 


'  Pfliiger's  ArcMv,  xvin. 
there  quoted. 


(1878)  p.   172.     See  also  many  previous  papers 


CHAP.    IV.]  THE   VASCULAR    MECHANISM.  I97 

as  we  have  seen,  continues  to  beat  for  some  considerable  time, 
though  apparently  empty  of  blood.  After  a  while  however  the 
beats  diminish  and  disappear ;  and  their  disappearance  is  greatly 
hastened  by  washing  out  the  heart  with  a  normal  saline  solution, 
which  when  allowed  to  flow  through  the  cavities  of  the  heart 
readily  permeates  the  tissues  on  account  of  the  peculiar  construc- 
tion of  the  frog's  cardiac  walls.  If  such  a  '  washed  out '  quiescent 
heart  be  fed  in  the  manner  described  at  p  188,  with  diluted  blood 
(of  the  rabbit,  sheep,  <S:c.)  it  may  be  restored  to  functional  ac- 
tivity. A  similar  but  less  complete  restoration  may  be  witnessed 
if  scrum  be  used  instead  of  blood  ;  and  a  heart  fed  regularly  with 
fresh  supplies  of  blood  or  even  of  serum  may  be  kept  beating 
for  a  very  great  length  of  time. 

The  beneficial  action  seems  to  be  partly  due  to  the  alkaline  serum 
neutralizing  the  acids  continually  produced  by  the  muscular  con- 
tractions ;  tor  dilute  alkaline  solutions,  ex.  gr.  a  solution  of  sodium 
hydrate  005  p.  c.  in  normal  saline  solution,  are  even  more  efficient 
than  serum'.  Gaule"  further  finds  that  the  beats  are  assisted,  especially 
as  regards  their  force,  by  adding  to  the  alkaline  solution  a  trace  of 
peptone. 

When  the  heart  is  fed  with  rabbit's  serum,  the  beats,  whether 
spontaneous  or  provoked  by  stimulation,  are  apt  to  become  inter- 
mittent and  to  arrange  themselves  into  groups.  This  intermittence 
is  due  to  the  chemical  action  of  the  serum  ;  and  it  is  probable  that 
cardiac  intcrmittences  seen  during  life  have  often  a  similar  causa- 
tion. Various  chemical  substances  m  the  blood,  natural  or 
morbid,  may  thus  affect  the  heart's  beat  by  acting  on  its  muscular 
fibres,  its  refle.x  or  automatic  ganglia,  or.  its  intrinsic  inhibitory 
apparatus. 

The  physical  or  mechanical  circumstances  of  the  heart  also 
aflfect  its  beat ;  of  these  perhaps  the  most  important  is  the  amount 
of  the  distension  of  its  cavities.  The  contractions  of  cardiac 
muscle,  like  those  of  ordinary  muscle  (see  p.  91), 'are  increased  up 
to  a  certain  limit  by  the  resistance  which  they  have  to  overcome  ; 
a  full  ventricle  will,  other  things  being  equal,  contract  more 
vigorously  than  one  less  full ;  though,  as  in  muscle,  the  limit  at 
which  resistance  is  beneficial  may  be  passed,  and  an  over-full 
ventricle  will  cease  to  beat  at  all. 

The  influences  of  resistance  in  the  case  of  the  heart  are,  however, 
more  complex  than  those  of  ordinary  muscle,  since  in  the  former  we 
have  to  deal  with  the  rate  as  well  as  the  vigour  of  the  beat. 

'  McruiK^vicz,  Ludwig's  Arbeiten,    1S75,  p.  132.     Gaule,  Arch,  f,  Anat.  m 
Phys.,  1878,  p.  291.  »  Op.  cU. 


198  INFLUENCES   AFFECTING   THE   EEAT.         [BOOK   I. 

Under  normal  conditions  the  ventricle  probably  empties  itself 
completely  at  each  systole.  Hence  an  increase  in  the  quantity 
of  blood  in  the  ventricle  would  augment  the  work  done  in  two 
ways  ;  the  quantity  thrown  out  would  be  greater,  and  the  increased 
quantity  would  be  ejected  with  greater  force.  Further,  since  the 
distension  of  the  ventricle  is  (at  the  commencement  of  the  systole 
at  all  events)  dependent  on  the  auricular  systole,,  the  work  of  the 
ventricle  (and  therefore  of  the  heart  as  a  whole)  is  in  a  measure 
governed  by  the  auricle.^ 

The  relation  of  the  heart's  beat  to  blocd-pressure. 

When  the  blood-pressure  is  high,  not  only  is  the  resistance  to  the 
ventricular  systole  increased,  but,  other  things  being  equal,  more 
blood  flows  through  the  coronary  artery.  Both  these  events  would 
increase  the  work  of  the  heart,  and  we  might  expect  that  the  in- 
crease would  be  manifest  in  the  rate  of  the  rhythm  as  well  as  in 
the  force  of  the  individual  beats.  As  a  matter  of  fact,  however, 
we  do  not  find  this.  On  the  contrary,  as  Marey  has  insisted,  the 
relation  of  heart-beat  to  pressure  may  be  put  almost  in  the  form 
of  a  law,  that  "the  rate  of  the  beat  is  in  invei'se  ratio  to  the 
arterial  pressure ; "  a  rise  of  pressure  being  accompanied  by  a 
diminution,  and  fall  of  pressure  with  an  increase  of  the  pulse-rate. 
This  however  only  holds  good  if  the  vagi  be  intact.  If  these  be  pre- 
viously divided,  then  in  whatever  way  the  blood  pressure  be  raised — 
whether  by  injecting  blood  or  clamping  the  aorta,  or  increasing  the 
peripheral  resistance,  through  tljat  action  of  the  vaso-motor  nerves 
which  we  shall  have  to  describe  directly— or  in  whatever  way  it  be 
lowered,  no  very  clear  and  decided  relation  between  blood-pressure 
and  pulse  rate  is  observed.^  It  is  inferred  therefore  that  increased 
blood-pressure  causes  a  slowing  of  the  pulse,  when  the  vagi  are 
intact,  because  the  cardio-inhibitory  centre  in  the  medulla  is 
thereby  stimulated,  and  the  heart  in  consequence  to  a  certain 
extent  inhibited. 

When  the  blood-pressure,  after  section  of  the  vagi,  is  raised  by  the 
injection  of  additional  blood  or  by  clamping  the  aorta,  the  heart's 
beats  are  increased  in  strength,  as  shewn  by  the  larger  excursions  of 
the  manometer  ;  the  fact  that  this  is  not  accompanied  by  any  change 
in  the  rate,  suggests  that  there  must  be  some  compensating  agency  at 
work.  Sometimes,  even  after  section  of  the  vagi,  a  slight  slowing  is 
observed  when  the  pressure  is  increased ;  this  has  been  attributed  to 
the  action  of  the  increased  arterial  pressure  on  the  endings  of  the 
vagus  fibres  in  the  heart  itself. 

'  Cf.  Roy,  Journ.  of  Pkys.  I.  (1878)  p.  452. 
^  Nawrocki,  Ludwig's  Festgabe,  p.  ccv. 


CHAP.    IV.]  THE   VASCULAR    ^^•:CHANISM.  199 

Th(  Effects  on  the  Circulation  of  Changes  in  the  Heart's  Beat. 

Any  variation  in  the  heart's  beat  directly  affects  the  blood- 
pressure  unless  some  compensating  influence  be  at  work.  The 
most  extreme  case  is  that  of  complete  inhibition.  Thus  if,  while 
a  tracing  of  arterial  pressure  is  being  taken,  the  beat  of  the  heart 
be  suddenly  arrested,  some  such  curve  as  that  represented  in  Fig, 
38  will  be  obtained.  It  will  be  observed  that  immediately  after 
the  last  beat,  there  is  a  sudden  rapid  fall  of  the  blood-pressure, 
the  curve  described  by  the  float  more  or  less  closely  rerembling  a 
parabola.  At  the  close  of  the  last  systole,  the  arterial  system  is 
at  its  maximum  of  distension  ;  forthwith  the  elastic  reaction  of 
the  arterial  walls  propels  the  blood  forward  into  the  veins,  and 
there  being  no  fresh  fluid  injected  from  the  heart,  the  fall  of  the 
mercury  is  unbroken,  being  rapid  at  first,  but  slower  afterwards,  as 
the  elastic  force  of  the  arterial  walls  is  more  and  more  used  up. 
■With  the  returning  beats,  the  mercury  correspondingly  rises  in 
successive  leaps  until  the  normal  pressure  is  regained.  The  size 
of  these  returning  leaps  of  the  mercury  may  seem  extraordinary, 
Fig.  39,  but  it  must  be  remembered  that  by  far  the  greater  part  of 
the  force  of  the  first  few  strokes  of  the  heart  is  expended  in 
distending  the  arterial  system,  a  small  portion  only  of  the  blood 
which  is  ejected  into  the  arteries  passing  on  into  the  veins.  As 
the  arterial  pressure  rises,  more  and  more  blood  passes  at  each 
beat  through  the  capillaries,  and  the  rise  of  the  mercury  at  each 
beat  becomes  less  and  less,  until  at  last  the  whole  contents  of  the 
ventricle  pass  at  each  stroke  into  the  veins,  and  the  mean  arterial 
pressure  is  established.  To  this  it  may  be  added,  that  the  force 
of  the  individual  beats  is  somewhat  greater  after  than  before 
inhibition  ;  that  is  to  say,  the  period  of  depression  is  followed  by 
a  period  of  reaction,  of  exaltation.  Besides,  the  inertia  of  the 
mercury  tends  to  magnify  the  effects  of  the  initial  beats. 

If  while  the  force  of  the  individual  beats  remains  constant  the 
frequency  is  increased  or  diminished — and  vice  versa,  if  while  the 
frequency  remains  the  same  the  force  is  increased  or  diminished — 
the  pressure  is  proportionately  increased  or  diminished.  This 
clearly  must  be  the  case ;  but  obviously  it  is  quite  possible  that 
the  beats  might,  while  more  frequent,  so  lose  in  force,  or  while  less 
frequent,  so  increase  in  force,  that  no  difference  in  the  mean 
pressure  should  result.  And  this  indeed  is  not  unfrcquentiy  the 
case.  So  much  so,  that  variations  in  the  heart-beat  must  always 
be  looked  upon  as  a  far  less  important  factor  of  blocd-pressure 
than  the  peripheral  resistance. 


200 


INHIBITION   AND  BLOOD   PRESSURE.      [BOOK   I. 


Thus  when  the  heart's  beat  is  quickened  by  stimulation  of  the 
accelerator,  no  increase  in  the  blood-pressure  is  observed.  This,  in 
the  absence  of  any  peripheral  changes,  must  result  from  a  proportionate 
diminution  of  the  force  of  the  individual  strokes. 


Fig.  38.  Tracing,  shewing  the  influence  of  Cardiac  Inhibition  on  Blood-pressure. 
From  a  Rabbit. 

The  current  was  thrown  into  the  vagus  at  a  and  shut  off  at  b.  It  will  be  observed  that 
one  beat  is  recorded  after  the  commencement  of  the  stimulation.  Then  follows  a  very  rapid 
fall,  continuing  after  the  cessation  of  the  stimulus.  With  the  returning  beats,  the  mercury 
rises  by  leaps  until  the  normal  pressure  is  regained. 

An  increase  in  the  quantity  of  blood  ejected  at  each  beat  must 
necessarily  augment,  and  a  decrease  diminish,  the  blood-pressure, 
other  things  remaining  the  same.  But  the  quantity  sent  out  at 
each  beat,  on  the  supposition  that  the  ventricle  always  empties 
itself  at  each  systole,  will  depend  on  the  quantity  entering  into 
the  ventricle  during  each  diastole,  and  that  will  be  determined  by 
the  circumstances  not  of  the  heart  itself,  but  of  some  other  part 
or  parts  of  the  body. 


Sec.  5.     Changes  in  the  Calibre  of  the  Minute  Arteries. 
Vaso-motor  Actions. 

The  middle  coat  of  all  arteries  contains  circularly  disposed 
plain  muscular  fibres.  As  the  arteries  become  smaller,  the  mus- 
cular element  becomes  more  and  more  prominent  as  compared 
with  the  elastic  element,  until,  in  the  minute  arteries,  the  middle 
coat  consists  entirely  of  a  series  of  plain  muscular  fibres  wrapped 
round  the  elastic  internal  coat.  Nerve-fibres  belonging  to  the 
sympathetic  system  are  distributed  largely  to   blood-vessels,  but 


CHAP.    IV^  THE   VASCULAR   MECHANISM. 


20I 


their  terminations  have  not  as  yet  been  clearly  made  out.  By 
galvanic,  or  still  better  by  mechanical  stimulation,  this  muscular 
coat  may,  in  the  living  artery,  be  made  to  contract.     During  this 


1    .    I 


-U 


Fig.  39.    Blood- Prkssurb  During  Cardiac  Inhibition.    From  a  Dog. 

(The  tracing  reads  from  right  to  left.) 

The  line  T  indicates  the  velocity  at  which  the  recording  surface  w.-is  travelling,  the  ver- 
tical lines  marking  seconds.  T  he  line  S  indicates  the  application  of  the  stimulus,  an  inter- 
rupted current  being  thrown  into  the  vagus  during  the  break  in  the  line.  It  will  be  noticed 
that  in  this  case,  the  stimulus  l)eing  comparatively  weak,  the  effect  is  ratheran  extreme  slowing 
than  an  actual  cessation  of  the  beats.  1  he  large  leaps  of  the  mercury,  b,  caused  partly  by  the 
slowness  of  the  beats,  are  very  conspicuous,  indeed  unusually  large. 


has    the    slow    character    belonging    to    the 
plain    muscle,   the  calibre   of   the   vessel   is 


contraction,  which 
contractions  of  all 
diminished. 

If  the  web  of  a  frog's  foot  be  examined  under  the  microscope, 
any  individual  small  artery  will  be  found  to  vary  in  calibre,  being 


202  VASO-MOTOR   NERVES.  ^     [BOOK   I. 

sometimes  narrowed  and  sometimes  dilated.  During  the  narrow- 
ing, which  is  obviously  due  to  a  contraction  of  the  muscular  coat 
of  the  artery,  the  attached  capillary  area  with  the  corresponding 
veins  becomes  less  filled  with  blood,  and  paler.  During  the  stage 
of  dilation,  which  corresponds  to  the  relaxation  of  the  muscular 
coat,  the  same  parts  are  fuller  of  blood  and  redder.  It  is  obvious 
that,  the  pressure  at  the  entrance  into  any  given  artery  remaining 
the  same,  more  blood  will  enter  the  artery  when  relaxation  takes 
place  and  consequently  the  resistance  offered  by  the  artery  is 
lessened,  and  less  when  contraction  occurs  and  the  resistance  is 
consequently  increased.  The  blood  always  flows  in  the  direction 
of  least  resistance. 

The  small  arteries  frequently  manifest  what  may  be  called  spon- 
taneous variations  in  their  calibre,  and  these  variations  are  very  apt  to 
take  on  a  distinctly  rhythmical  character.  If  a  small  artery  in  the 
web  of  the  frog  be  carefully  watched,  it  will  be  seen  from  time  to  time 
to  vary  very  considerably  in  width,  without  any  obvious  change  taking 
place  in  the  heart's  beat  or  any  events  occurring  in  the  general  vaso- 
motor system.  Similar  variations  may  be  witnessed  in  the  vessels  of 
the  meseniery  of  a  mammal. 

The  most  striking  and  most  easily  observed  instance  of  rhythmical 
constriction  and  dilation  is  to  be  found  in  the  median  artery  of  the  ear 
of  the  rabbit.  If  the  ear  be  held  up  before  the  light,  it  will  be  seen 
that  at  one  moment  the  artery  appears  as  a  delicate  hardly  visible  pale 
streak,  the  whole  ear  being  at  the  same  time  pallid.  After  a  while  the 
artery  slowly  widens  out,  becomes  thick  and  red,  the  whole  ear  blushing, 
and  many  small  vessels  previously  invisible  coming  into  view.  Again 
the  artery  narrows  and  the  blush  fades  away;  and  this  may  be  repeated 
at  somewhat  irregular  intervals  several  times  a  minute.  The  extent  and 
regularity  of  the  rhythm  are  usually  markedly  increased  if  fhe  rabbit  be 
held  up  by  the  ears  for  a  short  time  previous  to  the  observation.  If  the 
sympathetic  be  severed,  these  rhythmic  movements  cease  for  a  time ; 
but  in  the  course  of  a  few  days  are  re-established,  even  if  the  superior 
cervical  ganglion  be  removed.  Thus,  though  normally  dependent  on 
the  central  nervous  system  (unless  we  suppose  that  the  mere  section 
of  the  nerve  is  sufficient  to  create  a  shock  lasting  several  days)  these 
rhythmic  movements  can  make  their  appearance  independently  of 
that  system.  Some  local  mechanism  is  therefore  suggested ;  and  yet 
no  ganglionic  cells  have  been  discovered  which  would  serve  as  such  a 
mechanism.  Similar  rhythmic  variations  in  the  calibre  of  the  arteries 
have  been  observed  in  several  places,  ex.  gr.  in  the  saphena  artery  of 
the  rabbit,  in  the  axillary  artery  of  the  tortoise,  and  in  the  small  arteries 
of  the  muscles  of  the  frog  ;  probably  they  are  widely  spread.  They 
may  be  compared  ^¥ith  the  rhythmic  movements  of  the  veins  in  the 
bat's  wing  and  of  the  caudal  vein  of  the  eel.   ' 

The  extent  and  intensity  of  the  constriction  or  dilation  are 
found  to  vary  very  largely.     Irregular  variations  of  slight  extent 


CHAP.    IV.]  THE   VASCULAR    MFXHANISM.  203 

occur  even  when  the  animal  is  apparently  subjected  to  no  disturb- 
ing causes ;  while  as  the  result  of  experimental  interference  the 
arteries  may  become  either  constricted,  in  some  cases  almost  to 
obliteration,  or  dilated  until  they  acquire  double  or  more  than 
double  their  normal  diameter.  This  constriction  or  dilation  may 
be  brought  about  not  only  by  treatment  applied  directly  to  the  web, 
but  also  by  changes  atTecting  the  nerve  of  the  leg.  Thus  section 
of  the  sciatic  nerve  is  generally  followed  by  a  very  marked  dilation, 
while  stimulation  of  the  peripheral  stump  of  the  divided  nerve  by 
an  interrupted  current  of  moderate  intensity,  is  followed  by  a  con- 
striction, often* so  great  as  almost  to  obliterate  some  of  the  minute 
arteries. 

These  facts  shew  that  the  contractile  elements  of  the  minute 
arteries  of  the  web  of  the  frog's  foot  are  capable  by  contraction  or 
rcla.xation  of  causing  constriction  or  dilation  of  the  calibre  of  the 
arteries ;  and  that  this  condition  of  constriction  or  dilation  may 
be  brought  about  through  the  agency  of  nerves. 

These  effects  are  not  absolutely  constant.  Sometimes  the  dilation 
following  upon  section  is  preceded  by  a  passing  constriction,  and 
sometimes  the  section  is  followed  by  no  distinct  alteration  in  the 
calibre  of  the  vessels  of  the  web  beyond  perhaps  an  initial  constriction. 
Sometimes  the  constriction  consequent  on  stimulation  is  followed  by  a 
dilation,  which  may  or  may  not  be  marked.  The  constriction  of  the 
arteries  of  the  web  as  the  result  of  nen-e  stimulation,  is  more  certain 
when  the  small  nerve  supplying  the  foot  is  operated  on,  than  when  the 
main  trunk  of  the  sciatic  is  stimulated  high  up.  We  shall,  later  on, 
discuss  the  nature  of  these  variations. 

Vaso-motor  nerves.  In  warm-blooded  animals,  though 
we  cannot  readily,  as  in  the  frog,  watch  the  circulation  under  the 
microscope,  we  have  abundant  evidence  of  the  influence  of  the 
nervous  system  on  the  calibre  of  the  arteries.  Thus,  in  the 
mammal,  division  of  the  cervical  sympathetic  on  one  side  of  the 
neck  causes  a  dilation  of  the  minute  arteries  of  the  head  on  the 
same  side,  shewn  by  an  increased  supply  of  blood  to  the  parts. 
If  the  experiment  be  performed  on  a  rabbit,  the  effect  on  the 
circulation  in  the  ear  is  very  striking.  The  whole  ear  of  the  side 
operated  on  is  much  redder  than  normal,  its  arteries  are  obviously 
dilated,  its  veins  unusually  full,  innumerable  minute  vessels  before 
invisible  come  into  view,  and  the  temperature  may  be  more  than 
a  degree  higher  than  on  the  other  side. 

Division  of  the  sciatic  nerve  in  a  mammal  causes  a  similar 
dilation  of  the  small  arteries  of  the  foot  and  leg.  Where  the 
condition  of  the  circulation  can  be  readily  examined,  as  for 
instance  in  the  hairless  balls  of  the  toes,  especially  when  these 


204  VASO-MOTOR   NERVES.  [BOOK  I. 

are  not  pigmented,  the  vessels  are  seen  to  be  dilated  and  injected; 
and  a  thermometer  placed  between  the  toes  shews  a  rise  of  tem- 
perature amounting,  it  may  be,  to  several  degrees.  Division  of 
the  brachial  plexus  produces  a  similar  dilation  of  the  blood-vessels 
of  the  front  limb.  Division  of  the  splanchnic  nerve  produces  a 
dilation  of  the  blood-vessels  of  the  intestines  and  other  abdominal 
viscera.  Division  in  the  mammal  of  the  lingual  nerve  on  one  side 
of  the  head,  causes  a  dilation  of  the  vessels  in  the  corresponding 
half  of  the  tongue.  A  similar  effect  follows  division  of  the  hypo- 
glossal ;  and  if  both  lingual  and  hypoglossal  be  severed,  the  effect 
is  still  more  marked. 

Division  of  a  nerve  supplying  a  muscle  causes  a  large  and 
sudden  increase  in  the  venous  flow  from  the  muscle,  indicating 
that  the  muscular  arteries  have  become  dilated ;  and  in  the  frog 
this  dilation,  consequent  on  section  of  the  nerve,  may  be  actually 
observed  by  placing  a  thin  muscle  such  as  the  mylo-hyoid  under 
the  microscope  and  watching  the  calibre  of  the  small  arteries  and  the 
circulation  of  the  blood  through  them  while  the  nerve  is  being  cut. 

We  find  in  fact  that  in  almost  all  parts  of  the  body  certain 
*  vascular  areas '  stand  in  such  a  relation  to  certain  nerves  that  the 
division  of  one  of  these  nerves  causes  a  dilation  of  the  minute 
arteries  in,  and  consequently  an  increased  supply  of  blood  to,  a 
corresponding  vascular  area.  We  may  speak  of  these  nerves  as 
*vaso-motor'  nerves,  or  more  correctly  since  in  the  vast  majority 
of  cases  the  nerves  in  question  have  other  functions  than  that  of 
governing  arteries,  as  containing  vaso-motor  fibres,  much  in  the 
same  way  as  an  ordinary  spinal  nerve  is  spoken  of  as  containing 
sensory  and  motor  fibres;  and  from  what  has  been  said  above  it 
is  evident  that  these  vaso-motor  fibres  are  found  sometimes  in 
sympathetic,  sometimes  in  cerebro-spinal  nerves. 

Since  division  of  a  vaso-motor  nerve,  or  nerve  containing  vaso- 
motor fibres,  leads  to  the  dilation  of  the  arteries  of  its  appropriate 
vascular  area,  it  is  obvious  that  previous  to  that  division  these 
arteries  were  in  a  state  of  permanent  constriction,  due  to  a  per- 
manent contraction  of  their  muscular  coats.  This  permanent  con- 
striction, which  may  vary  considerably  in  degree  (the  dilating 
effects  of  section  of  the  vaso-motor  nerve  correspondingly  varying 
in  amount),  is  spoken  of  as  'tone,'  'arterial  tone.'  Arteries  in 
such  a  state  of  permanent  constriction  as  under  ordinary  circum- 
stances is  normal  to  arteries  whose  vaso-motor  fibres  have  not 
been  divided  and  which  are  otherwise  in  a  normal  condition,  are 
said  to  '  possess  tone.'  When,  as  after  division  of  the  vaso-motor 
fibres,  the  constriction  gives  place  to  dilation  the  arteries  are  said 
to  have  '  lost  tone,'  and  when,  under  various  circumstances  which 


CHAK    I\.J  THE   VASCULAR    MECHANISM.  205 

we  shall  study  hereafter,  the  constriction  becomes  greater  than 
normal,  their  tone  is  said  to  be  increased. 

A  very  little  consideration  will  shew  that  this  arterial  tone  is 
a  most  important  factor  in  the  circulation.  In  the  first  place  the 
whole  flow  of  blood  in  the  body  is  adapted  to  and  governed  by 
what  we  may  call  the  general  tone  of  the  arteries  of  the  body  at 
large.  In  a  normal  condition  of  the  body,  if  not  all,  at  least 
the  vast  majority  of  the  minute  arteries  of  the  body  are  in  a  state 
of  tonic,  i.e.  of  moderate,  constriction,  and  it  is  the  narrowing  due 
to  this  constriction  which  forms  a  large  item  of  that  peripheral 
resistance  which  we  have  seen  (p.  149)  to  be  one  of  the  two  great 
factors  of  blood-pressure.  The  normal  general  blood-pressure, 
and  therefore  the  normal  flow  of  blood,  is  in  fact  dependent  on 
the  'general  tone'  of  the  minute  arteries.  In  the  second  place, 
changes  in  local  tone,  i.e.  the  tone  of  any  particular  vascular  area, 
have  very  decided  effects  on  the  circulation.  These  effects  are 
both  local  and  general,  as  the  following  considerations  will  shew. 

Let  us  suppose  that  the  artery  -<4  is  in  a  condition  of  normal 
tone,  is  midway  between  extreme  constriction  and  dilation.  The 
flow  through  A  is  determined  by  the  resistance  in  A  and  in  the 
vascular  tract  which  it  supplies,  in  relation  to  the  mean  arterial 
pressure,  which  again  is  dependent  on  the  way  in  which  the  heart  is 
beating  and  on  the  peripheral  resistance  of  all  the  small  arteries 
and  capillaries,  A  included.  If,  while  the  heart  and  the  rest  of 
the  arteries  remain  unchanged,  A  be  constricted,  the  peripheral 
resistance  in  A  will  increase,  and  this  increase  of  resistance  will 
lead  to  an  increase  of  the  general  arterial  pressure.  This  increase 
of  pres.sure  will  tend  to  cause  the  blood  in  the  body  at  large  to 
flow  more  rapidly  from  the  arteries  into  the  veins.  The  constric- 
tion of  A  however  will  prevent  any  increase  of  the  flow  through  it, 
in  fact  will  make  the  flow  through  it  less  than  before.  Hence  the 
whole  increase  of  discharge  from  the  arterial  into  the  venous  system 
must  take  place  through  channels  other  than  A.  Thus  as  the 
result  of  the  constriction  of  any  artery  there  occur,  (i)  diminished 
flow  through  the  artery  itself,  (2)  increased  general  arterial  pressure, 
'ailing  to  13)  increased  flow  through  the  other  arteries.  If,  on  the 
ler  hand,  A  be  dilated,  while  the  heart  and  other  arteries  remain 
unchanged,  the  peripheral  resistance  in  A  is  diminished.  This  leads 
ti)  a  lowering  of  the  general  arterial  pressure,  which  in  turn  causes 
the  blood  to  flow  less  rapidly  from  the  arteries  into  the  veins.  The 
dilation  of  A  however  permits,  even  with  the  lowered  pressure, 
niore  blood  to  pass  through  it  than  before.  Hence  the  diminished 
flow  tells  all  the  more  on  the  rest  of  the  arteries.  Thus,  as  the 
result  of  the  dilation  of  any  artery,  there  occur  (i)  increased  flow 


206  VASO-MOTOR   NERVES.  [BOOK   I. 

of  blood  through  the  artery  itself,  (2)  diminished  general  pressure 
and  (3)  diminished  flow  through  the  other  arteries.  Where  the 
artery  thus  constricted  or  dilated  is  small,  the  local  effect,  the  di- 
minution or  increase  of  flow  through  itself,  is  much  more  marked 
than  the  general  effects,  the  change  in  blood-pressure  and  the  flow 
through  other  arteries.  When,  however,  the  area  the  arteries  of 
which  are  affected  is  large,  the  general  effects  are  very  striking. 
Thus  if  while  a  tracing  of  the  blood-pressure  is  being  taken  by 
means  of  a  monometer  connected  with  the  carotid  artery,  the 
splanchnic  nerves  be  divided,  a  conspicuous  but  steady  fall  of 
pressure  is  observed,  very  similar  to  that  which  is  seen  in  Fig.  40. 
The  section  of  the  splanchnic  nerves  causes  the  mesenteric  and 
other  abdominal  arteries  to  dilate,  and  these  being  very  numerous, 
a  large  amount  of  peripheral  resistance  is  taken  away,  and  the 
blood-pressure  falls  accordingly ;  a  large  increase  of  flow  into  the 
portal  veins  takes  place,  and  the  supply  of  blood  to  the  face,  arms, 
and  legs  is  proportionally  diminished.  It  will  be  observed  that  the 
dilation  of  the  arteries  is  not  instantaneous  but  somewhat  gradual, 
the  pressure  sinking  not  abruptly  but  with  a  gentle  curve. 

Arterial  tone  then,  both  general  and  local,  is  a  powerful  in- 
strument for  determining  the  flow  of  blood  to  the  various  organs 
and  tissues  of  the  body,  and  thus  becomes  a  means  of  indirectly 
influencing  their  functional  activity.  We  should  accordingly  ex- 
pect to  find  that  the  vaso-motor  nerves  were  connected  with,  aTid 
arterial  tone  regulated  by,  the  central  nervous  system,  in  order  that 
the  calibre  of  the  arteries  of,  and  the  supply  of  blood  sent  to,  this 
or  that  vascular  area  might  be  varied  according  to  the  varying  needs 
of  the  economy.     And  experiment  proves  this  to  be  the  case. 

We  stated  that  section  of  the  cervical  sympathetic  in  the  neck 
causes  dilation  or  loss  of  tone  in  the  blood-vessels  of  the  head  and 
face.  This  is  true  at  whatever  point  of  the  course  of  the  nerve 
from  the  upper  to  the  lower  cervical  ganglion,  both  included,  the 
section  be  made.  No  sucli  dilation  of  the  vessels  of  the  head  and 
face  takes  place  when  the  thoracic  sympathetic  chain  is  divided 
anywhere  below  the  upper  thoracic  ganghon ;  but  dilation  does 
occur  after  division  of  certain  of  the  7'amz  comnmnicanies  connect- 
ing the  spinal  cord  with  the  cervical  sympathetic  through  the  lower 
cervical  or  upper  thoracic  ganglion.  Hence  it  is  clear  that  the 
normal  tone  of  the  arteries  of  the  head  and  face  is  maintained  by 
influences  (whose  exact  nature  we  shall  study  presently)  proceeding 
from  the  central  nervous  system,  passing  through  certain  rami 
commutiicanies  (the  exact  path  being  somewhat  uncertain  or  possibly 
not  constant)  into  the  cervical  sympathetic,  and  ascending  to  the 
head  and  face  by  that  nerve.     In    other  words,  the  vaso-mctor 


CHAT.    IV. J  THE    VASCULAR    MKCHANISM.  207 

fibres  of  the  vessels  of  the  head  and  face  may  be  traced  down  the 
sympathetic  to  the  lower  cervical  ganglion,  and  thence  by  rami 
communicanles  into  the  spinal  cord. 

In  a  similar  manner  the  vaso-motor  fibres  of  the  splanchnic 
nerves  governing  the  mesenteric  and  other  abdominal  arteries  can 
also  be  traced  into  the  spinal  cord,  as  may  also  those  of  the  sciatic 
governing  the  blood-vessels  of  the  hind  limb  and  of  the  brachial 
nerves  governing  those  of  the  fure  limb.  In  fact  all  tiie  vaso-motor 
fibres  (with  certain  special  exceptions  which  will  be  discussed 
jiresently)  may  thus  be  traced  into  the  spinal  cord  ;  they  are  all 
connected  with  the  central  nervous  system.  There  is  at  present 
some  uncertainty  in  certain  cases  as  to  the  exact  manner  in  which  the 
fibres  pass  from  tlie  spinal  cord  to  this  or  liiat  nerve,  as.  for  instance, 
along  which  nerve-roots  the  vaso-motor  fibres  eventually  joining 
the  sciatic  trunk  run,  whether  they  all  pass  on  their  way  into  the 
abdominal  sympatlietic  or  no,  and  the  like  ;  but  these  are  questions 
which  need  not  delay  us  now  ;  in  whichever  way  they  may  be 
settled,  they  do  not  affect  the  important  fact  that  in  some  way  or 
other  all  vaso-motor  fibres  spring  from  the  central  nervous  system, 
aid  that  (with  certain  special  exceptions)  what  we  have  called 
the  normal  tone  of  the  various  vascular  areas  is  maintained  by 
influences  proceeding  from  the  central  nervous  system. 

Far  more  important  however  than  the  maintenance  of  a 
normal  tone,  which  indeed  might  be  at  once  and  for  ever  arranged 
for  by  the  proper  natural  calibre  of  the  elastic  blood-vessels,  is  the 
power  which  the  central  nervous  system  possesses  of  varying  the 
tone  of  this  or  that  artery  or  group  of  arteries,  of  increasing  it  or 
of  diminishing);  it,  of  producing  constriction  or  dilation  in  those 
arteries,  and  thus,  as  we  have  seen  p.  205,  of  effecting  changes 
in  general  or  local  blood-pressure  or  in  both,  and  consequently  of 
determining  a  flow  of  blood  in  this  or  that  direction,  according 
to  the  needs  of  the  economy.  And  the  exercise  of  this  carefully 
arranged  manipulation  of  the  muscular  walls  of  the  arteries  may 
be  called  forth  in  either  direction,  in  the  way  of  constriction,  or 
in  the  way  of  dilation  (or  of  both  at  the  same  time,  one  in  one 
area  and  the  other  in  others),  by  means  of  nervous  impulses  either 
originating  in  the  central  nervous  system  itself  or  started  by 
afferent  impulses  passing  up  to  the  central  nervous  system  from 
some  sentient  surface. 

Blushing  is  a  familiar  instance  of  vascular  dilation  brought 
about  by  the  action  of  the  central  nervous  system.  Nervous 
imimlses  started  in  some  parts  of  the  brain  by  an  emotion  pro- 
duie  certain  changes  in  the  central  nervous  system  (the  exact 
nature  and  locality  of  these  changes  we  shall  discuss  presently) 


208  VASO-MOTOR   NERVES.  [BOOK   I. 

which  have  in  turn  an  effect  on  the  vaso-motor  fibres  of  the 
cervical  sympathetic  almost  exactly  the  same  as  that  produced  by 
section  of  the  nerve.  In  consequence  the  muscular  walls  of  the 
arteries  of  the  head  and  face  relax,-  the  arteries  dilate  and  the 
whole  region  becomes  suffused".  Sometimes  an  emotion  gives 
rise  not  to  blushing  but  to  the  opposite  pallor.  In  a  great 
number  of  cases  this  has  quite  a  different  cause,  being  due  to  a 
sudden  diminution  or  even  temporary  arrest  of  the  heart's  beats ; 
but  in  some  cases  it  may  occur  without  any  change  in  the  beat 
of  the  heart,  and  is  then  due  to  a  condition  the  very  converse  of 
that  of  blushing,  that  is,  to  an  increased  arterial  constriction  ;  and 
this  increased  constriction,  like  the  dilation  of  blushing,  is  effected 
through  the  agency  of  the  central  nervous  system  and  the  cer- 
vical sympathetic.  These  are  familiar  examples,  but  we  have  in 
abundance  exact  experimental  evidence  of  the  effect  of  afferent 
impulses  in  inducing  through  the  central  nervous  system  vaso- 
motor changes  and  thus  bringing  about  sometimes  constriction, 
sometimes  dilation,  sometimes  the  two  together.  The  action  of 
the  so-called  depressor  nerve  is  a  striking  instance  of  reflex 
dilation  as  it  may  be  called. 

If  while  the  pressure  in  an  artery  such  as  the  carotid  is  being 
registered,  the  depressor  nerve,  which  is  a  branch  of  the  vagus 
running  alongside  the  carotid  artery  and  sympathetic  nerve 
(Fig.  36,  n.  dep.),  be  divided,  and  its  central  end  [i.e.  the  one 
connected  with  the  brain)  be  stimulated  with  the  interrupted 
current,  a  gradual  but  marked  fall  of  pressure  in  the  carotid  is 
observed,  lasting,  where  the  period  of  stimulation  is  short,  some 
time  after  the  removal  of  the  stimulus  (Fig.  40).  Since  the  beat 
of  the  heart  is  not  markedly  changed,  the  fall  of  pressure  must  be 
due  to  the  diminution  of  peripheral  resistance  occasioned  by  the 
dilation  of  some  arteries.  And  there  is  evidence  that  the 
arteries  thus  dilated  are  chiefly  if  not  exclusively  those  arteries  of 
the  abdominal  viscera  which  are  governed  by  the  splanchnic  nerve. 
For  if  both  the  splanchnic  nerves  are  divided  previous  to  the 
experiment,  the  fall  of  pressure  when  the  depressor  is  stimulated 
is  very  small,  in  fact  almost  insignificant.  The  inference  from 
this  is  clear ;  the  afferent  impulses  passing  along  the  depressor 
have  so  affected  some  part  of  the  central  nervous  system  that 
the  influences  which,  in  a  normal  condition  of  things,  passing 
along  the  splanchnic  nerves  keep  the  minute  arteries  of  the 
abdominal  viscera  in  a  state  of  moderate  tonic  constriction,  fail 
altogether,  and  those  arteries  in  consequence  dilate  just  as  they  do 
when  the  splanchnic  nerves  are  divided,  the  effect  being  possibly 
increased  by  the  similar  dilation  of  other  smaller  vascular  areas. 


CHAP.    IV.]  THE   VASCULAR    MECHANISM. 


209 


The  condition  of  the  splanchnic  or  other  vascular  areas  may 
moreover  be  changed,  and  thus  the  general  blood-pressure 
modified,  by  afterent  impulses  passing  along  other  nerves  than 
the  depressor,  the  modification  taking  on  according  to  circum- 
stances the  form  either  of  decrease  or  of  increase. 

Thus,  if  ia  an  animal  placed  under  the  mfluence  of  urari  the 
central  stump  of  the  divided  sciatic  ncr\'e  be  stimulated,  an 
increase  of  blood-pressure,  almost  exactly  the  reverse  of  the 
decrease  brought  about  by  stimulating  the  depressor,  is  observed. 


..^^r-y^ 


.AJULAJ_Xi_Jl_0_AJLAJULJLXXXXJl^^ 


Fio.  40.     Tracing  shewing  the  Effect  on  Blood-pressure  oy  Stimulating  thb 
Central  End  of  the  Depressor  Nerve  in  the  Rabbit. 

(To  be  read  from  right  10  left.) 

T  indicates  the  rate  at  which  the  recording  surface  was  travelling  ;  the  intervals  marked 
correspond  to  seconds.  C  the  niomcn;  at  which  tl.e  current  was  throw  n  into  the  nerve  ;  O  the 
mjineni  at  which  it  was  shut  off.  7he  effect  is  s  me  time'  in  developing  and  Lists  after  the 
current  has  been  taken  off.  The  larger  undulations  are  the  respiratory  curves : — the  pulse- 
OiciU.'.tions  are  very  small. 

The  curve  of  the  blood-pressure,  after  a  latent  period  during 
wliich  no  changes  are  visible,  rises  steadily  without  any  corre- 
spond mg  cl^.ange  in  the  heart's  beat,  reaches  a  maximum  and 
alter  a  while  slowly  falls  again,  the  fall  sometimes  beginning  to 
.ppear  betore  the  stimulus  has  been  removed.  There  can  be  no 
i-ioubt  that  the  rise  of  pressure  is  due  to  the  constriction  of  certain 
arteries  :  the  arteries  in  qut^stion  being  those  of  the  splanchnic 
area  certainly,  and  possibly  of  other  vascular  areas  as  well.  The 
effect  is  not  confined  to  the  sciatic  ;  stimulation  of  any  nerve 
containing  afferent  fibres  will  produce  the  same  rise  of  pressure, 
F.  P.  14 


2IO  VASO-MOTOR   NERVES.  [BOOK   I. 

and  so  constant  is  the  result  that  the  experiment  may  be  made 
use  of  as  a  method  for  determining  the  existence  of  afferent 
fibres  in  any  given  nerve  and  even  the  paths  of  centripetal 
impulses  through  the  spinal  cord.  ♦ 

If,  on  tlie  other  hand,  the  animal  be  under  not  urari  but 
chloral,  instead  of  a  rise  of  blood-pressure  a  fall,  quite  similar  to 
that  caused  by  stimulating  the  depressor,  is  observed  when  an 
afferent  nerve  is  stimulated.  The  condition  of  the  central 
nervous  system  seems  to  determine  whether  the  reflex  effect  on 
the  vaso-motor  fibres  is  in  the  direction  of  constriction  leading  to 
a  rise,  or  of  dilation  leading  to  a  fall  of  blood-pressure. 

The  causes  of  the  difference  between  chloral  and  urari  are  not  yet 
clearly  worked  out.  Variations  in  respiration  will  not  explain  it.  Nor 
can  the  solution  be  found  by  supposing  that  in  urari  poisoning  cerebral 
functions  are  active  while  in  chloral  poisoning  they  are  in  abeyance. 
If  the  brain  be  removed  without  much  bleeding,  subsequent  stimulation 
of  a  sensory  nerve  under  urari  still  gives  a  rise  4>f  pressure.  If  there 
be  much  bleeding  however  a  fall  is  witnessed.  This  suggests  the  idea 
that  after  bleeding  and  under  chloral,  the  part  of  the  central  nervous 
system  concerned  in  the  action,  and  serving  a  nervous  centre,  is 
enfeebled  or  exhausted,  and  that  stimulation  of  the  enfeebled  or 
exhausted  centre  always  causes  depression.  This  view  is  supported 
by  the  fact,  that  in  ordinary  stimulation  under  urari  the  decline  of 
the  rise  appears  sooner,  the  more  often  the  stimulation  is  repeated, 
and  that  after  many  repetitions  the  decline  passes  into  a  distinct 
fall,  and  at  last  only  a  fall  is  observed^ 

In  the  instances  just  quoted,  the  effect  of  the  stimulation  of 
the  afferent  nerve  may  be  spoken  of  as  a  general  one  ;  it  is  the 
general  blood-pressure  which  is  diminished  or  increased ;  though 
in  the  case  of  the  depressor  at  all  events  it  is  chiefly,  in  the 
splanchnic  area  that  the  constriction  or  dilation  takes  place. 

There  are  however  some  remarkable  cases  where  a  local  effect 
can  be  readily  distinguished  from  the  general  effect,  because  the 
two  are  in  opposite  directions.  Thus  if  in  a  rabbit  under  urari, 
the  central  stump  of  the  auricularis  magnus  nerve  or  of  the 
auricularis  posterior  be  stimulated,  the  rise  of  general  pressure 
which  is  caused  by  the  stimulation  of  this  as  of  any  other  afferent 
nerve,  is  accompanied  by  a  dilation  of  the  artery  of  the  ear. 
That  is  to  say,  the  afferent  impulses  passing  along  the  auricular 
nerve  while  affecting  the  central  nervous  system  in  an  ordinary 
way,  so  as  to  cause  constriction  of  many  of  the  arteries  of  the 
body  (but  chiefly  probably  the  splanchnic  vessels),  at  the  same 
time   so   affect  some  particular  part  more  especially  connected 

'  Cf .  Latschenberger  and  Deahna,  Pfliiger's  Archiv,  xii..  (1876)  p.  157. 


CHAl'.    IV. J  THE    VASCULAR    MECHAiNJSM.  211 

with  the  vaso-motor  fibres  governing  the  artery  of  tlie  ear,  as  to 
lead  to  the  dihxtion  of  that  vessel. 

According  to  Lov<5n',  to  whom  we  arc  indebted  for  this  observation, 
the  lo -al  dilation  in  the  car  is  preceded  by  an  initial  constriction.  A 
similar  initial  conbtriction  has  been  witnessed  in  other  cases  of  reflex 
dilation. 

According  to  Heidenhain',  this  experiment  illustrates  not  so 
much  the  contrast  between  local  and  general  effects  as  the  difference 
of  behaviour  between  vessels  supplying  the  skin  and  those  distributed 
to  other  tissues  ;  for  he  affirms  that  retlex  vaso-motor  action  in  respect 
to  cutaneous  arteries  is  at  all  events  when  caused  by  artificial  stimula- 
tion always  in  the  direction  of  dilation. 

So  also  in  the  same  animal  stimulation  of  branches  of  the 
tibial  nerve  causes  dilation  of  the  saphena  artery,  together  with 
constriction  of  other  arteries,  as  shewn  by  the  concomitant  rise 
of  pressure.  And  there  are  probably  innumerable  instances  of 
the  same  kind  of  action  going  on  in  the  body  during  life,  for  it 
is  evident  that  the  increased  flow  of  blood  to  the  organ  which  is 
the  object  of  the  local  dilation,  must  be  assisted  if  a  general 
constriction  is  at  the  same  time  taking  place  in  other  regions. 

The  general  effect  may  not  always  be  obvious,  may  perhaps 
be  often  absent,  so  that  the  local  dilation  or  constriction,  as  the 
case  may  be,  is  the  only  obvious  result  of  the  vaso-motor  action. 
When  the  ear  of  the  rabbit  is  gently  tickled,  the  effect  that  is 
seen  is  a  blushing  of  the  ear,  and  though  this  may  be  in  part  due, 
as  we  shall  see  to  the  action  of  a  local  mechanism,  the  case  we 
have  just  cited  shews  that  the  central  nervous  system  must  be 
largely  engaged.  When  the  right  hand  is  dipped  in  cold  water, 
the  temperature  of  the  left  hand  falls,  on  account  of  a  reflex 
constriction  of  the  vessels  of  the  skin  of  that  hand  caused  by  the 
stim.ilus  applied  to  the  other.  Many  more  instances  might  be 
quoted,  and  we  shall  again  and  again  come  upon  examples.  The 
numerous  pathological  phenomena  classed  under  sympathetic 
action,  such  as  the  affection  of  one  eye  by  disease  in  the  other, 
are  probably  in  part  at  least  the  results  of  reflex  vaso-motor 
action. 

We  have  said  enough  to  shew  that  the  calibre  of  the  small 
arteries,  which  by  determining  the  peripheral  resistance  forms  one 
important  factor  regidating  the  flow  of  blood,  is  subject  to 
influences  proceeding  from  all  parts  of  the  boily,  the  influences 
reaching  the  arteries  in  a  reflex  manner  by  means  of  the  central 
nervous  system,   the  afferent  impulses  being  for  the   most  part 

'  Ludwig's  Arbeiten,  iS66. 

"  Cf.  Ostrjiimotr,  rHii,'ei's  Air/iiv,  XII.  (1876)  p.  219.  ► 

14—2 


212  -  VASO  MOTOR   NERVES.  [BOOK  1. 

carried  by  ordinary  sensory  nerves,  while  the  efferent  impulses 
pass  along  special  vaso-motor  nerves,  which,  though  the  centre  of 
the  reflex  action  lies  in  the  cerebro-spinal  axis,  have  a  great 
tendency  to  run  in  sympathetic  tracts. 

The  afferent  impulses  of  course  need  not  start  from  the  peri- 
pheral nerve-endings.  They  may  for  instance  arise  in  the  brain. 
Thus,  as  we  have  seen,  an  emotion  originating  in  the  cerebrum 
may  by  vaso-motor  action  give  rise  either  to  blushing  or  to  pallor. 
Nay  more,  changes  may  be  induced  in  the  .central  nervous 
system  itself  without  the  need  of  any  impulses  reaching  it  from 
without.  When  we  come  to  discuss  the  relations  of  respiration  to 
the  circulation,  we  shall  see  reason  to  think  that  the  vaso-motor 
action  of  the  central  nervous  system  may  be  directly  affected  by 
the  condition  of  the  blood  passing  through  it,  so  that  if  the 
quantity  of  oxygen  in  the  blood  be  reduced,  a  general  arterial 
constriction  takes  place,  and  a  rise  of  blood-pressure  follows  ; 
while  with  a  return  of  oxygen  to  the  blood,  the  vessels  dilate 
and  pressure  falls.     We  shall  return  to  these  phenomena  later  on. 

It  is  more  than  probable  that  many  substances  introduced  into  the 
blood,  or  arising  in  the  blood  from  natural  or  morbid  changes,  may 
affect  blood-pressure  by  acting  directly  on  the  nervous  centres. 

In  many  ways  then,  and  to  a  varying  degree  and  extent,  the 
central  nervous  system  can  bring  about  arterial  conscriction  or 
dilation,  general  or  local.  We  have  now  to  study  the  question, 
What  is  more  exactly  the  nature  of  the  nervous  influences  which 
lead  to  constriction  and  dilation  respectively  ?  How  do  those 
which  cause  constriction  differ  from  those  which  cause  dilation  ? 

In  the  fundamental  experiment  of  the  cervical  sympathetic, 
when  arterial  dilation  has  followed  upon  section  of  the  nerve,  if 
the  peripheral  stump  of  the  divided  nerve  be  stimulated,  the 
dilation  gives  place  to  constriction,  the  blush  is  replaced  by  pallor. 
If  the  stimulus  be  very  strong  the  constriction  is  greater  than 
normal,  but  by  carefully  adjusting  the  strength  of  the  stimulus, 
the  circulation  may  be  brought  to  quite  a  normal  condition,  the 
'  loss  of  tone  '  consequent  on  the  severance  of  the  vaso-motor 
fibres  from  the  central  nervous  system  may  be  replaced,  and  not 
more  than  replaced',  by  an  artificial  tone  generated  by  the  action  of 
the  stimulus  on  the  sympathetic  nerve.  The  most  natural  interpre- 
tation therefore  of  the  vaso-motor  action  in  this  case  is  to  suppose 
that  the  normal  tone  of  the  arteries  of  the  face  is  maintained  by 
'  tonic  '  constrictive  impulses  of  a  certain  intensity  which  pass 
from  the  central  nervous  system  along  the  sympathetic,  and  that 
the  dilation  of  the  same  arteries  is  due  simply  to  a  diminution  or 


CHAP.    1\.J  THE   VASCULAR    MECHANISM.  213 

absence  of  these  constrictive  impulses,  an  increased  constriction 
or  pallor  being  similarly  clue  to  an  increase  beyond  what  is 
normal  of  these  same  impulses.  In  other  words,  the  nervous 
inllucnces  leading  to  arterial  dilation  and  constriction  differ  in 
degree  only,  not  in  kind,  and  may  be  considered  as  being  merely 
phases  (of  decrease  or  of  increase  as  the  case  may  be)  of  the  same 
action.  Antl  if  we  turn  to  the  splanchnic  nerve  we  lind  a  similar 
interpretation  equally  valid.  Stimulation  of  the  splanchnic  nerve 
causes  constriction  of  the  arteries  governed  by  that  nerve, 
apparently  because  the  stimulation  supplies  artificially  the 
constrictive  imi)ulses  which,  so  long  as  the  nerve  is  intact,  pass 
down  it  from  the  central  nervous  system,  giving  the  requisite  tone 
to  its  vascular  area,  and  tiie  loss  of  which  by  division  of  the  nerve 
gives  rise  to  dilation.  So  that  were  we  to  stop  our  inquiries  at 
this  point,  our  explanation  of  vaso-motor  action  would  be  very 
simple.  We  might  speak  of  constrictive  impulses  as  passing  from 
the  central  nervous  system  to  the  various  vascular  areas,  to  such 
an  extent  as  to  constitute  normal  tone,  but  as  being  susceptible 
either  of  inhibition,  complete  or  partial,  thus  leading  to  greater  or 
less  arterial  dilation,  or  of  augmentation,  thus  leading  to  excessive 
constriction. 

But  this  simple  view  appears  insufficient  when  we  push  our 
studies  further. 

In  the  first  place,  such  a  conception  does  not  cover  all  the 
facts  connected  even  with  the  two  nerves  just  mentioned.  For 
the  dilation  or  loss  of  tone  which  follows  upon  section  of  the 
cervical  sympathetic  (and  the  same  is  true  of  the  splanchnic)  is 
not  jjermanent;  after  a  while,  it  maybe  not  until  after  several 
days,  it  may  be  sooner,  the  dilation  disappears  and  the  arteries* 
regain  their  usual  calibre.  This  recovery  is  not  due  to  any 
regeneration  of  vaso-motor  fibres  in  the  sympathetic,  for  it  may 
be  observed  when  the  whole  length  of  the  nerve  including  the 
superior  cervical  ganglion  is  removed.  When  recovery  of  tone 
has  thus  taken  place,  dilation  or  increased  constriction  may  be 
occasioned  by  local  treatment  :  the  ear  may  be  made  to  blush  or 
to  pale  by  the  application  of  heat  or  cold,  by  gentle  stroking  or 
rough  handling  and  the  like  ;  but  neither  the  one  nor  the  other 
condition  can  be  brought  about  by  the  intervention  of  the  cential 
nervous  system.  From  this  it  is  clear  that  what  we  have  spoken 
of  as  the  tone  of  the  vessels  of  the  face,  though  intUienced  by 
and  in  a  measure  dependent  on  the  central  nervous  system,  is  not 
simply  the  result  of  an  effort  of  that  system.  The  muscular  walls 
ol  the  arteries  are  not  mere  ]jassive  instruments  worked  by  thi 
cerebro-spinal  axis   through   the   cervical   sympathetic  j  obviously 


214  VASO-MOTOR   NERVES.  [BOOK   I. 

tiiey  have  an  intrinsic  tone  of  their  OAvn,  dependent  possibly  on 
some  local  nervous  mechanism,  though  in  the  ear  at  least  no  such 
mechanism  has  yet  been  found ;  and  it  seems  natural  to  suppose 
that  when  the  central  nervous  system  causes  dilation  or  constric- 
tion of  the  vessels  of  the  face,  it  makes  use,  in  so  doing,  of  this 
intrinsic  local  tone.  But  if  so,  then  the  simple  view  entertained 
above,  that  arterial  dilation  and  constriction  are  simply  deter- 
mined by  the  decrease  or  increase  of  tonic  constrictive  impulses 
passing  directly  from  the  central  nervous  system,  is  not  a  complete 
representation  of  the  facts. 

In  the  second  place,  if  we  turn  from  the  sympathetic  or 
splanchnic  to  other  nerves  containing  vaso-motor  fibres,  we  meet 
with  still  greater  difficulties.  To  take,  for  instance,  a  nerve 
supplying  a  muscle,  such  as  that  going,  in  the  frog,  to  the  mylo- 
hyoid muscle.  Here,  as  in  the  cervical  sympathetic,  section  of 
the  nerve  produces  dilation,  but  that  dilation  is  even  more  tran- 
sient than  in  the  case  of  the  sympathetic  ;  the  vessels  speedily 
return  to  their  former  calibre.  And  then  it  is  found  that  stimula- 
tion of  whatever  strength  of  the  peripheral  portion  of  the  divided 
nerve  brings  about  not  constriction  but  dilation.  A  similar 
dilation  is  seen  when  the  nerve  of  a  mammalian  muscle  is 
stimulated,  and  probably  occurs  in  the  case  of  all  muscular 
nerves  ^.  So  also  witli  the  lingual,  section  of  which,  as  we  have 
already  stated,  produces  dilation  of  the  vessels  of  the  tongue ; 
stimulation  of  the  peripheral  portion  of  the  divided  nerve  gives 
rise  to  dilation,  no  constriction  ever  making  its  appearance. 
There  are  therefore  in  the  body  nerves,  stimulation  of  which, 
as  well  as  mere  section,  always  brings  about  arterial  dilation. 
,  There  are  other  nerves  in  the  body  of  a  mixed  character, 
intermediate  between  the  cervical  sympathetic  on  the  one  hand, 
and  the  lingual  or  muscular  nerves  on  the  other,  stimulation 
producing  now  constriction,  now  dilation.  Such  a  nerve  is  the 
sciatic  of  a  mammal.  We  have  already  seen  that  section  of  this 
nerve  produces  dilation  of  the  vessels  of  the  foot ;  but  the  dila- 
tion so  caused  after  a  (ew  days  disappears ;  the  foot  on  the  side 
on  which  the  nerve  was  divided  becomes  not  only  as  cool  and 
pale,  but  frequently  cooler  and  paler  than  the  foot  on  the  sound 
side.  If  the  peripheral  portion  of  the  divided  nerve  be  stimulated 
with  an  interrupted  current,  immediately  or  very  shortly  after 
division,  the  dilation  due  to  the  division  gives  place  to  constric- 
tion ;  the  sciatic  acts  then  quite  like  the  cervical  sympathetic, 
except  perhaps  that  this  artificial  constriction  cannot  be  main- 
tained for  so  long  a  time,  and  is  very  apt  to  be  followed  by 

^  Gaskell,  Journal  Physiol,  I.  (1878)  p.  262. 


CHAP.   IV.]  THE   VASCULAR   MECHANISM.  21 5 

increased  (Hlation.  If  however  the  stimulation  be  deferred  for 
some  tlays,  until  the  dilation  has  given  place  to  a  retljrning 
constriction,  the  eftect  is  not  constriction  but  dilation  ;  the  nerve 
then  acts  like  a  muscular  nerve  and  not  like  the  cervical  sympathetic. 
In  fact,  by  variations  in  the  attendant  circumstances,  and  in  the 
mode  of  stimulation,  into  the  details  of  which  we  cannot  enter 
now,  stimulation  of  the  divided  sciatic  may  at  the  will  of  the 
experimenter  be  made  to  produce  either  arterial  dilation  or 
arterial  constriction. 

In  all  the  above  cases  section  of  the  nerve  produces  dilation, 
whether  the  subsequent  stimulation  causes  constriction  or  dilation  ; 
the  dilation  after  section  may  be  sometimes  not  very  marked,  but 
is  always  present  to  some  extent  or  other.  But  there  are  certain 
nerves,  section  of  which  produces  no  marked  changes  in  the 
vascular  areas  to  which  they  are  distributed,  and  yet  stimulation 
of  which  brings  about  dilation  often  of  an  extreme  character.  A 
striking  example  of  this  is  seen  in  the  so-called  nervi  erigentes. 
The  erection  of  the  penis  is,  putting  aside  the  subsidiary  action  of 
muscular  bands  in  restraining  the  outflow  through  the  veins, 
chiefly  due  to  the  dilation  of  branches  of  the  pudic  arteries, 
whereby  a  large  quantity  of  blood  is  discharged  into  the  venous 
sinuses.  Erection  may  in  the  dog  be  artifically  produced  by 
stimulating  the  peripheral  ends  of  the  divided  nervi  erigentes, 
which  are  branches  from  the  first  and  second  and  sometimes  from 
the  third  sacral  nerve  passing  across  the  pelvis.  On  applying 
the  interrupted  current  to  the  peripheral  ends  of  these  nerves, 
the  corpora  cavernosa  at  once  become  turgid.  And  yet  simple 
section  of  these  nervi  erigentes  will  not  in  itself  give  rise  to 
erection. 

According  to  Lov($n '  and  Nicohki^  section  of  the  pudic  nerves 
causes  a  partial  dilation  of  the  vessels  of  the  penis,  under  which 
circumstances  Ni:olski  finds  section  of  the  nervi  erigentes  to  produce 
a  constriction,  which  also  appears  even  when  the  pudic  nerves  have 
not  previously  been  divided.  This  result  indicates  the  existence  of 
tonic  dilating  impulses  passing  norniilly  down  the  nervi  erigentes 
and  normally  restrained  by  antagonistic  constrictive  impulses  passing 
along  the  pudic  nerves, 

A  similar  case  is  presented  by  the  .submaxillary  gland.  As 
will  be  explained  more  in  detail  in  treating  of  secretion,  this 
gland  is  sujiplied  by  two  nerves,  by  branches  of  the  chorda 
tympani  reaching  it  along  its  duct,  and  by  branches  of  the 
cervical   sympathetic   reaching   it    along    its    arteries.      Neither 

•  Op.  cil  »  Hofmann  ii  Schwalbe,  Bcricht.  vi.  (1S77)  p.  79 


2l6  VASO-MOTOR   NERVES.  [BOOK   I. 

section  of  the  chorda  tympani  nor  section  of  the  cervical  sympa- 
thetic produces  any  very  marked  effect  in  the  circulation  of  the 
gland.  Yet  stimulation  of  the  former  will  bring  about  a  most  striking 
dilation,  of  the  latter  a  no  less  striking  constriction,  of  the  arteries 
of  the  gland. 

How  can  we  construct  a  view  of  the  action  of  vaso- 
motor nerves  which  will  be  consistent  with  all  these  various 
facts  ? 

In  the  first  place  we  must  admit  the  existence  of  a  local  tone^ 
in  the  several  vascular  areas,  independent  of  the  central  nervous 
system.  In  such  cases  as  the  corpora  cavernosa  of  the  penis,  and 
the  submaxillary  gland,  this  independence  is  unmistakable ;  in 
other  regions  it  is  not  at  first  sight  so  apparent,  but  as  we  have 
already  urged,  must  be  admitted  even  for  these. 

In  the  second  place,  as  is  strikingly  shewn  by  the  case  of  the 
submaxillary  gland,  there  are  nerves  which,  since  they  always 
cause  dilation,  may  be  called  vaso-dilator  nerves,  and  nerves 
which,  since  they  always  cause  constriction,  may  be  called  vaso- 
consti'ictor  nerves.  Examples  of  the  first  are  seen  in  the  nervi 
erigentes,  the  chorda  tympani,  the  nerves  of  muscles,  &c.  ;  of  the 
second,  in  the  cervical  sympathetic,  the  splanchnic,  &c.  Or  to  be 
more  exact,  we  may  say  that  the  vaso-motor  fibres  of  the  former 
are  vaso-dilator,  of  the  latter,  vaso-constrictor.  It  will  not  escape 
notice  that  the  vaso-dilator  fibres  run  chiefly  at  least  in  the 
cerebro-spinal,  vaso-constrictor  in  the  sympathetic  nerves. 

In  the  third  place,  the  cases  of  the  corpora  cavernosa  of  the 
penis  and  the  submaxillary  gland  suggest  the  idea  that  dilation  is 
the  refiilt  of  the  complete  or  partial  loss  of  local  tone,  that  in  fact 
vaso-dilators  act  by  inhibiting,  and  vaso-constrictors  by  augmenting, 
the  activity  of  the  mechanism  (whatever  it  be)  which  gives  rise  to 
the  local  tone. 

The  erection  of  the  penis  which  follows  stimulation  of  the 
nervi  erigentes,  and  the  injection  of  the  submaxillary  gland  which 
follows  stimulation  of  the  chorda  tympani,  present  a  very  close 
analogy  to  the  inhibition  of  the  heart  by  stimulation  of  the  vagus. 
Just  as  the  rhythmic  contraction  of  the  cardiac  fibre  is  stopped  by 
the  vagus,  so  the  tonic  contraction  of  the  arterial  fibre  (and  this 
tonic  contraction  is  indeed  at  bottom  an  obscure  rhythmic  con- 
traction) is  stopped  by  the  chorda  or  the  nervi  erigentes.  And 
it  seems  to  be  very  natural  to  draw  the  conclusion  that  dilation 
is  in  all  cases  mere  inhibition,  and  constriction  in  all  cases  mere 
augmentation,  of  local  tone.  But  tempting  as  this  view  is,  and 
useful  perhaps  as  it  may  be  as  a  working  hypothesis,  it  must  not 
.  be  regarded  as  definitely  proved.     It  is  quite  possible  that  dilation 


CHAP.    IV.]  THE   VASCULAR    MECHANISM.  21/ 

may  be  brought  about  in  different  ways  in  different  cases  ;  and  so 
also  with  constriction. 

The  'inhibitory'  explanation  of  dilation  must  of  necessity  remain 
unsatislactory  until  our  information  concerning  the  nature  of  the  local 
mech;:nism  is  increased. 

Alonj^  the  course  both  of  the  chorda  tympani  and  nervi  erigentes 
numerous  ganghon  cells  are  distributed,  and  their  presence  gives 
additional  point  to  the  comparison  of  the  local  mechanism  with  the 
intrinsic  nervous  mechanism  of  the  heart.  Nicolski'  has  still  further 
extended  the  analogy  of  the  nervi  erigentes  with  the  inhibitory  fibres 
of  the  pneumogastric,  by  shewing  that  atropin  paralyses  the  dilating 
fibres  of  the  nervi  erigentes,  while  muscarin  produces  erection  ap- 
parently by  stimulating  the  local  dilator  mechanism.  Still,  atropin 
does  not  paralyse  the  dilator  fibres  of  the  chorda. 

Further,  the  occurrence  of  dilation  after  simple  section  of  a 
nerve  raises  an  interesting  question.  Do  the  arteries  in  such  a 
case  dilate  because  the  very  section  of  the  nerve  acts  as  a  stimulus 
to  vaso-dilator  fibres,  or  because  the  local  tone  is  insufticient  to 
keep  up  an  adequate  arterial  constriction  unless  it  be  supplemented 
by  additional  tonic  impulses  reaching  the  local  mechanism  from 
the  central  nervous  system,  which  supplement  is  lost  by  section 
of  the  nerve  ?  Obviously,  if  mere  section  is  a  stimulus  to  vaso- 
dilator fibres  of  such  a  potency  as  to  give  rise  to  a  dilation  lasting 
hours  or  it  may  be  days,  all  evidence  of  'tonic'  impulses  pro- 
ceeding from  the  central  nervous  system  is  done  away  with.  We 
can  then  only  speak  of  dilation  and  constriction  as  being  the 
result  of  the  action  of  vaso-dilator  and  vaso-constrictor  fibres 
respectively,  both  worked  in  a  reflex  manner  by  the  central 
nervous  system.  Into  the  discussion  whether  such  an  interpre- 
tation of  the  effects  of  simple  section  is  justified  by  facts  or  not, 
and  into  the  allied  controversy  concejping  the  reason  why  the 
vaso-motor  effects  of  stimulating  the  afferent  fibres  of  the  sciatic 
and  other  nerves  vary  so  much  under  different  circumstances,  we 
cannot  enter  here.  We  must  content  ourselves  with  the  general 
conclusion  that  though  local  tone  may  exist  independently  of 
the  central  nervous  system,  the  condition  of  the  various  vascular 
areas,  in  the  living  body  in  a  normal  condition,  is  arranged  and 
modified  to  meet  passing  or  permanent  needs,  by  the  central 
nervous  system  through  the  agency  of  vaso-motor  nerves,  and 
that  these  vaso-motor  nerves  in  some  cases,  since  they  are  used  to 
give  rise  to  dilation  only,  may  be  spoken  of  as  vaso-dilator  nerves, 
or  as  containing  vaso-dilator  fibres,  in  other  cases  may  similarly 
be  called  vasoconstrictor,  and  in  yet  a  third  class  of  cases  be 

•   Op.  cii. 


2l8  VASO-MOTOR   NERVES.  [BOOK   I. 

regarded  as  mixed  in  character,  since  according  to  circumstances 
they  give  rise  either  to  dilation  or  to  constriction. 

There  remains  the  important  question,  What  part  of  the 
central  nervous  system  is  it  which  intermediates  as  a  nervous 
vaso-motor  centre  or  centres  either  of  purely  reflex  or  of  partly 
reflex  and  partly  automatic  action,  between  various  afferent 
impulses  and  the  efferent  vaso-motor  impulses  leading  either  to 
dilation  or  constriction  ? 

We  have  seen  (p.  209)  that  stimulation  of  the  central  stump 
of  the  divided  sciatic  gives  rise,  in  an  animal  under  urari,  to  an 
increase  of  general  blood-pressure,  brought  about  chiefly,  if  not 
entirely,  by  an  augmentation  of  constrictive  impulses  passing  along 
the  splanchnic  nerves.  This  increase  of  blood-pressure  is  mani- 
fested, with  (in  satisfactory  experiments)  undiminished  intensity, 
even  when  the  whole  of  the  brain,  down  to  a  certain  limit  in  the 
medulla  oblongata,  has  been  remioved.  But  if  the  removal  be 
carried  beyond  this  limit,  or  if  a  small  area  of  the  medulla 
oblongata  lying  above  the,  calamus  scriptorius  be  removed,  the 
effect  on  the  general  blood-pressure  of  stimulating  the  central 
stump  of  the  sciatic,  we  might  add,  of  any  other  afferent  nerve, 
is  comparatively  insignificant.  Obviously  this  small  portion  of 
the  medulla  oblongata  acts  as  a  vaso-motor  centre,  by  the  action 
of  which  ordinary  afferent  impulses  coming  from  the  sciatic  or  any 
other  afferent  nerve,  are  transformed  into  vaso-motor  impulses  of 
constrictive,  or  as  in  the  case  of  an  animal  under  chloral  (see 
p.  2 to),  of  dilating  effect,  and  so  discharged  along  the  splanchnic 
nerves. 

The  vaso-motor  fibres  of  the  cervical  sympathetic  and  of  many 
other  nerves  may  similarly  be  traced  to  this  same  region  of  the 
medulla  oblongata.  V/h#ther  all  vaso-motor  fibres  are  actually 
in  connection  with  it  is  more  than  doubtful ;  but  at  all  events 
the  fibres  passing  to  so  many  vascular  areas,  and  those  of  such 
magnitude  and  importance,  are  by  means  of  it  brought  into 
functional  relationship  with  so  many,  if  not  all,  the  afferent  nerves 
of  the  body,  that  it  may  fairly  be  spoken  of  as  the  general 
vaso-motor  centre. 

Owsjannikow'  places  the  lower  limit  of  this  medullary  vaso-motor 
centre  in  the  rabbit  at  a  horizontal  line  drawn  about  4  or  5  mm  above 
the  point  of  the  calainus  scriptorius,  and  the  upper  limit  at  about 
4  mm.  higher  up,  i.e.  about  i  or  2  mm.  below  the  corpora  quadrigeniina. 
When  in  carrying  transverse  sections  of  the  brain  successively  Iom  er 
and  lower  dov/n   the  unoer  limit  was  first  reached,  the  first  effects  in 

^  Ludwig's  Arbeiten,  1871,  p.  21. 


I 


CHAP.    IV.]  THE   VASCULAR   MECHANISM.  219 

the  way  of  diminisliinp  the  rise  of  blood  pressure  resulting  from 
stinnilation  of  the  sciatic,  were  observed.  On  carryinfj  tlic  sections 
biill  lower,  the  etfcjls  of  the  stimulation  of  the  sciatic  became  less 
and  less,  until  when  the  lower  limit  was  reached  no  eficcls  at  all  were 
observed,  'fhe  centre  is  accordin.ij  to  him  bilateral,  the  halves  being 
placed  not  in  the  middl-e  line  but  more  sideways  and  rather  nearer  the 
anterior  than  the  posterior  surface. 

Dittmar',  while  confirming  in  general  Owsjannikow's  results,  limits 
the  nervous  area  thus  capable  of  acting  as  a  reflex  vaso-motor  centre 
to  a  small  prismatic  space  in  the  forward  prolongation  of  the  lateral 
columns  after  they  have  given  off  their  fibres  to  the  decussating 
pyramids.  This  space  is  largely  occupied  by  a  mass  of  grey  matter, 
called  by  Clarke  the  antcro-Iatcr.d  nucleus,  containing  large  multipolar 
cells,  and  lying  close  to  the  origin  of  the  facial.  Miescher^  had  pre- 
viously shewn  that  the  afferent  impulses  which  affect  the  vaso-motor 
centre  run  in  the  lateral  columns. 

Whether  this  medullary  vaso-motor  centre  has  any  distinct 
automatic  action,  whether  it  may  be  regarded  as  continually  gene- 
rating out  of  its  own  molecular  oscillations  and  discharging  along 
the  vaso-motor  fibres,  impulses  whereby  the  general  arterial  tone 
is  maintained,  is  a  question  wliicli,  like  the  allied  question  mooted 
on  p.  213  need  not  be  discussed  here.  Granting  even  the  existence 
of  siicli  automatic  functions,  they  must  be  of  secondary  importance. 
As  we  have  already  lirged,  the  great  use  of  the  whole  vaso-motor 
system  is  not  to  maintain  a  general  arterial  tone,  but  to  modify 
according  to  the  needs  of  the  economy  the  condition  of  this  or 
that  vascular  area. 

Besides  this  general  vaso-motor  centre  in  the  medulla,  other 
parts  of  the  spinal  cord  are  capable  of  acting  as  vaso-motor 
centres,  i.e.  of  transforming  afterent  impulses  into  efferent  vaso- 
motor impulses  of  dilation  or  constriction.  Thus  when  in  the  dog 
tiie  spinal  chord  is  divided  in  the  dorsal  region,  the  vascular  areas 
of  tlie  hinder  part  of  the  body,  after  a  temporary  dilation  (which 
may  be  due  in  ])art  at  least  to  their  severance  from  the  medullary 
vaso-motor  centre,  but  which  probably  is  rather  to  be  attributed  to 
the  shock  of  the  operation  on  the  lumbar  cord  and  the  nervous 
mechanisms  connected  with  it),  regain  their  tone  ;  and  then  the 
tone  of  one  or  otiier  of  these  areas  may  be  modified  in  the 
direction  certainly  of  dilation,  and  possil)Iy,  but  this  is  by  no 
means  so  certain,  pf  constriction  by  afferent  impulses  reaching 
the  lumbar  cord.  Erection  of  penis  through  the  nervi  erigentes 
may  be  brought  about  by  suitable  stimulation  of  sensory  surfaces, 
and  dilation  of  various  vessels  of  the  limbs  readily  produced  by 
sUmulation  of  the  central  stump  of  one  or  another  nerve. 


k 


'  Ludwig'.s  Arbeiten,  1873,  p.  103.  »  Ibid.,  i860,  p.  172. 


220  VASO-MOTOR   NERVES.  [BOOK.    I. 

And  what  is  true  of  the  lumbar,  is  apparently  true  also  of  the 
dorsal  cord,  and  indeed  of  all  parts  of  the  spinal  cord.  Inter- 
laced with  the  reflex  and  other  mechanisms  for  the  contraction  of 
the  skeletal  muscles,  with  which  the  spinal  cord,  ^s  we  shall 
hereafter  see,  is  crowded,  are  probably  vaso-motor  centres  or 
mechanisms,  the  details  of  whose  topography  and  functions  have 
yet  to  be  worked  out.  Prominent  among  them,  whether  by 
reason  solely  of  its  special  connection  with  the  splanchnic  nerves, 
and  thus  with  the  capacious  vascular  area  of  the  abdominal 
viscera,  or  whether  because  in  addition  it  exercises  a  controlling 
co-ordinating  power  over  the  minor  centres  in  the  rest  of  the  cord, 
is  the  centre  or  mechanism  placed  in  the  particular  part  of  the 
medulla  oblongata  spoken  of  above.  Through  it,  and  through 
them,  the  delicate  machinery  of  the  circuladon,  which  determines 
the  blood  supply,  and  so  the  activity  of  each  tissue  and  organ,  is 
able  to  respond  by  narrowing  or  widening  arteries  to  the  ever 
varying  demands,  and  to  meet  by  compensating  changes  the 
shocks  and  strains,  of  daily  life. 

Vaso-constrictor  and  Vaso-dilator  Nerves.  The  problems  con- 
nected with  this  topic  may  profitably  be  studied  under  three  heads. 

I.  Is  dilation  merely  the  consequence  of  the  diminution,  partial 
or  complete,  of  what  we  may  call  central  tonicity,  i.e.  of  constrictive 
impulses  proceeding  from  the  central  nervous  system,  or  may  it  occur 
as  the  direct  result  of  the  stimulation  of  dilator  fibres  ? 

There  is  no  difficulty  in  answering  this  question  in  favour  of  the 
latter  view.  In  such  cases  as  those  of  the  chorda  tympani  and  nervi 
erigentes,  stimulation  of  the  peripheral  portion  of  the  nerve  brings 
about  a  dilation  far  exceeding  that  resulting  from  simple  section. 

Further,  Luchsinger^,  reviving  and  extending  a  very  old  experiment 
of  Schiff's^,  finds  that  when  an  animal,  a  kitten,  is  warmed  in  a 
heated  chamber  till  the  feet  become  red  from  dilation  of  the  blood- 
vessels, division  of  the  sciatic  nerve  causes  the  foot  of  the  same  side 
to  become  paler.  Similarly  if  the  sciatic  on  one  side,  say  the  left, 
is  first  divided,  the  left  foot  in  consequence  becoming  warmer  and 
redder,  and  the  animal  then  exposed  to  heat,  not  only  does  the  right 
foot  become  redder,  but  the  left  foot  (in  consequence  of  the  blood- 
current  being  diverted  to  other  parts)  even  paler  than  before,  so  that 
the  difference  in  respect  to  dilation  in  favour  of  the  right  foot  becomes 
very  marked.  That  is  to  say,  the  influence  of  the  heat  on  the  central 
nervous  system  produces  by  the  agency  of  vaso-motor  nerves  a 
dilation  greater  than  that  which  results  from  the  mere  loss  of 
central  tonicity  t-h  -ough  severance  of  the  peripheral  vessels  from  the 
central  nervous  system. 

'  Pfliig-er's  Arckiv,  XIV.  (1877)  391. 

'  Milth.  d.  Naturforsch.  Gesellsch.  in  Bern,,  1865,  p.  69. 


CHAl'.    IV.]  THE   VASCULAR    MECHANISM.  221 

2.  The  more  difficult  question  then  arises,  Is  the  dilation  which 
follows  section  of  a  nerve  always  due  to  the  section  acting  as  a 
stimulus  to  dilator  fibres,  or  may  it  in  some  cases  at  least  have  its 
origin  in  a  loss  of  central  tonicity,  or  may  it  in  still  a  third  class  of 
cases  be  brdught  about  by  both  causes  combined  ? 

doltz'  was  led  to  insist  on  the  view  that  dilation  following  section 
is  the  result  of  the  stimulation  of  dilator  fibres,  from  the  following 
experiment.  The  sciatic  of  a  dog  is  divided  and  carefully  replaced  in 
the  wound.  In  the  course  of  a  few  days,  when  the  vascular  tone  of 
the  foot  has  been  regained,  the  nerve  is  again  laid  bare,  and  a  cut 
ma^e  in  the  peripheral  stump  ;  forthwith  the  vessels  of  the  foot  dilate, 
and  if  the. nerve  be  crimped  by  a  series  of  cuts  carried  successively 
downwards,  a  very  marked  dilation  of  the  blood-vessels  and  rise  of 
temperature  in  the  foot  is  observed.  The  question  why  dilation  only 
results  under  these  circumstances,  whereas  when  the  nerve  is  in  the 
first  instance  divided,  a  passing  constriction  followed  by  the  more 
lasting  dilation  is  observed,  is  answered  by  the  hypothesis  that  the 
constrictor  fibres,  which  are  present  in  the  nerve  together  with  the 
dilator  fibres,  degenerate  rapidly,  so  that  at  the  time  the  crimping 
produces  dilation,  the  latter  fibres  only  are  in  functional  activity. 
This  experiment  undoubtedly  shews  that  the  effects  of  mere  section  in 
the  way  of  a  stimulus  must  not  be  underrated;  but  is  not  valid  as  an 
argument  against  the  view  that  dilation  may  be  the  result  of  mere  loss 
of  central  tonicity.  For  besides  the  fact  that  the  dilation  which 
follows  upon  crimping  is  far  more  transient  than  the  initial  dilation 
which  results  from  the  primary  division  of  the  nerve,  section  of  an 
undoubted  dilator  nerve  such  as  the  chorda  tympani  does  not  produce 
anything  more  than  the  slightest  and  briefest  dilation,  and  even  that 
sometimes  is  absent^.  Moreover  if  mere  section  were  so  powerful  a 
stimulus  to  dilator  fibres,  it  ought,  unless  the  contrary  can  be  shewn, 
to  act  similarly  as  a  stimulus  to  constrictor  fibres  when  these  are  in 
functional  activity  ;  and  indeed  such  an  eflect  on  constrictor  fibres 
may  be  supposed  to  be  indicated  by  the  initial  constriction  which 
sometimes  may  be  seen  to  precede  the  dilation  following  on  section  of 
the  sciatic.  But  in  a  section  of  a  purely  constrictive  nerve,  like  the 
cervical  sympathetic,  the  initial  constriction,  which  is  sometimes  but 
not  always  seen  to  precede  the  more  lasting  dilation,  is  of  the  slightest 
kind. 

We  must  therefore  conclude  that  the  dilation  which  follows  section 
of  the  nerve  is  due  largely,  and  probably  in  some  cases  e.\clusively,  to 
actual  loss  of  central  tonicity. 

3.  The  third  question  suggested  is,  What  is  the  nature  and  mode 
of  action  of  vaso-dilator  and  vaso-constrictor  fibres  respectively? 
Are  they  separate  and  distinct  fibres,  with  altogether  ditTerent  mechan- 
isms.-' Or  may  the  same  fibre  according  to  circumstances  act  now  as 
a  dilator  now  as  a  constrictor.'' 

In  reference  to  this  the  following  facts  deserve  attention.     When 

'  Pfluger's  Archiv,  IX.  (iS74)  p.  174  :  XI.  (1S75)  p   52. 

■  Kendall  and  Luchsinger,  Pfliigers  Archiv,  Xin.  (1876)  p.  197. 


222  VASO-MOTOR   NERVES.  [BOOK   I. 

the  sciatic  nerve  is  stimulated  with  an  interrupted  current  immediately 
after  division,  constriction  in  the  vessels  of  the  foot,  as  shewn  by  a 
fall  of  temperature,  or  diminished  injection  of  vascular  surfaces,  or 
diminished  outflow  from  an  incision,  is  the  result  which  has  been 
observed  by  nearly  all  experimenters.  In  a  degenerating  nerve  {i.e. 
one  which  has  been  divided  some  days  previously)  stimulation  produces 
dilation\  Indeed  the  same  stimulation  which  on  an  early  day  after 
division  causes  constriction  may  on  a  later  day  give  rise  to  dilation^ 
Single  induction  shocks  repeated  'at  intervals  (one  or  two  seconds) 
applied  to  a  fresh  nerve  give  when  weak  dilation,  when  strong  con- 
striction ;  the  same  rhythmical  stimulus',  however  strong,  applied  to  a 
degenerating  nerve  causes  dilation,  even  in  cases  where  the  inter- 
rupted current  still  gives  rise  to  constriction^.  Similarly  with  the 
degenerating  peripheral  stump  of  the  auricularis  magnus  in  the 
rabbit  weak  stimulition  sometimes  causes  dilation,  strong  stimulation 
constriction.  So  that  in  general  when  the  stimulus  is  weak  in  relation 
to  the  irritability  of  the  nerve,  dilation  results;  when  it  is  strong, 
constriction.  When  the  stimulus  is  very  strong  and  prolonged  the 
constriction  may  be  followed  by  dilation,  but  this  appears  to  be  merely 
the  result  of  exhaustion''. 

On  the  other  hand,  stimulation  of  the  chorda  tympani  produces 
dilation,  never  constriction,  whatever  be  the  strength  of  the  stimulus  ; 
and  stimulation  of  the  cervical  sympathetic  similarly  always  causes 
constriction. 

In  the  case  of  the  mylo-hyoid  of  the  frog  stimulation  of  the  nerve 
always  produces  dilation,  though  constriction  may  be  brought  about 
by  applying  the  electrodes  directly  to  the  muscle^. 

So  far  facts  are  compatible  with  the  hypothesis  that  while  the 
cervical  sympathetic  contains  only  constrictor  and  the  chorda  tympani 
only  dilator  fibres,  the  sciatic  nerves  contain  both  kinds  of  fibres,  the 

'  Goltz,  op.  cit.  2  Kendall  and  Luchsinger,  op.  cit. 

3  Kendall  and  Luchsinger,  op.  cit. 

4  Dastre  and  Morat  {Conipt.  Rend.  T.  87  (1878)  p.  771,  p.  880)  judging  of 
the  condition  of  the  vessels  governed  by  the  cervical  sympathetic,  by  reladve 
variations  in  the  arterial  and  venous  pressure  of  the  region,  find  that  the  con- 
striction which  is  caused  by  stimulation  of  the  sympathetic  is  of  short  duration, 
and  is  foUov/ed,  even  before  the  removal  of  the  stimulus  when  this  is  of  long 
duration,  by  a  dilation  greater  than  that  which  existed  before  the  application  of 
the  stimulus,  by  in  fact,  a  super-dilation.  The  same  phenomenon  was  seen  in 
the  vessels  of  the  foot  (of  the  horse  or  ass)  when  the  posterior  tibial  nerve  was 
stimulated,  and  it  may  be  remarked  that  the  authors  never  in  any  case  saw  the 
stimulus  fail  to  produce  constriction  :  whether  the  stimulus  was  weak  or  strong, 
rhythmic  or  tetanic,  whether  the  nerve  had  been  divided  recently,  or  for  days 
before,  stimulation  always  caused  constriction  ;  dilation  never  occurred  other- 
wise than  as  subsequent  super-dilation.  The  effects  then  observed  by  these 
authors  on  stimulating  this  smaller  branch  in  the  horse  are  opposed  to  those  of 
stimulating  the  sciatic  trunk  in  other  animals,  for  the  dilation  spoken  of  above 
has  been  repeatedly  observed  without  any  previous  constriction,  even  when  the 
state  of  the  vessels  was  judged  by  inspection  of  the  unpigmented  feet,  and  not 
merely  inferred  from  a  rise  of  temperature. 

s  Gaskell,  Journ.  Anat,  Phys.  xi.  (1877)  p.  720. 


CHAP.    IV. j  TIIL:    vascular    MKCHANISM.  2J3 

constrictor  fibres  being  less  irritable,  and  degenerating  sooner,  the 
dilating  effects  in  consequence  appearing  as  degeneration  is  setting  in 
and  when  the  stimulus  used  is  too  weak  to  evcite  the  constrictor 
fibres.  But  Bernstein'  finds  that  the  transition  from  constriction  may 
be  cfTccted  without  any  change  in  the  nerve-trunk  itself.  It  is  simply 
sufficient  in  the  case  of  the  sciatic  of  the  dog  to  reduce  the  tem- 
perature of  the  foot  by  plunging  it  into  a  cold  bath,  in  order  that 
stimulation  of  even  the  just  divided  sciatic,  whether  by  rhythmical 
induction  shocks,  or  by  the  interrupted  current,  or  by  crimping,  may 
bring  about  dilation.  And  Lepine*  had  previously  arrived  at  a 
similar  conclusion  with  regard  to  the  sciatic  of  the  frog.  From  this 
we  may  infer  that  the  same  fibre  may  act  as  dilator  or  constrictor 
accordini^  to  the  coiidilion  of  the  peripheral  tnechanism ;  at  all  events, 
these  results  throw  great  doubt  on  the  necessity  of  supposing  the 
existence  of  two  kinds  of  tibres.  Moreover  we  e  the  two  kinds  of 
fibres  distinct  we  should  e.xpect  to  find  them  running  in  some  part  of 
their  course  at  least,  in  different  tracts  ;  but  this  has  not  as  yet 
been  observed,  as  will  appear  from  the  following  paragraph. 

The  course  of  vaso-inotor  fibres.  S:hiff^  conclu  led  thit  the  vaso- 
motor fibres  for  the  front  and  hy:id  limbs  passed  partly  directly  from 
the  cord  through  the  anterior  roots  of  the  nerves  forming  the  sciatic 
and  br.ichial  plexuses  respectively,  and  partly  indirectly  from  the 
anterior  roots  of  the  last  three  or  five  dorsal  nerves  to  the  abdominal 
sympathetic  and  thus  to  the  trunk  of  the  sciatic^  and  from  the  anterior 
roots  of  the  3rd,  4th,  5th  or  sometimes  6th  dor^^al  nerves  to  the  thoracic 
sympathetic,  and  thence  by  the  stellate  or  first  thoracic  ganglion  to  the 
brachial  ple.xus.  Schiff  made  no  distinction  between  the  paths  of 
constrictor  and  dil  itor  fibres  ;  he  supposed  the  fibres  of  direct  origin 
to  supply  the  lower  parts,  those  of  indirect  origin  the  upper  and  middle 
parts,  of  the  respective  limbs.  Bernard  ■•  on  the  contrary  found  that 
all  the  fibres  for  both  limbs  took  the  indirect  course  through  the 
sympathetic.  And  subsequent  observers  have  supported  now  one, 
now  the  other  view.  E.  Cyon  s  in  respect  to  the  fore-limb  (the  fibres 
running  in  a  single  nerve  passing  from  the  thoracic  chain  to  the 
stellate  ganglion),  and  Ostroumoff"  in  respect  to  the  hind  limb,  support 
Bernard;  while  Luchsinger  and  Pueima '  agree  with  Schift'  in  so  far 
that  some  of  the  fibres  issue  from  the  cord  through  the  proper  anterior 
roots  of  the  nerve.  Heidenhain  and  Gaskell  ^  find  that  the  vaso- 
motor nerves  of  the  muscles  of  the  leg  run,  in  the  dog,  in  the  ab- 
dominal sympathetic,  but  apparently  not  exclusively  so.  All  these 
observers  either  find  constrictors  and  dilators  running  in  the  same 
tract,  or  at  least  make  no  difference  between  them.     The  evidence 

'  Pfluger's  ^/rr///z'.  XV.  (1877)  p.  575. 

'  Compt.  Rend.  Soc.  Biol.,  March  4,  1S76. 

S  Coiiiptts  Renaus,  1S62,  II.  p.  400,  p.  425,  and   previously,    Untersuch,  s. 
Physiol,  d.  Nervm-^ysletn,  1855. 

♦  Comples  Reiidus,  1S62,  II.  p.  228,  p.  305. 
s  Luciwig's^/rM/<r«,  186S,  p.  62. 

*  Pllii^^er's  Archiv,  xil.  (1S76)  p.  219. 
'  Plluger,  XVIII.  (1S78)  p.  4S9. 

'  Journ.  Physiol,  I.  (1878)  p.  262, 


224  VAS0-MOTOR   NERVES.  [BOOK   I. 

however  as  to  the  exact  course  is  more  satisfactory  in  the  case  of  the 
constrictors  than  in  the  case  of  the  dilators.  The  view  of  Strieker  * 
that  dilator  fibres  for  the  hind-limb  run  in  the  posterior  roots  of  4th 
and  5th  lumbar  nerves,  has  been  contested  by  Cossy^  and  Vulpian^. 
In  the  frog  the  vaso-motor  fibres  for  the  hind  limb,  at  least  the  web, 
appear  to  leave  the  cord  through  the  anterior  roots  of  the  sciatic 
nerve  *.  Lastly  it  may  be  observed  that  Bernard  ^  traces  the  vaso- 
motor fibres  of  the  cervical  sympathetic  into  the  first  thoracic  ganglion 
on  their  way  from  the  spinal  cord. 

Spinal  vaso-motor  ce7itres.  Evidence  has  already  been  given 
(p.  218)  of  the  existence  even  in  the  mammal  of  spinal  vaso-motor 
centres,  in  addition  to  the  medullary  centre.  In  the  frog  this  power 
of  the  spinal  cord  to  act  as  a  vaso-motor  centre  is  still  more  marked 
and  general*.  And  even  the  statement  on  p.  218  that  the  rise  of 
pressure  following  upon  stimulation  of  an  afferent  nerve  is  absent  or 
very  slight  when  the  medullary  vaso-motor  has  been  removed,  does 
not  apply  in  certain  conditions.  Thus  in  strychnised  animals,  such  a 
rise  when  an  afferent  nerve  is  stimulated  is  quite  distinct  t.  A  rise  of 
pressure  is  similarly  observed,  in  the  absence  of  the  medulla,  as  a 
consequence  of  dyspnoea  s,  and  as  the  direct  result,  without  any  con- 
comitant stimulation  of  afferent  nerves,  of  poisoning  by  picrotoxin' 
and  by  antiarin  "  and  by  strychnia  ".  It  is  probable  at  all  events  that 
in  these  cases  the  rise  in  blood-pressure  is  due  to  constrictive  impulses 
passing  down  the  splanchnic  nerves.  If  so,  then  the  vaso-motor 
mechanism  of  the  spinal  cord  would  bear  to  the  ordinary  reflex 
mechanisms  by  which  the  skeletal  muscles  are  worked,  the  additional 
analogy  that  the  paths  along  which  the  impulses  of  afferent  or  central 
origin  issue  as  efferent  impulses  are  determined  in  part  by  the  condition 
of  the  cord  and  the  character  of  the  afterent  impulses  or  of  the  central 
disturbances  ". 

Tlie  Effects  of  Local  Vascular  Constriction  or  Dilation. 

Whatever  be  determined  ultimately  to  be  the  modus  operandi 
of  vaso-motor  mechanisms,  the  following  fundamental  facts  reinain 
of  prime  importance. 

'   VVien.  Sitzungsberichte,  LXXIV.  (July,  1876). 

=  Archives  de Physiolog.  in.  (1876)  p.  832.  3  Ibid.,  V.  {1878)  p,  336. 

4  Pfliiger,  Allg.  Med.  Central  Zeiiung,  Jahrg.  XXIV.  No.  6876.  Nussbaum, 
Pfllig-er's  Archiv,  X.  (1875)  P-  374- 

s   Comptes  Rendtcs,  1862,  II.  p.  381. 

^  Cf.  Lister,  Phil.  Trans.,  1858,  II.  p.  607  ;  Nussbaum,  Pfliiger's  Archiv. 
X.  (1875)  p.  374. 

7  Schlesinger,  Wien.  Med.  Jahrb.,  1874;  Heidenliain,  Pfliiger's  ^;r/4?V, 
XIV.  (1876)  p.  518. 

^  Schlesinger,  op.  cit.  ;  Luchsinger,  Pfliiger's  Archiv,  XVI.  (1877)  p.  510. 

5  Luchsinger,  op.  cit. 

'°  Strieker,    Wien.  Sitzungsberichte,  LXXV.,   March,    1877  ;  Schroff,  Wien 
Med.  Jahrb.,  1874,  p,  259, 
''  Strieker,  op.  c't. 
"  Cf.  Heidenhain,  Pfliiger's  Archiv,  xiv.  (1877)  p,  518. 


CHAP.   IV.J  THE   VASCULAR    MECHANISM.  22$ 

The  tone  of  any  given  vascular  area  may  be  altered,  positively 
in  the  direction  of  augmentation  (constriction),  or  negatively  in 
the  way  of  inhibition  (dilation),  quite  independently  of  what  is 
going  on  in  other  areas.  The  change  may  be  brought  about  by 
(i)  stimuli  applied  to  the  spot  itself,  and  acting  either  directly  on 
some  local  mechanism,  or  indirectly  by  reflex  action  through  the 
general  central  nervous  system  ;  (2)  by  stimuli  applied  to  some 
other  sentient  surface,  and  acting  by  reflex  action  through  the 
central  nervous  system  ;  (3)  by  stimuli  (chemical,  blood  stimuli) 
acting  directly  on  the  central  nervous  system. 

The  effects  of  local  dilation  are  local  and  general. 

Local  effects  of  dilation.  The  arteries  in  the  area  being 
dilated  offer  less  resistance  than  before  to  the  passage  of  blood. 
Consequently,  more  blood  than  usual  passes  through  them,  filling 
up  the  capillaries  and  distending  the  veins.  Owing  to  the  diminu- 
tion of  the  resistance,  the  fall  of  pressure  in  passing  from  the 
arteries  to  the  veins  will  be  less,  marked  than  usual ;  that  in  the 
small  arteries  themselves  will  be  lowered,  that  in  the  corresponding 
veins  heightened.  The  lowering  of  the  pressure  in  the  arteries 
means  that  their  elastic  coats  are  not  put  to  the  stretch  as  much 
as  usual ;  i.e.  their  elasticity  is  not  called  into  play  to  the  same 
extent  as  before.  Now,  as  has  been  seen,  every  portion  of  the 
arterial  wall  has  its  share  in  destroying  the  pulse  by  converting  the 
intermittent  into  a  continous  flow.  Hence,  the  dilated  arteries, 
their  elasticity  not  being  called  into  play  so  much  as  before,  will 
not  contribute  their  usual  share  towards  destroying  the  pulsations 
which  reach  them  at  the  cardiac  side.  The  pulsations  will 
travel  through  them  less  changed  than  before,  and  may,  in  certain 
cases,  pnss  right  on  into  the  veins.  This  is  frequently  seen  in  the 
submaxillary  gland,  when  the  chorda  tympani  is  stimulated.  The 
channels  being  wider,  resistance  being  less,  and  the  force  of  the 
heart  behind  remaining  the  same,  more  blood  than  before  passes 
through  the  area  in  a  given  time ;  or,  put  differently,  the  same 
quantity  of  blood  passes  through  the  area  in  a  shorter  time.  The 
blood,  consequently,  as  it  passes  into  the  veins  is  less  changed 
than  in  the  normal  condition  of  the  area.  Usually  the  flow  is  so 
rapid  that  the  oxy-hcemoglobin  of  the  corpuscles  is  deoxidised  to 
a  much  less  extent  than  usual,  and  the  venous  blood  still  possesses 
an  arterial  hue.  On  the  other  hand,  since  more  blood  passes  in  a 
given  time,  there  is  an  opj^ortunity  for  an  increase  in  the  total 
interchange  between  the  blood  and  the  tissue.  Thus  the  total 
work  may  be  greater,  though  the  share  borne  by  each  quantity  of 
blood  is  less, 

F.  F.  15 


226  VASO-MOTOR   NERVES,  [BOOK   I. 

General  effects  of  dilation.  Supposing  that  the  total 
quantity  of  blood  issuing  from  the  ventricle  remains  the  same,  that 
is  to  say,,  supposing  that  the  quantity  of  blood  put  into  circulation 
is  constant,  the  surplus  passing  through  the  dilated  area  must  be 
taken  away  from  the  rest  of  the  circulation.  Consequently  the 
fulness  of  the  dilated  area  will  lead  to  an  emptying  of  the  other 
areas.  This  is  seen  very  clearly  when  the  dilated  area  is  a 
capacious  one.  At  the  same  time,  local  dilation  causes  a  local 
diminution  of  peripheral  resistance.  This  in  turn  causes  a  lower- 
ing of  the  general  arterial  pressure ;  to  this  we  have  already  called 
attention. 

The  Effects  of  local  constriction,  similarly  local  and 
general,  are  naturally  the  reverse  of  those  of  dilation. 

In  the  vascular  area  directly  affected,  less  blood  passes  through 
the  capillaries  in  a  given  time,  and  in  consequence  less  total 
interchange  between  the  blood  and  the  tissues  takes  place,  though 
each  unit  volume  of  blood  which  does  pass  through  is  more 
deeply  affected.  The  blood-pressure  in  the  corresponding  arteries 
is  increased,  and,  if  the  area  be  large,  the  pressure  in  even  distant 
arteries  may  be  heightened. 

Thus,  to  indicate  results  in  a  general  manner,  local  dilation 
encourages  a  copious  flow  of  blood  through  the  area  where  the 
dilation  is  taking  place,  and,  by  reducing  the  blood-pressure, 
hinders  the  flow  of  blood  into  other  areas.  Local  constriction,  on 
the  other  hand,  lessens  the  flow  of  blood  in  the  particular  area, 
and  by  heightening  the  blood-pressure  tends  to  throw  the  mass 
of  the  blood  on  to  other  areas.  Hence  the  great  regulative  value 
of  the  vaso-motor  system.  By  augmenting  or  inhibitory  influences 
(constrictor  or  dilating)  applied  either  to  peripheral  mechanisms 
or  to  cerebro-spinal  centres,  and  called  forth  by  stimuli  either 
intrinsic  and  acting  through  the  blood,  or  extrinsic  and  acting 
through  nervous  tracts,  the  supply  of  blood  to  this  or  that  organ 
or  tissue  may  be  increased  or  reduced  :  the  surplus  or  deficit  being 
carried  away  to,  or  brought  up  from,  either  the  rest  of  the  body 
generally,  or  some  other  special  organ  or  tissue. 

Sec.  6.     Changes  in  the  Capillary  Districts. 

Possessing  no  muscular  element  in  their  texture,  the  capillaries, 
unlike  the  arteries,  are  subject  to  no  active  change  of  calibre. 
They  are  expanded  Avhen  a  large  supply  of  blood  reaches  them 
through  the  supplying  arteries,  and,  by  virtue  of  their  elasticity, 
shrink  again  when  the  supply  is  lessened  or  withdrawn ;  in  both 
these  events  their  share  is  a  passive  one. 


CHAP.   IV.]  THE   VASCULAR    MECHANISM.  227 

It  is  true  that  certain  active  changes  of  form,  due  to  movements  in 
the  protoplasm  of  their  walls,  have  been  described  ;  but  the  cftccts  of 
any  such  changes,  even  if  common,  must  be  quite  subordinate. 

Nevertheless  the  capillaries  do  possess  active  properties  of  a 
I dtain  kind,  which  cause  them  to  play  an  important  part  in  the 
work  of  tlie  circulation.  They  are  concerned  in  maintaining  the 
vital  equilibrium  which  exists  between  the  intra-vascular  blood  and 
the  extra-vascular  tissue,  an  equilibrium  which  is  the  central  fact 
of  a  normal  capillary  circulation,  of  a  normal  interchange  between 
the  blood  and  the  tissue,  and  thus  of  a  normal  life  of  the  tissue. 
The  existence  of  this  equilibrium  is  best  shewn  when  it  is  over- 
thrown, as  in  the  condition  known  as  inflammation. 

If  an  irritant,  such  as  silver  nitrate,  or  mustard,  &c.  be  applied 
to  a  small  portion  of  a  frog's  web,  or  a  frog's  tongue,  inflammation 
is  set  up  over  a  circumscril^ed  area.  In  this  area  the  following 
changes  may  be  successively  observed  under  the  microscope. 
'Ihe  first  effect  that  is  noticed  is  a  dilation  of  the  arteries,  ac- 
companied by  a  quickening  of  the  stream.  The  capillaries 
become  filled  with  corpuscles,  and  many  passages  previously 
invisible  or  nearly  so  on  account  of  their  containing  no  corpuscles 
come  into  view.  The  veins  at  the  same  time  appear  enlarged  and 
full.  These  events,  the  filling  of  the  capillaries  and  veins,  and 
the  quickening  of  the  stream,  are  all  simply  the  results  of  the 
diminution  of  peripheral  resistance  caused  by  the  dilation  of  the 
small  arteries.  If  the  stimulus  be  very  slight,  this  may  all  pass 
away,  the  arteries  gaining  their  normal  constriction,  and  the 
capillaries  and  veins  in  consequence  returning  to  their  half-filled 
condition  ;  in  other  words,  the  effect  of  the  stimulus  in  such  a 
case  is  rather  a  temporary  blush  than  actual  inflammation.  When 
the  stimulus  however  is  stronger,  the  quickening  of  the  stream 
gives  way  to  a  slackening;  this  is  not  due  to  any  returning  con- 
striction of  the  arteries,  for  they  still  continue  dilated.  The 
capillaries  and  veins  get  more  and  more  crowded  with  corpuscles, 
the  stream  becomes  slower  and  slower,  until  at  last  the  movement 
of  the  blood  in  the  now  distinctly  inflamed  area  ceases  altogether. 
The  phase  of  accelerated  flow  has  given  place  to  s/asis.  The 
capillaries,  veins  and  small  arteries  are  choked  with  corpuscles, 
and  it  may  now  be  remarked  that  the  red  corpuscles  seem  to  run 
together,  so  that  their  outlines  are  no  longer  distinguishable;  they 
appear  to  have  become  fused  into  a  yellow  homogeneous  mass. 
The  Lnrge  number  of  white  corpuscles  in  the  capillaries  and  veins 
is  also  a  conspicuous  feature,  'i'his  stasis,  this  arrest  of  the  current, 
is  not  due  to  any  lessening  of  the  heart's  beat ;  the  arterial  i)ulsa- 
tions,  or  at  least  the  arterial  flow,  may  be  seen  to  be  continued 

1=;— 2 


228  CHANGES   IN   THE   CAPILLARIES.  [BOOK   L 

down  to  the  inflamed  area,  and  there  to  cease  very  suddenly.  It 
is  not  due  to  any  increase  of  peripheral  resistance  caused  by 
constriction  of  the  small  arteries,  for  these  continue  dilated  rather 
than  constricted.  It  must  therefore  be  due  to  some  new  and 
uimsual  resistance  occurring  in  the  capillary  area  ilself.  The 
increase  of  resistance  is  not  caused  by  any  change  confined  to  the 
corpuscles  themselves ;  for  if  after  a  temporary  delay  one  set  of 
corpuscles  has  managed  to  pass  away  from  the  inflamed  area,  the 
next  set  of  corpuscles  is  subjected  to  the  same  delay  and  the  same 
apparent  fusion. 

The  cause  of  the  resistance  must  therefore  lie  in  the  capillary 
walls,  or  in  the  tissue  surrounding  them,  or,  to  speak  perhaps 
more  correctly,  it  depends  on  a  disturbance  of  the  relations  which 
in  a  healthy  area  subsist  between  the  blood  in  the  capillaries  on 
the  one  hand,  and  the  capillary  walls,  with  the  tissue  of  which 
they  are  a  part,  on  the  other.  After  stasis  has  continued  for  some 
time,  the  tissue  outside  the  capillary  wall  is  seen  to  become 
crowded  with  white  corpuscles,  and  in  the  tissue  outside  the  veins 
are  seen  not  only  white  but  also  red  corpuscles.  There  can  be 
no  doubt  that  these  have  passed  through  the  capiUary  and  venous 
walls ;  they  may  indeed  be  seen  in  transit,  but  the  mechanism  of 
their  passage  is  not  exactly  known.  We  have  no  clear  proof  that 
any  distinct  pores  do  exist  in  the  vascular  walls ;  and  it  seems 
probable  that  in  the  protoplasmic  tissue  which  constitues  these 
walls,  a  temporary  breach  made  by  the  passage  of  a  corpuscle 
may  be  immediately  and  completely  obliterated,  just  as  a  body 
may  be  thrust  through  a  film  such  as  that  of  a  soap-bubble,  and 
yet  leave  the  film  apparently  entire,  the  internal  cohesion  of  the 
film  at  once  repairing  the  breach. 

Except  in  cases  where  the  stimulus  produces  permanent  mis- 
chief, the  inflammation  after  a  while  subsides.  The  outlines  of 
the  corpuscles  become  once  more  distinct,  those  on  the  venous 
side  of  the  block  gradually  drop  away  in  the  neighbouring  currents, 
little  by  little  the  whole  obstruction  is  removed,  the  current 
through  the  area  is  re-established,  and  though  the  arteries  and 
capillaries  remain  dilated  for  some  considerable  time,  they  eventu- 
ally return  to  their  normal  calibre.  Thus  it  is  evident  that  the 
peripheral  resistance  in  the  capillaries  (and  consequently  all  that 
depends  on  peripheral  resistance)  is  not  merely  a  matter  of  the 
mechanical  friction  of  the  blood  against  the  smooth  walls  of  the 
blood-vessels,  but  is  concerned  with  the  vital  condition  of  the 
tissues.  When  the  tissue  is  in  health,  a  certain  resistance  is 
offered  to  the  passage  of  blood  through  the  capillaries,  and  the 
whole  vascular  mechanism  is  adapted  to  overcome  this  resistance 


CHAP.    IV.]  THL   VASCULAR    MECHANISM.  229 

to  such  an  extent  that  a  normal  circulation  can  take  place.  When 
the  tissue  becomes  inflamed,  the  disturbance  of  the  equilibrium 
between  the  tissue  and  the  blood  so  augments  the  resistance  that 
the  passage  of  tne  blood  becomes  difiicult  or  impossible.  And  it 
is  quite  open  to  us  to  suppose  that  there  are  conditions  the 
reverse  of  inflammation,  in  which  the  resistance  may  be  lowered 
below  the  normal,  and  the  circulation  in  the  area  quicicened. 

Such  a  diminution  of  peripheral  resistance  may  possibly  in  part 
explain  the  remarkable  quickening  of  the  flow  of  bloocl,  which  is  seen 
in  any  tisHie  after  a  tamporary  interruption  of  the  stream,  and  which  is 
also  witnessed  in  the  case  of  an  artificial  stream  kept  up  in  an  organ 
such  as  the  liver  or  kidney  removed  from  the  body.  .Mosio  '  by  means 
of  the  Plethysmography  determined  that  the  amount  of  resistance 
offered  to  the  artificial  flow  of  blood  through  an  excised  kidney, 
depends  upon  the  gases  present  in  the  blood  passed  through,  the 
resistance  being  greater  in  proportion  to  the  amount  of  carbonic  acid 
irrespective  of  the  quantity  of  oxygen. 

Thus  the  vital  condition  of  the  tissue  becomes  a  factor  in  the 
maintenance  of  the  circulation. 

It  is  perhaps  hardly  necessary  to  observe  that  the  considerations 
urged  above  are  quite  distinct  from  what  is  sometimes  spoken  of  under 
the  name  or  '  capillary '  force,  as  an  agent  of  the  circulation.  If  by 
capillary  force  it  is  intended  to  refer  to  the  rise  of  fluids  in  capillary 
tubes,  it  is  evident  that  since  such  phenomena  are  the  results  of 
adhesion,  capillarity  can  only  be  a  greater  or  less  hindrance  to  the 
flow  of  bloo  ',  seeing  that  this  is  propelled  by  a  force  (the  heart's  beat) 
which  has  been  proved  by  experiment  to  be  equal  to  the  task  of  driving 
the  blood  from  ventricle  to  auricle  through  the  capillary  regions.  If 
by  capillary  force  it  is  meant  that  the  tissues  have  some  vital  power  of 
withdrawing  the  fluid  parts  of  the  blood  from  the  small  arteries  and 
thus  of  assisting  an  onward  flow,  it  be:onies  necessary  also  to  assume 
that  they  have  as  well  the  po^ver  of  returning  the  fluid  parts  to 
the  veins.  Both  these  assumptions  are  unnecessary  and  without 
foundation. 

Sec.  7.     Changes  in  the  Quantity  of  Blood. 

In  an  artificial  scheme,  changes  in  the  total  quantity  of  fluid  in 
c.rculation  will  have  an  immediate  and  direct  ef?ect  on  the  arterial 

'  I.udwig's  Arbeiten,  1874.  • 

*  By  this  intrument  variations  in  vnhime  are  measured,  and  where  these 
depend  on  variation^  in  the  quantity  of  blood  pa  sing  the  or^ran  which  is  being 
studied,  chanijes  in  the  circulation  may  ihertby  be  inve--tigated.  Cf  Mosso, 
'  S  ipra  un  nuo\  o  metodo  per  scrivere  movimenti  dci  vasi  sangui.:;ni  ncU'  uomo," 
.//  (/.  Real.  Accad.  d.  Sci.  d.  Torino,  Vol.  XI.  ;  Fran9oisFranck,  Marey's 
I'ravaux  du  Lahorat.,  Vol.  II.  p.  I  ;  and  the  earlier  memoir  of  Fick,  Untersuch, 
Ziirich.  Physiol,  Lab.,  Hft.  I,  p.  5 1. 


230      CHANGES   IN   THE   QUANTITY   OF   BLOOD.      [BOOK   I. 

pressure,  increase  of  the  quantity  heightening  and  decrease 
diminishing  it.  This  effect  will  be  produced  partly  by  the  pump 
being  more  or  less  filled  at  each  stroke,  and  parriy  by  the 
peripheral  resistance  being  increased  or  diminished  by  the  greater 
or  less  fulness  of  the  capillaries.  The  venous  pressme  will  under 
all  circumstances  be  raised  with  the  increase  of  fluid,  but  the 
arterial  pressure  will  be  raised  in  proportion  only  so  long  as  the 
elastic  walls  of  the  arterial  tubes  are  able  to  exert  their  elasticity. 

In  the  natural  circulation,  the  direct  results  of  change  of 
quantity  are  obscured  by  compensatory  arrangements.  Thus 
experiment  shews  ^  that  when  an  animal  with  normal  blood- 
pressure  is  bled  from  one  carotid,  the  pressure  in  the  other  carotid 
sinks  so  long  as  the  bleeding  is  going  on  (this  of  course  not  so 
much  from  loss  of  blood  as  from  diminution  of  peripheral  resis- 
tance in  the  open  artery),  and  remains  depressed  for  a  brief  period 
after  the  bleeding  has  ceased.  In  a  short  time  however  it  regains 
or  nearly  regains  the  normal  height.  This  recovery  of  blood- 
pressure,  after  haemorrhage,  is  witnessed  until  the  loss  of  blood 
amounts  to  about  3  per  cent,  of  the  body-weight.  Beyond  that, 
a  large  and  frequently  a  sudden  dangerous  permanent  depression 
is  obser^'-ed. 

The  restoration  of  the  pressure  after  the  cessation  of  the 
bleeding  is  too  rapid  to  permit  us  to  suppose  that  the  quantity  of 
fluid  in  the  blood-vessels  is  repaired  by  the  withdrawal  of  lymph 
from  the  extra-vascular  elements  of  the  tissues.  In  all  probability 
the  result  is  gained  by  an  increased  action  of  the  vaso-motor 
nerves,  increasing  the  peripheral  resistance,  the  vaso-motor  centres 
being  thrown  into  increased  action  by  the  diminution  of  their 
blood-supply.  When  the  loss  of  blood  has  gone  beyond  a  certain 
limit,  this  vaso-motor  action  is  insufficient  to  compensate  the 
dmiinished  quantity,  (possibly  the  vaso-motor  centres  in  part 
become  exhausted,)  and  a  considerable  depression  takes  place ; 
but  at  this  epoch  the  loss  of  blood  frequently  causes  anaemic 
convulsions. 

Similarly  when  an  additional  quantity  of  blood  is  injected  into 
the  vessels,  no  marked  increase  of  blood-pressure  is  observed  so 
long  as  the  vaso-motor  centre  in  the  medulla  oblongata  is  intact. 
If  however  the  cervical  spinal  cord  be  divided  previous  to  the 
injection,  the  p'ressure,  which  on  account  of  the  removal  of  the 
medullary  vaso-motor  centre,  is  very  low,  is  permanently  raised 
by  the  injection  of  blood.  At  each  injection  the  pressure  rises, 
falls  somewhat  afterwards,  but  eventually  remains  at  a  higher  level 

*  Worm  Miiller,   Lud wig's  A7-bdien,   1873,   p.    159.      Lesser,   ibid.,    1874, 
p.  SO- 


CHAP.   IV. J  THE    VASCULAR    MECHANISM.  23 1 

than  before.  This  rise  continues  until  the  amount  of  blood  in 
the  vessels  above  the  normal  quantity  reaches  from  2  to  3  per 
cent,  of  the  body-weight.  Beyond  this  point  there  is  no  further 
rise  of  pressure. 

These  facts  shew,  in  the  first  place,  that  when  the  volume  of 
the  blood  is  increased,  compensation  is  effected  by  a  lessening  of 
the  peripheral  resistance  by  means  of  a  diminished  action  of  the 
vasomotor  centres,  so  that  the  normal  blood-pressure  remains 
constant.  They  further  shew  that  a  much  greater  quantity  of 
blood  can  be  lodged  in  tlie  blood-vessels  than  is  normally  present 
in  tliem.  That  the  additional  quantity  injected  does  remain  in 
the  vessels  is  proved  by  the  absence  of  extravasations,  and  of  any 
considerable  increase  of  the  extra-vascular  lymphatic  fluids.  It 
has  already  been  insisted  that  the  blood-vessels  are,  in  health,  but 
partially  filled,  that  the  veins  and  capillaries  are  alone  able  to 
receive  all  the  blood  in  the  body.  In  these  cases  of  large  addition 
of  blood,  the  extra  quantity  appears  to  be  lodged  in  the  small 
veins  and  capillaries,  (especially  of  the  internal  organs,)  which  are 
abnormally  distended  to  contain  the  surplus. 

We  learn  from  these  facts  the  two  practical  lessons,  first,  that 
blood-pressure  cannot  be  lowered  directly  by  bleeding,  unless  the 
quantity  removed  be  dangerously  large,  and  secondly,  that  there 
is  no  necessary  connection  between  a  high  blood-pressure  and 
fulness  of  blood  or  plethora,  since  an  enormous  quantity  of  blood 
may  be  driven  into  the  vessels  without  any  marked  rise  of 
pressure. 


The  Mutual  Rdatmis  and  the  Coordination  of  the  Vasadar  Factors. 

The  foregoing  considerations  shew  how  complicated,  and 
sensitive,  and  therefore  how  useful,  is  the  vascular  mechanism.  It 
may  be  worth  while  briefly  to  summarize  the  relations  of  the 
different  factors,  and  to  jjoint  out  the  manner  in  which  they  are 
made  to  work  in  harmony  for  the  good  of  the  body. 

Two  facts  stand  out  prominent  above  all  others:  (i)  the  heart's 
beat  may  be  made  slow  by  vagus  inhibition,  and,  probably, 
quickened  by  withdrawal  of  the  constant  inhibitory  influence 
exercised  by  the  cardio-inhibitory  centre  in  the  medulla.  (2)  The 
periplieral  resistance  may  be  (liminished  by  diminished  action 
(dilating  action)  of  the  vaso-motor  centres,  and  increased  by 
increased  action  (constricting  action)  of  the  same  centres. 

These  two  facts  are,  by  the  mediation  of  the  nervous  system, 
placed  in  mutual  regulative  dependence  on  each  other.     Tlius,  if 


232     RELATIONS   OF   THE   VASCULAR   FACTORS.      [BOOK  L 

with  a  given  peripheral  resistance,  and  proportionate  blood- 
pressure,  the  heart  begins  to  beat  violently,  afferent  impulses 
passing  up  the  depressor  nerves  diminish  peripheral  resistance  (by 
opening  the  splanchnic  flood-gates),  and  prevent  the  rise  of  blood- 
pressure  which  would  otherwise  take  place.  In  this  way  a  delicate 
organ,  such  for  instance  as  the  retina,  is  sheltered  from  the 
turbulence  of  the  heart  by  a  change  in  the  flow  of  blood  through 
the  less  noble  organs  of  the  abdomen.  Conversely,  if  peripheral 
resistance  be  in  any  area  increased,  the  general  blood-pressure  is 
prevented  from  rising  too  high,  by  reason  of  the  actual  increase  of 
blood-pressure  so  affecting  the  medulla,  that  inhibitory  impulses 
descend  the  vagus,  and,  by  producing  a  less  frequent  pulse,  tone 
down  the  distension  of  the  arteries. 

The  more  we  learn  of  the  working  of  the  body,  the  more 
aware  we  become  of  the  fact  that  it  is  crowded  with  regulative 
and  compensating  arrangements  no  less  striking  and  exquisite 
than  the  two  we  have  just  described.  Some  of  these  will  be  seen 
in  the  following  almost  tabular  statement  of  the  various  modifi- 
cations of  the  vascular  factors,  and  of  their  causes. 

A.     The  Beat  of  the  Heart  is  affected 

1.  By  the  amount  of  distension  of  the  ventricular  cavities 
preceding  the  systole.     This  will  depend  on 

a.  The  quantity  of  blood  passing  into  the  ventricular  cavities 
during  the  diastole.  This  in  turn  is  determined  by  the  flow  of 
blood  through  the  veins,  the  flow  itself  being  influenced  by  the 
arterial  pressure,  respiratory  movements,  &c.  &c. 

b.  The  force  of  the  auricular  contractions ^ 

c.  The  amount  of  resistance  which  has  to  be  overcome  by 
the  systole.  This  is  determined  by  the  mean  arterial  pressure, 
and  is  influenced  by  everything  which  influences  that. 

2.  By  the  quantity  of  the  blood  passing  through  the  coronary 
arteries.  In  the  frog  the  thin  walls  of  the  auricle  and  the  spongy 
texture  of  the  ventricle  permit  the  nourishment  of  the  cardiac 
substance  to  be  carried  on  by  direct  contact  with  the  blood  in  the 
cavities.  In  mammals  this  mode  of  nutrition  must  be  insignificant. 
In  them  the  condition  of  the  cardiac  muscles  and  nervous  appen- 
dages depends  almost  exclusively  on  the  blood  distributed  by  the 
coronary  arteries.  Putting  aside  the  vaso -motor  supply  of  the 
coronary  arteries,  of  which  we  know  nothing,  we  may  say  that 
the  amount  so  sent  will  depend  on  the  arterial  pressure  in  the 
aorta. 

^  Cf.  Roy,  Journ.  Physiol.,  I.  (1878)  p.  452. 


CHAI'.   IV.]  THE   VASCULAR    MECHANISM.  233 

If  the  blood-current  through  the  muscles  of  the  heart  be  inter- 
mittent, instead  of  constant  as  in  other  muscles,  the  beat  of  the  heart 
must  be  itself  self  regulative,  and  the  whole  matter  becomes  very 
complicated  '. 

3.  By  the  quality  of  the  blood  passing  through  the  coronary 
arteries,  and  acting  upon  simply  the  muscular  tissue,  or  upon  the 
various  nervous  mechanisms,  or  upon  both.  This  is  well  illustrated 
by  the  action  of  poisons  (see  p.  191).  The  quantitative  relations 
of  the  normal,  and  the  presence  of  abnormal,  constituents  must  of 
necessity  profoundly  affect  the  heart's  beat. 

4.  Through  the  inhibitory  fibres  of  the  vagus, 

a.  By  the  blood  directly  stimulating  the  endings  of  the  vagus 
fibres.     This  is  only  seen  in  the  case  of  poisons. 

b.  By  the  blood  directly  affecting  the  cardio-inhibitory  centre 
in  the  medulla  oblongata,  either  positively  by  augmenting  the 
normal  inhibitory  inlluences  and  so  slowing  the  heart,  or  negatively 
by  depressing  those  influences  and  so  quickening  the  heart. 

c.  By  reflex  stimulation  of  the  same  centre.  Cases  of  exal 
tation  through  reflex  stimulation  have  already  been  quoted. 
Instances  of  depression  leading  to  quickening  of  the  heart's 
beat  are  not  so  clear.  The  afterent  impulses  may  be  started 
in  any  part  of  the  body ;  but,  as  we  have  seen,  there  seems 
to  be  a  special  connection  between  this  centre  and  the  alimentary 
canal. 

5.  By  the  accelerator  nerves.  We  have  however,  at  present, 
no  evidence  of  the  natural  activity  of  this  nerve. 

B.     The  Peripheral  Resistance  is  affected 

1.  By  the  vital  i.e.  the  nutritive  condition  of  the  tissue  of  the 
part.     This  is  again  influenced  by 

a.  The  quality  (and  quantity  ?)  of  the  blood  brought  to  it. 

b.  Through  the  agency  of  the  nervous  system,  as  in  cases  of 
inflammation  caused  by  nervous  influences. 

Both  these  points  are  very  obscure. 

2.  By  the  varying  calibre  (constriction,  dilation)  of  the  minute 
arteries,  brought  about 

a.  By  the  blood  or  other  stimulus  acting  directly  on  the 
peripheral  vaso-motor  mechanism. 

b.  By  the  blood  acting  directly  on  the  vaso-motor  centres  in 
the  central  nervous  system. 

c.  By  reflex  stimulation  of  the  vaso-motor  centres. 

'  Cf.  Garrod,  Journ.  Anal,  and Phys.,  VII.  p.  219,  via.  p.  54. 


234     RELATIONS   OF   THE   VASCULAR   FACTORS.      [BOOK   I. 

d.  It  is  more  than  probable  that  the  peripheral  resistance, 
i.e.  the  amount  of  constriction  of  the  minute  arteries,  is  directly 
dependent  on  the  blood-pressure  itself.  In  common  with  all 
muscles,  the  contraction  of  the  circular  muscles  of  the  arteries 
will  be  greater  when  the  resistance  is  greater,  i.e.  when  the 
distension  of  the  vessels  is  greater.  That  is  to  say,  other  things 
being  equal,  with  an  increase  of  pressure,  due  for  instance  to  an 
increase  of  heart-beat,  the  distension  so  caused  will  be  more  than 
counterbalanced  by  the  increased  contraction  of  the  muscular 
fibre,  and  thus  the  pressure  still  further  increased.  This  of  course 
will  take  place  within  certain  limits  only'. 

Through  these  intricate  ties  it  comes  to  pass  that  an  event 
which  takes  place  in  one  part  of  the  body  is  felt,  to  a  greater  or 
less  extent,  by  all  parts.  To  take  a  simple  instance  :  a  change  in 
the  condition  of  the  skin  at  any  one  spot,  such  as  that  produced 
by  the  application  of  cold  or  heat,  may  lead, 

a.  By  direct  local  action  to  a  constriction  or  dilation  of  the 
vessels  of  the  part,  giving  rise  to  local  pallor  or  suffusion. 

y8.  By  reflex  action  through  the  central  nervous  system,  to  an 
increase  of  the  same  local  effects,  and  in  addition  to  a  change 
in  the  calibre  of  the  blood-vessels  in  other  parts.  This  distant 
reflex  change  may  be  of  the  same  or  the  opposite  nature  as  the 
local  change. 

y.  By  reflex  action  to  a  quickening  or  slowing  of  the  heart's 
beat,  though  the  heart  is  in  this  respect  less  intimately  connected 
with  the  skin  than  with  other  parts. 

Out  of  these  primary  effects  there  may  arise  secondary  effects ; 
the  constriction  or  dilation  produced  locally  will  affect  the  general 
blood-pressure,  which  in  turn  will  produce  all  its  effects. 

The  modifications  of  the  heart-beat  will  not  only  affect  the 
general  blood-pressure,  but  in  a  reflex  manner  may  affect  the 
peripheral  resistance,  and  hence  the  flow  of  blood  in  particular 
areas  {e.g.  the  splanchnic  area).  The  modifications  of  the  flow 
through  the  area  directly,  and  also  through  those  secondarily, 
affected,  will  influence  the  temperature  and  chemical  changes  of 
the  blood,  and  those  again  will  produce  their  effects  everywhere. 
And  so  on. 

On  the  other  hand,  the  turbulence  which  would  be  the  natural 
outcome  of  all  these  events  is  softened  down,  by  the  compensating 
effects  of  which  we  have  spoken,  into  the  smoothness  which  we 
call  health.  Still  the  greatness  of  the  possibiUties  of  change 
which  lie  hidden  in  the  body  are  clearly  enough  shewn  by  the 
violence  of  disease,  when  compensation  fails  of  accomplishment. 
»  Cf.  Latschenberger  and  Deahna,  Pfliiger's  Archiv,  Xli.  (1876)  p.  157. 


LIIAI'.    IV.]  THE   VASCULAR    MECHANISM.  235 

The  proofs  of  the  circulation  brouf^ht  forward  by  Harvey  (1628) 
required  for  their  completion  an  explanation  of  the  manner  in  which 
the  blood  passed  from  the  small  arteries  to  the  small  veins.  For  this 
the  use  of  the  microscope  was  necessary,  and  Malpighi  (1661)  was  the 
first  to  demonstrate  the  capillary  circulation.  Lcuwenhoek  afterwards 
(1674)  more  fully  described  the  passage  of  blood  through  the  capil- 
laries as  seen  in  the  wel)  of  the  frog's  foot,  in  the  fin  of  the  fish's  tail, 
and  in  other  transparent  structures. 

Observations  on  Blood- Pressure  were  first  made  by  Dr.  Stephen 
Hales",  vvho  inserted  a  tall  tube  into  the  crural  artery  of  a  mare,  and 
observed  the  height  (more  than  eight  feet)  to  which  the  column  of 
blood  rose.  He  thus  used  not  a  mercury,  nor  a  water,  but  a  blood, 
manometer.  Poiscuille^  introduced  the  mercury  manometer,  and  to 
him  we  arc  indebted  for  our  knowledge  of  the  fundamental  principles 
of  the  subject.  The  elaborate  treatise  of  Volkmann  ^  helped  to  formu- 
late our  knowledge  ;  and  we  are  indebted  to  Ludwig  for  many  of  our 
present  methods  of  investigation. 

Claude  Bernard  ■•  was  the  first  to  observe  that  section  of  the  cervical 
sympathetic  on  one  side  of  the  neck  was  followed  by  a  rise  of  temper- 
ature and  dilation  of  the  blood-vessels  of  the  same  side  of  the  head. 
Brown-Sdquard  in  the  same  years  was  apparently  the  first  to  observe 
that  stimulation  of  the  peripheral  portion  of  the  divided  sympathetic 
brought  about  a  return  of  the  pallor  and  a  fall  of  temperature  :  he 
clearly  recognised  that  the  effects  of  the  section  of  the  sympathetic 
were  the  results  of  a  paralysis  of  the  blood-vessels.  Bernard  himself, 
somewhat  later",  observed  the  effects  of  galvanic  stimulation  of  the 
divided  nerve,  though  he  seems  not  to  have  olitained  so  distinct  a 
grasp  of  the  matter  as  did  A.  Waller',  who  in  Feb.  1853  clearly  recog- 
nised the  vaso-motorial  functions  of  the  cervical  sympathetic,  and  the 
relation  of  these  functions  to  the  action  ot  the  same  nerve  on  the  iris. 
These  discoveries  formed  the  beginning  of  our  knowledge  of  the 
vaso-motor  nerves.  Among  the  numerous  investigations  which  have 
since  been  carried  on,  none  can  be  considered  more  important  than 
those  for  which  we  are  indebted  to  Ludwig  and  his  pupih. 

'  Statical  Essays,  Vol.  11.  (1732). 
'  Kech.  s.  I.  Causes  du  Mouvement  du  San^,  1831. 
3  Hdmodynaviik,  1850. 
^  Coinp'es  Rnidus,  XXXIV.  (1852)  p.  472. 

s  Phitaddph'a  Medical  Exavtincr,   kw%.  1852,  p.  489,  quoted  in  Experi- 
nf.'ittal  Researches  applied  to  Physiology    and  Pathology,    New   York,     1S53, 

P-9 
'  Comptes  Reudus  de  la  So:iiti  de  Biologie,  Nov.  1852. 
^  Comptes  Rendus,  X.XXVI.  (1853)  p.  378. 


BOOK    IL 

THE  TISSUES   OF  CHEMICAL  ACTION  WITH  THEIR 
RESPECTIVE    MECHANISMS.     NUTRITION. 


CHAPTER  I. 

THE  TISSUES  AND  MECHANISMS  OF  DIGESTION. 

The  food  in  passing  along  the  alimentary  canal  is  subjected  to  the 
action  of  certain  juices  which  are  the  products  of  the  secretory 
activity  of  the  epithelium-cells  of  the  alimentary  mucous  membrane 
itself,  or  of  the  glands  which  belong  to  it.  These  juices  (viz. 
saliva,  gastric  juice,  bile,  pancreatic  juice,  succus  entericus,  and 
the  secretion  of  the  large  intestine),  poured  upon  and  mingling 
with  the  food,  produce  in  it  such  changes,  that  from  being  largely 
insoluble  it  becomes  largely  soluble,  or  otherwise  modify  it  in  such 
a  way  that  the  larger  part  of  what  is  eaten  passes  into  the  blood, 
either  directly  by  means  of  the  capillaries  of  the  alimentary  canal 
or  indirectly  by  means  of  the  lacteal  system,  while  the  smaller 
part  is  discharged  as  excrement. 

We  have  therefore  to  consider — ist,  the  properties  of  the 
various  juices,  and  the  changes  they  bring  about  in  the  food  eaten. 
2nd,  the  nature  of  the  processes  by  means  of  which  the  various 
epithelium-cells  of  the  various  glands  and  various  tracts  of  the 
canal  are  able  to  manufacture  so  many  various  juices  out  of  the 
common  source,  the  blood,  and  the  manner  in  which  the  secretory 
activity  of  the  cells  is  regulated  and  subjected  to  the  needs  of  the 
economy.  3rd,  the  mechanisms,  here  as  elsewhere  chiefly  of  a 
muscular  nature,  by  which  the  food  is  passed  along  the  canal,  and 
most  efficiently  brought  in  contact  with  successive  juices.  And 
4th  and  lastly,  the  means  by  which  the  nutritious  digested  material 
is  separated  from  the  indigested  or  excremental  material,  and 
insorbed  into  the  blood. 

Sec.  I.     The  Properties  of  the  Digestive  Juices. 

Saliva. 

Mixed  saliva,  as  it  appears  in  the  mouth,  is  a  thick,  glairy, 
generally  frothy  and  turbid  fluid.     Under  the  microscope  it  is  seen 


240  SALIVA.  [BOOK   II. 

to  contain,  besides  the  molecular  debris  of  food  (and  frequently 
cryptogamic  spores),  epithelium-scales,  mucus-corpuscles  and 
granules,  and  the  so-called  salivary  corpuscles.  Its  reaction  in  a 
healthy  subject  is  alkaline,  especially  when  the  secretion  is 
abundant.  When  the  saliva  is  scanty,  or  when  the  subject  suffers 
from  dyspepsia,  the  reaction  of  the  mouth  may  be  acid.  Saliva 
contains  but  little  solid  matter,  on  an  average  probably  about 
•5  p.  c,  the  specific  gravity  varying  from  i"oo2  to  i'oo6.  Of 
these  solids,  rather  less  than  half,  about  '2  p.  c,  are  salts  (includ- 
ing a  small  quantity  of  potassium  sulphocyanate).  The  organic 
bodies  which  can  be  recognised  in  it  are  chiefly  mucin,  with  small 
quantities  of  globulin  and  serum-albumin. 

The  chief  purpose  served  by  the  saliva  in  digestion  is  to 
moisten  the  food,  and  to  assist  in  mastication  and  deglutition.  In 
some  animals  this  is  its  only  function.  In  other  animals  and  in 
man  it  has  a  specific  solvent  action  on  some  of  the  food-stuffs. 
Such  minerals  as  are  soluble  in  slightly  alkaline  fluids  are  dissolved 
by  it.  On  fats  it  has  no  effect  save  that  of  producing  a  very 
feeble  emulsion.  On  proteids  it  has  also  no  action.  Its  charac- 
teristic property  is  that  of  converting  starch  into  sugar  (grape-sugar, 
glucose,  dextrose). 

Action  of  Saliva  on  Starch.  If  to  a  quantity  of  thin 
boiled  starch,  which  has  been  ascertained  to  be  free  from  sugar,  a 
small  quantity  of  saliva  be  added,  it  will  be  found  after  a  time, 
that  the  whole  of  the  starch  has  disappeared,  having  been  replaced 
by  a  quantity  of  grape-sugar.  The  mixture  no  longer  gives  any 
blue  colour  with  iodine,  but  when  boiled  with  Fehling's  fluid 
(cupric  sulphate  dissolved  in  an  excess  of  a  concentrated  solution 
of  sodium  or  potassium  hydrate),  gives  a  copious  red  or  yellow 
deposit  of  cuprous  oxide.  If  iodine  be  added  to  the  mixture  in 
the  early  stages  of  the  action  of  the  saliva,  a  red  or  violet  colour 
(more  or  less  obscured  by  the  blue)  will  be  observed.  This  indi- 
cates the  presence  of  dextiin,  which  at  a  later  stage,  like  the 
starch  itself,  disappears.  In  fact  the  saliva  either  converts  the 
starch  into  dextrin  and  then  into  sugar,  or  first  splits  the  starch 
into  dextrin  and  sugar,  and  then  changes  the  dextrin  into  sugar. 
The  essence  of  both  changes  is  the  assumption  of  a  molecule  of 
water.     Thus  starch,  CgH^jOg,  or  more  probably 

(grape-sugar)  (dextrin) 

C18H30O15  -i-  3H2O  =  CeHiaOe  -}-  ^iSi^'A^^Q,)  +  2H2O  =  3(C6Hi20e). 

While  boiled  starch  is  thus  converted  into  grape-sugar  with  con- 
siderable rapidity,  raw  unboiled  starch  also  suffers  the  same  change, 
though  more  slowly.     If  a  quantity  of  raw  starch  be  suspended  in 


CHAP.    I.]  DIGESTION.  24I 

water  and  saliva  be  added,  the  water  will  after  a  time  be  found  to 
contain  sugar.  If  the  water  be  replaced  from  time  to  time,  the  starch 
will  gradually  disappear  until  a  remnant  is  left  which  gives  no  blue 
colour  with  iodine,  unless  acid  be  previously  added.  The  stirch- 
corpus:ie  consists  of  i^raniilose  giving  a  blue  colour  with  iodine  alone, 
and  cellulose  giving  a  blue  colour  with  io'Iine  on  the  addition  of 
sidphuric  acid.  The  siliva  acts  on  the  granulose,  converting  it  into 
sui^ar  ;  it  is  unable  to  act  on  the  cellulose.  When  starch  is  boiled,  the 
cellulose  coats  of  the  starch-corpuscle  are  ruptured  and  the  saliva  has 
ready  access  to  the  granulose.  Hence  the  comparative  rapidity  of  the 
action.  In  raw  starch  the  saliva  can  only  get  at  the  granulose  by 
traversing  the  coat  of  cellulose. 

Briicke  '  distinguishes  in  the  starch-corpuscle,  besides  granulose  and 
cellulose,  a  third  body  which  he  calls  oythrograiiulose.  This  gives  a 
red,  not  a  blue  colour  with  iodine,  not  usually  seen  when  iodine  is 
added  to  starch,  because  erythrcgranulose  is  much  less  abundant  than 
ordinary  granulose.  Erythrogranulose  is  converted  by  saliva  into  grape- 
sugar,  but  not  so  readily  as  granulose.  Briicke  further  regards  dextrin 
resulting  from  the  conversion  of  starch  as  a  mixture  of  c7ylhrodexl}in 
giving  a  red  colour  with  iodine,  and  achroodextrin  which  is  not  coloured 
by  iodine.  The  former  is  readily  converted  by  saliva  and  similar 
agents  into  grape-sugar,  the  latter  with  considerable  difficulty,  if  at 
all  ;  so  that  a  fluid  originally  containing  starch,  after  it  has  been  acted 
upon  by  saliva  until  iodine  gives  no  longer  either  a  blue  or  red  colour, 
may  still  contain  a  considerable  quantity  of  dextrin  in  the  form  of 
achroodextrin.  When  starch  is  acted  upon  by  dilute  acids,  the  con- 
version into  dextrin  is  preceded  by  the  appearance  of  soluble  starcJi, 
i.e.  of  starch  which  like  dextrin  forms  a  clear  solution  with  water  but 
unlike  dextrin  gives  a  blue  colour  with  iodine. 

There  is  moreover  some  doubt  whether  the  sugar  resulting  from  the 
action  of  saliva  on  starch  is  all,  or  indeed  even  in  part,  true  grape- 
sugar  or  dextrose.  .According  to  iMusculus  and  v.  Alering^'  the  products 
are  a  small  quantity  of  true  grape-sugar,  a  large  quantity  (70  p.  c.)  of 
the  kind  of  sugar  known  as  maltose,  and  achroodextrin.  Maltose, 
which,  as  its  name  implies,  is  produced 'by  the  |action  of  diastase  on 
starch,  is  a  sugar  with  stronger  rotatory  power,  but  with  less  reducing 
power  than  dextrose  ;  it  may  be  converted  into  dextrose  by  the  accion 
of  dilute  acids  3.  Other  observers'*  also  affirm  that  the  sugar  produced 
by  the  action  of  saliva  is  not  true  dextrose,  though  they  do  not  admit 
that  it  is  maltose.  It  is  very  probable  that  future  researches  may  bring 
to  light  many  varieties  of  sugar  allied  to  dextrose,  possibly  having 
different  pliysiologjical  properties,  as  well  as  many  varieties  of  dextrin. 
Since  achroodextrin,  which  appears  according  to  all  observers  to  be 
I  Hie  of  the  products  of  the  action  of  saliva,  itself  resists  the  further 
action  of  the  ferment,  all  the  starch  subjected  to  the  action  of  saliva 
does  not  pass  into  sugar. 

'   Vorlestnigtn,  i.  p.  221. 

'  Z'.f.  Physiol.  Chem.,  ii.  (1879)  p.  403.  3  See  Appendix, 

*■  Nasse,  Pflu;<er's  Archiv,  X(v.  (1S77)  p.  473.     Scegen,  i'nd.,  xrx.  (1S79) 
p.  106. 

P.  F,  16 


242  SALIVA.  [book   II. 

The  conversion  of  starch  into  sugar,  or  the  amylolytic  action 
of  saliva,  will  go  on  at  the  ordinary  temperature  of  the  atrao-- 
sphere.  The  lower  the  temperature  the  slower  the  change,  and 
at  about  o°  C.  the  conversion  is  indefinitely  prolonged.  After 
exposure  to  cold  of  even  as  much  as  some  degrees  below  o°,  when 
the  temperature  is  again  raised  the  action  recommences.  Increase 
of  temperature  up  to  about  35° — 40°,  or  even  higher,  favours  the 
change.  Beyond  60°  or  70°  increase  of  temperature  is  injurious, 
and  saliva  which  has  been  boiled  for  a  few  minutes  not  only  has 
no  action  on  starch  while  at  that  temperature,  but  does  not  regain 
its  powers  on  cooling.  By  being  boiled,  the  amylolytic  activity  of 
saliva  is  permanently  destroyed. 

The  action  of  saliva  on  starch  is  favoured  by  a  slightly  sikaline 
medium.  It  will,  however,  still  go  on  even  in  the  presence  of  a 
small  quantity  of  free  acid.  Increase  of  acidity,  however,  checks 
it.  Thus  in  a  mixture  containing  'i  per  cent,  of  free  hydrochloric 
acid,  the  conversion  of  starch  is  arrested.  After  a  short  exposure 
to  a  dilute  acid,  saliva  will  regain  its  powers  on  neutralisation.  Its 
activity  is,  however,  permanently  destroyed  by  long  exposure  to 
weak,  or  by  shorter  exposure  to  strong,  acids.  Strong  alkalies  also 
destroy  it. 

The  action  of  saliva  is  hampered  by  the  concentrated  presence 
of  the  product  of  its  own  action,  that  is,  of  sugar.  If  a  small 
quantity  of  saliva  be  added  to  a  thick  mass  of  boiled  starch,  the 
action  will  after  a  while  slacken,  and  eventually  come  to  almost  a 
stand-still  long  before  all  the  starch  has  been  converted.  On 
diluting  the  mixture  with  water,  the  action  will  recommence.  If 
the  products  of  action  be  removed  as  soon  as  they  are  formed, 
a  small  quantity  of  saliva  will,  if  sufficient  time  be  allowed,  con- 
vert into  sugar  a  very  large,  one  might  almost  say  an  indefinite, 
quantity  of  starch. 

It  is  at  present  uncertain  whether  the  constituent  of  the  saliva  on 
which  its  activity  depends,  is  at  all  consumed  in  its  action.  Paschutin  '^ 
argues  that  it  is  ;  but  other  observers  have  come  to  a  contrary  con- 
clusion. 

On  what  constituent  do  the  amylolytic  virtues  of  saliva 
depend? 

If  saliva,  filtered  and  thus  freed  from  mucus  and  the  formed 
constituents,  be  treated  with  ten  or  fifteen  times  its  bulk  of 
alcohol,  a  precipitate  containing  all  the  proteid  matters  takes  place. 
Upon  standing  under  the  alcohol  for  some  time  (several  days,  or, 
better,  weeks),  the  proteids  thus  precipitated  become  coagulated 

'  Centrbt.  f.  Med,  Wissen.,  187 1. 


CHAP.   I.]  DIGESTION.  243 

and  insoluble  in  water.  Hence,  an  aqueous  extract  of  the  pre- 
cipitate, made  after  this  interval,  contains  little  or  no  proteid 
material.  Yet  it  is  as  active,  or  ahnost  as  active,  as  the  original 
saliva  (the  solution  being  brought  to  the  same  bulk  as  the  saliva). 
If  the  precipitate  be  treated  with  concentrated  glycerine,  very 
little  passes  into  solution.  Nevertheless,  the  glycerine,  diluted 
with  water,  is  found  to  be  highly  amylolytic.  Now  we  cannot  say 
that  even  this  small  quantity  of  matter  which  is  thus  soluble  in 
glycerine  is  entirely  composed  of  the  really  active  constituents  ; 
it  may  be  and  probably  is  a  mixture  of  this  with  other  bodies.  An 
amylolytic  solution,  free  from  proteid  matter,  may  also  be  prepared 
by  Briicke's  method  for  isolating  pepsin  (see  p.  251)  ;  "but  this  also 
probably  contains  other  bodies  besides  the  really  active  con- 
stituent ;  whatever  the  active  substance  be  in  itself,  it  exists 
in  such  extremely  small  quantities,  that  it  has  never  yet  been 
satisfactorily  isolated  ;  and  indeed  the  only  evidence  we  have  of 
its  existence  is  the  manifestation  of  its  peculiar  powers. 

The  salient  features  of  this  body,  which  we  may  call  ptyaliriy 
are  then  ist,  its  presence  in  minute  and  almost  inappreciable 
quantity  ;  2nd,  the  close  dependence  of  its  activity  on  temperature  ; 
3rd,  its  permanent  and  total  destruction  by  a  high  temperature  and 
by  chemical  reagents  such  as  strong  acids ;  4th,  the  want  of  any 
clear  proof  that  it  itself  undergoes  any  change  during  the  mani- 
festation of  its  powers ;  that  is  to  say,  the  energy  necessary  for  the 
transformation  which  it  effects  does  not  come  out  of  itself.  If  it  is 
at  all  used  up  in  its  action,  the  loss  is  rather  that  of  simple  wear 
and  tear  of  a  machine,  than  that  of  a  substance  expended  to  do 
work  ;  5th,  the  action  which  it  induces  is  of  such  a  kind  (splitting 
up  of  a  molecule  with  assumption  of  water)  as  is  effected  by  the 
agents  called  catalytic,  and  by  that  particular  class  of  catalytic 
agents  called  hydrolytic. 

These  features  mark  out  the  amylolytic  active  body  of  saliva 
as  belonging  to  the  class  oi  ferments^  ;  and  we  may  henceforward 
speak  of  the  amylolytic  ferment  of  saliva. 

Mixed  saliva,  whose  properties  we  have  just  discussed,  is  the 
result  of  the  mingling  in  various  proportions  of  saliva  from  the 

'  Ferments  may,  for  the  present  at  least,  he  divided  into  two  classes,  com- 
monly called  ori^aiiisfd  ami  7iiior^aiiisci/.  Of  the  former,  yca-t  n;ay  be  taken 
a^  a  well-knjwn  example.  The  fermentative  activity  of  yeast  which  leads  to 
the  conversion  of  su'jar  int-^  alcoh  J,  is  dependenr  <>n  the  life  of  the  ycast-cell. 
UnIe^s  the  yeast-cell  be  living  and  functional,  fermentntinn  does  not  take 
jilace  ;  when  the  yeast-cell  dies  fermentation  ceases  ;  and  no  substance  ob- 
tained from  yeast,  by  precipitation  with  alcohol  or  otherwise,  will  give  rise  to 
alcoholic  fermentation.  The  salivary  ferment  belongs  to  the  latter  class  ;  it  is 
a  substance,  not  a  living  organism  like  yeast. 

16 — 2 


244  SALIVA.  [book   II. 

parotid,  submaxillary,  and  sublingual  glands  with  the  secretion 
from  the  buccal  glands. 

Parotid  saliva,  as  obtained  by  introducing  a  cannula  into  the 
Stenonian  duct,  is  clear  and  limpid,  not  viscid  ;  the  reaction  of  the 
first  drops  secreted  is  always  acid,  and  according  to  some  observers  the 
succeeding  portions  are  also  faintly  acid,  except  when  the  flow  is  very 
copious  ;  other  observers  however  find  with  even  a  moderate  flow  an 
alkaline  reaction  after  the  first  drops ".  Cn  standing,  it  becomes  turbid 
from  a  precipitate  of  calcic  carbonate,  due  to  an  escape  of  carbonic 
acid.  It  contains  globulin  and  some  other  forms  of  albumin,  with  little 
or  no  mucin.  Potassium  sulphocyanate  is  present,  but  structural 
elements  are  absent.      In  man,  at  least,  it  acts  powerfully  on  starch. 

Submaxillary  saliva,  as  obtained  by  introducing  a  cannula  into  the 
duct  of  Wharton,  differs  from  parotid  saliva  in  being  more  alkaline 
and,  from  the  presence  of  mucus,  more  viscid  ;  it  contains,  often  in 
abundance,  salivary  corpuscles,  and  amorphous  masses  of  proteid 
materia].  The  so-called  chorda  saliva  in  the  dog  (see  Sec.  2)  is  under 
ordinary  circumstances  thinner  and  less  viscid,  contains  less  mucus, 
and  fewer  structural  elements,  than  the  so-called  sympathetic  saliva, 
which  is  remarkable  for  its  viscidity,  its  structural  elements,  and  for  its 
larger  total  of  solids. 

Sublingual  saliva  is  more  viscid,  and  contains  more  mucin  and 
more  total  solids  (in  the  dog  275  p.  c),  than  even  the  submaxillary 
saliva. 

The  action  of  saliva  varies  in  intensity  in  different  animals. 

Thus  in  man,  the  pig,  the  guinea-pig,  and  the  rat,  both  parotid  and 
submaxillary  and  mixed  saliva  are  amylolytic  ;  the  submaxillary  saliva 
(or  infusion  of  gland)  being  in  most  cases  more  active  than  the 
parotid^  In  the  rabbit,  the  submaxillary  saUva  is  said  to  have  scarcely 
any  action,  while  that  of  the  parotid  is  energetic.  In  the  dog,  parotid 
saliva  is  wholly  inert  on  starch,  submaxillary  and  mixed  saliva  have  a 
slight  effect  only;  the  saliva  of  the  cat  is  more  active  than  that  of  the 
dog.  In  the  horse,  sheep,  and  ox,  the  amylolytic  powers  of  either  mixed 
saliva,  or  of  any  one  of  the  constituent  juices,  are  extremely  feeble. 

Where  the  saliva  of  any  gland  is  active,  an  aqueous  infusion  of 
the  same  gland  is  also  active.  The  importance  and  bearing  of  this 
statement  will  be  seen  later  on.  From  the  aqueous  infusion  of  the 
gland,  as  from  saliva  itself,  the  ferment  may  be  approximately 
isolated. 

In  some  cases  at  least  a  ferment  may  be  extracted  from  the  gland 
even  Avhen  the  secretion  is  itself  inactive. 

The  readiest  method  indeed  of  preparing  from  the  gland  a 
highly  amylolytic  liquid  as  free  as  possible  from  proteid  and  other 

'  Astaschewsky,  Cbt.  Med.  Wiss.,  1878,  p.  257. 
"  Griitzner,  Pfliiger's  Archiv,  XVI.  (1877)  p.  105. 


CHAP.    I.]  DIGESTION.  245 

impurities,  is  to  mince  tlie  glnnd  finely,  dehydrate  it  by  allowing 
it  to  stand  under  absolute  alcohol  for  some  days,  and  then,  having 
poured  off  most  of  the  alcohol,  and  removed  the  remainder  by 
evaporation  at  a  low  temperature,  to  cover  the  pieces  of  gland 
with  strong  glycerine.  A  mere  drop  of  such  a  glycerine  extract 
rapidly  converts  starch  into  grape-sugar. 

Gastric  J  nice. 

Gastric  juice,  obtained  by  artificial  stimulation  from  the  healthy 
stomach  of  a  fasting  dog,  by  means  of  a  gastric  fistula,  is  a  thin 
almost  colourless  fluid  with  a  sour  taste  and  odour. 

In  the  operation  for  gastric  fistula,  an  incision  is  made  through  the 
abdominal  walls,  along  the  liiica  alba,  the  stomach  is  opened,  and  the 
lips  of  the  gaotric  wound  securely  sewn  to  those  of  the  incision  in  the 
ab.lominal  walls.  Union  soon  takes  place,  so  that  a  permanent  open- 
ing from  the  exterior  into  the  inside  of  the  stomach  is  established.  A 
tube  of  proper  construction,  introduced  at  the  time  of  the  operation, 
becomes  firmly  secured  in  place  by  the  contraction  of  healing.  Through 
the  tube  the  contents  of  the  stomach  can  be  received,  and  the  mucous 
membrane  stimulated  at  pleasure. 

When  obtained  from  a  natural  fistula  in  man,  its  specific 
gravity  has  been  found  to  differ  little  from  that  of  water,  varying 
from  I •001  to  I'oio,  and  the  amount  of  solids  present  to  be  very 
small,  viz.  about  -56  per  cent. 

In  the  dog.  Bidder  and  Schmidt '  found  the  amount  of  solids  to  be  as 
much  as  27  per  cent.,  and  in  the  sheep  i"9;  from  this  it  might  be 
inferred  that  the  estimate  given  above  for  man  represents  not  a 
thoroughly  healthy  but  a  diluted  juice.  But  Heidenhain  =  finds  in  the 
dog,  that  the  se;retion  of  the  isolated  fundus  of  the  stomach  does  not 
contain  more  than  "45  p.  c.  of  solids,  and  the  higher  figures  of  Bidder 
and  Schmidt  are  probably  due  to  an  admi.xture  with  remnants  of 
digested  food  and  secretions  of  the  oesophagus  and  mouth. 

Of  these  about  half,  '24  p.  c,  are  inorganic  salts,  chiefly 
alkaline  (sodium)  chlorides,  with  small  quantities  of  phosphates. 
The  organic  material  consists  of  pepsin,  a  body  to  be  described 
immediately,  mi.xed  with  other  substances  of  undetermined  nature. 
In  a  healthy  stomach  gastric  juice  contains  a  very  small  quan- 
tity only  of  mucus,  unless  some  submaxillary  saliva  has  been 
swallowed. 

The  reaction  is  distinctly  acid,  and  the  acidity  is  normally  due 
to  free  hydrochloric  acid.     This  is  proved  by  the  fact  that  the 

'  Bidder  u.  Schmidt,  Die  Vmlaiiuu'^ssiifU,  p.  73. 
■  Pfluger's  .,4r<://»z/,  XIX.  (1879)  p.  I4S. 


246  GASTRIC  JUICE.  [BOOK   II. 

amount  of  hydrochloric  acid  is  more  than  can  be  neutraHsed  by 
the  bases,  and  the  excess  corresponds  to  the  quantity  of  free  acid 
present^.  Lactic  and  butyric  and  other  acids  when  present  are 
secondary  products,  arising  either  by  their  respective  fermenta- 
tions from  articles  of  food,  or  from  decomposition  of  their  alkaline 
or  other  salts.  In  man  the  amount  of  free  hydrochloric  acid  in 
healthy  juice  is  probably  about  -2  per  cent^. 

The  amount  of  free  acid  actually  found  by  Bidder  and  Schmidt  in 
the  juice  whose  specific  gravity  is  given  above  was  only  '02  p.  c,  but 
this  is  undoubtedly  below  the  normal  of  health,  ancl  indeed  in  the 
dog  Bidder  and  Schmidt  ^  found  free  acid  to  the  extent  of  '3  p.  c,  and 
in  the  sheep  "123  p.  c,  while  Heidenhain''  obtained  by  his  method  a 
percentage  in  the  dog  as  high  as  "5. 

According  to  Richet  ^  the  acid  does  not  behave  exactly  as  does 
absolutely  free  hydrochloric  acid  ;  he  infers  that  it  exists  in  combina- 
tion with  some  substance  which  does  not  destroy  its  free  acidity.  The 
same  observer  states  that  lactic  acid  makes  its  appearance  in  gastric 
juice  on  keeping,  even  when  unmixed  with  food. 

On  starch  gastric  juice  has  per  se  no  effect  whatever;  indeed 
the  acidity  of  the  juice  tends  to  weaken,  and  may  possibly  be 
sufficient  to  arrest,  the  amylolytic  action  of  any  saliva  with  which 
it  may  be  mixed. 

On  grape-sugar  and  cane-sugar  healthy  gastric  juice  has  no 
effect. 

When  the  stomach  contains  mucus,  gastric  juice  has  the  power  of 
converting  cane-sugar  into  grape-sugar.  This. power  seems  to  be  due 
to  the  presence  in  the  mucus  of  a  special  ferment,  analogous  to,  but 
quite  distinct  from,  the  ptyalin  of  saliva.  An  excessive  quantity  of 
cane-sugar  introduced  into  the  stomach  causes  a  secretion  of  mucus, 
and  hence  provides  for  its  own  conversion^ 

On  fats  gastric  juice  is  powerless.  They  undergo  by  reason 
of  it  no  change  whatever  in  themselves.  When  adipose  tissue 
is  eaten,  all  that  happens  in  the  stomach  is  that  the  proteid  and 
gelatiniferous  envelopes  of  the  fat-cells  are  dissolved,  and  the  fats 
set  free ;  the  fat  itself  undergoes  no  change  except  the  very 
slightest  emulsion. 

Such  minerals  as  are  soluble  in  free  hydrochloric  acid  are  for 
the  most  part  dissolved ;  though  there  is  a  difference  in  this 
respect  between  gastric  juice  and  simple  free  hydrochloric  acid 
diluted  with  water  to  the  same  degree  uf  acidity  as  the  juice. 

'  Bidder  u.  Schmidt,  op.  cit.  Richet,  Journ.  de  V Anat.  et  de  la  Physiol., 
XIV.  (1878)  p.  170.  Szabo,  Zt.f.  Physiol.  Cheni.,  I.  (1877)  p.  140.  Reoch, 
Jour 'I.  of  Anat.  and  Physiol.,  VIIT.  (1874)  p.  274. 

=  Richet,  op.  cit.     Szabo,  op.  cil.         3  Qp.  cit.         '■  Op.  cit.         s  Qp  cit. 

*  Hoppe-Seyler,  Virchow's  Archiv,  x.  {1856)  p.  144. 


CHAT.    I.j  DIGESTION.  247 

The  essential  property  of  gastric  juice  is  the  power  of  dis- 
solving proteid  matters,  and  of  converting  them  into  a  substance 
called  peptone. 

Action  of  gastric  juice  on  proteids.  The  results  are 
essentially  the  same  whether  natural  juice  obtained  by  means  of 
a  fistula  or  artificial  juice,  i.e.  an  acid  infusion  of  the  mucous 
membrane  of  the  stomach,  be  used. 

Artificial  gastric  juice  may  be  prepared  in  any  of  the  following 
ways. 

1.  By  scr.'iping  the  surface  of  a  (pig's  or  dog's)  stomach,  rubbing 
w\>  the  scrapings  with  pounded  glass  and  water  in  a  mortar,  filtering, 
and  adding  hydrochloric  acid,  till  the  filtrate,  which  is  in  itselt  some- 
what acid,  has  a  free  acidity  corresponding  to  '2  p.  c.  of  hydrochloric 
acid.  The  juice  thus  prepared  contains  but  little  peptone,  but  is  not 
very  potent. 

2.  By  removing  the  mucous  membrane  from  the  muscular  coat, 
mincing  the  former  finely,  and  allowing  it  to  digest  at  35'^  C.  in  a  large 
quantity  of  hydrochloric  acid  diluted  to  2  p.  c.  The  greater  part  of 
the  membrane  disappears,  shreds  only  being  left,  and  the  somewhat 
opalescent  liquid  can  be  decanted  and  filtered.  The  filtrate  has  power- 
ful digestive  (peptic)  properties,  but  contains  a  considerable  amount  of 
the  products  of  digestion  (peptone,  &c.),  arising  from  the  digestion  of 
the  mucous  raembrai!e  itself  '. 

3.  From  the  mucous  membrane,  similarly  prepared  and  minced, 
the  superfluous  moi-^ture  is  removed  with  blotting  paper,  and  the  pieces 
are  thrown  into  a  comparatively  large  quantity  of  concentrated  glycerine, 
and  allowed  to  stand.  The  membrane  may  be  previously  dehydrated 
by  being  allowed  to  stand  under  alcohol,  but  this  is  not  necessary. 
The  decanted  clear  glycerine,  in  which  scarcely  any  of  the  ordinary 
proteids  of  the  mucous  membrane  are  dissolved,  if  added  to  hydro- 
chloric acid  of  '2  p.  c.  (a  few  drops  of  glycerine  to  100  c.c.  of  the  dilute 
acid  are  sufficient),  makes  an  artificial  juice  free  from  ordinary  proteids 
and  peptone,  and  of  remarkable  potency,  the  presence  of  the  glycerine 
not  interfering  with  the  results. 

If  a  few  shreds  of  fibrin,  obtained  by  whipping  blood,  after 
being  thoroughly  washed  and  boiled,  be  thrown  into  a  quantity 
of  gastric  juice,  and  the  mixture  exposed  to  a  temperature  of 
from  35"  to  40°  C,  the  fibrin  will  speedily,  in  some  cases  in  a  few 
minutes,  be  dissolved.  The  shreds  first  swell  up  and  become 
transparent,  then  fall  to  pieces  into  flakes  especially  when  the 
vessel  containing  them  is  shaken,  and  finally  disappear  with  the 

'   These  however  may  be  removed  by  concentration  at  40'  C,  and  subse- 
quent dialysis. 


248  GASTRIC  JUICE.  [BOOK  II. 

exception  of  a  little  granular  debris,  the  amount  of  which  varies 
according  to  circumstances. 

If  small  morsels  of  coagulated  albumin,  such  as  white  of  egg, 
be  treated  in  the  same  way,  the  same  solution  is  observed.  The 
pieces  become  transparent  at  their  surfaces ;  this  is  especially- 
seen  at  the  edges,  which  gradually  become  rounded  down  ; 
and  solution  steadily  progresses  from  the  outside  of  the  pieces 
inwards. 

If  any  other  form  of  coagulated  albumin  {e.^.  precipitated  acid- 
or  alkali-albumin,  suspended  in  water  and  boiled)  be  treated  in 
the  same  way,  a  similar  solution  takes  place.  The  readiness  with 
which  the  solution  is  effected,  will  depend  ceteris  paribus,  on  the 
smallness  of  the  pieces,  or  rather  on  the  amount  of  surface  as 
compared  with  bulk,  which  is  presented  to  the  action  of  the 
juice. 

Gastric  juice  then  readily  dissolves  coagulated  proteids,  which 
otherwise  are  insoluble,  or  soluble  only,  and  that  with  difficulty, 
in  very  strong  acids. 

Nature  of  the  change  as  shewn  by  the  products  of 
the  action.  If  raw  white  of  egg,  largely  diluted  with  water  and 
strained,  be  treated  with  a  sufficient  quantity  of  dilute  hydro- 
chloric acid,  the  opalescence  or  turbidity  which  appeared  in  the 
white  of  egg  on  dilution,  and  which  is  due  t6  the  precipitation  of 
various  forms  of  globulin,  disappears,  and  a  clear  mixture  results. 
If  a  portion  of  the  mixture  be  at  once  boiled,  a  large  deposit  of 
coagulated  albumin  occurs.  If,  however,  the  mixture  be  exposed 
to  35°  or  40°  C.  for  some  time,  the  amount  of  coagulation  which  is 
produced  by  boiling  a  specimen  becomes  less,  and,  finally,  boiling 
produces  no  coagulation  whatever..  By  neutralisation,  however, 
the  whole  of  the  albumin  (with  such  restrictions  as  the  presence 
of  certain  neutral  salts  may  cause)  may  be  obtained  in  the  form 
of  acid-albumin  or  syntonin,  the  filtrate  after  neutralisation  con- 
taining no  proteids  at  all  (or  a  very  small  quantity).  Thus  the 
whole  of  the  albumin  present  in  the  white  of  egg  is  converted, 
by  the  simple  action  of  dilute  hydrochloric  acid,  into  acid-albumin 
or  syntonin. 

if  the  same  white  of  egg  be  treated  with  gastric  juice  instead 
of  simple  dilute  hydrochloric  acid,  the  events  for  some  time  seem 
the  same.  Thus  after  a  while  boiling  causes  no  coagulation,  while 
neutralisation  gives  a  considerable  precipitate  of  a  proteid  body, 
which,  being  insoluble  in  water  and  in  dilute  sodium  chloride 
solutions,  and  soluble  in  dilute  alkaU  and  acids,  at  least  closely 
resembles  syntonin.     But  it  is  found  that  only  a  portion  of  the 


CliAl*.    I.]  DIGESTION.  249 

proteids  originally  present  in  the  white  of  egg  can  thus  be  re- 
gained by  precipitation.  A  great  deal  i.s  still  retained  in  the 
filtrate  alter  neutralisatiop,  in  the  form  of  what  is  called  peptone, 
and,  on  the  whole,  the  longer  the  digestion  is  carried  on,  the 
"reater  is  the  proportion  borne  by  the  peptone  to  the  precipitate 
thrown  down  on  neutralisation  ;  indeed,  in  some  cases  at  all 
events,  all  the  proteids  are  brought  into  the  condition  of  peptone. 
Peptone  is  a  proteid,  having  the  same  approximate  elementary 
composition  as  other  proteids,  and  giving  most  of  the  usual 
proteid  reactions. 

It  is  distinguished  from  other  proteids  by  the  following  marked 
features : 

I  St.  It  is  not  precipitated  by  potassium  ferrocyanide  and 
acetic  acid,  as  are  all  other  proteids. 

2nd.  Though  soluble  in  distilled  water  and  in  neutral  saline 
solutions,  even  the  most  dilute,  and  therefore  not  precipitated 
from  its  acid  or  alkaline  solutions  by  neutralisation,  it  is  not,  like 
the  other  similarly  soluble  proteids,  coagulated  by  heat. 

3rd.  It  is  highly  diffusible,  passing  through  membranes  with 
the  greatest  ease.  (For  the  other  less  important  reactions  see 
Appendix.) 

The  neutralisation  precipitate  resembles,  in  its  general  cha- 
lacters,  acid-albumin  or  syntonin.  Since,  however,  it  probably  is 
distinguishable  from  the  body  or  bodies  produced  by  the  action 
of  simple  acid  on  muscle  or  white  of  egg,  it  is  best  to  reserve  for 
it  the  name  of  parapeptone.  Thus  the  digestion  by  gastric  juice 
of  white  of  egg  results  in  the  conversion  of  all  the  proteids  present 
into  peptone  and  parapeptone,  of  which  the  former  must  be  con- 
sidered as  the  final  and  chief  product,  the  latter  a  bye  product  or 
initial  product  of  variable  occurrence  and  importance.  The  gastric 
digestion  of  fibrin,  either  raw  or  boiled,  and  of  all  forms  of  coagu- 
lated albumin,  gives  rise  to  the  same  products,  peptone  and 
parapeptone.  Milk  when  treated  with  gastric  juice  is  first  of  all 
coagulated  or  curdled.  This  is  the  result  partly  of  the  action  of 
the  free  acid  and  partly  of  the  special  action  of  a  particular 
constituent  of  gastric  juice,  of  which  we  shall  speak  hereafter. 
The  coagulated  milk  is  subsequently  dissolved  with  the  same 
appearance  of  peptone  and  parapeptone  as  in  the  case  of  other 
proteids.  In  fact,  the  digestion  by  gastric  juice  of  all  the  varieties 
of  proteids  consists  in  the  conversion  of  the  proteid  into  peptone, 


250  GASTRIC   JUICE.  [BOOK   II. 

with  the  concomitant  appearance  of  a  certain  variable  amount  of 
parapeptone. 

When  raw  unboiled  fibrin  is  treated  with  gastric  juice,  the  digesting 
mixture  is  found,  when  examined  immediately  after  the  solution  of  the 
fibrin,  to  contain,  in  addition  to  peptone  and  parapeptone,  soluble 
albumin  coagulable  by  heat.  No  such  soluble  albumin  is  formed 
during  the  digestion  of  boiled  fibrin  or  of  any  form  of  coagulated 
albumin. 

Circumstances  affecting  gastric  digestion.  In  order 
to  come  to  a  satisfactory  conclusion  on  this  matter,  it  is  desirable 
to  use  the  same  proteid  in  all  the  experiments  ;  and  of  all  proteids, 
boiled  fibrin  is  most  convenient.  It  should  be  boiled  rather 
tha'n  raw,  because  the  latter  is,  for  reasons  of  which  we  shall  speak 
presently,  soluble  to  a  certain  extent  in  dilute  acids  alone.  Since, 
as  will  be  seen,  a  given  amount  of  gastric  juice  may  by  proper 
management  be  made  to  digest  an  almost  indefinite  quantity  of 
fibrin  if  sufiicient  time  be  allowed,  we  are  obliged  to  take,  as  a 
measure  of  the  activity  of  a  specimen  of  gastric  juice,  the  rapidity 
with  which  it  dissolves  a  given  quantity  of  fibrin. 

The  greater  the  surface  presented  to  the  action  of  the  juice, 
the  more  rapid  the  solution.  Hence  minute  division  and  constant 
movement  favour  digestion.  Neutralisation  of  the  juice  wholly 
arrests  digestion.  Fibrin  may  be  submitted  for  an  almost  indefi- 
nite time  to  the  action  of  neutralised  gastric  juice  without  being 
digested.  If  the  neutralised  juice  be  again  properly  acidified,  it 
becomes  quite  as  active  as  before.  Digestion  is  most  rapid  with 
dilute  hydrochloric  acid  of  "2  p.  c.  {the  acidity  of  natural  gastric 
juice).  If  the  juice  contains  much  more  or  much  less  free  acid 
than  this,  its  activity  is  visibly  impaired.  Other  acids,  lactic, 
phosphoric,  &c.  may  be  substituted  for  hydrochloric ;  but  they 
are  not  so  effectual,  and  the  degree  of  acidity  most  useful  varies 
with  the  different  acids.  The  presence  of  neutral  salts,  especially 
sodium  chloride,  in  excess  is  injurious '.  The  presence  in  a  con- 
centrated form  of  the  products  of  digestion  hinders  the  process. 
If  a  large  quantity  of  fibrin  be  placed  in  a  small  quantity  of  juice, 
digestion  is  soon  arrested  ;  on  dilution  with  the  normal  hydro- 
chloric acid  ('2  p.  c),  or  if  the  mixture  be  submitted  to  dialysis, 
and  its  acidity  be  kept  up  to  the  normal,  the  action  recommences. 
Digestion  is  most  rapid  at  about  35° — 40°  C. ;  at  the  ordinary 
temperature  it  is  much  slower,  and  at  about  0°  C.  ceases  alto- 
gether. Gastric  juice  may  be  kept  however  at  0°  C.  for  an 
indefinite  period  without  injury  to  its  powers. 

'  A.  Schmidt,  Pfliiger's  Archiv,  xiii.  (1876)  p.  93. 


CHAP.    I.]  DIGESTION.  2$  I 

The  gastric  juice  of  cold-blooded  vertebrates  it  relatively  more 
active  at  low  temperatures  than  that  of  warm-blooded  mammals  or 
birds  ;  whether  this  is  due  to  a  different  nature  of  the  };astric  jui'  c,  or 
to  attendant  circumstances,  is  uncertain'.  The  dij^tstive  fluids  in  the 
stomachs  or  intestines  of  invertebrata  frequently  contain  a  ferment 
wholly  similar  to  pepsin  but  mixed  with  another  proteolytic  ferment 
resembling  that  of  the  pancreas^ 

At  temperatures  much  above  40°  or  45"  the  action  of  the 
juice  is  im[)airecl.  By  boiling  for  a  few  minutes  the  activity  of 
the  most  powerful  juice  is  irrevocably  destroyed.  By  removing 
the  products  of  digestion  as  fast  as  they  are  formed,  and  by 
keeping  up  the  acidity  to  the  normal,  a  given  amount  of  gastric 
juice  may  be  made  to  digest  an  almost  unlimited  quantity  of 
proteid.  This  shews  that  the  energies  of  the  juice  are  not 
exhausted  by  the  act  of  digestion. 

It  has  been  debated  whether  this  statement  is  absolutely  true- 
Ransomed  however,  thinks  that  the  powers  of  the  juice  are  even  in- 
creased by  action. 

Nature  of  the  action.  All  these  facts  go  to  shew  that  the 
digestive  action  of  gastric  juice  on  proteids,  like  that  of  saliva  on 
starch,  is  a  ferment-action  ;  in  other  words,  that  the  solvent  action 
of  gastric  juice  is  essentially  due  to  the  presence  in  it  of  a  ferment- 
body.  To  this  ferment-body,  which  as  yet  has  been  only  approxi- 
mately isolated,  the  name  oi  pepsin  has  been  given.  The  glycerine 
extract  of  mucous  membrane,  especially  of  that  which  has  been 
dehydrated,  contains  a  minimal  quantity  of  proteid  matter,  and 
yet  is  intensely  active.  The  elaborate  method  of  Briicke  gives 
us  a  residue  which  possesses  none  of  the  ordinary  proteid  re- 
actions, and  yet  in  concert  witti  normal  dilute  hydrochloric  acid 
is  peptic  in  the  highest  degree.  We  may  therefore  safely  assert 
that  pepsin  is  not  a  proteid.  Briicke's  residue  contained  nitrogen, 
but  it  would  be  hazardous  to  assert  that  that  residue  was  nothing 
but  pepsin.  At  present  the  manifestation  of  peptic  powers  is  our 
only  test  of  the  presence  of  pepsin. 

Briicke's*  method  is  as  follows.  Gastric  mucous  membrane  is 
digested  with  dilute  phosphoric  instead  of  hydrochloric  acid.  To  the 
filtered  digest  clear  lime-water  is  added,  until  a  violet  reaction  with 
litmus  is  gained.     The  bulky  precipitate  of  calcium  phosphate  carries 

•  Pick,  Arbeiten  Physiol.  Lab.  lyUn.  II.  (1873)  p.  181. 

•  Krukcnbcrp,  L'ni.  Fhys.  Inst.  IletJtlbtrg,  I.  (1877)  p.  327,  II.  (l877)p.  I, 
p.  261  ;  al'O  llup]H:-ScyIcr,  Plliii^cr's  Arckiv,  XIV.  (1877)  p.  395. 

J  Jourft.  Anat.  Phys.  (1876),  Vol.  X. 

«  Moleschott's  UtHtrnuh.  vi.  (1859)  p.  479. 


252  GASTRIC  JUICE.  [BOOK   II. 

down  with  it  mechanically  the  greater  part  of  the  pepsin  ;  the  super- 
natant fluid  when  reacidified  has  very  little  peptic  power.  The  pre- 
cipitate is  collected,  pressed,  suspended  in  water,  and  redissolved  care- 
fully, with  a  minimal  quantity  of  dilute  hydrochloric  acid,  and  repre- 
cipitated  with  lime-water  ;  much  of  the  peptone  which  went  down  with 
the  first  precipitate  is  thus  left  behind,  while  the  pepsin  still  clings  to 
the  calcic  salt.  The  precipitate  is  again  dissolved  in  dilute  hydroch- 
loric acid,  placed  in  a  flask,  and  a  solution  of  cholesterin  in  4  parts 
alcohol  to  I  ether  is  poured  in  slowly,  through  a  long  funnel  reaching 
to  the  bottom  of  the  flask.  The  cholesterin  rises  as  a  bulky  mass  to  the 
top  of  the  liquid,  carrying  the  pepsin  with  it.  After  several  shakings 
the  cholesterin  is  collected,  washed  with  water  acidulated  with  acetic 
acid,  and  then  with  pure  water.  While  still  moist,  it  is  transferred  to 
a  vessel  and  shaken  with  alcohol-free  ether,  which,  dissolving  the 
cholesterin  and  floating  on  the  top,  leaves  a  watery  stratum  below. 
This  must  be  repeated  until  all  the  cholesterin  is  dissolved.  The  ether 
is  removed,  and  the  watery  residue  is  filtered.  The  filtrate,  though  it 
does  not  give  the  ordinary  reactions  of  proteids,  is,  when  acidulated, 
most  strongly  peptic.  By  dialysis  it  may  be  still  further  purified  (for 
pepsin  will  not  pass  through  ordinary  dialysis  paper)  ;  but  even  the 
dialysed  fluid  gives  a  precipitate  with  basic  and  neutral  lead-acetate. 

In  one  important  respect  pepsin,  the  ferment  of  gastric  juice, 
differs  from  ptyalin,  the  ferment  of  saliva.  Though  saliva  is  most 
active  in  a  faintly  alkaline  medium,  there  seems  to  be  no  special 
connection  between  the  ferment  and  any  alkali.  In  gastric  juice, 
however,  thex'e  is  a  strong  tie  between  the  acid  and  the  ferment,  so 
strong  that  some  writers  spealc  of  pepsin  and  hydrochloric  acid  as 
forming  together  a  compound,  pepto-hydrochloric  acid. 

In  the  absence  of  exact  knowledge  of  the  constitution  of  pro- 
teids, we  cannot  state  distinctly  what  is  the  precise  nature  of  the 
change  into  peptone.  Judging  from  the  analogy  with  the  action  of 
saliva  on  starch,  we  may  fairly  suppose  that  the  process  is  at 
bottom  one  of  hydration  ;  but  we  have  no  exact  proof  that  it  is, 
and  it  is  at  least  quite  as  probable  that  peptone  arises  by  a  simple 
splitting  up  of  larger  proteid  molecules.  Peptone  closely  re- 
sembling, if  not  identical  with,  that  obtained  by  gastric  digestion, 
may  be  obtained  by  the  action  of  strong  acids,  by  the  prolonged 
action  of  dilute  acids  especially  at  high  temperature,  or  simply  by 
digestion  with  superheated  water  in  a  Papin's  digester.  The  role 
of  pepsin  therefore  is  only  to  facilitate  a  change  which  may  be 
effected  without  it.  Since,  in  the  act  of  digestion,  the  pepsin  itself 
is  not  exhausted,  it  is  clear  that  the  energy  which  is  spent  in  the 
conversion  of  the  proteid  into  peptone  does  not  come  from  the 
ferment. 

We  have  seen  that  a  particular  acid  and  a  particular  dilution  are 
most  favourable  to  digestion.     We  may  add,  that  the  natural  action  of 


CHAP.    I]  DIGESTION.  253 

the  acid  is  modified  by  the  presence  of  the  pepsin.  It  is  not  that  in 
digestion  the  a  id  cinvcrts  the  prutcid  into  acid-albumin,  which,  in 
turn,  is  converted  by  thepep-^in  into  peptone.  Ordinary  albumin  is  less 
readily  converted  into  neutralisation  products  when  pepsin  is  present, 
than  when  pepsin  is  absent,  and,  as  we  shall  see,  the  neutralisation 
pro  lucts  probably  differ  also  in  nature  in  the  two  cases.  When  bones 
arc  treated  with  simple  hydrochloric  acid,  the  earthy  salts  are  dis- 
solved out,  and  the  animtil  basis  left  ;  when  bones  are  treated  with 
gastric  juice,  the  animal  basis  is  acted  on  more  speedily  than  the 
earthy  salts'.  The  nature  of  peptic  digestion  will  however  be  more 
fully  dis-'ussed  under  pancreatic  digestion. 

All  proteids,  as  far  as  we  know,  are  converted  by  pepsin  into 
peptone.  Of  its  action  on  other  nitrogenous  substances  not  truly 
proteid  in  nature,  we  need  only  say  that  mucin,  nuclein,  and  the 
chemical  basis  of  horny  tissues  are  wholly  unaffected  by  it,  but 
that  the  gelatiniferous  tissues  are  dissolved  and  changed  into  a 
substance  so  far  analogous  with  peptone,  that  the  characteristic 
property  of  gelatinisation  is  entirely  lost. 

Chondrin  and  the  elastic  tissues  are  also  dissolved*. 

Milk  is  peculiarly  atfected  by  gastric  juice,  whether  natural  or 
artificial.  It  is  curdled,  that  is  to  say,  its  casein  is  precipitated. 
The  change  will  go  on  at  the  ordinary  temperature,  but  is  favoured 
by  that  of  35° — 40°.  This  properly  of  gastric  juice  (which  has 
long  been  known  in  domestic  life,  the  rennet  used  for  the  putpose 
of  curdling  milk  in  the  manufacture  of  cheese,  or  for  other  pur- 
poses, being  an  infusion  of  calves'  stomach)  does  not  depend  on 
the  acidity  of  the  juice,  i.e.  the  casein  is  not  directly  precipitated 
by  the  free  acid  of  the  juice  ;  for  neutralised  gastric  juire  is 
efficacious.  Since  the  property  is  lost  when  the  neutralised  juice 
is  boiled,  and  the  eftccts  are  so  closely  dependent  on  temperature, 
it  seems  probable — and  tlic  conclusion  is  supported  by  other  facts 
— that  the  effect  is  produced  by  the  action  of  a  special  ferment. 

This  ferment  is  not  identical  with  pepsin,  and  Hammarsten'  has 
succeeded  in  separating  the  two.  According  to  him  the  presence  of 
niilk-sug.ir  is  not  necessary  to  the  change,  and  the  ferment  itself  does 
not  give  rise  to  a  lactic  a:id  fermentation.  He  therefore  does  not  re- 
gard the  curdling  as  the  mere  precipitation  of  casein  caused  by  the 
development  of  lactic  acid.  He  believes  the  process  to  be  a  species 
of  coagulation,  in  which  an  insoluble  casein  arises  from  the  splitting 
up,  under  the  influence  of  the  ferment,  of  a  previously  soluble  body. 

'  Kiihnc,  Lehrb.  p.  40. 

»  Eliinger,  Zl.  f.  Biolog.  X.  (1874)  84. 

'   Upxala  LMartforeninp  Fdrkandlingar,  Bd.  VIII.  (1S73)  p.  63. 


254  BILE.  [book   II. 


Bile. 

The  quality  of  bile  varies  much,  not  only  in  different  animals, 
but  in  the  same  animal  at  different  times.  It  is  moreover  affected 
by  the  length  of  the  sojourn  in  the  gall-bladder  ;  bile  taken  direct 
from  the  hepatic  duct,  especially  when  secreted  rapidly,  contains 
little  or  no  mucus ;  that  taken  from  the  gall-bladder,  as  of 
slaughtered  oxen  or  sheep,  is  loaded  with  mucus.  The  colour  of 
the  bile  of  carnivorous  and  omnivorous  animals,  and  of  man,  is  a 
bright  golden  red  :  of  graminivorous  animals,  a  golden  green,  or  a 
bright  green,  or  a  dirty  green,  according  to  circumstances,  being 
much  modified  by  retention  in  the  gall-bladder.  The  reaction  is 
alkaline.  The  following  may  be  taken  as  the  average  composition 
of  human  bile  (Frerichs). 

In  looo  parts. 

Water         ...  ...         ...         ...  ...  859-2 

Solids  :— 
Bile  Salts  ... 
Fats,  &c 

Cholesterin 

Mucus  and  Pigment 

Inorganic  Salts 


9i°4 
92 
2-6 

29-8 
7-8 


♦  140*8 

The  entire  absence  of  proteids  is  a  marked  feature  of  bile. 
With  regard  to  the  inorganic  salts,  the  points  of  interest  are  the 
presence  of  a  large  quantity  of  sodium  chloride  ('2  to  -27  per 
cent.),  the  presence  of  phosphates,  of  iron  (about  "006.  p  c.  Fe), 
manganese,  and  occasionally,  at  all  events,  of  copper.  The  ash 
contains  soda  in  a  very  large  amount,  and  also  sulphates,  both 
coming  from  the  bile-salts.  The  constituents  which  deserve  chief 
attention  are  the  pigments  and  the  bile-salts. 

Pigments  of  Bile.  The  natural  golden  red  colour  of  normal 
human  or  carnivorous  bile,  is  due  to  the  presence  oi  Bilirubin. 
This,  which  is  also  the  chief  pigmentary  constituent  of  gall-stones, 
and  occurs  largely  in  the  urine  of  jaundice,  may  be  obtained  in 
the  form  either  of  an  orange-coloured  powder,  or  of  well-formed 
rhombic  tablets  and  prisms.  Insoluble  in  water,  and  but  little 
soluble  in  ether  and  alcohol,  it  is  readily  soluble  in  chloroform, 
and  in  alkahne  fluids.  Its  composition  is  CjgH^gNgOg.  Treated 
with  oxidizing  agents,  such  as  nitric  acid  yellow  with  nitrous  acid, 
it  displays  a  succession  of  colours  in  order  of  the  spectrum.     The  , 


ciiAi'.  I.]  Di(;Ksri(»N'.  255 

yellowish  goUlon  red  becomes  green,  this  a  greenish  blue,  then  blue, 
next  violet,  afterwards  a  dirty  red,  an<l  finally  a  pale  yellow.  This 
characteristic  reaction  of  bilirubin  is  the  basis  of  the  so-called 
Gmelin's  test  for  bile-pigments.  Each  of  these  stages  represents 
a  distinct  pigmentary  substance.  An  alkaline  solution  of  bilirubin, 
exposed  in  a  shallow  vessel  to  the  action  of  the  air,  turns  green, 
becoming  converted  into  Bilivcrdin  (CigHjoNoOj  or  Ci^HjgNjO^ 
Maly),  the  green  pigment  of  herbivorous  bile.  Biliverdin  is  also 
found  in  the  edges  of  the  placenta  of  the  bitch,  and  at  times  in  the 
urine  of  jaundice,  and  is  probably  the  body  which  gives  to  bile  which 
has  been  exposed  to  the  action  of  gastric  juice,  as  in  biliary  vomits, 
its  characteristic  green  hue.  It  is  the  first  stage  of  the  oxidation 
of  bilirubin  in  Gmelin's  test.  Treated  with  oxidizing  agents 
biliverdin  runs  through  the  same  scries  of  colours  as  bilirubin,  with 
the  exception  of  the  initial  golden  red. 

We  have  already  discussed,  p.  39,  the  relation  of  bilirubin  to  haema- 
toidin.  Other  pigments,  bili/uscin,biliprasin,  have  been  found  in  small 
quantities  in  gall-stones. 

Fresh  normal  bile,  either  of  man,  the  cow,  the  pig,  or  dog,  exhibits 
no  absorption-bands,  thou-jh  these  mike  their  appearance  in  the 
alcoholic  extracts,  and  when  the  bile  has  become  altered. 

When  bihrubin  has  been  oxidized  down  to  the  last  (yellowish)  stage 
in  Gmelin's  test,  the  liquid  is  found  to  contain  a  body  with  character- 
istic absorption-bands.  To  this  the  name  of  choletelin  '  has  been 
given.  Bilirubin  treated,  on  the  other  hand,  with  reducing  agents 
(sodium  amalgam)  is  converted  into  a  body  called  urobilin  (hydro- 
bilirubin),  also  with  characteristic  spectrum  appearances^ 

The  bile-salts.  These  consist,  in  man  and  many  animals, 
of  sodium  glycocholate  and  taurocholate :  the  proportion  of  the  two 
varying  in  different  animals.  In  man  both  the  total  quantity  of 
bile-salts  and  the  proportion  of  the  one  bile  salt  to  the  other  seem 
to  vary  a  good  deal,  but  the  glycocholate  is  always  the  more 
abundant 3.  In  ox-gall,  sodium  glycocholate  is  abundant,  and 
taurocholate  scanty.  The  bile-salts  of  the  dog,  cat,  bear,  and 
other  carnivora,  consist  exclusively  of  the  latter,  the  former  being 
entirely  absent. 

In  the  bile  of  the  pig  two  peculiar  acids  are  present,  in  union  with 
sodium,  viz.  glycohyocholic  and  taurohyocholic,  differing  however  but 
slightly  from  the  above.  Similarly,  the  bile  of  the  goose  contains 
taurochenocholic  acid. 

'  Maly,  IVun.  SUzungsberichU,  Bd.  59  (1869).  »  See  p.  39. 

3  Cf.  Jacobsen,  Ber.  d.  Jctitsch.   Chem.  Gesfll.  VI.  p.  1026.     Trifanow.ski, 

Pfliiger's  Archiv,  IX.  (1874)  p.  492.  Socoloff,  ibid.  Xli.  (1875)  p.  54. 
Iloppe-Seyler,  Lehrb.  (1S7S)  p.  301. 


256  BILE.  [book   II. 

Insoluble  in  ether  but  soluble  in  alcohol  and  in  water,  the 
aqueous  solutions  having  a  decided  alkaline  reaction,  both  salts 
may  be  obtained  by  crystallisation  in  fine  acicular  needles.  They 
are  exceedingly  deliquescent.  The  solutions  of  both  acids  have  a 
dextro-rotatory  action  on  polarized  light. 

Preparation.  Bile,  mixed  with  animal  charcoal,  is  evaporated  to 
dryness  and  extracted  with  alcohol.  If  not  colourless,  the  alcoholic 
filtrate  must  be  further  decolorized  with  animal  charcoal,  and  the 
alcohol  distilled  off  The  dry  residue  is  treated  with  absolute  alcohol, 
and  to  the  alcoholic  filtrate  anhydrous  ether  is  added  as  long  as  any 
precipitate  is  formed.  On  standing  the  cloudy  precipitate  becomes 
transformed  into  a  crystalline  mass  at  the  bottom  of  the  vessel.  If 
the  alcohol  be  not  absolute,  the  crystals  are  very  apt  to  be  changed 
into  a  thick  syrupy  fluid.  This  mass  of  crystals  has  been  often  spoken 
of  as  bilin.  Both  salts  are  thus  precipitated,  so  that  in  such  a  bile  as 
that  of  the  ox  or  man  bilin  consists  both  of  sodium  glycocholate  and 
sodium  taurocholate.  The  two  may  be  separated  by  precipitation 
from  their  aqueous  solutions  with  sugar  of  lead,  which  throws  down 
the  former  much  more  readily  than  the  latter.  The -acids  maybe 
separated  from  their  respective  salts  by  dilute  sulphuric  acid,  or  by  the 
action  of  lead-acetate  and  sulphydric  acid. 

On  boiling  with  dilute  acids  (sulphuric,  hydrochloric),  or 
caustic  potash,  or  baryta  water,  glycocholic  acid  is  split  up  into 
cholalic  (cholic)  acid  and  glycin.  Taurocholic  acid  may  similarly 
be  split  up  into  cholalic  acid  and  taurin.     Thus — 

glycocholic  acid  cholalic  acid  glycin 

taurocholic  acid  cholalic  acid  taurin 

C^eH^^NSO,  +  H2O  =  C24H40O,  +  C^H.NSOs. 

Both  acids  contain  the  same  nitrogenless  acid,  cholalic  acid ; 
but  this  acid  is  in  the  first  case  associated  or  conjugated  with  the 
important  nitrogenous  body  glycin,  or  amido-acetic  acid,  and  in  the 
second  case  with  taurin,  or  amido-isethionic  (amido-ethyl-sul- 
phuric)  acid.  The  decomposition  of  the  bile  acids  into  cholalic 
acid  and  taurin  or  glycin  respectively  takes  place  naturally  in  the 
intestine  *  \  so  that  from  the  two  acids,  after  they  have  served 
their  purpose  in.  digestion,  the  two  ammonia  compounds  are 
returned  into  the  blood.  Either  of  the  two  acids,  or  cholalic  acid 
alone,  when  treated  with  sulphuric  acid  and  cane-sugar,  gives  a 
magnificent  purple  colour  (Pettenkofer's  test)  with  a  characteristic 
spectrum,  A  similar  colour  is  produced  by  the  action  of  the 
same  bodies  on  albumin,  amyl  alcohol,  and  sorae  other  organic 
bodies. 

'  Hoppe-Seyler,  Nxxch-oyfi's  Archiv,  xxv.  181  ;  xxvi.  (1863)  519. 


CHAP.    I.J  UIGKSTION.  257 

By  dehydration,  cholalic  acid  is  converted  in  choloidic  acid 
CoiHsgO^,  or  into  dyslysin  C24H3CO3. 

Action  of  Bile  on  Food.  In  sonic  animals  at  least  bile 
contains  a  ferment  capable  of  converting  starch  into  sugar;  but 
its  action  in  this  respect  is  wholly  subordinate. 

On  proteids  bile  has  no  direct  digestive  action  whatever.  But 
when  bile,  or  a  solution  of  bile-salts,  is  added  to  a  fluid  containing 
the  products  of  gastric  digestion,  a  copious  precipitate  takes  place, 
consisting  both  of  parapeptone  and  peptone,  the  greater  part  of  the 
pepsin  present  being  at  the  same  time  carried  down  rrechanically, 
^o  that  the  supernatant  liquid,  even  when  reacidified,  has  little  or 
no  peptic  powers.  The  precipitate  however  is  redissolved  in  an 
excess  of  bile  or  solution  of  bile-salts.  The  purpose  of  this  pre- 
cipitation, which  actually  takes  place  in  the  duodenum,  is  probably 
to  shield  the  ferment  of  the  pancreatic  juice  (see  below)  from  the 
destructive  action  of  the  pepsin.  And  in  general,  the  alkaline  bile, 
by  neutralising  the  acid  contents  of  the  stomach  as  they  pass  into 
the  duodenum,  prepares  the  way  for  the  action  of  the  pancreatic 
juice. 

With  regard  to  the  action  of  bile  on  fats  the  following  state- 
ments may  be  made  : 

Bile  has  a  slight  solvent  action  on  fats,  as  seen  in  its  use  by 
painters.  It  has  by  itself  a  slight  but  only  slight  emulsifying 
power ;  a  mixture  of  oil  and  bile  separate  after  shaking  rather  le.ss 
rapidly  than  a  mixture  of  oil  and  water.  With  free  fatty  acids, 
bile  forms  soaps.  It  is  moreover  a  solvent  of  solid  soaps,  and  it 
would  appear  that  the  emulsion  of  fats  is  under  certain  circum- 
stances at  all  events  facilifeited  by  the  presence  of  soaps  in  solution. 
Hence  bile  is  probably  of  much  greater  use  as  an  emulsion  agent 
when  mixed  with  pancreatic  juice  than  when  acting  by  itself  alone. 
To  this  point  we  shall  return.  Lastl),  the  wetting  of  membranes 
with  bile,  or  with  a  solution  of  bile-salts,  assists  in  the  passage  of 
fats  through  membranes.  Oil  passes  with  considerable  ease  through 
a  filter-paper  kept  wet  with  a  solution  of  bile-salts,  whereas  it 
passes  with  extreme  difficulty  through  one  kept  constantly  wet 
with  distilled  water. 

Pancreatic  yuice. 

Natural  healthy  pancreatic  juice  obtained  by  means  of  a  tem- 
porary pancreatic  fistula  dilTers  from  the  i)receding  lluids  in  the 
comparatively  large  quantity  of  proteids  which  it  contains.  Its 
composition  varies  according  to  the  rate  of  secretion,  for  wiui 
the  more  rapid  flow  the  increase  of  total   solids  does  not  keep 

F.  P.  i; 


258  PANCREATIC  JUICE.  [^OOK   II. 

pace  with  that  of  the  water,  though  the  ash  remains  remarkably 
constant. 

By  an  incision  through  the  Hnea  alba  the  pancreatic  duct  can  easily 
be  found  either  in  the  rabbit  or  in  the  dog,  and  a  cannula  secured  in  it. 
There  is  no  difficulty  about  a  temporary  fistula  ;  but  Bernard  found 
that  with  permanent  fistulae  the  secretion  altered  in  nature,  and  lost 
many  of  its  characteristic  properties.  N.  O.  Bernstein',  however,  has 
succeeded  in  obtaining  permanent  fistulce  without  any  impairment  of 
the  secretion. 

Healthy  pancreatic  juice  is  a  clear  viscid  fluid,  frothing  when 
shaken.  It  has  a. very  decided  alkaline  reaction,  and  contains 
few  oir  no  structural  constituents. 

The  average  amount  of  solids  in  the  pancreatic  juice  of  the  dog 
when  obtained  from  a  temporary  fistula  is  about  8  to  10  p.  c.%  but 
Bernstein  3  found  in  the  thoroughly  active  secretion  from  a  per- 
manent fistula  about  2-5  p.  c.  (i-68 — 5 "39),  "8  being  inorganic 
matter.  The  important  constituents  are  albumin,  a  peculiar  form 
of  casein,  or  alkali-albumin  (precipitable  by  saturation  with  mag- 
nesium sulphate),  leucin  and  tyrosin,  a  small  amount  of  fats  and 
soaps,  and  a  comparatively  large  quantity  of  sodium  carbonate,  to 
which  the  alkaline  reaction  of  the  juice  is  due,  and  which  seems 
to  be  peculiarly  associated  with  the  albumin. 

When  cooled  to  0°  C.  it  is  apt  to  undergo  a  sort  of  coagulation, 
becoming  fluid  again  on  being  gently  heated'*. 

According  to  Kiihnes,  fresh  pancreatic  juice  of  the  dog  always  con- 
tains corpuscles  similar  to  salivary  corpuscles,  and  the  coagulation 
observed  by  Bernard  is  a  true  coagulation,  resulting  in  a  product  very 
similar  to  myosin.  The  coagulum  however  is  speedily  digested.  Per- 
fectly fresh  juice,  Kiihne  states,  contains  neither  peptone  nor  tyrosin, 
and  only  the  barest  trace  of  leucin. 

Action  on  food-stuffs.  On  starch,  raw  or  boiled,  pan- 
creatic juice  acts  with  great  energy,  rapidly  converting  it  into 
grape-sugar.  All  that  has  been  said  in  this  respect  concerning 
saliva  might  be  repeated  in  the  case  of  pancreatit  juice,  except 
that  the  activity  of  the  latter  is  far  greater  than  that  of  the  former ; 
the  pancreatic  juice  and  the  aqueous  infusion  of  the  gland  are 
always  capable  of  converting  starch  into  grape-sugar,  whether  the 
animal  from  which  they  were  taken  be  starving  or  well  fed. 

As  in  the  case  of  saliva  (p.  241),  it  is  probable  that  the  sugar  formed 
is  not  true  grape-sugar. 

'  Ludwig's  Arbeiten,  1869,  p.  i. 

*  Bernard,  Le^.  Phys.  Exp,,  1855,  il.  237.  3  Op.  cit. 

4  Bernard,  Le^.  Phys.  Exp.  11.  230. 

s  Vei-handl.  Heidelb.  Naturhist.  Med.   Vereins,  1876, 


CHAP.    I.J  DIGESTION.  ^59 

From  the  juice,  or,  by  the  glycerine  method,  from  the  gland 
itself,  an  amylolytic  ferment  may  be  appro.ximately  isolated.  On 
protcids  pancreatic  juice  also  exercises  a  solvent  action,  so  far 
similar  to  that  of  gastric  juice  that  by  it  proteids  are  converted 
into  peptone.  If  a  icw  shreds  of  fibrin  are  thrown  into  a  small 
quantity  of  pancreatic  juice,  they  speedily  disappear,  especially 
at  a  temperature  of  35°  C,  and  the  mixture  is  found  to  contain 
peptone.  The  activity  of  the  juice  in  thus  converting  proteids 
into  peptone,  is  favoured  by  increase  of  temperature  up  to  40°  or 
thereabouts,  and  hindered  by  low  temperatures  ;  it  is  permanendy 
destroyed  by  boiling.  The  digestive  powers  of  the  juice  in  fact 
depend,  like  those  of  gastric  juice,  on  the  presence  of  a  ferment, 
to  which  the  name  trypsin  has  been  given.  A  glycerine  extract 
of  pancreas,  prepared  in  the  same  method  as  that  of  the  gastric 
mucous  membrane,  is  (under  appropriate  conditions)  active  on 
proteids,  like  the  native  juice. 

The  appearance  of  fibrin  undergoing  pancreatic  digestion  is 
however  ditterent  from  that  undergoing  peptic  digestion.  In  the 
former  case  the  fibrin  does  not  swell  up,  but  remains  as  opaque  as 
before,  and  appears  to  suffer  corrosion  rather  than  solution.  But 
there  is  a  still  more  important  distinction  between  pancreatic  and 
peptic  digesdon  of  protcids.  Peptic  digestion  is  essentially  an 
acid  digestion  ;  we  have  seen  that  the  action  only  takes  place  in 
the  presence  of  an  acid,  and  is  arrested  by  neutralisation.  Pan- 
creatic digestion,  on  the  other  hand,  is  essentially  an  alkaline 
digestion;  the  action  will  not  take  place  unless  some  alkali  be 
present ;  and  the  activity  of  an  alkaline  juice  is  arrested  by  acidi- 
fication, and  hindered  by  neutralisation.  The  glycerine  extract  of 
pancreas  is  under  all  circumstances  as  inert  in  the  presence  of 
free  acid  as  that  of  the  stomach  in  the  presence  of  alkalis.  If 
the  digestive  mixture  be  supplied  with  sodium  carbonate  to  the 
extent  of  i  p.  c,  digestion  proceeds  rapidly,  just  as  does  a  peptic 
mixture  when  acidulated  with  hydrochloric  acid  to  the  extent  of 
•2  p.  c  Sodium  carbonate  of  i  p.  c.  seems  in  fact  to  play  in 
pancreatic  digestion  a  part  altogether  comparable  to  that  of 
hydrochloric  acid,  2  p.  c.  in  gastric  digestion. 

With  distilled  water  the  digestion  goes  on  but  very  slowly,  and  the 
addition  of  sodium  carbonate  quickens  the  change,  in  proportion  to  the 
quantity  added,  up  to  about  '9  or  I "2  p.  c.  Beyond  this,  further  alkali 
is  a  hindrance,  and  large  quantities  stop  the  process  altogether.  Bile, 
which  arrests  peptic  digestion,  seems,  it  anything,  favourable  to  pan- 
cre?.tic  digestion'.     When  isolated  ferment,  as  the  glycerine  extract  of 

'  Heidenhain,  Pfluger's  Archiv,  X.  (1875)  P-  557- 

17—2 


26o  PANCREATIC  JUICE.  [BOOK   II. 

pancreas,  is  operated  with,  'i  p.  c.  of  free  hydrochloric  acid  is  sufficient 
to  arrest  the  action. 

Corresponding  to  this  difference  in  the  helpmate  of  the  ferment, 
there  is  in  the  two  cases  a  difference  in  the  nature  of  the  products. 
In  both  cases  peptone  is  produced,  and  such  differences  as  can  at 
present  be  detected  between  pancreatic  and  gastric  peptones  are 
comparatively  slight ;  but  in  pancreatic  digestion  the  bye-product 
is  not,  as  in  gastric  digestion,  a  kind  of  acid-albumin,  iDut  a  body 
having  more  analogy  with  alkali-albumin.  .. 

Before  solution  has  actually  taken  place  the  iibrin  becomes 
altered  in  character  It  is  soluble  not  only  in  dilute  acids  and 
alkalis,  but  also  in  a  lo  per  cent,  solution  of  sodium  chloride,  and 
the  solutions  obtained  by  the  latter  reagent  are  coagulable  on  boil- 
ing and  on  the  addition  of  strong  nitric  acid.  The  first  action  of 
the  pancreatic  juice  therefore  seems  to  be  to  convert  the  proteid 
under  digestion  into  a  body  intermediate  between  alkali-albumin 
and  ordinary  native  albumin. 

But  though  the  general  characters  of  pancreatic  and  gastric 
digestion  are  on  the  surface  so  similar,  it  is  more  than  probable 
that  profound  differences  do  exist  between  them.  This  is  shewn 
by  the  appearance,  in  the  pancreatic  digestion  of  proteids,  of  two 
remarkable  nitrogenous  crystalline  bodies,  leucin  and  tyrosin. 
When  fibrin  (or  other  proteid)  is  submitted  to  the  action  of  pan- 
creatic juice,  the  amount  of  peptone  which  can  be  recovered  from 
the  mixture  falls  far  short  of  the  original  amount  of  proteids,  much 
more  so  than  in  the  case  of  gastric  juice;  and  the  longer  the 
digestive  actign,  the  greater  is  this  apparent  loss.  If  a  pancreatic 
digestion  mixture  .be  freed  from  the  alkali-albumin  by  neutralisa- 
tion, and  after  concentration  by  evaporation  be  treated  with  excess 
of  alcohol,  most  of  the  peptone  will  be  precipitated.  The 
alcoholic  filtrate  when  concentrated,  gives,  on  cooling,  crystals  of 
tyrosin,  and  the  mother  liquor  from  these  crystals  will  afford 
abundance  of  crystals  of  leucin.  Thus  by  the  action  of  the  pan- 
creatic juice  a  considerable  amount  of  the  proteid,  which  is  being 
digested,  is  so  broken  up  as  to  give  rise  to  products  which  are  no 
longer  proteid  in  nature.  From  its  decomposition  there  arise 
leucin,  tyrosin,  and  probably  several  other  bodies,  such  as  fatty 
acids  and  volatile  substances.  In  gastric  digestion  such  a  complete 
destruction  of  proteid  material  occurs  to  a  much  less  extent ;  neidaer 
leucin  nor  tyrosin  can  at  present  be  considered  as  natural  products 
of  the  action  of  pepsin. 

As  is  well  known,  leucin  and  tyrosin  are  the  bodies  which 
make  their  appearance  when  proteids  or  gelatin  are  acted  on  by 
dilute  acids,  alkalis,  or  various  oxidising  agents.     Now  leucin  is 


CIIAT.    I.]  DIGESTION.  26 1 

amidocaproic  acid,  and  thus  belongs  distinctly  to  the  fatty  bodies, 
while  tyrosin  is  a  member  of  the  aromatic  group,  being  closely 
related  to  benzoic  acid.  So  that  in  pancreatic  digestion  we  have 
the  large  complex  proteid  molecule  split  up  into  its  constituent 
fatty  acid  and  aromatic  molecules,  and  into  its  other  less  distinctly 
known  components. 

The  presence  of  these  bodies  and  of  the  alkali-albumin  in  pancreatic 
juice  is  probably  due  to  an  intrinsic  digestion  taking  place  in  the  secre- 
tion as  it  passes  along  the  duct  or  after  it  has  been  collected.  Among 
the  supplementary  products  of  pancreatic  digestion  may  be  enumerated 
a  body  which  gives  a  violet  colour  with  chlorine  water  (this  reaction  is 
often  seen  in  the  juice  itself),  and  indol,  to  which  apparently  the  strong 
and  peculiarly  faecal  odour  which  makes  its  appearance  during 
pancreatic  digestion  is  due. 

Indol,  however,  unlike  the  leucin  and  tyrosin,  is  possibly  not  a  pro- 
duct of  pure  pancreatic  digestion,  but  of  an  accompanying  decomposi- 
tion due  to  the  action  of  organised  ferments.  A  pancreatic  digesstive 
mi.xture  soon  becomes  swarming  with  bacteria,  in  spite  of  careful  pre- 
cautions, wlien  natural  juice  or  an  infusion  of  the  gland  is  used.  When 
isolated  ferment  is  u^ed,  and  atmospheric  germs  e>  eluded,  no  odour 
whatever  is  produced',  though  carbonic  acid  and  nitrogen  are  set  free ; 
and  Kiihne  found  no  indol  produced  when  pancreatic  digestion  was 
carried  on  in  the  presence  of  salicylic  acid,  which  prevents  the 
development  of  bacteria  and  like  organisms. 

H  After  long-continued  digestion,  especially  when  accompanied  by 
putrefactive  decomposition,  the  amount  of  proteids  which  are  carried 
beyond  the  peptone  stage  and  broken  up,  may  be  very  great.  A 
slight  diftercnce  between  pancreatic  and  gastric  digestion  may  be 
found  in  the  fact,  that  while  fibrin  boiled  as  well  as  raw  is  readily 
acted  on  by  pancreatic  juice,  boiled  albumin,  syntonin,  &c.  resist  the 
action  of  pancreatic  juice  to  a  much  greater  extent  than  they  do  that  of 
gastric  juice. 

Theory  of  digestive  Proteolysis.  The  simplest  view  of  peptic 
digestion  is  that  of  Bru:ke-,  that  the  fibrin  or  albumin,  &c.  is  first 
converted  into  syntonin  (parapcptone),  and  that  the  syntonin  (para- 
peptone)  is  converted  into  peptone  ;  and  is  moreover  supported  by  the 
fact  that  the  final  result  of  di^iestion  with  a  very  active  juice  is  nothing 
but  peptone.  There  arc  facts  however  which  shew  that  so  simple  a 
view  cannot  be  accepted.  Meissner^  came  to  the  conclusion,  based 
on  very  laborious  researches,  that  the  conversion  into  syntonin  was 
followed  by  the  splitting  up  of  that  body  \\\io  peptotu  a.r\d  pampeploite, 
the  latter  being  distinguished  from  ordinary  syntonin  not  by  its  general 
characters,  but  by  the  fact  that  it  was  incapable  of  being  further  con- 
verted into  peptone  by  the  action  of  gastric  juice,  though  it  could 
undergo   that   change  under  the  influence  of  pancreatic  juice.      He 

'  Hiifner,  J./.  Prakt.  Chem.  N.  F.  x.  I. 

'    Wiftt.  Sitzungsbericht,  XXXVI I.  131,  XLIII.  60 1. 

3  Zt.f.  KaL  Med,  Vil.  i,  vili.  2S0,  X.  i,  xii.  46,  XIV.  303. 


262  PANCREATIC  JUICE.  [BOOK   II. 

further  described  two  subsidiary  products,  vtetapeptotie  and  dyspeptone, 
but  the  characters  he  assigned  to  those  bodies  were  unsatisfactory 
He  moreover  spoke  of  three  kinds  of  peptone,  A,  B  and  C  peptone,  the 
last  not  being  precipitable,  whilst  the  first  two  are,  by  acetic  acid  and 
potassium  ferrocyanide,  A  in  a  weakly  acid,  ^  in  a  strongly  acid  solu- 
tion ;  in  other  words,  C  is  a  perfect  peptone  and  A  and  B  are  imperfect 
peptones.  Kiihne  ^  is  of  opinion  that  every  natural  proteid  consists  of, 
and  may  be  split  up  into,  two  elements,  belonging  to  what  he  calls  re- 
spectively the  anti  group  and  the  hemi  group.  When  a  proteid  \r 
digested  by  trypsin,  two  peptones  are  produced,  a?itipeptone  and  a 
hemipeptone.  Of  these  the  first,  antipeptone,  undergoes  no  further 
change  under  the  action  of  trypsin  ;  it  remains  a  peptone.  Hemipep- 
tone on  the  other  hand  is  readily  decomposed  by  trypsin  into  leucin, 
tyrosin  and  the  other  products  of  pancreatic  digestion.  So  also  when 
a  proteid  is  digested  by  pepsin,  the  same  antipeptone  and  hemipeptone 
are  formed  ;  but,  unlike  trypsin,  pepsin  cannot  produce  any  further 
change  in  the  hemipeptone.  (The  assertion  that  leucin  and  tyrosin 
appear  as  products  of  peptic  digestion,  is  explained  by  the  fact  that 
pepsin  is  associated  in  the  gastric  membrane  with  a  proteid  body, 
which  gives  up  considerable  quantities  of  leucin  and  tyrosin  when  dis- 
solved in  a  dilute  acid.  Trypsin  also  is  associated  with  a  similar  body 
in  the  pancreas.)  Thus  the  results  of  peptic  and  tryptic  digestion 
together  are  antipeptone  with  leucin,  tyrosin,  &c.,  the  latter  arising 
from  the  profounder  tryptic  digestion  of  hemipeptone.  Between  these 
peptones  however  and  the  original  proteid  are  various  stages,  and, 
under  certain  circumstances,  various  bye-products.  Thus  antipeptone 
has  for  its  antecedent  aiitialbutnose  (Briicke's  parapeptone)  agreeing  H 
its  general  characters  with  the  syntonins,  but  capable  of  conversion  into 
antipeptone  only,  never  into  hemipeptone.  Similarly  hemipeptone  has 
an  antecedent  heitiialbumose  (apparently  Meissner'  s  A  peptone)  soluble 
in  dilute  acids  and  alkalis  and  in  a  lo  p.  c.  sodium-chloride  solution, 
and  convertible,  by  the  agency  of  pepsin  or  trypsin,  into  hemipeptone, 
and  of  trypsin  alone  into  leucin,  tyrosin,  &c.  The  action  of  dilute 
hydrochloric  acid  at  40°  on  proteids  gives  rise,  on  the  side  of  the  hemi- 
group,  to  hemialbumose  and  so  to  hemipeptone.  By  the  action  of 
sulphuric  acid  at  100°  C.  the  hemipeptone  is  further  reduced  to  leucin, 
tyrosin,  &c.  On  the  side  of  the  anti-group  these  agents  give  rise  to  a 
body  which  Kiihne  calls  antialbumate.  This  substance  also  occurs  in 
digestive  mixtures  where  the  pepsin  is  insufficient.  It  is  not  capable 
of  any  change  under  the  influence  of  pepsin,  but  by  trypsin  is  con- 
verted into  antipeptone.  It  is  evidently  the  real  parapeptone  of 
Meissner.  These  results  of  Kiihne  it  will  be  seen  reconcile  some 
previous  contradictions  ;  and  the  distinction  of  the  anti-  and  hemi- 
groups,  if  it  prove  as  general  as  Kiihne  supposes,  throws  a  great  light 
on  proteid  metabolism.  It  may  be  remarked,  in  passing,  that  hemi- 
albumose agrees  very  closely  with  the  peculiar  proteid  body  discovered 
by  Bence  Jones  in  the  urine  of  a  case  of  osteomalacia.  According  to 
Kiihne,  while  the  activity  of  trypsin  is  entirely  destroyed  by  digestion 
with  pepsin,  trypsin  has  no  such  effect  on  pepsin. 

^    Verhandl.  Naturhist.  Med.  Vereins,  Heidel.  1876. 


CHAP.    I.]  DIGESTION.  263 

On  the  gelantiniferous  elements  of  the  tissues,  unless  they  have 
been  previously  treated  with  acid  or  heated  with  water,  pancreatic 
juice  appears  to  have  no  solvent  action.  In  this  respect  it  affords 
a  striking  contrast  to  gastric  juice'. 

Trypsin,  unlike  pepsin,  will  dissolve  mucin.  Like  pepsin,  it  is  inert 
towards  nuclein,  horny  tissues,  and  the  so-called  amyloid  matter. 

On  Fats  pancreatic  juice  has  a  twofold  action  :  it  emulsifies 
them,  and  it  splits  up  neutral  fats  into  their  respective  acids  and 
glycerine. 

If  hog's  lard  be  gently  heated  till  it  melts  and  be  then  mixed 
with  pancreatic  juice  before  it  solidifies  on  cooling,  a  creamy 
emulsion,  lasting  for  almost  an  indefinite  time,  is  formed.  So  also 
when  olive  oil  is  shaken  up  with  pancreatic  juice,  the  separation 
of  the  two  tiuids  takes  place  very  slowly,  and  a  drop  of  the  mix- 
ture under  the  microscope  shews  that  the  division  of  the  fat  is 
very  minute.  An  alkaline  aqueous  infusion  of  the  gland  has 
similar  emulsifying  powers. 

If  perfectly  neutral  fat  be  treated  with  pancreatic  juice, 
especially  at  the  body-temperature,  the  emulsion  speedily  takes  on 
an  acid  reaction,  and  by  appropriate  means  not  only  the  corre- 
sponding fatty  acids  but  glycerine  may  be  obtained  from  the 
mixture.  When  an  alkali  is  present,  the  fatty  acids  thus  set  free 
form  their  corresponding  soaps. 

Pancreatic  juice  contains  fats,  and  is  consequently  apt  after  collec- 
tion to  have  its  alkalinity  reduced,  and  an  aqueous  infusion  of  a 
pancreatic  gland  (which  always  contains  a  considerable  amount  of  fat) 
very  speeuily  becomes  acid. 

Thus  pancreatic  juice  is  remarkable  for  the  power  it  possesses 
of  acting  on  all  the  food-stuffs,  on  starch,  fats  and  proteids. 

The  action  on  starch  and  on  proteids  is  certainly,  and  the  splitting 
up  of  fatty  acids  is  probably,  due  to  the  presence  of  distinct  ferments, 
and  Danilewsky^'  has  suggested  a  method  for  isolating  these  three 
ferments.  The  emulsifying  power,  on  the  other  hand,  is  connected 
with  the  general  composition  of  thejui -e  (or  of  the  aqueous  infusion  of 
the  glandj,  being  probably  in  large  measure  dependent  on  the  alkali- 
albumin  present.  The  proteolytic  ferment  trypsin  contains,  according 
to  Kiihne,  a  considerable  quantity  of  nitrogen  ;  and  the  fact  that  it  can 
be  digested  by  pepsin  would  seem  to  indicate  that  it  is  really  proteid  in 
nature.  There  are  no  means  of  distinguishing  the  amylolytic  ferment 
of  the  pancreas  from  ptyalin. 

The  action  of  pancreatic  juice,  or  of  the  infusion  or  extract  of 
the  gland,  on  starch,  is  seen  under  all  circumstances,  whether  the 

'  Ewald  and  Kiihne,   Vtrhandl.  A'atur/tist.  Mi  J.   I'ctcins,  Heiddberg,  Bd.  I 
(1876).  »  Virchow's  Archiv,  xxv.  p.  297. 


264  SUCCUS   ENTERICUS.  [BOOK   II. 

animal  be  fasting  or  not.     The  same  may  probably  be  said  of  the 
action  on  fats. 

Pancreatic  juice,  when  secreted  in  a  normal  state,  is  always 
active  on  proteids^  The  glycerine  extract  or  aqueous  infusion  of 
the  gland,  on  the  contrary,  differs  at  different  times;  prepared 
from  an  animal  some  4  to  lo  hours  after  food  has  been  taken, 
it  is  very  powerful ;  prepared  from  a  fasting  animal,  it  exhibits 
scarcely  any  action  at  all.  To  this  point  we  shall  return  imm3- 
diately. 

Succus  Entericus. 

When,  in  a  living  animal,  a  portion  of  the  small  intestine  is 
ligatured,  so  that  the  secretions  coming  down  from  above  cannot 
enter  its  canal,  while  yet  the  blood-supply  is  maintained  as  usual, 
.a  small  amount  of  secretion  collects  in  its  interior.  This  is 
spoken  of  as  the  succus  entericus,  and  is  supposed  to  be  furnished 
by  the  glands  of  Lieberkiihn.  We  have  no  exact  knowledge 
however  as  to  what  extent  such  a  secretion  takes  place  under 
normal  circumstances ;  and  the  statements  with  regard  to  its 
action  are  conflicting.  Probably  it  has  no  direct  action  on 
either  fats  or  proteids  ;  but  is  amylolytic  in  some  animals,  though 
not  in  all. 

Thiry^  divided  the  small  intestine  in  two  places  at  some  distance 
apart.  By  fine  sutures  he  united  the  lower  end  of  the  upper  with  the 
upper  end  of  the  lower  section,  thus  as  it  were  cutting  out  a  whole 
piece  of  the  small  intestine  from  the  alimentary  tract.  In  successful 
cases,  union  between  the  cut  surfaces  took  place,  and  a  shortened  but 
otherwise  satisfactory  canal  was  re-established.  Of  the  isolated  piece 
the  lower  end  was  carefully  closed  by  sutures,  while  the  upper  was 
brought  to  the  wound  in  the  abdominal  wall  and  secured  there.  A 
fistula  was  thus  formed,  leading  into  a  short  piece  of  intestine  quite 
isolated  from  the  rest  of  the  alimentary  canal.  From  this  isolated 
intestine  Thiry  obtained  a  thin  yellowish  alkaline  albuminous  secretion 
which  dissolved  fibrin  very  much  in  the  same  way  as  does  pancreatic 
juice,  but  was  ineffectual  on  other  proteids  and  had  no  action  on  starch. 
Masloff3  finds  that  the  juice  obtained  (from  dogs)  by  Thiry's  method,  acts 
on  starch  feebly,  but  has  no  action  on  fibrin  or  other  proteids  in  neutral 
or  alkaline  solutions  if  putrefactive  changes  be  carefully  avoided, 
Kolliker  and  H.  Miiller  found  that  proteids  introduced  into  the 
intestines  were  digested  in  the  case  of  oarnivora,  but  not  in  the  case 
of  herbivora.  Funkctalso  agrees  with  Thiry  that  starch  injected  into 
isolated  loops  of  rabbit's  intestine  is  not  converted  into  sugar  ;  while 

^  N.  O.  Bernstein,  /.  c. 

=  Wien.  Siizungsbericht,  Bd.  L.  (1864)  p.  77. 

3  Unters.  Physiol.  Inst.  Heidelberg,  II.  (1879)  p.  290. 

■♦  Lehrb.  p.  190. 


CHAP.    I.J  DIGESTION.  265 

Frcrichs  and  Busch  came  to  the  opposite  concliiiion'.  Certainly  pieces 
of  the  intestine  of  the  pig  or  of  the  rabbit,  or  a  glycerine  extract  of 
the  pieces,  will  r.ipidiy  convert  starch  into  sugar  ;  and  it  is  difficult  to 
suppose  that  this  action  is  due  to  an  admixture  of  pancreatic  juice 
which  had  not  been  thoroughly  removed  by  washing,  since  pieces  of 
the  intestine  of  the  sheep,  which  are  also  suljject  to  admixture  with 
active  pancreatic  juice,  arc,  when  similarly  treated,  inert  as  far  as 
starch  is  concerned.  Still  no  great  stress  can  be  laid  on  this,  since 
an  amylolytic  ferment  can  be  obtained  from  almost  every  part  of  the 
body  of  a  pig  or  a  rabbit. 

Succus  entericus  has  also  been  said  to  change  cane-  into  grape- 
sugar,  and  by  a  fermentative  action  to  convert  cane-sugar  into  lactic 
acid,  and  this  again  into  butyric  acid  with  the  evolution  of  carbonic 
acid  and  free  hydrogen. 

Of  the  possible  action  of  other  secretions  of  the  alimentary 
canal,  as  of  the  ccecum  and  large  intestine,  we  shall  speak  when 
we  come  to  consider  the  changes  in  the  alimentary  canal. 

Concerning  the  secretion  of  Brunner's  glands  our  information  is  at 
present  imperfect.  The  cells  of  the  glands  closely  resemble  the  ceAtral 
cells  of  the  gastric  glands  =  ;  and  Griitzner  ^  finds  that  an  extract  of 
the  gland  will  digest  fibrin  in  an  acid  solution,  but  has  no  distinct 
amylolytic  action. 


Sec.  2.     The  Act  of  Secretion  in  the  case  of  the  Digestive 
Juices  and  the  Nervous  Mechanisms  which  regulate  it. 

The  various  juices  whose  properties  we  have  just  studied, 
though  so  different  from  each  other,  are  all  drawn  ultimately  from 
one  common  source,  the  blood,  and  they  are  poured  into  the  ali- 
mentary canal,  not  in  a  continuous  flow,  but  intermittently  as 
occasion  may  demand.  The  epithelium  cells  which  supply  them 
have  their  periods  of  rest  and  of  activity,  and  the  amount  and 
quality  of  the  fluids  which  these  cells  secrete  are  determined  by  the 
needs  of  the  economy  as  the  food  passes  along  the  canal.  We  have 
therefore  to  consider  how  the  epithelium  cell  manufactures  its 
special  secretion  out  of  the  materials  supplied  to  it  by  the  blood, 
and  how  the  cell  is  called  into  activity  by  the  presence  of  food  at 
some  distance  from  itself,  or  by  circumstances  which  do  not  bear 
directly  on  itself.  In  dealing  with  these  matters  in  connection 
with  the  digestive  juices,  we  shall  have  to  enter  at  some  length 
into  the  physiology  of  secretion  in  general. 

'  Cf.  also  Paschutln,   Archtv  Anat.    Physiol.,    1S71,   p.    305.     Eichhorst, 
rfluger's  Archiv,  IV.  (1871)  p.  575. 

'  Schwalbe,  Arch./,  micro.  Ana/  ,  viil.  (1872)  p.  97. 
3  Pfliiger's  Air/iiv,  xu.  (1876)  p.  2.S8. 


266  THE   ACT   OF   SECRETION.  [BOOK   II. 

The  question  which  presents  itself  first  is,  Does  the  epitheHum 
cell  simply  serve  as  a  filter,  merely  draining  off  from  the  blood 
the  already  formed  constituents  of  its  secretion,  each  cell  being 
fitted  in  some  way  to  catch  and  deliver  particular  substances  ?  in 
other  words,  Is  secretion  merely  selection,  just  as  from  a  mixture 
of  shots  of  various  sizes  a  selection  might  be  made  by  passing 
them  over  a  series  of  sieves  with  meshes  of  varying  width  ?  or 
does  the  cell  draw  upon  the  blood  for  the  nutritive  elements 
required  for  the  growth  of  all  protoplasm,  and  out  of  those  com- 
mon elements  manufacture  in  the  recesses  of  its  own  substance 
the  chemical  bodies  which  characterize  the  fluid  it  pours  forth  ? 

This  question  is  naturally  the  first  to  be  asked,  nevertheless  it 
will  be  of  advantage  to  defer  it  for  the  present,  and,  while  still 
bearing  it  in  mind,  to  pass  on  to  the  second  question  :  By  what 
mechanism  is  the  activity  of  the  secreting  cells  brought  into  play  ? 

While  fasting,  a  small  quantity  only  of  saliva  is  poured  into 
the  mouth  ;  the  buccal  cavity  is  just  moist  and  nothing  more. 
When  food  is  taken,  or  when  any  sapid  or  stimulating  substance, 
or  indeed  a  body  of  any  kind,  is  introduced  into  the  mouth,  the 
flow  induced  may  be  very  copious.  Indeed  the  quantity  secreted 
in  ordinary  life  during  24  hours  has  been  roughly  calculated  at  as 
much  as  from  i  to  2  litres.  An  abundant  secretion  in  the  absence 
of  food  in  the  mouth  may  be  called  forth  by  an  emotion,  as  when 
the  mouth  waters  at  the  sight  of  food,  or  by  a  smell,  or  by  events 
occurring  in  the  stomach,  as  in  some  cases  of  nausea.  Evidently 
in  these  cases  some  nervous  mechanism  is  at  work.  In  studying 
the  action  of  this  nervous  mechanism,  it  will  be  of  advantage  to 
confine  our  attention  at  first  to  the  submaxillary  gland. 

The  submaxillary  gland  (Fig.  41)  is  supplied  with  nerves  from 
two  sources  :  from  the  cervical  sympathetic  along  the  submaxillary 
arteries,  and  from  the  seventh  or  facial  nerve  by  fibres,  which, 
running  in  the  chorda  tympani,  join  the  lingual  branch  of  the  fifth 
nerve,  from  which  they  diverge  close  under  the  lower  jaw,  and 
run  as  a  small  nerve  close  beside  the  duct  to  the  gland. 

If  a  tube  be  placed  in  the  duct,  it  is  seen  that  when  sapid 
substances  are  placed  on  the  tongue,  or  the  tongue  is  stimulated 
in  any  other  way,  or  the  lingual  nerve  is  laid  bare  and  stimulated 
with  an  interrupted  current,  a  copious  flow  of  saliva  takes  place. 
If  the  sympathetic  be  divided,  stimulation  of  the  tongue  or  lingual 
nerve  still  produces  a  flow.  But  if  the»  small  chorda  nerve  spoken 
of  above  be  divided,  stimulation  of  the  tongue  or  lingual  nerve 
produces  no  flow. 

Evidently  the  flow  of  saliva  is  a  nervous  reflex  action,  the 
lingual  nerve  serving  as  the  channel  for  the  afferent  and  the  small 


CIIAr.    I.J  DIGESTION.  267 

chorda  nerve  for  the  efferent  impulses.  If  the  trunk  of  the 
lingual  be  divided  above  the  point  where  the  chorda  leaves  it,  as 
at  Fig.  41  n.  /',  stimulation  of  the  tongue  produces,  under  ordinary 
circumstances,  no  flow.  Tiiis  shews  that  the  centre  of  the  reflex 
action  is  higher  up  than  the  point  of  section ;  it  lies  in  fact  in 
the  brain. 

In  the  angle  between  the  lingual  and  the  chorda,  where  the  latter 
leaves  the  former  to  pass  to  the  gland,  lies  the  small  submaxillary 
ganglion  (represented  diagrammatically  in  Fig.  41,  j;«.  ^l.),  from 
which  branches  pass  to  the  lingual  on  the  one  hand  and  to  the  chorda 
on  the  other  ;  branches  may  also  be  tniced  towards  the  ducts  and 
glands  and  towards  the  tongue.  It  has  been  much  debated  whether 
this  ganglion  can  act  as  a  centre  of  reflex  action. 

Bernard  *  found  that  after  he  had  divided  the  conjoined  lingual  and 
chorda  at  about  one  cm,  above  the  place  where  the  chorda  diverges  to 
the  gland  (as  at  //.  /'  Fig.  41),  stimulation  of  the  lingual  at  about  3  or 
4  cm.  distance  below  the  ganglion  still  caused  a  flow  of  saliva  ;  this 
effect  however  was  no  longer  seen  when  the  branches  passing  from  the 
ganglion  to  the  lingual  had  been  previously  divided.  He  explained  the 
result  by  supposing  that  the  impulses  generated  by  the  stimulus  were 
conveyed  by  afferent  fibres  in  the  lingual,  along  the  lingual  roots  of  the 
ganglion  to  the  ganglion,  and  were  thence  reflected  by  efferent  fibres 
along  the  branches  from  the  ganglion  to  the  chorda  and  so  to  the 
gland.  The  ganglion,  in  fact,  acted  as  a  reflex  centre.  The  same 
apparent  reflex  secretion  could  also  be  induced,  but  less  readily,  by 
•pinching  the  peripheral  branches  of  the  lingual  near  the  tongue,  or  by 
dipping  them  into  concentrated  salt  solution.  In  this  case  also  the 
secretion  failed  to  appear  if  the  lingual  roots  of  the  ganglion  were 
divided.  Such  a  reflex  secretion  was  very  difficult  to  obtain  by  stimu- 
lation of  the  mucous  membrane  of  the  tongue  ;  but  Bernard  was 
successful  when  he  stimulated  the  tongue  directly  with  a  galvanic 
current  or  drew  the  tongue  out  and  placed  ether  on  its  surface.  The 
secretion  in  all  these  cases  was  accompanied  by  a  dilation  of  the  blood- 
vessels of  the  gland,  and  the  effect  on  the  gland  was  indeed  wholly 
similar  to  that  of  directly  stimulating  the  chorda.  Bernard  further 
insisted  that  in  these  experiments  no  anaesthetics  were  to  be  used,  and 
observed  that  the  reflex  effect  was  no  longer  visible  when  two  or  three 
days  had  elapsed  after  section  of  the  conjoined  lingual  and  chorda 
trunks.  Both  these  facts  rather  militate  against  his  view,  since  it 
seems  improbable  that  a  sporadic  ganglion  should  be  so  susceptible  of 
anaesthetics,  or  than  degeneration  and  functional  incapacity  of  the 
ganglion  should  follow  upon  section  of  the  conjoined  lingual  and 
chorda  so  long  as  the  afferent  and  efferent  connections  of  the  ganglion 
with  the  gland  and  tongue  w^re  kept  up. 

Eckhard  "  in  repeating  Bernard's  experiments  failed  to  obtain  any 
effect  from  dipping  the  endings  of  the  lingual  nerve  in  salt  solution  or 

'  Comptes  Reudus,  1862,  ir.  341. 

•  Zt.f.  rat.  Med.,  XXIX.  (1 86 7)  p.  74, 


268 


SUBMAXILLARY   GANGLION. 


[book  II. 


from  placing  ether  on  the  tongue,  and  he  very  naturally  argued  (being 
supported  in  this  by  Heidenhain')  that  the  effects  seen  when  galvanic 
stimulation  was  employed  were  due  to  an  escape  of  the  current  upon 
the  chorda  fibres.  Schiff  ^  did  obtain  reflex  secretion  after  section  of 
the  conjoined  lingual  and  chorda,  by  direct  galvanic  stimulation  of  the 


V.  sym. 


n.si/m.sm. 


T.sjrt.73.      V  snv. 


Fig.  41.     Diagrammatic   Representation    of   the    Submaxillary  Gland   of   the 

Dog  with  its  Nerves  and  Blood-Vessels. 

(This  is  not  intended  to  illustrate  the  exact  anatomical  relations  of  the  several  structures.) 

sni.  gld.  The  submaxillary  gland,  into  the  duct  (s?7z.  d.)  of  which  a  cannula  has  been 
tied.     The  sublingual  gland  and  duet  are  not  shewn. 

«.  /.,  n.  I'.  1  he  lingual  branch  nerve,  ch.  t..  ch.  t'.  The  chorda  tympani,  proceeding  from 
the  facial  nerve,  becoming  conjoined  with  the  lingual  at  71.  i  and  afterwards  diverging  and 
passing  to  the  gland  along  the  duct. 

sin.  g:l.  The  submaxillary  ganglion  with  its  several  roots,  n.  I.  The  lingual  proceeding 
to  the  tongue. 

a.  car.  The  carotid  artery,  two  branches  of  which,  a.sm.a.  and  r.  sm.  p.,  pass  to  the 
anterior  and  posterior  parts  of  the  gland,  v.  sm.  the  anterior  and  posterior  veins  from  the 
gland,  falling  into  v.  j.  the  jugular  vein. 

V.  sym.  The  conjoined  vagus  and  sympathetic  trunks. 

§■/.  cer.  s.  The  super-cervical  ganglion,  two  branches  of  which  forming  a  plexus  (a.  f.)  over 
the  facial  artery,  are  distributed  («.  sy>i!.  sm.)  along  the  two  glandular  arteries  to  the  anterior 
and  posterior  portions  of  the  gland. 

The  arrows  indicate  the  direction  taken  by  the  nervous  impulses  during  reflex  stimulation 
of  the  gland.     They  ascend  to  the  brain  by  the  lingual  and  descend  by  the  chorda  tympani. 

tongue,  and  by  pouring  ether  on  the  surface  of  that  organ  ;  but  the 
currents  necessary  in  the  first  case  to  produce  any  effect  were  so  strong 
that  escape  must  have  taken  place,  and  in  the  second  case  the  secretion 

'  Breslau.  Studien,  1868. 

*  Moleschott's  Untersuckungen,  x.  {1870),  423. 


CHAP.   I.J  DIGESTION.  269 

appeared  even  though  the  lingual  was  divided  close  under  the  tongue, 
and  when  therefore  this  nerve  could  not  have  been  the  channel  for 
convoying  impulses  to  the  submaxillary  ganglion.  He  further  pointed 
out  that  in  large  dogs  at  all  events,  certain  fibres  of  the  chorda  after 
running  along  the  conjoined  lingual  and  chorda  do  not  leave  the  lingual 
with  the  rest  of  the  fibres  going  straight  to  the  gland,  but  continue  in  the 
lingual  close  up  to  the  tongue,  then  bend  round  and  as  recurrent  fibres 
run  back  and  eventually  join  the  nerve  going  to  the  gland.  He  in  con- 
sequence argued  that  Bernard  in  stimulating  the  lingual  below  the 
divergence  of  the  chorda  was  in  reality  stimulating  not  afferent  but 
efferent  fibres.  But  in  such  a  case,  these  recurrent  fibres  must  pass  to 
the  chorda  through  the  ■  ganglion,  if  Bernard's  result  be  true  that  the 
reflex  eftect  ceases  when  the  lingual  roots  of  the  ganglion  are  divided, 
Schifi' further  states,  that  these  recurrent  fibres  degeneiate  in  the  retro- 
grade portion  of  their  course  when  the  lingual  is  divided  near  the 
tongue,  and  that  no  effect  follows  upon  stimulation  of  the  lingual  after 
section  of  the  conjoined  chorda  and  lingual  if  the  lingual  have  some 
five  or  six  days  previously  been  divided  close  to  the  tongue  so  as  to 
cause  degeneration  of  the  recurrent  fibres,  provided  that  the  stimula- 
tion be  not  so  strong  as  to  lead  to  an  escape  of  the  current  to  the  main 
chorda  fibres.  In  small  dogs  S.hifF  could  not  so  readily  demonstrate 
these  recurrent  fibres,  and  though  he  says  the  apparent  reflex  secretion 
is  more  easily  obtained  in  large  dogs,  such  as  Bernard  probably  used, 
than  in  smaller  ones,  it  is  improbable  that  mere  size  should  make  such  a 
difference  in  nervous  distribution  ;  and  if  an  escape  of  current  can 
explain  the  results  in  the  one  case  itcanalso  probably  in  the  other. 

Bidder's  3  account  of  the  nerves  of  the  ganglion  at  first  sight  offers 
suppoit  to  Bernard's  views.  In  the  dog  he  finds,  passing  from  the 
ganglion  direct  to  the  tongue,  medullated  nerve-fibres  which  do  not 
degenerate  when  the  chorda  is  divided  at  its  exit  from  the  skull.  These 
fibres  accordingly  would  seem  to  take  their  origin  in  the  ganglion  and 
to  be  the  afferent  nerves  required  for  Bernard's  views.  When  Bidder 
divided  the  conjoined  lingual  and  chorda,  he  found  the  chorda  fibres 
after  about  three  weekscompletely  degenerated,  not  only  those  forming 
the  nerve  going  to  the  gland  but  also  those  constituting  the  branches 
going  to  the  ganglion  : — i.e.  the  chorda  roots  of  the  ganglion.  In  the 
ganglion  and*in  the  branches  going  from  the  ganglion  to  the  gland 
were  seen  numerous  degenerated  fibres  in  the  midst  of  undegenerated 
(but  non-meduUated)  fibres  which  seemed  to  have  their  origin  in  the 
ganglion  itself.  Thus  after  complete  degeneration  of  the  true  chorda 
fibres  there  still  remained  intact,  (i)  the  ganglion,  (2)  fibres  from  the 
ganglion  to  the  tongue,  and  (3)  fibres  from  the  ganglion  to  the  gland, 
in  fact,  exactly  the  nervous  mechanism  demanded  by  Bernard's  view. 
But  Bidder,  like  Kckhard,  failed  to  obtain  a  reflex  secretion  by  pouring 
ether  on  tlic  tongue  after  division  of  the  conjoined  lingual  and  chorda, 
and  he  found  that  galvanic  stimulation  of  the  nerves  going  from  the 
ganglior.  to  the  tongue  was  of  no  effect,  provided  that  errors  due  to 
escape  of  current  on  to  the  main  chorda  fibres  ere  avoided  by  pre- 
viously inducing  through  section  degeneration  of   the  chorda  fibres 

•  Reichert  u.  du  Bois-Reymond's  Archiv,  1867,  p.  l. 


270  ACTION   OF   CHORDA   TYMPANI.  [BOOK   II. 

including  the  chorda  roots  of  the  ganglion.  So  that  Bidder's  results  in 
the  end  oppose  the  view  that  the  ganglion  can  act  as  a  centre  of  reflex 
action.  In  fact,  such  a  view  must  be  regarded  at  present  as  not 
proven. 

We  have  contrary  to  our  wont  given  this  controversy  in  detail  on 
account  of  the  great  importance  of  the  subject.  The  submaxillary 
ganglion  is  almost  the  only  case  in  which  it  has  been  with  any  success 
attempted  to  demonstrate  by  experiment  the  reflex  action  of  a  sporadic 
ganglion,  and  the  question  whether  sporadic  ganglia  can  or  cannot 
serve  as  centres  of  reflex  action  is  at  the  present  time  at  least  a  question 
of  much  interest. 

Stimulation  of  the  glossopharyngeal  is  even  more  effectual 
than  that  of  the  lingual.  Probably  this  indeed  is  the  chief  afferent 
nerve  in  ordinary  secretion.  Stimulation  of  the  mucous  mem- 
brane of  the  stomach  (as  by  food  introduced  through  a  gastric 
fistula)  or  of  the  vagus  also  produces  a  flow  of  saliva,  as  indeed 
may  stimulation  of  the  sciatic,  and  probably  of  many  other 
afferent  nerves.  All  these  cases  are  instances  of  reflex  action,  the 
cerebro-spinal  system  acting  as  a  centre.  In  most  cases  the 
centre  lies  in  the  medulla  oblongata,  and  secretion  may  be  caused 
by  direct  stimulation  of  this  organ ;  where  ideas  or  emotions 
cause  a  flow,  the  stimulation  begins  higher  up  in  the  brain ;  and 
in  cases  where  the  sense  of  taste,  as  distinguished  from  general 
sensation,  is  concerned  in  the  matter,  it  is  probable  that  the 
afferent  impulses  ascend  into  the  brain  higher  up  than  the  medulla, 
before  they  return  as  efferent  impulses.  In  all  these  cases  the 
chorda  tympani  is  the  sole  efferent  nerve.  Section  of  that  nerve, 
either  where  the  fibres  pass  from  the  lingual  nerve  and  the  sub- 
maxillary ganghon  to  the  gland,  or  where  it  runs  in  the  same 
sheath  as  the  lingual,  or  in  any  part  of  its  course  from  the  main 
facial  trunk  to  the  lingual,  puts  an  end  at  once  (with  the  disputed 
exception  mentioned  above)  to  the  possibility  of  any  flow  being- 
excited  by  stimuli  applied  to  the  mouth,  or  any  partf  of  the  body 
other  than  the  gland  itself 

This  statement  is  probably  too  absolute ;  for  though  satisfactory 
evidence  of  reflex  excitation  of  the  submaxillary  gland  by  means  of 
the  sympathetic  is  not  forthcoming,  it  seems  unlikely  that  the  secretory 
as  distinguished  from  the  vaso-motor  activity  of  this  nerve  should 
never  be  put  to  use  in  actual  life. 

In  life,  then,  the  flow  of  saliva  is  brought  about  by  the  advent 
to  the  gland  along  the  chorda  tympani  of  efferent  impulses,  started 
chiefly  by  reflex  actions.  The  inquiry  thus  narrows  itself  to  the 
question :  In  what  manner  do  these  efferent  impulses  cause  the 
increase  of  flow? 


CHAP.   II.J  DIGESTION.  2/ 1 

If  in  a  clog  a  tube  be  introduced  into  Wharton's  duct,  and  the 
choriia  be  divided,  the  flow,  if  any  be  going  on,  is  from  the  lack 
of  etlerent  impulses  arrested.  On  passing  an  interrupted  current 
through  the  peripheral  portion  of  the  chorda,  a  copious  secretion 
at  once  takes  place,  and  die  saliva  begins  to  rise  rapidly  in  the 
tube ;  a  very  short  time  after  the  application  of  the  current  the 
flow  reaches  a  ma.ximum  which  is  maintained  for  some  time,  and 
then,  if  the  current  be  long  continued,  gradually  lessens.  If  the 
current  be  applied  for  a  short  time  only,  the  secretion  may  last  for 
some  time  alter  the  current  has  been  shut  off.  The  saliva  thus 
obtained  is  but  slightly  viscid,  and  contains  but  few  salivary 
corpuscles  or  jnotoplasmic  lumps.  If  the  gland  itself  be  watched, 
while  its  activity  is  thus  roused,  it  will  be  seen  that  its  arteries  are 
dilated,  and  its  capillaries  filled,  and  that  the  blood  flows  rapidly 
through  the  veins  in  a  full  stream  and  of  bright  arterial  hue,  fre- 
quently with  pulsating  movements.  If  a  vein  be  opened,  this 
large  increase  of  flow,  and  the  lessening  of  the  ordinary  deoxygen- 
ation  of  the  blood  consequent  upon  the  rapid  stream,  will  be 
still  more  evident.  It  is  clear  that  excitation  of  the  chorda  acts 
on  some  local  vaso-motor  centre  in  the  gland,  and  largely  dilates 
the  arteries ;  the  nerve  acts  energetically  as  a  dilator  nerve. 

Thus  stimulation  of  the  chorda  brings  about  two  events :  a 
dilation  of  the  blood-vessels  of  the  gland,  and  a  flow  of  saliva. 
The  question  at  once  arises,  Is  not  the  latter  simply  the  result  of 
the  former?  The  activity  of  the  epithelial  secreting  cell,  like 
that  of  any  other  form  of  protoplasm,  is  dependent  on  blood- 
supply.  When  the  small  arteries  of  the  gland  dilate,  the  capil- 
laries become  fuller,  more  blood  passes  through  them  in  a  given 
time,  a  larger  amount  of  nutritive  material  passes  away  from  them 
into  the  surrounding  lymph-spaces,  and  so  into  the  epithelium 
cells  (and  it  must  be  remembered  that  though  by  the  dilation  the 
pressure  in  the  arteries  of  the  gland  is  diminished,  that  of  the 
capillaries  and  veins  is  increased),  the  result  of  which  must  be  to 
quicken  the  processes  going  on  in  the  cells,  and  to  stir  these  up 
to  greater  activity.  This  must  be  so ;  but  it  does  not  necessarily 
follow  that  the  activity  thus  excited  should  take  on  the  form  of 
secretion.  It  is  quite  possible  to  conceive  that  the  increased 
blood-.supply  should  lead  only  to  the  accumulation  in  the  cell  of 
the  constituents  of  the  saliva  or  of  the  materials  for  their  con- 
struction, and  not  to  a  discharge  of  the  secretion.  A  man  works 
better  for  being  fed,  but  feeding  does  not  make  him  work  in  the 
absence  of  any  stimulus.  The  increased  blood-supply  therefore, 
while  favourable  to  active  secretion,  need  not  necessarily  bring  it 
about.     Moreover  the  following  facts  deserve  attention.     When 


2/2  ACTION    0¥   CHORDA   TYMPANI.  [BOOK   11. 

the  chorda  is  energetically  stimulated,  the  pressure  acquired  by 
the  saliva  in  the  duct  exceeds  the  arterial  blood-pressure  for  the 
time  being ;  that  is  to  say,  the  pressure  of  fluid  in  the  gland  out- 
side the  blood-vessels  is  greater  than  that  of  the  blood  inside  the 
blood-vessels.  This  must,  whatever  be  the  exact  mode  of  transit 
of  nutritive  material  through  the  vascular  walls,  tend  to  check 
that  transit.  Again,  if  the  head  of  an  animal  be  rapidly  cut  off, 
and  the  chorda  immediately  stimulated,  a  flow  of  saliva  takes 
place  far  too  copious  to  be  accounted  for  by  the  emptying  of  the 
salivary  channels  through  any  supposed  contraction  of  their  walls. 
In  this  case  secretion  is  excited  in  the  absence  of  blood-supply. 
Lastly,  if  a  small  quantity  of  atropin  be  injected  into  the  veins, 
stimulation  of  the  chorda  produces  no  secretion  of  saliva  at  all, 
though  the  dilation  of  the  blood-vessels  takes  place  as  usual. 
This  remarkable  fact  can  only  be  accounted  for  by  supposing  that 
the  chorda  contains  two  sets  of  fibres,  one  secreting  fibres,  acting 
directly  on  the  epithelium  cells  only,  and  the  other  vaso-motor  or 
dilating  fibres,  acting  on  the  blood-vessels  only,  and  that  atropin, 
while  it  has  no  eff'ect  on  the  latter,  paralyses  the  former  just  as  it 
paralyses  the  inhibitory  fibres  of  the  vagus.  These  facts,  and 
especially  the  last,  clearly  prove  that  when  the  chorda  is  stimulated, 
there  pass  dov/n  the  nerve,  in  addition  to  impulses  affecting  the 
blood-supply,  impulses  affecting  directly  the  protoplasm  of  the 
sefcreting  cells,  and  calling  it  info  action,  just  as  similar  impulses 
call  into  action  the  contractility  of  the  protoplasm  of  a  muscular 
fibre.  Indeed  the  two  things,  secreting  activity  and  contracting 
activity,  are  quite  parallel.  We  know  that  when  a  muscle  con- 
tracts, its  blood-vessels  dilate ;  and  just  as  by  atropin  the  secret- 
ing action  of  the  gland  may  be  isolated  from  the  vascular  dilation, 
so  by  urari  muscular  contraction  may  be  removed,  and  leave 
dilation  of  the  blood-vessels  as  the  only  effect  of  stimulating  the 
muscular  nerve.  In  both  cases  the  greater  flow  of  blood  is 
an  adjuvant  to,  not  the  exciting  cause  of,  the  activity  of  the 
protoplasm. 

If  the  chorda  acts  thus  directly  on  the  secreting  cell,  there  must  be 
a  physiological  and  probably  an  anatomical  connection  between  the 
cell  and  the  nerve-fibre.  Although  Pfliiger's  "^  observations  as  to  the 
actual  mode  in  which  the  nerves  end  in  the  gland  have  not  been  gener- 
ally accepted,  nerve-fibres  have  been  traced  to  the  exterior  of  the 
alveoli,  and  Kupffer^  has  shewn  that  in  the  so-called  sahvary  glands  of 
Blatta,  the  nerve-fibres  certainly  pass  into  the  protoplasm  and  appar- 
ently end  in  the  nuclei  of  the  cells. 

'  Strieker's  Histology,  Syd.  Soc.  Trans.  Art,  Salivary  Glands  (by  PflUger). 
'  Ludwig's  Festgabe,  p.  Ixiv. 


CIIA1\    I.]  DIGESTION.  273 

When  the  cervical  sympathetic  is  stimulated,  the  vascular 
effects  are  the  exact  contrary  of  those  seen  when  the  chorda  is 
stimulated.  The  small  arteries  are  contracted,  and  a  small 
quantity  of  dark  venous  blood  escapes  by  the  vein.  Sometimes, 
indeed,  the  flow  through  the  gland  is  almost  arrested.  The 
sympathetic  therefore  acts  as  a  constrictor  nerve,  and  in  this  sense 
is  antagonistic  to  the  chorda.  We  have  already  referred  to  the 
probable  existence  of  a  local  vaso-motor  centre  situated  in  the 
gland  itself,  in  which  indeed  there  are  found  ganglionic  cells  in 
abundance.  The  fact  that  section  of  the  cervical  sympathetic 
does  not  cause  complete  dilation  of  the  vessels  of  the  gland — 
the  dilating  effects  of  stimulation  of  the  chorda  being  fully  evident 
after  previous  section  of  the  sympathetic — affords  additional 
support  to  this  view.  We  may  accordingly  state  that,  while  the 
chorda  tympani  inhibits,  the  sympathetic  exalts,  the  action  of  this 
local  centre. 

The  antagonism  between  the  two,  as  far  as  the  blood-supply  is  con- 
cerned, is  very  imperfect,  the  sympathetic  being  the  more  powerful ; 
thus  stimulation  of  the  chorda  produces  very  little  effect  in  altering 
the  results  of  a  concomitant  strong  stimulation  of  the  sympathetic  '. 

The  effects  on  the  flow  of  saliva  from  the  submaxillary  gland 
of  the  dog  brought  about  by  stimulation  of  the  sympathetic,  are 
very  peculiar.  A  slight  increase  of  flow  is  seen,  but  this  soon 
passes  off,  and  what  saliva  is  secreted  is  remarkably  viscid,  of 
higher  specific  gravity,  and  richer  in  corpuscles  and  protoplasmic 
lumps,  and  it  is  said  to  be  more  active  on  starch  than  the 
chorda  saliva^.  This  action  of  the  sympathetic  is  not  affected  by 
atropin. 

In  the  cat  on  the  contrary  the  chorda  saliva  is  distinctly  more 
viscid  than  the  sympathetic  saliva,  though  it  is  produced  in  greater 
abundance  upon  stimulation.  The  secretory  activity  of  the  cat's 
sympathetic  is  also  arrested  by  atropin,  though  a  larger  dose  than 
that  which  paralyzes  the  chorda  is  required  3.  In  the  rabbit  both 
chorda  and  sympathetic  saliva  are  free  from  mucus,  though  the 
latter  is  secreted  more  scantily  than  the  former.  The  marked 
contrast  therefore  shewn  in  the  dog  between  the  two  kinds  of 
saliva  must  not  be  considered  as  of  fundamental  origin.  We 
shall  return  later  on  to  a  discussion  of  the  essential  differences 
between  chorda  and  sympathetic  action. 

'  Frey,  Ludwig's  Arbeiten,  1876,  p.  89. 

'  Eckhard,  Batrdge,  II.  (i860)  p.  81  ;  in.  (1864)  p,  39. 

^  Langley,  Jourii.  Physiol.,  I.  (1S78)  p.  96. 
F.  P.  IS 


2/4  CHORDA   AND    SYMPATHETIC.  [BOOK   II. 

Most  observers  agree  that  when  both  chorda  and  sympathetic  are 
stimulated  at  the  same  time  with  strong  currents,  the  action  of  ihe 
chorda,  contrary  to  what  takes  place  as  far  as  the  blood-supply  is  con- 
cerned, prevails  as  far  as  secretion  is  concerned,  i.e.  the  flow  is  copious 
and  watery.  But  the  nature  of  the  differences  exhibited  by  the  chorda 
and  sympathetic  in  reference  to  the  character  of  the  secretion  and  the 
relations  of  the  two  will  be  discussed  later  on,  see  p.  288. 

Bernard '  observed  that  after  section  of  all  the  nerves  going  to  the 
gland,  a  continuous  and  fairly  copious  secretion  of  a  watery  saliva  soon 
set  in  and  continued  for  some  time.  Heidenhain^  observed  the  same 
thing,  the  continuous  flow  beginning  from  four  to  twenty-four  hours 
after  section  of  the  nerves,  soon  reaching  a  maximum,  and  after  some 
weeks  decreasing  again  as  regeneration  of  the  nerves  took  place. 
During  this  '  paralytic  secretion,'  as  it  is  called,  the  gland  diminishes  in 
size,  and  in  some  cases  where  the  nerves  are  not  restored  appears  to 
undergo  degeneration.  A  paralytic  secretion  also  appears  if  the  chorda 
only  be  divided  ;  and  urari  poisoning  ^  produces  a  similar  flow.  The 
paralytic  secretion  is  watery  but  contains  both  mucin  and  sahvary 
corpuscles.  The  mechanism  of  its  production  is  obscure,  but  Heiden- 
hain  observed  a  similar  continuous  secretion  to  result  when  the  duct 
of  the  gland  was  kept  hgatured  for  twenty-four  hours  and  then  opened. 
Heidenhain  also  observed  that  when  the  nerves  of  the  gland  on  one 
side  were  cut,  a  paralytic  secretion  appeared  in  the  gland  of  the  other 
side  also. 

The  natural  reflex  act  of  secretion  may  be  inhibited,  like  the 
reflex  action  of  the  vaso-motor  nerves,  at  its  cerebral  centre. 
Thus  when,  as  in  the  old  rice  ordeal,  fear  parches  the  mouth,  it  is 
probable  that  the  afferent  impulses  passing  from  the  mouth  cease, 
through  emotional  inhibition  of  their  reflex  centre,  to  give  rise  to 
efferent  impulses. 

The  history  of  the  submaxillary  gland  then  teaches  us  that 
secretion  in  this  instance  is  a  reflex  action,  the  efferent  impulses 
of  which  directly  affect  the  secreting  cells,  and  that  the  vascular 
phenomena  may  assist,  but  are  not  the  direct  cause  of,  the  flow. 
We  have  dwelt  long  on  this  gland  because  it  has  been  more  fruit- 
fully studied  than  any  other.  The  nervous  mechanisms  of  the 
other  secretions  may  be  passed  over  much  more  rapidly. 

Parotid.  The  secretion  of  this  gland,  like  that  of  the  sub- 
maxillary, is  governed  by  two  sets  of  fibres  :  one  of  cerebro-spinal 
origin,  running  along  the  auriculo-temporal  branch  of  the  fifth 
nerve  but  originating  either  in  the  glosso -pharyngeal  or  the  facial, 
and  the  other  of  sympathetic  origin  coming  from  the  cervical 
sympathetic.  Stimulation  of  the  cerebro-spinal  fibres  produces  a 
copious  flow   of  watery  saliva,  free   from   mucus,  the   secretion 

'  Robin's  yourn.  deVAnat.  et  dela  Physiolog.,  i.  (1864)  p.  511. 
*  Op.  cit.  ^  Bernard,  op.  cit. 


CHAP.   I.]  DIGJiSTION.  275 

reaching  in  the  dog  a  pressure  of  118  mm.  mercury;  stimulation 
of  the  cervical  sympathetic  gives  rise  in  the  rabbit  to  a  secretion 
free  from  miicus  but  rich  in  organic  matter  and  of  greater  amylo- 
lytic  power  than  the  cercbro-spinal  secretion,  but  in  the  dog  little 
or  no  secretion  is  produced,  though  as  we  shall  see  later  on, 
certain  changes  arc  brought  about  in  the  gland  itself.  In  both 
animals  the  cerebro-spinal  fibres  arc  vaso-dilator  and  the  sympa- 
thetic fibres  vasoconstrictor  in  action.  Stimulation  of  the  central 
end  of  the  glosso-pharyngeal  produces  by  reficx  action  a  secretion 
of  the  parotid,  but  that  of  the  lingual  is  said  to  be  without 
effect'. 

In  the  dog,  the  secretory  fibres  of  cerebro-spinal  origin  arise  from 
the  glosso-pharyngeal  nerve,  pass  by  the  ramus  tympanictts  glosso- 
pJiaryngei  to  the  tympanum,  and  then  join  the  furvus  pclrostts  super- 
fkialis  iniitor,  by  which  they  reach  the  lainus  auriculo-teinporalis  of 
the  fifthl  In  the  rabbit  the  fibres  also  run  in  the  raviits  ajdiculo- 
tciiiporalts,  but  it  does  not  seem  clear  whether  they  spring  from  the 
glosso-pharyngeal  as  in  the  dog,  or  from  the  facial. 

Eckhard  ■•  failed,  in  the  parotid  of  the  sheep,  to  get  any  effect,  what- 
ever nerve  be  stimulated  ;  a  continuous  secretion  going  on,  and  being 
neither  increased  or  decreased  by  nerve  stimulation. 

Gastric  juice.  The  presence  of  food  in  the  stomach  causes 
a  copious  flow  of  gastric  juice.  The  quantity  secreted  in  man  in 
the  twenty-four  hours  has  been  calculated  at  from  13  to  14  litres. 
When  the  gastric  mucous  membrane  is  stimulated  mechanically, 
as  with  a  feather,  secretion  is  excited  :  but  to  a  very  small  amount 
even  when  the  whole  inteiior  surface  of  the  stomach  is  thus 
repeatedly  stimulated.  The  most  efficient  stimulus  is  the  natural 
stimulus,  viz.  (ood ;  but  dilute  alkalis  seem  to  have  unusually 
powerful  stimulating  effects ;  thus  the  swallowing  of  saliva  at  once 
provokes  a  flow  of  gastric  juice.  During  fasting  the  gastric  mem- 
brane is  of  a  pale  grey  colour;  during  digestion  it  becomes  red 
and  flushed,  and  to  a  certain  extent  tumid.  The  secretion  of 
gastric  juice  therefore  seems  to  be  accompanied  by  vascular 
dilation  in  the  same  way  as  in  the  secretion  ol  saliva. 

Seeing  that,  unlike  the  case  of  the  salivary  secretion,  food  is 
brought  into  the  immediate  neighbourhood  of  the  secreting  cells, 
it  is  exceedingly  probable  that  a  great  deal  of  the  secretion  is 
the   result  of  the  working  of  a  local  mechanism  ;  and  when  a 

»  Ileidenhain,  Pfluger's  Wrc///:/,  xvii.  (1878)  p.  I. 
'  Nawrocki,  Bnslau.  Stuaicn^  iv.  (iS6S)p.  125. 

3  Nawrocki,  op.  cit.  Loeb,  Kckhard's  Z>W//a^<',  v.  {lS69)p.  I.  Heidenhain, 
op.  tit. 

*  lieUrdge,  Vli.  (1876)  p.  161. 

18—2 


2/6  SECRETION   OF   GASTRIC  JUICE.         {"BOOK  II. 

mechanical  stimulus  is  applied  to  one  spot  of  the  gastric  membrane 
the  secretion  is  limited  to  the  neighbourhood  of  that  spot  and  is 
not  excited  in  distant  parts.  Nevertheless,  since  the  flow  of 
gastric  juice  may  be  excited  or  arrested  by  events  in  distant  parts, 
as  by  emotions,  the  gastric  membrane  must  be  in  some  way  or 
other  brought  into  relation  with  the  central  nervous  system ;  and 
probably  future  inquiries  will  disclose  a  mechanism  as  complete 
as  that  of  the  submaxillary  gland.  At  present,  however,  the 
matter  is  very  imperfectly  known. 

Heidenhain  ^  has  succeeded  in  the  dog  in  isolating  (after  the  manner 
of  Thiry's  method  with  the  intestine)  a  portion  of  the  fundus  from  the 
rest  of  the  stomach.  He  finds  that  introduction  of  food  into  the  (main) 
stomach  gives  rise  to  a  secretion  of  gastric  juice  in  the  isolated  fundus 
portion.  This  v.'ould  at  first  sight  seem  to  indicate  a  nervous  action, 
but  the  secretion  in  the  isolated  fundus  is  insignificant  unless  the 
material  introduced  into  the  main  stomach  be  such  as  can  be  digested 
and  absorbed.  A  similar  connection  between  the  act  of  secretion  and 
the  absorption  of  digested  material  is  indicated  by  the  rate  of  secre- 
tion of  pepsin  after  a  meal.  Griitzner^  states  that  the  rate  of  secre- 
tion of  pepsin,  abundant  immediately  upon  food  being  taken,  falls 
during  the  first  and  second  hours  afterwards,  rises  again  up  to  a  second 
maximum  at  the  fourth  or  fi'fth  hours,  after  which  it  finally  but  gradu- 
ally sinks,  the  curve  in  fact  being  not  unlike  that  of  the  pancreatic 
secretion.  (See  Fig.  42.)  And  Heidenhain  3  finds  this  to  be  true  also 
of  the  secretion  of  the  isolated  fundus  excited  by  the  introduction  of 
food  into  the  main  stomach.  Schiff -*  has  for  many  years  maintained 
that  the  secretion  of  gastric  juice  is  dependent  on  the  gastric  cells 
becoming  '  laden '  with  pepsinogenous  material  derived  from  the  ab- 
sorbed products  of  digestion  and  especially  from  absorbed  dextrin. 
But  the  amount  either  of  pepsin  or  pepsinogenous  material  in  the 
gastric  membrane  does  not,  according  to  Griitzner,  run  parallel  to  the 
amount  of  pepsin  in  the  secretion. 

The  amount  of  acid  in  the  secretion  is  much  more  constant  than 
the  pepsin,  in  fact  varies  but  slightly.  The  increase  of  acidity  in  the 
contents  of  a  meal  is  due  simply  to  the  fact  that  the  acid  accumulates 
as  the  gastric  juice  continues  to  be  secreted. 

Rutherford  5  found  that  the  gastric  membrane,  flushed  during  diges- 
tion, became  pale  when  the  vagi  were  cut.  Stimulation  of  the  central 
end  of  either  vagus  caused  a  reddening  of  the  gastric  membrane,  but 
stimulation  of  the  peripheral  end  produced  no  constant  effect.  From 
these  results  we  may  infer  that  afferent  impulses  pass  up  the  vagus  and 
by  inhibiting  in  the  medulla  the  vaso-motor  centre  governing  the 
gastric  blood-vessels,  cause  a  dilation  of  the  latter.  The  efferent  im- 
pulses  evidently  do  not  descend   by   the  vagus  ;  probably  therefore 

'  Pfluger's  Archiv,  xix.  (1879)  p.  148. 

^   Untersuch.  ii.  Bildiwg  u.  Ausscheidung  des  Pepsin,  1875.  ^  Op.  cit. 

*  See  also  Legons  sur  la  Physiologie  de  la  Digestion,  II.  1867. 

5  Fhil.  Trans.  Edin.,  xxvi.  (1870). 


ClIAl'.    l]  DIGESTION.  277 

their  path  is  aion^  the  sympathetic.  After  division  of  both  vagi,  gastric 
juice  of  normal  acidity  and  peptic  power  continues  to  be  scncted. 
The  same  occurs  after  division  of  both  splanchnic  nerves,  and  even 
after  extirpation  of  the  ca-liac  ganglion. 

Bile.  When  the  acid  contents  of  the  stomach  are  poured 
over  the  orifice  of  the  biliary  duct,  a  gush  of  bile  takes  place. 
Indeed,  stimulation  of  this  region  of  the  duodenum  with  a  dilute 
acid  at  once  calls  forth  a  flow,  whereas  alkaline  fluids  so  applied 
have  little  or  no  eftect.  This,  probably,  is  a  reflex  action  leading 
to  the  contraction  of  the  muscular  walls  of  the  gall-bladder  and 
ducts,  accompanied  by  a  relaxation  of  the  sphincter  of  the 
orifice  ;  it  refers  therefore  to  the  discharge  rather  than  to  the 
secretion  of  bile. 

When  the  secretion  of  the  bile  is  studied  by  means  of  a  biliary 
fistula  (which,  however,  probably  induces  errors  by  the  total  with- 
drawal from  the  body  of  the  bile  which  should  naturally  flow  into 
the  intestine),  it  is  seen  to  rise  rapidly  after  meals,  reaching  its 
maximum  in  from  four  to  ten  hours.  There  seems  to  be  an  im- 
mediate, sudden  rise  when  food  is  taken,  then  a  fall,  followed 
subsequently  by  a  more  gradual  rise  up  to  the  maximum,  and 
ending  in  a  final  fall.  It  is  exceedingly  probable  that  these 
variations  are  due  to  the  action  of  the  nervous  system,  but  the 
exact  nature  of  the  nervous  mechanism  is  unknown. 

Stimulation  of  the  splanchnics  causes  an  increase  in  the  flow 
from  a  biliary  fistula,  but  this  is  probably  due  to  contraction  of  the 
bile-ducts. 

Rutherford '  finds  that  the  injection  of  various  substances,  ipeca- 
cuanha, podophyllin,  &c.,  into  the  duodenum  causes  an  increase  in  the 
actual  secretion,  but  the  nianner  of  the  increase  is  not  yet  explained. 

Unlike  the  case  of  saliva,  the  pressure  under  which  the  bile  is 
secreted  never  exceeds  that  of  the  blood,  and  is  in  general  very 
low.  When  a  water  manometer  is  connected  with  the  gall- bladder 
of  a  guinea-pig,  the  ductus  clwlcdochus  being  ligatured,  the  fluid 
may  rise  in  the  manometer  to  about  200  mm.  (equivalent  to  about 
16  mm.  mercury),  but  not  much  beyond.  If  water  be  poured  into 
the  open  end  of  the  manometer  so  as  to  raise  the  pressure  much 
above  200  nmi.,  resorption  into  the  circulation  takes  place,  and 
the  fluid  in  the  manometer  sinks  to,  or  even  below,  the  normal 
levels  The  quantity  secreted  in  man  in  the  24  hours  has  been 
estimated  rougiily  at  about  10  kilos,  but  the  calculations  are  based 
on  very  imperfect  data. 

'  Jotirn.  Anat.  Phys.,  X.  XI.  (1876.  77);  Brit.  Med.  J.,  1878,  1879. 
'  FricdliiiiiicT  u.   Barisch  (Hcidcnhain),  Du  Bois-keyuiond's  Arctiix',  i860, 
p.  O46. 


2/8 


SECRETION   OF   PANCREATIC  JUICE.      [BOOK   II. 


Pancreatic  juice.  The  relation  of  the  nervous  system  to 
the  secretion  of  the  pancreatic  juice  has  been  studied  rather  more 
fully.  N.  O.  Bernstein'  finds  that  in  the  dog  the  secretion,  after 
food  has  been  taken,  follows  the  curve  given  in  Fig.  42.  There  is 
a  sudden  maximum  rise  immediately  after  food  has  been  taken. 
This  must  be  due  to  nervous  action.  Then  follows  a  fall,  after 
which  there  is,  as  in  bile,  a  secondary  rise,  the  causation  of  which 


Fig.  42. — Diagram  illustrating  the   influence  of  Food  on  the  Secretion  op 
Pancreatic  Juice.      (N.  O.  Bernstein.) 

The  abscissae  represent  hours  after  taking  food  ;  the  ordinates  represent  in  c.c.  the  amount 
of  secretion  in  lo  min.  A  marked  rise  is  seen  at  B  immediately  after  food  was  taken,  with  a 
secondary  rise  between  the  4th  and  sth  hours  afterwards.  Where  the  line  is  dotted  the  obser- 
vation was  interrupted.  On  food  being  again  given  at  C.  another  rise  is  seen,  followed  in  turn 
by  a  depression  and  a  secondary  rise  at  the  4th  hour.  A  very  similar  curve  would  represent 
the  secretion  of  bile. 


may,  or  may  not,  be  nervous  in  nature.  The  quantity  secreted  in 
24  hours  by  man  has  been  calculated  at  300  cc.  Like  the  salivary 
glands,  the  pancreas  while  secreting  is  flushed,  through  dilation 
of  its  blood-vessels. 

According  to  N.  O.  Bernstein^  the  secretion  is  at  once  stopped  by 
nausea  or  vomiting.  Section  of  the  vagus  stops  the  secretion  for  a 
short  time  ;  it  soon  however  recommences.     Stimulation  of  the  central 


Lud wig's  Arbiitei7,  1869. 


Op.  cU. 


CHAP.   I.]  .  DIGESTION.  279 

vagus  causes  an  arrest  lasting  for  sonic  time  after  the  stimulus  has 
been  removed.  It  is  probable  therefore  that  the  arrest  of  secretion 
during  vomiting  is  due  to  afferent  im|)ulses  ascending  die  vagus  and 
descending  by  some  other  channel.  If  all- the  nerves  going  to  the 
pancreas  around  the  pancreatic  artery  be  severed  as  completely  as 
possible,  a  continuous  paralytic  flow,  not  increased  but  rather  dimin- 
ished by  food,  and  very  slightly  if  at  all  hindered  by  nausea  or 
stimulation  of  vagus,  is  brought  on.  Hcidenhain'  states  that  stimula- 
tion of  the  medulla  oblongata  causes  an  increased  flow. 

Succus  entericus.  With  regard  to  the  secretion  furnished 
by  the  intestine  itself  our  information  is  very  limited.  Thirv ' 
found  that  in  the  isolated  intestine  the  secretion  was  not  a  coi. 
stant  one,  but  needed  for  its  production  some  stimulus  (mechanical 
or  other)  which  probably  acted  in  a  reflex  manner. 

Moreau3  found  that  after  section  of  the  nerves  going  to  a  piece  of 
intestine  isolated  after  I'hiry's  method,  a  copious  flow  of  a  dilute  intes- 
tinal juice  takes  place.  This  appears  to  be  comparable  to  the  paralytic 
flow  of  saliva  and  pancreatic  juice. 

Thus,  while  the  influence  of  the  nervous  system  is  in  the  case 
of  the  submaxillary  gland  tolerably  clear,  in  the  case  ot  the  other 
secretions  we  have  much  jet  to  learn,  and  must  rest  rather  on  the 
analogy  with  the  submaxillary  gland,  than  on  any  known  facts. 
We  cannot,  however,  go  far  wrong,  if  we  conclude  that  in  all 
cases  secretion  is  essentially  due  to  an  increase  in  the  activity  of 
the  epithelium  cells,  and  that  variations  in  the  blood-supply  have 
a  secondary  eftect  only. 

It  must  however  be  borne  in  mind  that  substances  brought  to  the 
secreting  cell  by  the  blood  may  possibly  act  as  chemical  stimuli  of  its 
protoplasm,  just  as  certain  chemical  substances  may  stimulate  a 
muscular  libre  to  contraction  in  the  absence  of  all  nerves.  Thus  any 
substance,  such  as  a  therapeutic  drug,  may  affect  any  given  secretion, 
in  various  ways,  viz.  (i)  by  dilating  the  blood-vessels  and  mcreasing 
the  blood-supply,  (2)  by  acting  as  a  direct  chemical  stimulus  on  the 
protoplasm,  (3)  by  exciting  secretion  in  the  cell  through  reflex  action 
of  the  nervous  mechanism  belonging  to  the  cell,  (4)  by  acting  directly 
on  the  nervous  centre  of  that  mechanism.  We  shall  return  to  these 
questions  when  we  come  to  speak  of  the  secretion  of  urine. 

We  are  now  in  a  position  to  attack  the  second  problem. 
What  is  the  exact  nature  of  the  activity  which  is  thus  called 
forth  ? 

We  learn    from   the    researches    of    Heidenhain'*   that    each 

•  Pfluger's  Archiv,  X.  (1875)  p.  557. 
'   H^iat.  Sitzi4tigsi>rric/it,  L.  p.  77. 

3  Centrbt.  Med.  li'iss.,  186S,  p.  209. 

♦  Pfliiger's  Archiv,  X.  (1857)  p.  557. 


28o  SECRETORY   CHANGES   IN    PANCREAS.     [BOOK   II. 

secreting  cell  of  a  pancreas  of  an  animal  (dog)  which  has  been 
fasting  for  30  hours  or  more  consists  of  two  zones  :  an  inner  zone, 
next  to  the  lumen  of  the  alveolus,  which  is  studded  with  fine 
granules,  and  a  smaller  outer  zone,  which  is  homogeneous  or 
marked  with  delicate  stris.  Carmine  stains  the  outer  zone  easily, 
the  inner  zone  with  difficulty.  The  nucleus,  more  or  less  irregular 
in  shape,  is  placed  partly  in  the  one  and  partly  in  the  other 
zone.  When  however  the  pancreas  of  an  animal  in  full  digestion 
(about  six  hours  after  food  and  onwards)  is  examined,  the  outer 
homogeneolis  zone  is  found  to  be  much  wider,  the  granular  inner 
zone  being  correspondingly  narrower,  and  in  some  cases  actually 
disappearing.  The  whole  cell  is  smaller,  and  owing  to  the  rela- 
tively larger  size  of  the  outer  zone,  stains  well.  The  nucleus  is 
spherical  and  well  formed.  If  the  pancreas  be  examined  at  the 
end  of  digestion,  when  its  activity  has  once  more  ceased,  and  it 
has  entered  into  a  state  of  rest,  the  outer  zone  is  again  found  to 
be  narrow,  the  granular  inner  zone  occupying  the  greater  part  of 
the  cell,  which  in  consequence  stains  with  difficulty  ;  and  the 
whole  cell  has  once  more  become  larger.  There  seems  to  be  but 
one  interpretation  of  these  facts.  During  the  time  that  the  pan- 
creas is  secreting  most  rapidly,  there  is  a  diminution  of  the  inner 
zone  ;  that  is  to  say,  the  inner  zone  furnishes  material  for  the  secre- 
tion. But  while  the  inner  zone  is  diminishing,  the  outer  zone  is 
increasing,  that  is  to  say,  the  outer  zone  is  being  built  up  again  out 
of  materials  brought  to  it  from  the  blood,  though  not  to  such  an 
extent  as  to  prevent  the  whole  cell  from  becoming  smaller.  When 
digestion  is  ended,  after  the  pancreas  has  ceased  to  secrete,  the 
inner  zone  again  enlarges,  evidently  at  the  expense  of  the  outer 
zone,  though  the  latter  also  continues  to  increase,  causing  the  whole 
cell  to  become  bigger.  From  thence  till  the  next  meal,  there  occurs 
a  partial  consumption  of  the  inner  zone,  so  that  the  outer  zone 
becomes  more  conspicuous  again,  though  the  whole  cell  becomes 
smaller.  Evidently  out  of  the  protoplasm  of  the  cell,  which  is 
itself  formed  at  the  expense  of  the  blood,  the  granules  are  formed, 
and  these  being  deposited  towards  the  lumen  of  the  alveolus 
distinguish  the  outer  homogeneous  from  the  inner  granular  zone, 
and  the  secretion  is  produced  at  the  expense  of  the  granules. 

Kiihne  and  Sheridan  Lea^,  observing,  under  the  microscope, 
the  pancreas  of  the  living  rabbit,  have  been  able  to  watch  the 
actual  process  of  secretion  ;  and  their  results,  while  they  extend, 
in  the  main  corroborate  those  of  Heidenhain.  In  the  quiescent 
pancreas  of  the  rabbit.  Fig.  43  A,  the  cells  are  for  the  most  part 
filled  with  granules,  the  transparent  outer  zone  being  reduced  to 
»   Verhaiidl.  Naturhist.  Med.  Vereins,  Heidelberg,  Bd.  i.  (1877)  Hft.  5. 


CHAP.    1.] 


DIGESTION. 


!8l 


small  dimensions ;  the  outlines  of  the  individual  cells  are  very 
indistinct,  with  the  margins  of  the  alveoli  smooth  ;  the  lumen  of  the 
alveolus  is  obscure;  and  the  l)lood-su])ply  is  scanty.  Upon  secre- 
tion being  set  up,  Fig.  43  13,  the  margins  of  the  active  alveoli 
become  indented  through  a  bulging  of  their  constituent  cells,  the 
outlines  of  which  now  become  distinct;  the  granules  retreat 
towards  the  inner  zone,  bordering  on  the  cavity  of  ihe  alveolus, 
and  as  secretion  goes  on,  evidently  diminish  in  number,  the  whole 
cell  becoming  hyaline  and  transparent  from  the  outer  border 
inwards  ;  at  the  same  time  the  blood-vessels  dilate  largely,  and  the 
stream  of  blood  through  the  capillaries  becomes  full  and  rapid. 

We  have  already  seen,   p.    268,  that  in  order  to  obtain  an 
actively  proteolytic  aqueous  pancreatic  extract,  the  animal  must 


Fig.  43.    A  Portion  of  the  Pancreas  of  the  Rabbit  (Kuhne  and  Sheridan  Lea) 
A  at  rest,  iff  in  a  st.-ite  of  activity, 

a  the  inner  granular  zone,  which  in  A  is  larger,  and  more  closely  studded  with  fine 
granules,  than  in  />'.  in  which  the  f;ranules  are  fewer  and  coar.ser. 

6  the  onier  transp.ircnt  zone,  small  in  .1,  larger  in  Ji,  and  in  the  latter  marked  with  faint 
strix. 

c  the  lumen,  very  obvious  in  />.  but  indistinct  in  A. 

d  an  indentation  at  the  junciion  of  two  cells,  seen  in  B,  but  not  occurring  in  A. 

be  killed    during  full    digestion.     This    statement   now   requires 
modification. 

If  the  pancreas  of  an  animal,  c\en  in  full  liigestion,  be  treated, 
uihtle  still  warm  from  the  body,  with  glycerine,  the  glycerine  extract 
is  inert  or  nearly  so  as  regards  proteid  bodies,  H,  however,  the 
same  pancreas  be  kept  for  24  hours  before  treating  with  glycerine, 
the  glycerine  extract  readily  digests  fibrin  and  other  proteids  in  the 
presence  of  an  alkali.  If  the  pancreas,  while  still  warm,  be  rubbed 
up  in  a  mortar  for  a  few  minutes  with  dilute  acetic  acid,  and  then 
treated  with  glycerine,  the  glycerine  extract  is  strongly  proteolytic. 
If  the  glycerine  extrrtct  obtained  without  acid  from  the  warm 
pancreas,  and  therefore  inert,  be  diluted  largely  with  water,  and 


282  ZYMOGEN.  [BOOK  II. 

kept  at  35°  C.  for  some  time,  it  becomes  active.  If  treated  with 
acidulated  instead  of  distilled  water,  its  activit}^,  as  judged  of  by 
its  action  on  fibrin  in  the  presence  of  sodium  carbonate,  is  much 
sooner  developed.  If  the  inert  glycerine  extract  of  warm  pancreas 
be  precipitated  with  alcohol  in  excess,  the  precipitate,  inert  as  a 
proteolytic  ferment  when  fresh,  becomes  active  when  exposed  for 
som3  time  in  an  aqueous  solution,  rapidly  so  when  treated  with 
acidulated  water.  These  facts  shew  that  a  pancreas  taken  fresh 
from  the  body,  even  during  full  digestion,  contains  but  little  ready- 
made  ferment,  though  there  is  present  in  it  a  body  which,  by  some 
"kind  of  decomposition,  gives  birth  to  the  ferment.  They  further 
shew  that  though  the  presence  of  an  alkali  is  essential  to  proteo- 
lytic action  of  the  actual  ferment,  the  formation  of  the  ferment 
out  of  the  body  in  question  is  favoured  by  the  presence  of  an 
acid.  To  this  body,  this  mother  of  the  ferment,  Heidenhain  has 
given  the  name  oi  zymogen'^.  It  has  not  at  present  been  satis- 
factorily isolated. 

Hence,  in  judging  of  the  functional  activity  of  the  pancreas 
under  various  circumstances,  we  must  look  to  not  the  ready-made 
ferment,  but  the  ferment-giving  zymogen.  And  Heidenhain  has 
made  the  important  observation  that  the  amount  of  zymogen  in  a 
pancreas  at  any  given  time  rises  and  sinks  pari  passu  with  the 
granular  inner  zone.  The  wider  the  inner  zone  the  larger  the 
amount,  the  narrower  the  zone  the  smaller  the  amount  of  zymo- 
gen ;  and  in  the  cases  of  so-called  paralytic  secretions  from  old- 
established  fistulas,  where  the  juice  is  wholly  inert  over  proteids, 
the  inner  granular  zone  is  absent  from  the  cells.  Evidently  so  far 
from  the  proteolytic  ferment  being  simply  drained  off  from  the  blood, 
in  the  first  place  the  actual  ferment  is  formed  in  the  pancreas  out 
of  the  zymogen,  and  in  the  second  place  the  zymogen  of  the  inner 
granular  zone  is  formed  in  the  cell  itself  out  of  the  homogeneous 
outer  zone.  We  have  in  fact  two  distinct  processes  to  deal  with : 
(i)  the  manufacture  of  zymogen  ;  this  is  part  of  the  growth  or 
nutrition  of  the  cell,  and  is  slow  and  continued;  (2)  the  splitting 
up  or  conversion  of  the  zymogen  into  the  proteolytic  ferment;  this 
is  the  real  act  of  secreting,  and  is  intermittent  and  rapid ;  this  is 
the  form  of  activity  which  can  be  called  forth  by  nervous  im- 
pulses, the  form  of  activity  which  is  comparable  to  a  muscular 
contraction. 

The  thought  at  once  suggests  itself  that  the  appearance  of  an  acid 
in  ,the  protoplasm  of  the  cell  under  circumstances  similar  to  those 

^  Or  zymogen  may  be  reserved  as  a  generic  name  for  '  mother  of  ferment ' ; 
in  that  case  the  particular  mother  of  the  pancreatic  proteolytic  ferment  might 
be  called  tripsinogen. 


CHAr.   I.]  DIGESTION.  283 

whic'i  give  rise  to  the  acid  formed  during  muscular  contraction,  might 
be  tlie  immediate  cause  of  the  zymogen  becoming  converted  into 
ferment. 

In  the  case,  tlien,  of  the  proteolytic  ferment  of  the  pancreas 
we  have  striking  jjroof  that  the  process  of  secretion,  both  in  its 
preparatory  and  executive  stages,  is  a  laborious,  active,  manu- 
facturing function  of  the  cell,  and  not  simply  a  passive,  selective, 
filtering  function.  How  far  this  is  also  true  of  the  other  ferments 
of  the  pancreas,  and  of  the  active  constituents  of  the  other  diges- 
tive juices,  cannot  at  present  be  authoritatively  affirmed,  but  we 
have,  both  in  the  case  of  the  stomach  and  of  the  salivary  glands, 
facts  pointing  very  distinctly  in  that  direction. 

In  the  gastric  glands  of  an  animal  previous  to  taking  a  meal, 
the  central  (as  distinguished  from  the  ovoid  or  'peptic')  cells 
are  pale,  and  finely  granular,  and  in  sections  taken  from  glands 
hardened  in  alcohol,  do  not  stain  readily  with  carmine  and  other 
dyes.  During  the  early  stages  of  gastric  digestion,  the  same  cells 
are  found  somewhat  swollen,  but  turbid  and  more  coarsely  granu- 
lar ;  they  stain  much  more  readily.  At  a  later  stage  they  become 
smaller  and  shrunken,  but  are  even  more  turbid  and  granular  than 
before,  and  stain  even  still  more  deeply.  This  is  true,  not  only  of 
the  central  cells  of  the  so-called  peptic  glands,  but  also  of  the  cells 
of  which  the  so-called  mucous  glands  of  the  pyloric  end  of  the 
stomach  are  built  up.  (The  ovoid  or  peptic  cells  themselves 
during  digestion  appear  swoll'en,  and  project  more  on  the  outside 
of  the  gland,  but  otherwise  appear  unchanged.)  Evidently,  during 
digestion,  the  central  cells  become  changed  in  nature  so  as  to  be 
more  readily  stained  with  carmine  and  at  the  same  time  loaded 
with  a  more  coarsely  granular  material'. 

In  the  glands  of  the  pylorus  there  is  seen  in  the  lumen  also  of  the 
gland,  a  granular  material,  which,  since  it  makes  its  appearance  after 
the  mechanical  stimulation  of  the  membrane  of  an  empty  stomarh. 
cannot,  when  it  occurs  during  digestion,  be  regarded  as  simply  digested 
food  about  to  be  absorbed.  The  granular  character  of  the  cells 
themselves  therefore  must  also  come  from  within,  and  cannot  be  due 
to  material  absorbed  from  the  cavity  of  the  stomach. 

It  will  be  observed  that  the  phenomena  of  the  gastric  cells  are 
somewhat  different  from  those  of  the  pancreatic  cells.  In  the  case  of 
the  pancreatic  cell  it  is  the  part  of  the  cell  which  contains  the  granules 
whii  h  does  not  stain  readily  ;  and  the  granules  make  their  appearance 
during  rest,  and  disappear  upon  stimulation.  In  the  case  of  gastric 
central  ceils,  it  is  when  the  cell  becomes  loaded  with  granules  that  it 
stains  most  deeply,  and  it  becomes  loaded  with  granules  not  during 

*  Heidcnhain,  Archiv  f.  mici:  Anat.,  vi.  (1870)  p.  368.     Rollett,   Unler' 
such.  a.  d.  Inst./.  Physio!,  u.  Hist,  in  Graz,  lift    11.(1871)  p.  143. 


284  SECRETION    OF   GASTRIC  JUICE.  [BOOK   II. 

rest  but  during  stimulation,  or  at  least  when  the  stomach  is  digesting. 
The  observations  of  Kiihne  and  Lea  shew  that  in  the  pancreas  the 
granules  are  actually  used  up  to  form  the  secretion.  If  in  the  gastric 
cell  the  granules  are  really  elements  of  the  secretion,  they  must  during 
active  digestion  be  formed  more  rapidly  than  they  are  used  up,  and 
must  cease  to  be  formed  as  the  work  of  digestion  languishes. 

There  has  been  a  great  dispute  as  to  whether  the  pyloric  end  of  the 
stomach,  that  containing  the  so-called  mucous  glands  only,  has  peptic 
powers.  But  the  researches  of  Heidenhain^  have  decided  the 
question  in  the  affirmative.  This  observer  succeeded  in  isolating 
the  pylorus  from  the  rest  of  the  stomach  after  the  manner  of  Thiry's 
operation  on  the  small  intestine,  and  obtained  from  the  isolated  portion 
a  small  quantity  of  viscid  alkaline  secretion,  which  when  treated  with 
dilute  hydrochloric  acid  rapidly  digested  fibrin.  The  secretion  also, 
without  the  addition  of  acid,  rapidly  curdled  milk,  but  shewed  no 
amylolytic  action.  A  reconciliation  of  some  of  the  previous  contra- 
dictory statements  may  perhaps  be  found  in  the  fact"",  that  while  the 
glycerine  extract  of  the  fresh  pylorus,  even  in  the  presence  of  free 
hydrochloric  acid,  is  inert,  care  being  taken  to  avoid  admixture  with 
the  secretion  of  the  cardiac  end,  an  acid  infusion  of  the  same  part 
rapidly  becomes  peptic.  This  would  seern  to  indicate  that  the  pyloric 
glands  are  free  from  actual  pepsin  but  contain  a  pepsinogen,  com- 
parable to  pancreatic  zymogen,  which  by  the  action  of  an  acid  is  split 
up  into  pepsin.  Apparently  however,  pepsinogen  differs  from  zymogen 
in  being  insoluble  in  glycerine,  while  the  latter  is,  as  we  have  seen, 
freely  soluble  in  that  fluid.  This  point  requires  to  be  more  fully 
worked  out. 

We  may  therefore  with  good  reason  suppose  that  pepsin  is 
formed  by  the  direct  activity  of  the  gastric  cells  ;  and  in  that  case 
the  pepsin  which  is  present  in  blood 3,  in  muscle,  and  in  urine*, 
is  not  the  source  of  the  pepsin  in  the  gastric  juice,  but  is  already- 
used  pepsin  reabsorbed  from  the  stomach  and  intestine,  and  on  its 
way  ,to  be  discharged  from  the  body. 

The  formation  of  the  free  acid  of  the  gastric  juice  is  very 
obscure.  It  seems  natural  to  suppose  that  it  arises  in  some  way 
from  the  decomposition  of  sodium  chloride;  but  nothing  definite 
can  at  present  be  stated  as  to  the  mechanism  of  that  decomposi- 
tion ;  and  even  admitting  that  sodium  chloride  is  the  ultimate 
source  of  the  chlorine  element  of  the  acid,  it  appears  more  likely 
that   that   element  should  be  set   free   in   the   stomach   by    the 

'  Pfliiger's  Archiv,  XVIII.  (1878)  p.  169  ;  also  Klemensiewicz,  Wien. 
Sitzungs  Bericht.,  Bd.  71,  March,  1875. 

.  =  Ebstein  and  Griitzner,   Pfliiger's  Archiv,  VIII.  {1874)  p.  122.     Griitzner, 
'  Utttersuch.  ii.  Bild.  ti.  Ausscheid.  d.  Pepsin,  1875. 

3  The  presence  of  pepsin  in  blood  is  one  reason  why  boiled  fibrin  should  be 
used  in  peptic  experiments  rather  than  raw.  The  boiling  destroys  the  pepsin 
clinging  to  the  fibrin. 

<  Briicke,  Moleschott's  Unttrstich.,  VI.  474. 


CHAP.    i.J  DIULSTION.  2S5 

decomposition  of  some  highly  complex  and  unstable  chlorine  com- 
pouiid  previously  generated,  than  that  it  should  arise  by  the  direct 
splitting  up  of  so  stable  a  body  as  sodium  chloride,  at  the  time 
when  the  acid  is  secreted'.  One  thing  however  seems  certain, 
that  the  acid  is  formed  only  at  the  surface  of  the  gastric 
membrane. 

If  the  reaction  of  the  mucous  membrane  of  the  stomach  be  tested 
.It  different  depths  from  the  surface,  as  in  the  long  tubular  glands  of  a 
bird,  it  will  be  seen  that  the  acidity  is  confined  to  the  upper  portion, 
indeed  to  the  mouths  of  the  glands.  So  also  when  potassium  ferrocy- 
anidc  and  an  iron  salt  are  injected  into  the  veins,  a  blue  colour  is 
develojied  only  on  the  surface  of  the  mucous  membrane,  and  not  in 
the  depths  of  the  gland,  shewing  that  an  acidity  sufficient  to  allow  of 
the  development  of  the  blue  is  present  only  at  the  surface. 

Heidenhain  has  made  the  suggestion  not  only  that  the  central  cells 
manufacture  pepsin  (or  pepsinogen),  (and  of  this  after  the  proved 
peptic  powers  of  the  pylorus  there  can  be  hardly  any  doubt),  but  also 
that  the  large  ovoid  (peptic)  cells  manufacture  the  acid  of  the  gastric 
juice.  Since  the  ovoid  cells  lie  chiefly  in  middle  portions  of  the  gland, 
the  superficial  development  of  the  acid  requires,  on  this  view,  some 
special  explanation.  In  favour  of  such  a  fum^tion  of  the  'ovoid'  cells 
has  been  adduced  the  curious  circumstance  that  in  the  frog  pepsin  is 
largely  present  in  the  lower  part  of  the  CESophagus,  where  cells  alto- 
gether like  the  '  central '  cells  of  the  gastric  glands  are  abundant, 
whereas  the  stomach  itself,  which  is  richly  supplied  v/ith  '  ovoid '  or 
peptic  cells,  appears  to  secrete  an  acid  fluid,  which  when  the  oesopha- 
gus is  ligatured  is  extremely  poor  in  pepsins 

In  the  case  of  the  salivary  glands  the  phenomena  to  a  certain 
extent  differ  according  as  the  gland  is  a  '  mucous  '  gland,  i.e.  one 
coritaining  a  larger  or  smaller  number  of  mucus-producing  cells, 
and  secreting  a  more  or  less  viscid  mucous  saliva,  or  a  '  serous ' 
gland,  i.e.  one  containing  no  such  mucus-producing  cells,  and 
secreting  a  thin  limpid  sali\a  free  from  mucus.  The  submax- 
illary gland  of  the  dog  may  be  taken  as  the  type  of  mucous  glands. 
If  a  section  is  prepared  of  this  gland  when  at  rest,  i.e.  when  it  has 
not  for  some  time  been  actively  secreting,  the  cells  of  the  alveoli 
(Fig.  44)  are  found  not  to  stain  readily  with  carmine ;  and  this 
lack  of  staining  appears  to  be  due  to  the  fact  that  the  greater  part 
of  the  protoplasm  of  the  cells  has  become  converted  into  a  mucin- 
bearing  substance,  only  a  small  portion  of  unchanged  i)rotoplasni, 
easily  staining  with  carmine,  remaining  round  the  nucleus.  In 
addition  to  these  *  muciparous  cells  '  are  seen  a  number  of  smaller 

'  Cf.  Maly,  I.iebi<j's  Annalen,  Bd.  173  (1874),  p.  227. 

^  hJwiccicki,  Pfliiger's  Aichiv,  XI II.  (1S76)  p.  444.    Pait;ch,  Archiv f.  micros. 
Af.at.,  Xiv.  (1S77)  179. 


286 


MUCOUS   AND   SEROUS   GLANDS.         TbOOK   II. 


half-mooii-shaped  (demilune)  cells,  the  protoplasm  of  which  stains 
deeply  with  carmine.  These  half-moon  cells,  which  lie  outside  the 
muciparous  cells,  between  them  and  the  basement  membrane,  are 
apparently  young  cells,  frequently  possess  two  or  more  nuclei, 
and  in  general  seem  to  be  in  a  state  of  active  growth  and 
multiplication. 

When  similar  sections  are  prepared  from  a  gland  which  has 
been  thrown  into  long-continued  activity  by  stimulation  of  the 
chorda*,  the  muciparous  portion  of  the  alveolar  cells,  that  portion 


V^-%1^ 


'  Mucous '  Gland,  A  in  ^  state  of  rest,  B  after  it  has  been  for 
(After  Lavdowsky.) 

a  demilune  cells,     c  leucocytes  lying  in  the  inter-alveolar  spaces.     The  darker  shading 
in  both  figures  is  intended  to  indicate  the  amount  of  staining. 


Fig.  44.     Section  of  a 
some  time  actively  secreting 


which  does  not  stain  rapidly,  is  found  to  have  diminished,  and  the 
protoplasmic  staining  portion  to  have  increased  in  quantity  in  pro- 
portion to  the  amount  of  stimulation  (Fig.  44  £).  In  some  cases 
no  muciparous  cells  can  anywhere  be  seen  ;  all  the  cells  are  smalV 
all  are  alike  composed  of  protoplasm,  and  all  stain  deeply.  It  has 
been  disputed  whether  a  muciparous  cell  simply  discharges  its 
mucin,  the  removal  of  the  mucin  being  followed  by  a  growth  of 
the  protoplasm  round  the  nucleus,  to  be  in  turn  followed  by  a  new 
development  of  mucin,  the  same  cell  thus  forming  and  discharging 
mucin  again  and  again  ;  or  whether  the  whole  cell  goes  to  pieces 
at  the  time  it  discharges  the  mucus,  its  place  being  taken  by  one 
of  the  half-moon  cells,  which  grows  up  rapidly  for  that  purpose. 
In  all  probability  both  events  occur,  at  least  after  prolonged  stimu- 
lation, the  simple  discharge  of  mucus  and  regeneration  of  the  cell 


Cf.  Lavdowsky,  Archiv  f.  micros.  Anat.,  XIll.  (1877)  p.  281. 


CHAP.   I.]  DIGESTION.  287 

being  analogous  to  what  takes  place  in  the  pancreas,  while  the 
substitution  of  the  young  half-moon  cell,  in  place  of  the  old 
disintegrated  muciparous  cell,  is  something  special  to  the  sub- 
maxillary gland. 

In  the  case  of  a  '  serous  '  gland  such  as  the  submaxillary  of  the 
rabbit,  no  very  marked  differences  in  microscopic  appearance  can 
be  rccogiused  even  after  long-continued  stimulation  of  the  chorda 
tympani,  and  a  similar  absence  of  structural  changes  seems  to 
be  characteristic  of  the  parotid  of  the  rabbit,  also  a  serous  gland, 
even  wlicn  a  most  copious  secretion  has  been  called  forth  by 
stimulation  of  the  auriculo-temporal.  When  however  the  cervical 
sympathetic  is  stimulated,  either  in  the  rabbit  or  the  dog,  very 
marked  changes  occur  in  the  parotid,  although  in  the  dog  no  saliva 
whatever  may  be  secreted  ;  and  these  changes  are  quite  similar  t<j 
those  witnessed  in  the  central  cells  of  the  gastric  glands.  During 
rest  the  cells  of  the  parotid  as  seen  in  sections  of  the  gland 
hardened  in  alcohol  (Fig.  45  A),  are  pale,  transparent,  with  sparse 
granules,  staining  with  difficulty,  and  the  nuclei  possess  irregular 


Fig.  45.     Section  or  a  '  Serous  '  Gland:  the  Parotid  of  the  Rabbit.    A  at  rest 
B  after  stimulaiion  of  the  cervical  sympathetic.    (After  Heidcnhain.) 

outlines  as  if  shrunken.  After  stimulation  of  the  sympathetic,  the 
protoplasm  of  the  cells  becomes  turbid,  and  ladtn  with  granules 
(Fig.  45  Jy),  and  stains  much  more  readily,  and  the  nuclei  losing 
their  irregular  outline  grow  round  and  larger,  wiUi  conspicuous 
nucleoli,  the  whole  cell  at  the  same  time,  at  least  after  prolonged 
stimulation,  becoming  distinctly  smaller,' 

Putting  all  the  above  facts  together  it  is  clear  that  in  the  case 
of  the  salivary  glands,  gastric  glands,  and  pancreas,  and  presumably 
in  the  case  of  all  secreting  glands,  the  secretion  is  the  result  of 
the  activity  of  the  protoplasm  of  the  secreting  cell.  Where  mucin 
is  an  important  element  of  the  secretion  the  microscopic  changes 
are  very  conspicuous.     During  rest  the  protojlasm   of   the  cell 

•  Heidcnhain,  Pflui^er's  Archiv,  xvii.  (1S7S)  p.  i. 


2«8  THEORY   OF   SECRETION.  [BOOK   II. 

becomes  converted  into  a  mucigenous  substance  ;  when  the  gland 
i'i  excited  to  activity  the  mucigenous  substance  gives  rise  to  mucin, 
which  is  ejected  from  the  cell.  The  cell  is  either  thus  broken  up 
entirely  or  reduced  in  dimensions ;  but  coincidently  a  rejuve- 
nescence of  the  protoplasm  either  of  the  remnant  of  the  cell  itself 
or  of  the  adjoining  demilune  takes  place,  and  the  old  cell  is  thus 
replaced  by  a  new  cell  of  smaller  size  but  composed  of  fresh 
deeply-staining  protoplasm,  which  at  first  is  native  undifferentiated 
protoplasm,  but  which  subsequently  generates  out  of  itself  fresh 
mucigenous  material.  Where  the  secretion  does  not  contain  mucus 
the  changes  are  less  gross  and  not  so  readily  recognisable,  but  we 
have  a  descending  series  from  the  mucous  salivary  gland,  through 
the  pancreas  and  gastric  gland  and  serous  gland  stimulated,  by  the 
sympathetic  to  the  serous  gland  stimulated  by  a  cerebro-spinal 
nerve,  in  each  of  which  more  or  less  distinctly  an  explosive  decom- 
position, leading  to  a  discharge  of  the  secreted  material,  is  accom- 
panied by  an  increased  growth  of  protoplasm  whereby  the  supply 
of  a  further  secretion  is  provided  for.  In  the  last  case,  the  serous 
gland  stimulated  by  means  of  a  cerebro-spinal  nerve,  the  destruc- 
tive and  constructive  metabolic  processes  appear  to  be  so  exactly 
adjusted  that  no  obvious  change  in  the  appearance  of  the  cells 
results.  It  must  be  left  for  future  inquiry  to  determine  the  nature 
of  the  various  granules,  which  make  their  appearance  in  the 
various  cases,  and  their  relation  to  the  ferments  or  other  con- 
stituents of  the  secretions. 

We  are  now  in  a  better  position  to  discuss  the  exact  nature  of  the 
changes  effected  in  the  sahvary  gland  by  stimulation  of  the  chorda 
tympani  (or  auriculo-temporal)  and  sympathetic  nerves  respectively. 

Czermak '  was  the  first  to  point  out  that  in  the  dog  the  effect  of 
chorda  stimulation  was  hindered  by  a  concomitant  stimulation  of  the 
sympathetic  ;  and  Kiihne^  observed  that  no  flow  at  all  took  place  when 
both  nerves  were  simultaneously  stimulated  with  minimum  currents, 
i.e.  with  currents  which  applied  to  either  nerve  separately  were  just 
sufficient  to  produce  an  obvious  flow ;  each  nerve  in  fact  seemed  to  be 
the  antagonist  of  the  other. 

But  Langleys  finds  that  in  the  cat  (in  which  animal,  contrary  to 
what  occurs  in  the  dog,  the  sympathetic  saliva  is  less  viscid  than  the 
chorda  saliva,  and  the  action  of  the  sympathetic  is  like  the  chorda 
paralysed  by  atropin),  minimal  stimuli  when  applied  simultaneously  to 
the  chorda  and  sympathetic  nerves  are  not  antagonistic  as  regards 
secretion  ;  on  the  contrary,  the  amount  of  secretion  following  simul- 
taneous stimulation  of  the  two  nerves  is  at  least  equal  to  the  sum  of 
the  amounts  of  separate  stimulation. 

Ludwig  and  Becker*  observed,  in  the  submaxillary  gland  of  the 

'   Wien.  Sitztmosberkhte.  xxv.  (1857)  p.  3.  -  Lehrb.  p.  5  (1866). 

3  Journal  Phy'siol.  I.  (1878)  p.  96.  4  Zt.  f.  rat.  Med.  i.  278. 


CHAl-   I.]  DIGKSTION.  289 

do^  that  after  continued  stimulation  of  the  chorda  {i.e.  a  long  series  ol 
stimulations  repeated  with  very  brief  intervals)  the  percentage  of  solids 
in  llie  saliva  very  considerably  diminished,  the  lessening  being  largely 
confined  to  the  organic  matter,  and  the  inorganic  salts  being  only 
slightly  affected.  Heidenhain '  confirmed  this  result,  and  extended  it  to 
the  sympathetic  as  well  ;  he  found  in  fact  that  after  prolonged  stimu- 
lation the  sympathetic  saliva  be  ame  watery.  He  also  observed  that 
prolonged  stimulation  of  the  chorda  or  sympathetic  diminished  the 
organic  matter  in  the  saliva  produced  by  a  stimulation  of  the  sympa- 
thetic or  chorda  immediately  following.  These  facts  shew  that  there 
is  in  the  salivary  cell  a  store  of  material  upon  which  both  chorda  and 
sympathetic  can  alike  draw,  material  which  may  give  rise  to  the  organic 
constituents  of  either  chorda  or  sympathetic  saliva,  according  as  the 
one  or  the  other  nerve  is  stimulated  ;  and  further  that  during  nerve- 
stimulation  the  supply  of  this  material  does  not  keep  pace  with  its 
consumption. 

These  results  Heidenhain^  has  confirmed  and  extended  by  addi- 
tional recent  observations.  Thus  he  finds  that  in  the  case  of  the  sub- 
maxillary and  parotid  of  the  dog,  the  rate  of  secretion  when  the 
cerebro-spinal  nerves  are  stimulated,  exhaustion  being  avoided,  in- 
creases up  to  a  maximum  with  increase  of  the  stimulation,  and  that  the 
percentage  of  saline  viatlcrs  in  the  saliva  increases  similarly  up  to  a 
certain  maximum,  whatever  may  have  been  the  condition  of  the  gland 
before  the  beginning  of  the  stimulation  ;  but  th:it  the  percentage  of 
ort^anic  matter,  though  aUo  a  function  of  the  strength  of  the  stimulus, 
is  dependent  on  the  condition  of  the  gland,  increasing  with  the  stimulus 
if  the  gland  had  been  pieviously  at  rest,  but  not  so  increasing  if  the 
gland  had  been  previously  thrown  into  a  state  of  prolonged  activity ; 
moreover,  so  long  as  the  gland  has  not  become  completely  exhausted, 
strong  stimulation  may  be  followed  by  a  period  of  aftef-action,  during 
which  the  percentage  of  organic  matter  is  once  more  increased.  In 
other  words,  the  organic  constituents  of  the  secretion  are  derived  from 
the  store  of  material  laid  up  in  the  cell,  which  store  is  comparatively 
soon  exhausted  and  requires  time  and  nutritive  labour  for  its  restora- 
tion. The  saline  constituents,  on  the  other  hand,  seem  to  be  ejected 
from  the  gland  dining  secretion  by  some  operation  of  a  more  simple 
and  of  presumably  a  more  physical  nature,  being  apparently  taken  up 
from  the  surrounding  lymph  and  merely  passed  through  the  cell,  so  that 
an  unlimited  quantity  may  be  got  rid  of  without  the  loss  being  felt  by 
the  gland  cell.  He  moreover  has  ascertained  that  in  the  parotid  of  the 
dog,  stimulation  of  the  sympathetic,  even  when  it  gives  rise  of  itself  to 
no  secretion,  has  a  remarkable  elTect  on  the  constitution  of  the  secre- 
tion produced  by  simultaneous  or  sequent  stimulation  of  the  cerebro- 
spinal secretory  fibres  :  the  percentage  of  organic  constituents  of  the 
saliva  secreted  under  the  influence  of  stimulation  of  the  cerebro-spinal 
nerve  is  very  largely  increased  by  a  previous  or  >imultaneous  stimula- 
tion of  the  cervical  sympathetic.  In  the  parotid  of  the  rabbit  (and 
sometimes  in  the  parotid  of  the  dog)  stimulation  of  the  sympathetic 
docs   produce   a   secretion  ;    and   since   the    saliva  thus   secreted  is 

'      •  Breslau  Studien,  IV.  (186S).  '  Pflii^er's  .-/rr^/V^    XVII.  (1S7S)  p.  i. 

F.  r.  19 


290  THEORY  OF   SECRETION.  [BOOK   11. 

markedly  richer  in  organic  matter  than  that  secreted  under  stimula- 
tion of  the  cerebro-spinal  nerve,  the  larger  amount  of  organic  matter 
which  is  observed  in  the  saliva  secreted  under  simultaneous  stimula- 
tion of  both  nerves  as  compared  with  the  amount  in  that  secreted  under 
stimulation  of  the  cerebro-spinal  nerve  alone,  might  be  explained  as 
the  result  of  mere  admixture  with  sympathetic  secretion.  No  such  ex- 
planation can  be  given  of  the  change  which  sympathetic  stimulation 
produces  in  the  character  of  the  cerebro-spinal  secretion,  when,  as  is 
generally  the  case  in  the  parotid  of  the  dog,  it  is  unable  by  itself  to  give 
rise  to  any  secretion.  And,  in  all  cases  the  microscopic  changes  in  the 
parotid  gland  induced  by  sympathetic  stimulation  are  very  pronounced, 
while  those  resulting  from  cerebro-spinal  stimulation  are  comparatively 
slight.  The  interpretation  which  Heidenhain  puts  on  his  results  is  that 
in  the  act  of  secretion  of  saliva  there  are  at  least  two  processes  :  one  by 
•which  the  stored-up  organic  material  of  the  cell  is  converted  into  the 
soluble  organic  constituents  of  the  secretion,  and  a  second  by  which  a 
stream  of  saline-holding  fluid  passes  from  the  lymph  spaces  around  the 
alveolus  through  the  cell  into  the  lumen  of  the  duct,  carrying  with  it  as 
it  goes  the  organic  material  furnished  by  the  first  process.  Both  these 
processes  he  suggests,  are  governed  by  distinct  fibres,  which  he  calls 
respectively  trophic  filsres,  viz.  those  bringing  about  the  metabolism  of 
the  cell-substance,  and  secretory  fibres,  i.e.  those  giving  rise  to  the  flow 
of  fluid  outwards  to  the  duct.  The  latter  may  be  regarded  as  dominant 
in  those  nerves,  such  as  the  chorda  tympani  of  the  dog,  stimulation  of 
which  produces  a  copious  but  watery  solution  ;■  the  former  in  those, 
such  as  the  cervical  sympathetic  of  the  same  animal,  stimula,tion  of 
which  produces  a  secretion  rich  in  organic  matter.  In  other  words, 
the  quantity  and  quality  of  the  secretion  produced  by  the  stimulation 
of  any  nerve,  sympathetic  or  cerebro-spinal,  will  depend  on  the  relative 
amount  of  trophic  and  secretory  fibres  present  in  the  nerve.  This  view 
of  Heidenhain's  is  very  acceptable  as  enabling  us  to  form  clearer 
notions  of  the  complex  act  of  secretion,  but  it  obviously  leaves  much 
yet  to  be  cleared  up.  The  metabolic  action  of  the  trophic  fibres  is 
fairly  comparable  to  the  explosive  decomposition  which  is  the  basis  of 
a  muscular  contraction,  but  the  hypothesis  of  a  purely  secretory  activity, 
of  the  starting  and  maintenance  of  a  rapid  flow  through  the  cell  inde- 
pendent of  physiological  changes  in  the  substance  of  the  protoplasm, 
and  yet  directly  dependent  on  the  action  of  nerves,  lands  us  in 
considerable  difficulties^ 

Relying  on  the  analogy  of  the  glands  just  studied,  we  may 
fairly'  assume  that  the  secretion  of  even  such  a  complex  fluid  as 
the  bile  is  in  the  main  the  result  of  the  direct  metabolic  activity  of 
the  protoplasm  of  the  hepatic  cells.  And  this  view  is  supported 
by  the  fact  that  after  extirpation  of  the  liver,  no  accumulation  of 
the  biliary  constituents  is  observed  to  take  place  during  the  few 
hours  of  life  remaining  to  the  animal  after  the  operation.  Still 
the  great    complexity  of   the   secretion   introduces   several   very 

'  Cf.  Hering,   VVien.  Sitzttngsberichte,  Bd.  66  (1872),  p.  83. 


CHAP.   I.]  DIGESTION.  29I 

important  considerations.  In  the  first  place,  tlie  liver,  unlike  the 
other  digestive  glands,  has  a  double  supply  of  blood  ;  and  vin 
attempts  have  been  made  to  settle  by  direct  experiment  the 
question  whether  the  hepatic  artery  or  the  vena  portre  is  the  more 
closely  concerned  in  the  production  of  bile.  Ligature  of  the 
he))atic  artery  has  sometimes  had  no  effect  on  the  secretion, 
sometimes  has  interfered  \vitii  it.  Sudden  ligature  of  the  vena 
portal  at  once  stops  the  flow  of  bile  ;  but  gradual  obliteration 
may  be  effected  without  either  causing  death  or  even  interfering 
with  the  secretion,  anastomotic  branches  forming  a  collateral 
circulation  and  thus  maintaining  an  efficient  flow  of  blood  through 
the  liver.  The  problem,  which  is  probably  a  barren  one,  cannot 
be  settled  in  this  way. 

In  the  second  place,  the  hepatic  cells  not  only  secrete  bile, 
but  as  we  shall  sec  later  on,  take  an  active  part  in  other  operations 
of  even  greater  importance.  The  consideration  of  the  question 
in  what  way  these  several  functions  of  the  hepatic  cells  are  related 
to  each  other  must  be  deferred  for  the  present. 

In  the  third  place,  even  if  we  maintain  that  the  chief  con- 
stituents of  the  bile  are  manufactured  in  the  hepatic  cells,  and 
not  simply  drained  off  from  the  blood,  we  are  not  thereby  pre- 
cluded from  admitting  that  the  hepatic  cells  may  avail  them- 
selves of  certain  half-made  materials,  the  arrival  of  which  in  the 
blood  may  so  to  speak  lighten  their  labours,  or  that  they  may 
even  boldly  seize  upon  and  pass  off  as  their  own  handiwork  any 
wholly  manufactured  constituents  which  may  offered  to  them. 
Thus  we  have  already  seen  reasons  for  thinking  that  the 
bile-pigments  are  not  made  de  novo  in  the  hepatic  cells,  but 
spring  from  haemoglobin,  the  change  in  the  liver  being  simple 
transformation.  So  also  it  is  quite  possible,  though  not  proved, 
that  much  if  not  all  of  the  cholestcrin  of  bile  is  merely  withdrawn 
by  the  liver  from  the  body  at  large.  And  even  with  the  central 
components  of  bile,  the  bile  salts,  we  know  that  in  the  case  of 
taurochloric  acid,  taurin  is  normally  present  in  certain  tissues,  and 
that  in  the  case  of  glycocholic  acid,  glycin,  if  not  a  normal  con- 
stituent of  any  tissue,  is  present  in  the  liver,  since  the  liver  can 
convert  benzoic  into  hippuric  acid,  as  we  shall  see  in  a  succeeding 
section  ;  so  that  the  formation  of  these  bodies  by  the  hepatic  cells 
may  be  limited  to  the  production  of  cholalic  acid  and  its  con- 
jugation with  one  or  other  of  the  above  amido-acids.  Moreover 
as  a  matter  of  fact,  we  find  that  the  flow  of  bile  from  a  biliary 
fistula  is  much  increased  by  the  injection  of  bile  into  the  small 
intestine'.  This  experiment  renders  it  possible  that  some  of  tho 
'  Schiff,  Pfliiyer's  Archtv,  iii.  (1870),  p.  39S. 

IQ — 2 


292  SECRETION    OF   BILE.  [BOOK   II. 

bile  Avhich  in  natural  digestion  is  poured  into  the  intestine 
is  re-absorbed,  and  carried  back  to  the  liver  to  do  duty  over 
again. 

Possibly  however,  the  efifect  may  be  explained  by  some  more  indirect 
action  of  the  bile  in  the  intestine. 

In  medical  practice,  distinction  is  drawn  between  jaundice  by 
suppression  of  the  secreting  functions  of  the  liver  and  jaundice  by 
retention,  brought  about  by  an  obstruction  existing  in  some  part  of  the 
biliary  passages.  The  gravity  of  the  symptoms  in  the  first  class  of 
cases  shews  that  an  arrest  or  a  too  great  diminution  of  the  normal 
functions  of  the  hepatic  cells  is  at  least  accompanied  by  the  presence 
in  the  blood  of  substances  injurious  to  life  ;  but  how  far  the  presence 
of  those  substances  is  due  to  a  failure  of  the  manufacture  of  bile 
and  the  accumulation  in  the  system  of  the  materials  for  the  formation 
of  bile,  or  to  a  failure  of  other  functions  of  the  hepatic  cells,  must  be 
regarded  as  at  present  undetermined.  The  presence  of  the  bile- 
pigment  in  this  form  of  jaundice  would  seem  to  indicate  that  the  for- 
mation of  the  pigment,  i.e.  the  transformation  of  haemoglobin  into 
bilirubin,  requires  but  little  labour  on  the  part  of  the  cell,  and  may 
be  carried  on  even  when  the  protoplasm  of  the  cell  is  highly 
deranged. 

Seeing  the  great  siolvent  power  of  both  gastric  and  pancreatic  juice, 
the  question  is  naturally  suggested.  Why  does  not  the  stomach  digest 
itself  ?  After  death  the  stomach  is  frequently  found  partially  digested, 
viz.  in  cases  when  death  has  taken  place  suddenly  on  a  full  stomach. 
In  an  ordinary  death,  the  membrane  ceases  to  secrete  before  the  circu- 
lation is  at  an  end.  That  there  is  no  special  virtue  in  living  things 
which  prevents  their  being  digested  is  shewn  by  the  fact,  that  the  legs 
of  a  frog  or  the  ear  of  a  rabbit  introduced  into  a  gastric  fistula  are 
readily  digested.  Pavy  ^  has  suggested  that  the  blood-current  keeps 
up  an  alkalinity  sufficient  to  neutralize  the  acidity  of  the  juice  ;  and 
he  shews  by  experiment  that  tracts  of  the  gastric  membrane,  from  which 
the  circulation  is  cut  off,  are  digested.  But  tracts  so  cut  off  soon  die, 
they  lose  not  only  the  alkalinity  of  the  blood  but  also  all  their  powers  ; 
and  the  alkalinity  of  the  blood  will  not  explain  why  the  mouths  of  the 
glands,  which  are  acid,  are  not  digested,  or  why  the  pancreatic  juice, 
which  is  active  in  an  alkaline  medium,  does  not  digest  the  proteids  of 
the  pancreas  itself,  or  why  the  gastric  membrane  of  the  bloodless  acti- 
nozoon  or  hydrozoon  does  not  digest  itself.  We  might  add,  it  does 
not  explain  why  the  amoeba,  while  dissolving  the  protoplasm  of  the 
swallowed  diatom,  does  not  dissolve  its  own  protoplasm.  We  cannot 
answer  this  question  at  all  at  present,  any  more  than  the  similar  one, 
why  the  dehcate  protoplasm  of  the  amoeba  resists  during  life  all 
osmosis,  while  a  few  moments  after  it  is  dead,  osmotic  effects  become 
abundantly  evident. 

^  Proc.  Roy.  Soc,  xii.  3S6,  559. 


CHAP.   l]  DIGESTION.  293 


Sec.  3.    The  Muscular  Mechanisms  of  Digestion. 

From  its  entrance  into  the  mouth  until  such  remnant  of  it  as 
is  undigested  leaves  the  body,  the  food  is  continually  subjected  to 
movements  having  for  their  object  the  trituration  of  the  food 
as  in  mastication,  or  its  more  complete  mixture  with  the 
digestive  juices,  or  its  forward  progress  through  the  alimentary 
canal.  These  various  movements  may  briefly  be  considered  in 
detail. 

Mastication.  Of  this  it  need  only  be  said  that  in  man  it 
consists  chiefly  of  an  up  and  down  movement  of  the  lower  jaw, 
combined,  in  the  grinding  action  of  the  molar  teeth,  with  a 
certain  amount  of  lateral  and  fore  and  aft  movement.  The 
lower  jaw  is  raised  by  means  of  the  temporal,  masseter,  and 
internal  pter}'goid  muscles.  The  slighter  eff"ort  of  depression 
brings  into  action  chiefly  the  digastric  muscle,  though  the  mylo- 
hyoid and  geniohyoid  probably  share  in  the  matter.  Contraction 
of  the  external  pterygoids  pulls  forward  the  condyles,  and  thrusts 
the  lower  teeth  in  front  of  the  upper.  Contraction  of  the  ptery- 
goids on  one  side  will  also  throw  the  teeth  on  to  the  opposite  side. 
The  lower  horizontally  placed  fibres  of  the  temporal  serve  to 
retract  the  jaw. 

During  mastication  the  food  is  moved  to  and  fro,  and  rolled 
about  by  the  movements  of  the  tongue.  These  are  effected 
by  the  muscles  of  that  organ  governed  by  the  hypoglossal 
nerve. 

The  act  of  mastication  is  a  voluntary  one,  guided,  as  are  so 
many  voluntary  acts,  not  only  by  muscular  sense  but  also  by 
contact  sensations.  The  motor  fibres  of  the  fifth  cranial  nerve 
convey  motor  impulses  from  the  brain  to  the  muscles ;  but 
paralysis  of  the  sensory  fibres  of  the  same  nerve  renders  masti- 
cation difficult  by  depriving  the  will  of  the  aid  of  the  usual 
sensations. 

Deglutition.  The  food  when  suflliciently  masticated  is,  by 
the  movements  of  the  tongue,  gathered  up  into  a  bolus  on  the 
middle  of  the  upper  surface  of  that  organ.  The  front  of  the 
tongue  being  raised — partly  by  its  intrinsic  muscles,  and  partly  by 
the  styloglossus — the  bolus  is  thrust  back  between  the  tongue  and 
the  palate  through  the  anterior  pillars  of  the  fauces  or  isthmus 
faucium.  Immediately  before  it  arrives  there,  the  soft  palate  is 
raised  by  the  levator  palati,  and  so  brought  to  touch  the  posterior 


294  DEGLUTITION.  [BOOK   11. 

wall  of  the  pharynx,  which,  by  the  contraction  of  the  upper 
margin  of  the  superior  constrictor  of  the  pharynx,  bulges  some- 
what forward.  The  elevation  of  the  soft  palate  causes  a  distinct 
rise  of  pressure  in  the  nasal  chambers  ;  this  can  be  shewn  by 
introducing  a  water  manometer  into  one  nostril,  and  closing  the 
other  just  previous  to  swallowing.  By  the  contraction  of  the 
palato-pharyngeal  museles  which  lie  in  the  posterior  pillars  of  the 
fauces,  the  curved  edges  of  those  pillars  are  made  straight,  and 
thus  tend  to  meet  in  the  middle  line,  the  small  gap  between  them 
being  filled  up  by  the  uvula.  Through  these  manoeuvres,  the 
entrance  into  the  posterior  nares  is  blocked,  while  the  soft  palate 
form.s  a  sloping  roof,  guiding  the  bolus  down  the  pharynx.  By 
the  contraction  of  the  stylo-pharyngeus  and  palato-pharyngeus, 
the  funnel-shaped  bag  of  the  pharynx  is  brought  up  to  meet  the 
descending  morsel,  very  much  as  a  glove  may  be  drawn  up  over 
the  finger. 

Meanwhile  in  the  larynx,  as  shewn  by  the  laryngoscope,  the 
arytenoid  cartilages  and  vocal  cords  are  approximated  :  the  latter 
being  also  raised  so  that  they  come  very  near  to  the  false  vocal 
cords  :  the  cushion  at  the  base  of  the  epiglottis  covers  the  rima 
glottidis,  while  the  epiglottis  itself  is  depressed  over  the  larynx. 
The  thyroid  cartilage  is  now,  by  the  action  of  the  laryngeal 
muscles,  suddenly  raised  up  behind  the  hyoid  bone,  and  thus 
assists  the  epiglottis  to  cover  the  glottis.  This  movement  of  the 
thyroid  can  easily  be  felt  on  the  outside.  Thus,  both  the  entrance 
into  the  posterior  nares  and  that  into  the  larynx  being  closed,  the 
impulse  given  to  the  bolus  by  the  tongue  can  have  no  other  effect 
than  to  propel  it  beneath  the  sloping  soft  palate,  over  the  incline 
formed  by  the  root  of  the  tongue  and  the  epiglottis,  into  the  grasp 
of  the  constrictor  muscles  of  the  pharynx :  the  palato-glossi  or 
consh'idores  isthmi faucimn,  which  lie  in  the  anterior  pillars  of  the 
fauces,  by  contracting,  close  the  door  behind  the  food  which  has 
passed  them.  The  morsel  being  now  within  the  reach  of  the 
constrictors  of  the  pharynx,  these  contract  in  sequence  from 
above  downwards,  and  thus  necessarily  thrust  the  food  into  the 
oesophagus. 

Deglutition  therefore,  though  a  continuous  act,  may  be  regarded 
as  divided  into  three  stages.  The  first  stage  is  the  tln-usting  of  the 
food  through  the  isthmus  fauchwi ;  this  being  a  voluntary  act,  may 
be  either  of  long  or  short  duration.  The  second  stage  is  the 
passage  through  the  upper  part  of  the  pharynx.  Here  the  food 
traverses  a  region  common  both  to  the  food  and  to  respiration,  and 
in  consequence  the  movement  is  as  rapid  as  possible.  The  third 
stage  is  the  descent  through  the  grasp  of  the  constrictors.     Here 


CHAI'.   l]  DIGESTION.  295 

the  food  has  passed  the  respiratory  orifice,  and  in  consequence  its 
passage  may  again  become  comparatively  slow. 

The  first  stage  in  this  compHcated  process  is  undoubtedly  a 
voluntary  action  ;  the  raising  of  the  soft  palate  and  the  approxima- 
tion of  the  posterior  pillars  must  also  be  in  a  measure  voluntary, 
since  they  were  seen,  in  a  case  where  the  pharynx  was  laid  bare  by 
an  operation,  to  take  place  before  the  food  had  touched  them'; 
but  they  may  take  place  without  any  exercise  of  the  will  or  pre- 
sence of  consciousness,  and  indeed  the  whole  part  of  the  act  of 
deglutition  which  follows  upon  the  passing  of  the  food  through  the 
anterior  pillars  of  the  fauces  must  be  regarded  as  a  reflex  act : 
though  some  of  the  earlier  comportent  movements  are,  as  it  were, 
on  the  borderland  between  the  voluntary  and  involuntary  king- 
doms. The  constricting  action  of  the  constrictors  on  the  other 
hand  is  purely  reflex  ;  the  will  has  no  power  whatever  over  it ;  it 
cannot  either  originate,  stop,  or  modify  it. 

Deglutition  as  a  whole  is  a  reflex  act,  and  cannot  take  place 
unless  some  stimulus  be  applied  to  tiie  mucous  membrane  of  the 
fauces.  When  we  voluntarily  bring  about  swallowing  movements 
with  the  mouth  empty,  we  supply  the  necessary  stimulus  by  forcing 
with  the  tongue  a  small  quantity  of  saliva  into  the  fauces,  or  by 
touching  the  fauces  with  the  tongue  itself. 

In  the  reflex  act  of  deglutition  the  afferent  impulses  originated 
in  the  fauces  are  carried  up  chiefly  by  the  glosso-pharyngeal,  but 
also  by  branches  of  the  fifth,  and  by  the  pharyngeal  branches  of 
the  superior  laryngeal  division  of  the  vagus.  The  efferent  impulses 
descend  the  hypoglossal  to  the  muscles  of  the  tongue,  and  pass 
down  the  glosso-pharyngeal,  the  vagus  through  the  pharyngeal 
plexus,  the  fifth  and  the  facial,  to  the  muscles  of  the  fauces  and 
pharynx  :  their  exact  parts  being  as  yet  not  fully  known,  and 
probably  varying  in  different  animals.  The  laryngeal  muscles  are 
governed  by  the  laryngeal  branches  of  the  vagus. 

The  centre  of  the  reflex  act  lies  in  the  medulla  oblongata. 
Deglutition  can  be  excited,  by  tickling  the  fauces,  in  an  animal 
rendered  unconscious  by  removal  of  the  brain,  provided  the 
medulla  be  left.  If  the  medulla  be  destroyed,  deglutition  is  im- 
possible. The  centre  for  deglutition  lies  higher  up  tlian  that  of 
respiration,  so  that  the  former  act  is  frequently  impaired  or  ren- 
dered impossible  while  the  latter  remains  untouched.  It  is 
probable  that,  as  is  the  case  in  so  many  other  reflex  acts,  the 
whole  movement  can  be  called  forth  by  stimuli  afTecting  the  centre 
directly,  and  not  acting  on  the  usual  afferent  nerves. 

As  each  successive  segment  of  the  pharyngeal  constrictprs 
'  Briicke,  Vorlesungen,  I.  p.  281. 


296  PERISTALTIC   ACTION.      ,  [BOOK   II. 

contracts  in  sequence  from  above  downwards,  the  bolus  is  carried 
down  into  the  upper  end  of  the  oesophagus.  Here  it  is  subjected 
to  the  influence  of  a  pecuHar  muscular  action  known  as  '  peri- 
staltic '.  Since  this  kind  of  muscular  action  is,  with  local  variations, 
characteristic  of  the  whole  aUmentary  canal  from  the  beginning  of 
the  oesophagus  to  the  end  of  the  rectum,  it  will  be  of  advantage  to 
disregard  the  strict  topographical  order  of  events,  and  to  consider, 
first  of  all,  the  movement  in  that  part  of  the  canal  where  it  is  com- 
paratively simple  in  nature,  and  has  been  best  studied :  viz.  in  the 
small  intestine ;  and  afterwards  to  deal  with  the  variations  occurring 
in  particular  places  and  under  special  circumstances. 

Peristaltic  action  of  the  small  intestine.  "We  have 
already  seen,  in  treating  of  unstriated  muscular  fibre  (p.  119),  that 
a  stimulus  applied  to  any  part  of  the  small  intestine  gives  rise  to  a 
circular  contraction,  or  contraction  of  the  circular  muscular  coat, 
which  travels  lengthways  as  a  wave  along  the  intestine,  and  also  to 
a  longitudinal  contraction,  or  contraction  of  the  longitudinal  coat, 
which  also  travels  lengthways  as  a  wave  along  the  intestine.  Since 
the  circular  coat  is  much  thicker  than  the  longitudinal  one,  the 
circular  wave  is  more  powerful  and  more  important  than  the  longi- 
tudinal one ;  the  circular  coat  has  by  far  the  greater  share  in 
propelling  the  food  along  the  intestine.  It  is  obvious  that  a  cir- 
cular contraction  travelling  down  the  intestine  (and  in  the  natural 
state  of  things  it  does  travel  downwards,  and  not  both  upwards 
and  downwards)  must  drive  the  contents  of  the  intestine  onwards 
towards  the  caecum.  And  practically  when  the  intestines  are 
watched  after  opening  the  abdomen,  the  contents  are  seen  to  be 
thus  thrust  onward  by  the  contraction  of  the  circular  coat.  The 
contractions  of  the  longitudinal  coat  appear  to  be  chiefly  of  use  in 
producing  peculiar  oscillating  movements  of  the  pendent  loops  in 
which  the  intestine  is  arranged.  The  rhythmic  occurrence  of 
these  circular  and  to-and-fro  movements,  cogether  with  the  passive 
movements  caused  by  the  entrance  of  the  fluid  contents  into  or 
their  exit  from  the  various  loops,  gives  rise  to  the  peculiar  writhing 
of  the  intestines  which  is  known  as  peristaltic  action. 

The  movements,  as  we  have  said,  take  place  from  above  down- 
wards, and  a  wave  beginning  at  the  pylorus  may  be  traced  a  long 
way  down.  But  contractions  may,  and  in  all  probability  occasion- 
ally do,  begin  at  various  points  along  the  length  of  the  intestine. 
In  the  living  body  the  intestines  have  periods  of  rest,  alternating 
with  periods  of  activity,  the  occurrence  of  tlie  periods  depending 
on  various  circumstances. 

With  regard  to  the  causation  of  the  peristaltic  movements  of 


CllAl'.    l.J  DIGESTION.  2<j7 

the  intestine,  this  much  may  be  affirmed.  They  may  occur,  as  in 
a  piece  of  intestine  cut  out  from  tlie  body,  wholly  independently 
of  the  central  nervous  system.  The  only  nervous  elements  which 
can  be  regarded  as  essential  to  their  development  are  the  ganglia 
of  Auerbach  or  those  of  Meissner  in  the  intestinal  walls. 

Though  peristaltic  movements  can  readily  be  excited  by  stimuli, 
applied  cillicr  to  the  outside,  or,  more  especially,  to  tiie  inside  of  the 
intestine,  they  are  probably  at  bottom  automatic.  The  presence  of 
food,  especially  of  food  in  motion,  may  at  times  act  as  a  stimulus,  and 
may  in  all  ca-^cs  bj  a  condition  affeclmg  the  nature  and  extent  of  the 
movement  ;  but  cannot  be  regarded  as  the  real  cause  of  the  action. 
When  any  body  is  intioduced  into  the  intcstme,  a  contraction  at  first 
occurs,  but  soon  passes  oft" as  the  intestine  becomes  accustomed  to  the 
presence  of  the  body.  There  is  no  reason  why  the  intestine  should  not 
become  equally  accustomed  to  the  presence  ot  food  ;  and,  as  a  matter 
of  fact,  peristaltic  movements  are  often  absent  when  the  intestines  are 
full.  The  presence  of  food  bears  about  the  same  relation  to  the 
movements  of  the  intestine,  that  the  presence  of  blood  bears  to  the 
beat  of  the  heart.  Both  are  favouring  but  not  indispensable  condi- 
tions :  in  both  cases  the  action  can  go  on  without  them.  We  may 
add  that  just  as  the  tension  of  a  muscle  increases  up  to  a  certain  extent 
the  amount  of  its  contraction,  and  a  full  heart  beats  more  strongly  than 
an  empty  one,  so  distension  of  the  intestine  largely  increases  peristaltic 
action.  Hence  in  cases  of  obstruction  of  the  bowels,  the  movements 
become  distressing  by  their  violence. 

Among  the  chief  circumstances  affecting  peristaltic  action  may 
be  mentioned  in  the  first  place  the  condition  of  the  blood.  A 
lack  of  oxygen  or  an  excess  of  carbonic  acid  in  the  blood  excites 
powerful  movements.  This  is  well  seen  in  asphyxia,  and  the 
post-mortem  peristaltic  movements  witnessed  on  opening  a 
recently-killed  animal,  arc  probably  due  to  the  deficiency  of 
oxygen  or  the  accumulation  of  carbonic  acid  in  the  blood  and 
tissues  of  the  intestinal  walls.  Conversely,  saturation  of  the  blood 
with  oxygen,  as  in  the  peculiar  condition  known  as  apnaa  (see 
chapter  on  Respiration),  tends  to  check  peristaltic  movements. 

Judging  from  the  analogy  of  the  respiratory  and  other  nervous 
centres,  the  effects  should  be  attributed  to  variations  in  the  cjuantity  of 
oxygen  rather  than  of  carbonic  acid  ;  this  however  does  not  at  present 
seem  clearly  proved. 

In  the  second  place,  peristaltic  action  is  largely  influenced  by 
nervous  influences  passing  along  the  splanchnic  and  vagus  nerves. 
The  movements  will  go  on  after  section  of  both  these  nerves  ;  but 
as  a  general  rule,  while  stimulation  of  the  splanchnic  tends  to 
check ',  that  of  the  vagus  tends  to  excite  them.  It  is  probably 
through  the  vagus  that   peristaltic    movements   can  be    eliected 

"   Pfluger,  Die  Ihiinnungsna-ven  da  Darnis,  1857. 


29B  PERISTALTIC   ACTION.  [BOOK   II. 

in  a  reflex  manner,  as  in  that  increase  of  the  movements  of  the 
intestine  in  consequence  of  emotions,  which  has  given  rise  to  the 
phrase  '  ray  bowels  yearned.' 

It.  is  generally  stated  that  sudden  stoppage  of  the  blood-current 
excites  peristaltic  action,  the  explanation  given  being  that,  as  after 
general  death,  there  is  an  accumulation  of  carbonic  acid  and  a  lack  of 
oxygen  in  the  intestinal  tissues.  Van  Braam  Houckgeest',  however, 
states,  on  the  contrary,  that  it  bi-ings  the  intestine  to  rest  ;  and  Nasse  ^ 
found  that  the  injection  of  arterial  blood,  at  a  high  pressure,  caused 
very  powerful  movements.  On  the  other  hand,  exposure  to  air  has 
been  considered  as  an  exciting  cause  of  the  movements  ;  and  un- 
doubtedly a  very  large  amount  of  movement  rnay  frequently  be  ob- 
served, on  laying  open  the  abdomen,  even  in  animals  whose  circulation 
is  active.  Since  however  the  movements  continue  when  the  body  is 
immersed  in  weak  sodium  chloride  solution  and  the  intestine  thereby 
excluded  from  direct  contact  with  air,  they  cannot  be  attributed  to 
mere  exposure.  If  the  splanchnic  nerve  be  stimulated  while  active 
movement  is  going  on,  the  intestine  is  undoubtedly  brought  to  rest. 
Since  at  the  same  time  the  blood-vessels  of  the  intestine  are  by  the 
vaso-constrictor  action  of  the  splanchnic  constricted,  the  quiescence 
of  the  intestine  may  be  indirectly  due  to  insufficient  blood-supply 3. 
Houckgeest  however  denies  this,  on  the  ground  that  when  by  exposure 
to  the  air  the  blood-vessels  of  the  intestine  are  so  far  paralysed  as  to 
be  no  longer  constricted  by  the  action  of  the  splanchnic,  quiescence  of 
the  intestine  is  still  observed  on  irritating  that  nerve.  The  splanchnic 
thus  appears  to  be  a  direct  inhibitory  nerve  as  regards  peristaltic 
action,  while  the  vagus  is  undoubtedly  an  adjuvant  or  accelerator 
nerve.  It  is  stated  that  after  section  of  the  splanchnics  peristaltic 
movements  are  more  active  and  more  readily  brought  about  by  stimu- 
lation of  the  vagus  than  when  the  splanchnics  are  entire.  According 
to  Ludwig  't,  however,  stimulation  of  the  splanchnic,  while  it  stops  an 
already-developed  peristaltic  action,  will  bring  on  the  movement  when 
brought  to  bear  on  an  intestine  previously  at  rest. 

When  the  vagus  is  stimulated,  peristaltic  contraction  is  seen  to 
begin  at  the  pylorus  of  the  stomach  and  so  to  descend  along  the  intes- 
tine. It  has  been  stated  that  no  so-called  antiperistaltic  action,  that 
is,  a  wave  of  contraction  passing  upwards  instead  of  downwards  along 
the  intestine,  ever  occurs  naturally  in  the  intestine,  the  backward  flow 
undoubtedly  seen  when  an  obstruction  exists  being  explained  as  being 
simply  due  to  a  central  return  current.  When  however  the  duodenum 
is  mechanically  stimulated  both  a  peristaltic  and  an  antiperistaltic 
wave  may  be  observed,  the  former  passing  downward  and  ceasing  at 
the  ileo-cascal  valve  if  not  before,  the  latter  passing  up  and  ceasing 
at  the  pylorus.  And  when  in  the  exposed  intestines  a  wave,  as 
occasionally   happens,  begins  spontaneously  in  the  duodenum,  it  may 

•  Pfliiger's  Archiv,  VI.  (1872)  p.  266. 

^  Beitr.  z.  Physiol,  d.  Darmbcwegmtgen,  1866, 
3  Basch,   Wien.  Sitzungsberickt,  LXVIII.  (1873). 

♦  Lehrb.,  Bd.  11.  p.  616. 


CilAP.    I.]  DIGESTION.  299 

sometimes  be  seen  to  pass  both  upwards  ani  downwards.  It  is  worthy 
of  notice  that  stimulation  of  the  small  intestine  is  said  not  to  cause 
movement  either  in  the  stomach  or  large  intestine,  and  stimulation 
of  the  large  causes  no  movement  of  the  small  intestine,  the  ileo-caecal 
valve  and  the  pylorus  barring  the  progress  of  the  waves'. 

Certain  dni;4s,  such  as  nijotin,  in'lu:e  strong  peristaltic  action  ;  the 
modus  operan  ii  of  these  and  of  the  more  specific  purgative  drugs  is  at 
present  uncertain. 

Having  thus  studied  the  general  characters  of  peristaltic  action 
in  its  most  marked  form,  we  may  briefly  consider  the  same  move- 
ment in  other  parts  of  the  alimentary  canal. 

Movements  of  the  CEsophagus.  The  descent  of  the 
food  along  the  oesophagus  is  eft'ected  by  a  peristaltic  contraction 
of  the  circular  and  longitudinal  coats,  resembling  in  its  general 
characters  that  of  the  intestine.  It  differs  however  in  being  more 
closely  dependent  on  the  central  nervous  system,  and  may  in  fact 
be  considered  as  being  in  large  measure  a  reflex  act,  with  the 
centre  in  the  medulla  oblongata,  both  afferent  and  efferent  impulses 
being  supplied  by  the  vagus.  It  may  be  readily  excited  by 
stimulating  the  central  end  of  the  superior  laryngeal  nerve ;  and 
this  nerve,  since  it  is  connected  by  its  pharyngeal  branch  both 
with  the  mucous  membrane  of  the  pharynx  and  with  the  lower 
pharyngeal  constrictor,  may  serve  to  inaugurate  the  oesophageal 
movement,  by  carrying  afferent  impulses  started  by  the  presence 
of  food  in  the  pharynx  or  by  the  muscular  act  of  swallowing. 
Section  of  the  trunk  of  the  vagus,  renders  difficult  the  passage  of 
food  along  the  oesophagus,  and  stimulation  of  the  peripheral 
stump  causes  oesophageal  contractions.  Hence  the  motor  tracts 
of  the  reflex  act  are  to  be  sought  for  in  the  vagus  also.  The 
force  of  this  movement  is  considerable  ;  thus  Mosso^  found  that 
in  the  dog  a  ball  pulling  by  means  of  a  pulley  against  a  weight  of » 
250  grammes  was  readily  carried  down  from  the  pharynx  to  the 
stomach. 

Mosso  3  states  that  section  and  even  removal  of  portions  of  the 
cesophagus  do  not  prevent  tiie  progression  of  a  peristaltic  wave  from 
the  pharynx  to  the  stomach,  provided  the  reflex  machinery  of  the 
medulla  be  intact.  He  argues  in  consequence  that  the  natural  move- 
ment in  swallowing  is  entirely  carried  on  by  the  medulla  as  a  reflex 
act.  Nevertheless  an  cesophagus  according  to  his  own  account  will 
when  removed  from  the  body,  and  therefore  entirely  separated  from 
any  extrinsic  nervous  mechanism,  exhibit  good  peristaltic  movements. 
The   extrinsic  central  mechanism   therefore  would  seem   only  to  be 

'  •Engelmann,  Pfliiger's  Archiv,  iv.  (1S71),  p.  33. 

»  Moleschott's  Untersuch.  xi.  (1874)  p.  327.  3  l^c.  cU. 


300  MOVEMENTS   OF   THE   STOMACH.         [BOOK   II. 

useful   in   perfecting    a  movement  which   in  its   absence  would   be 
imperfect  and  inefficient. 

Goltz^  has  shewn  that  if,  in  a  urarized  frog,  fluid  be  poured  down 
the  throat,  both  stomach  and  oesophagus  will,  after  the  first  peristaltic 
movements  carrying  down  the  first  portions  of  fluid  have  passed  away, 
remain  perfectly  quiescent  in  an  enormously  distended  condition  (the 
contraction  of  the  pylorus  preventing  the  descent  of  the  fluid  into  the 
duodenum),  so  long  as  the  medulla  oblongata  and  vagi  are  intact. 
Destruction  of  the  medulla  or  section  of  the  vagi  gives  rise  to  the 
development  of  abundant  downward  and  upward  peristaltic  waves  of 
contraction,  by  which  the  stomach  becomes  wrinkled  and  the  top  of 
the  cesophagus  closed  ;  and  these  movements  last  as  long  as  the  irri- 
tability of  the  organs  continues.  During  the  quiescence  observed  with 
intact  vagi  and  medulla,  temporary  peristaltic  action  may  be  induced 
by  direct  irritation  of  the  vagus,  or  in  a  reflex  manner  through  the 
medulla,  by  stimulation  of  the  skin  or  intestine.  Chauveau^  and  Schiff^ 
also  saw  occasional  movements  in  the  oesophagus  after  section  of  the 
vagus.  Goltz  interprets  his  result  by  supposing  that  the  movements 
are  primarily  caused  by  local  motor  centres  in  the  cesophagus  and 
stomach,  habitually  inhibited  by  the  action  of  a  centre  in  the  medulla. 
Hence  when  this  inhibition  is  removed  by  destruction  of  the  medulla 
or  section  of  the  vagi,  the  energy  of  the  local  centres  is  free  to  act. 
Stimulation  of  the  skin  or  other  distant  spots  produces  movements  by 
depressing  the  medullary  inhibitory  centre.  Stimulation  of  the  vagus 
probably  produces  movements  by  directly  augmenting  the  local 
centres. 

The  junction  of  the  oesophagus  with  the  stomach  remains  in  a 
more  or  less  permanent  condition  of  tonic  or  obscurely  rhythmic 
contraction,  more  particularly  when  the  stomach  is  full  of  food, 
and  thus  serves  as  a  sphincter  to  prevent  the  return  of  food  from 
the  stomach  into  the  oesophagus.  During  the  passage  of  the  food 
from  the  oesophagus  into  the  stomach  this  sphincter  becomes 
relaxed,  probably  by  a  mechanism  which  will  be  described  in 
treating  of  vomiting. 

Movements  of  the  Stomach.  These  are  at  bottom 
peristaltic  in  nature,  though  largely  modified  by  the  peculiar 
arrangement  of  the  gastric  muscular  fibres.  When  food  first 
enters  the  stomach,  the  movements  are  feeble  and  slight,  but  as 
digestion  goes  on  they  become  more  and  more  vigorous,  giving 
rise  to  a  sort  of  churning  within  the  stomach,  the  food  travelling 
from  the  cardiac  orifice  along  the  greater  curvature  to  the  pylorus, 
and  returning  by  the  lesser  curvature,  while  at  the  same  time 
subsidiary  currents  tend  to  carry  the  food  which  has  been  passing 

'  Pfliiger's  Archiv,  VI.  (1872)  p.  616. 

^  yournal  de  Pkysiologie,  V.  (1863)  p.  337. 

3  Lemons  sur  la  Pkysiologie  de  Digestion,  p.  377. 


CHAI'.    l]  DIGESTION.  3OI 

close  to  the  mucous  membrane  towards  the  middle  of  the  stomach, 
and  vice  versa.  At  the  pyloric  end  strong  circular  contractions  are 
set  up,  by  which  portions  of  footl,  more  especially  the  dissolved 
jjarts,  but  also'  small  solid  pieces,  are  carrieti  through  trie  relaxed 
sphincter  into  the  duodenum.  As  digestion  proceeds,  more  and 
more  material  leaves  the  stomach,  which  is  thus  gradually  eniptied, 
the  last  portions  which  are  carried  through  being  those  matters 
which  are  least  digestible,  and  foreign  bodies  which  happen  to 
have  been  swallowed.  The  presence  of  food  then  leads  to  the 
development  of  obscurely  peristaltic  rhythmic  movements,  the 
stomach  when  empty  being  contracted,  but  (juiesccnt ;  but  evidently 
it  is  not  the  mere  mechanical  repletion  of  the  organ  which  is  the 
cause  of  the  movements,  since  the  stomach  is  fullest  at  the 
beginning  when  the  movements  are  slight,  and  becomes  empty  as 
they  grow  more  forcible.  The  one  thing  which  does  increase 
/(//'/  passu  with  the  movements  is  the  acidity,  which  is  at  a 
minimum  when  the  (generally  alkaline)  food  has  been  swallowed, 
and  increases  steadily  onwards.  It  has  not  however  been  definitely 
shewn  that  the  increasing  acidity  is  the  efficient  stimulus,  giving 
rise  to  the  movements. 

The  iicrvous  mechanism  of  the  gastric  movements  is  very  perplex- 
ing. Judgin'^  from  the  analogy  of  the  intestine,  one  would  imagine 
that  tlicy  originated  in  tlie  stomach  itself,  being  modified  but  not 
dirAtly  caused  by  the  action  of  the  central  nervous  system.  Sponta- 
neous movements,  however,  of  a  stomach,  whose  nervous  connections 
have  been  severed,  even  of  a  full  one,  are  at  least  much  more  rare  than 
those  se-^n  in  the  intestine  or  even  in  the  oesophagus  ;  and  such  move- 
ments as  are  occasioned  by  local  mechanical  or  other  stimulation  are 
limited  in  extent,  and  rarely  put  on  all  the  characters  of  the  natural 
complex  contractions.  Since  there  are  abundant  ganglia  in  the  walls 
of 'the  stomach,  it  may  fairly  be  doubted  whether  the  automatic  move- 
ments of  the  excised  intestine  arc  due  to  the  action  of  ganglia, 
otherwise  why  should  not  the  ganglia  in  the  stomach  set  up  spontaneous 
movements  in  that  organ  also  .''  For  if  ganglia  are  far  excellence  the 
organs  of  automatic  actions  we  should  expect  spontaneous  movements 
to  accompany  their  presence. 

The  stomach  receives  its  nervous  supply  from  the  vagi  and  also 
from  the  solar  plexus,  with  which  the  splanchnics  are  connected. 
When  the  vagi  are  divided,  a  spasmodic  constriction  of  the  cardiac 
oritice  takes  place,  the  tonic  action  of  the  sphincter  is  in  reascd,  no 
dilation  takes  place,  and  food  is  thus  prevented,  for  a  time  at  least, 
from  leaving  the  oesophagus  This  result  is  in  harmony  with  the 
observations  of  Goltz  on  the  frog.  In  addition  the  natural  movements 
of  the  stomach  itself  cease,  though  the  introduction  of  food  after 
section  of  the  vagi  is  said  to  cause  some  amount  of  contraction.     They 

•  Kuhne,  Lehrb.,  p.  53. 


302  DEFECATION.  [BOOK   II. 

may  be  induced  by  stimulation  of  the  peripheral  stumps  of  the  vagi, 
when  the  stomach  is  full,  but  not  if  it  be  empty.  Neither  section  nor 
stimulation  of  the  splanchnics  or  of  the  branches  from  the  solar  plexus 
produce,  it  is  said,  any  effect  on  the  stomach  as  far  as  its  movements 
are  concerned.  Evidently  the  movements  of  the  stomach,  far  more 
than  those  of  the  intestine,  are  dependent  on  and  governed  by  the 
central  nervous  system,  but  the  exact  manner  in  whi:h  they  are 
governed,  and  the  proper  share  to  be  allotted  to  exciting  and  inhibitory 
mechanisms,  remain  yet  to  be  discovered.  The  sort  of  tonic  contrac- 
tion, into  which  the  walls  of  the  stomach  fall  when  its  cavity  is  empty, 
does  not  occur  in  the  intestine  ;  and  this  feature  probably  modifies  all 
the  nervous  working  of  the  organ.  Nor  do  we  know  the  exact 
mechanism  by  which  the  pyloric  sphincter  is  used  to  strain  off 
gradually  the  more  digested  portions  of  the  food.  The  movements  of 
even  a  full  stomach  are  said  by  Busch'  to  cease  during  sleep. 

Movements  of  the  large  Intestine.  These  are  funda- 
mentally the  same  as  those  of  the  small  intestine,  but  distinct  in 
so  far  as  the  latter  cease  at  the  ileo-ca^cal  valve,  at  which  spot  the 
former  normally  begin. 

They  are  said,  however,  not  to  be  inhibited  by  stimulation  of  the 
splanchnics.^ 

The  faeces  in  their  passage  through  the  colon  are  lodged  in  the 
sacculi  during  the  pauses  between  the  peristaltic  waves.  Arrived 
at  the  sigmoid  flexure,  they  are  supported  by  the  bladder  and»the 
sacrum,  so  that  they  do  not  press  on  the  sphincter  ani. 

Defaecation.  This  is  a  mixed  act,  being  superficially  the 
result  of  an  effort  of  the  will,  and  yet  carried  out  by  means  of  an 
involuntary  mechanism.  Part  of  the  voluntary  effort  .consists  in 
producing  a  pressure-effect,  by  means  of  the  abdominal  muscles. 
These  are  contracted  forcibly  as  in  expiration,  but  the  glottis  being 
closed,  and  the  escape  of  air  from  the  lungs  prevented,  the  whole 
force  of  the  pressure  is  brought  to  bear  on  the  abdomen  itself, 
and  so  drives  the  contents  of  the  descending  colon  onward  into 
the  rectum.  The  sigmoid  flexure  is  by  its  position  sheltered  from 
this  pressure ;  a  body  introduced  per  anum  into  the  empty  rectum 
is  not  affected  by  even  forcible  contractions  of  the  abdominal  walls. 

The  anus  is  guarded  by  the  sphincter  ani,  which  is  habitually 
in  a  state  of  normal  tonic  contraction,  capable  of  being  increased 
or  diminished  by  a  stimulus  applied,  either  internally  or  externally, 
to  the  anus.  The  tonic  contraction  is  in  part  at  least  due  to  the 
action  of  a  nervous  centre  situated  in  the  lumbar  spinal  cord3.     If 

'  Virch.  Archiv,  xiv.  p.  i66.  ^  Pfliiger,  op.  cit.  ;  Nasse,  oj>.  cit, 

3  Masius,  Bull,  de  I' Acad.  R.  de  Belgique,  XXIV.  (1867),  p.  312. 


CHAP.   I.]  DIGESTION.  303 

the  nervous  connexion  of  the  spliincier  with  the  spinal  cord  be 
broken,  rehxxation  lakes  place.  W  the  spinal  cord  be  divided  in 
the  dorsal  region,  the  sphincter,  after  the  depressing  effect  of  the 
operation,  which  may  last  several  days,  has  passed  off,  still 
maintains  its  tonicity,  shewing  that  the  centre  is  not  placed  higher 
up  than  tiie  lumbar  region  of  the  cord.  The  increased  or  dimin- 
isheil  contraction  following  on  local  stimulation  is  probably  due  to 
a  reflex  augmentation  or  inhibition  of  the  action  of  this  centre. 
The  centre  is  also  subject  to  influences  proceeding  from  higher 
regions  of  the  cord,  and  from  tlie  brain.  By  the  action  of  the  will, 
by  emotions,  or  by  other  nervous  events,  the  lumbar  sphincter  centre 
may  be  inhibited,  and  thus  the  spliincter  itself  relaxed ;  or  aug- 
mented, and  thus  the  sphincter  tightened.  A  second  item  therefore 
of  the  voluntary  process  in  defalcation  is  the,  inhibition  of  the 
lumbar  sphincter  centre,  and  consequent  relaxation  of  the  sphincter 
muscle. 

According  to  Goltz",  in  the  dog  after  division  of  the  dorsal  cord, 
and  consequent  separation  of  the  sphincter  centre  from  the  cerebrum, 
local  stimulation,  such  as  the  introduction  of  the  finger,  causes  not  a 
steady  increase  or  decrease  of  the  action  of  the  sphincter,  but  a 
rhythmic  alternation  of  tightening  and  relaxing.  The  absence  of  this 
rhythm  with  an  intact  cord  indicates  some  obscure  action  of  the 
cerebral  centres  on  the  lumbar  centre.  The  conversion  of  the  tonic 
into  the  rhythmic  action  also  illustrates  the  close  relationship  between 
these  two  kinds  of  movements. 

Though  the  tonic  contraction  of  the  sphincter  seems  so  largely 
dependent  on  the  lumbar  centre,  still  this  dependence  is  probably  not 
an  absolute  one.  In  the  case  of  a  man  in  whom  as  the  result  of  injury 
the  sacral  nerves  were  entirely  paralysed,  and  the  sphincter  accordingly 
had  no  nervous  connection  with  the  lumbar  centre  (unless  there  were  a 
roundabout  connection  by  means  of  the  sympathetic),  Gower^' observed 
the  maintenance  of  a  certain  amount  of  tonic  contraction  which  could 
be  inhibited,  and  relaxation  induced,  by  stimulation  of  the  mucous 
membrane  of  the  rectum  and  anus.  As  in  the  case  of  the  arteries, 
we  have  apparently  to  deal  here  with  a  tonic  ontraction  which  is 
habitually  dependent  on  a  spinal  centre,  but  which  may  nevertheless 
exist  without  the  action  of  that  centre. 

Since  the  lumbar  centre  is  wholly  efficient  when  separated  from  the 
brain,  the  paralysis  of  the  sphincter  which  occurs  in  certain  cerebral 
diseases  is  probably  due  to  inhibition  of  this  centre,  and  not  to 
paralysis  of  any  cerebral  centre. 

Thus  a  voluntary  contraction  of  the  abdominal  walls,  accom- 
panied by  a  relaxation  of  the  sphincter,  might  press  the  contents 

'  Pfliiger's  Archiv,  Vlll.  (1874),  460. 
»  Proc.  Roy.  Soc.  XXVI.  (1S77),  p.  77. 


304  VOMITING.  [book   II. 

of  the  descending  colon  into  the  rectum  and  out  at  the  anus. 
Since  however,  as  we  have  seen,  the  pressure  of  the  abdominal 
walls  is  warded  off  the  sigmoid  flexure,  such  a  mode  of  defecation 
would  always  end  in  leaving  the  sigmoid  flexure  full.  Hence  the 
necessity  for  these  more  or  less  voluntary  acts  being  accompanied 
by  an  entirely  involuntary  augmentation  of  the  peristaltic  action  of 
the  large  intestine  and  sigmoid  flexure.  Or  rather,  to  describe 
matters  in  their  proper  order,  defecation  takes  place  in  the  follow- 
ing manner.  The  sigmoid  flexure  and  large  intestine  becoming 
more  and  more  full,  stronger  and  stronger  peristaltic  action  is 
excited  in  their  walls.  By  this  means  the  fseces  are  driven  against 
the  sphincter.  Through  a  voluntary  act,  or  sometimes  at  least  by 
a  simple  reflex  action,  the  lumbar  sphincter  centre  is  inhibited  and 
the  sphincter  relaxed.  At  the  same  time  the  contraction  of  the 
abdominal  muscles  presses  firmly  on  the  descending  colon,  and 
thus  the  contents  of  the  rectum  are  ejected. 

It  must  however  be  remembered  that,  while  in  appealing  to 
our  own  consciousness,  the  contraction  of  the  abdominal  walls  and 
the  relaxation  of  tTie  sphincter  seem  purely  voluntary  efforts,  the 
whole  act  of  defsecation,  including  both  of  these  seemingly  so 
voluntary  components,  may  take  place  in  the  absence  of  conscious- 
ness, and  indeed,  in  the  case  of  Goltz's  dog^,  after  the  complete 
severance  of  tlie  lumbar  from  the  dorsal  cord.  In  such  cases  the 
whole  act  must  be  purely  reflex,  excited  by  the  presence  of  fseces 
in  the  rectum. 

Vomiting.  In  a  conscious  individual  this  act  is  preceded 
by  feelings  of  nausea,  during  which  a  copious  flow  of  saliva  into 
the  mouth  takes  place.  This  being  swallowed  carries  down  with 
it  a  certain  quantity  of  air,  the  presence  of  which  in  the  stomach, 
by  assisting  in  the  opening  of  the  cardiac  sphincter,  subsequently 
facilitates  the  discharge  of  the  gastric  contents.  The  nausea 
is  generally  succeeded  at  first  by  ineffectual  retching  in  which 
a  deep  inspiratory  effort  is  made,  so  that  the  diaphragm  is  thrust 
down  as  low  as  possible  against  the  stomach,  the  lower  ribs 
being  at  the  same  time  forcibly  drawn  ia;  since  during  this  in- 
spirator)' eftbrt  the  glottis  is  kept  closed,  no  air  can  enter  into  the 
lungs  ;  but  some  is  drawn  into  the  pharynx,  and  thence  probably 
descends  by  a  swallowing  action  into  the  stomach.  In  actual 
vomiting  this  inspiratory  effort  is  succeeded  by  a  sudden  violent 
expiratory  contraction  of  the  abdominal  walls,  the  glottis  still 
being  closed,  so  that  the  whole  force  of  .the  effort  is  spent,  as  in 
defaecation,  in  pressure  on  the  abdominal  contents.     The  stomach 

'   Op.  cit. 


CHAP.   I.]  DIGESTION.  305 

is  therefore  forril)ly  compressed  from  without.     At  the  same  time, 
or  ratlicr  immediately  belore  the  exi)iratory  effort,  by  a  contraction 
of   its  longitudinal   fihres   the  ce-iophagus   is  shortened  and   the 
cardiac  orifice  of  the  stomach  brought  close  under  the  diaphragm, 
while  apparently  by  a  contraction  of  the  fibres  which  radiate  from 
the  end  of  the  ccsophagus  over  the  stomach,  the  cardiac  orifice, 
which  is  normally  closed,    is  somewhat  suddenly  dilated.     This 
dilation  opens  a  way  for  the  contents  of  the  stomach,   which, 
])rcssed  upon  by  the  contraction  of  the  abdomen,  and  to  a  certain 
l)ut  probably  only  to  a  slight   extent  by  the  contraction    of  the 
gastric    walls,    are    driven    forcibly    up     the    oesophagus,    their 
passage  along  that  channel  being  possibly  assisted   by  the  con- 
traction  of  the   longitudinal   muscles.     The  mouth  being  widely 
open,  and  the  neck  stretched  to  afford  as   straight   a  course   as 
possible,  the  vomit  is  ejected  from  the  body.     At  this  moment 
there  is  an  additional    expiratory  effort  which  serves  to  ])revent 
the  vomit  passing  into  the  larynx.    In  most  cases  too  the  posterior 
pillars  of  the  fauces  are  approximated,  in  order  to  close  the  nasal 
passage  against  the   ascending  stream.     This  however  in  severe 
vomiting  is  frequently  ineffectual. 

Thus  in  vomiting  there  are  two  distinct  acts ;  the  dilation  of 
the  cardiac  orifice  and  the  extrinsic  pressure  of  the  abdominal 
walls  in  an  expiratory  effort.  Without  the  former  the  latter,  even 
when  distressingly  vigorous,  is  ineffectual.  Without  the  latter,  as 
in  urari  poisoning,  the  intrinsic  movements  of  the  stomach  itself 
are  rarely  sufficient  to  do  more  than  eject  gas,  and  it  may  be,  a 
very  small  quantity  of  food  or  fluid.  Pyrosis  or  waterbrash  is 
probably  brought  about  by  this  intrinsic  action  of  the  stomach. 

During  vomiting  the  pylorus  is  generally  closed,  so  that  but 
little  material  escapes  into  tlie  duodenum.  When  the  gall- 
bladder is  full,  a  copious  flow  of  bile  into  the  duodenum 
accompanies  the  act  of  vomiting.  Part  of  this  may  find  its 
way  into  the  stomach,  as  in  bilious  vomiting,  the  pylorus  then 
being  evidently  open. 

The  experiment  of  Majendie,  shewing  that  vomiting  can  take  place 
when  a  simple  bladder  is  substituted  for  the  stomach,  is  said  to  fail 
unless  the  oesophageal  sphincter  be  removed  or  the  dilating  mechanism 
be  left  intact.  Schiff ,  by  introducing  his  finger  through  a  gastric 
fistula,  was  able  to  ascertain  by  direct  touch,  both  the  normal  occlu- 
sion ot  the  cardiac  orifice,  broken  only  during  the  descent  of  food,  and 
its  sudden  dilation  just  preceding  the  expiratory  pressure  during 
vomiiing.  lie  found  that  v  hen  the  muscular  fibres  radiating  from  the 
oesophagus  over  the  stomach  were  injured,  as  by  crushing  them  with  a 

'  Molcschott's  Untfisuch,  X.  (1S70),  p.  353. 
F.  P.  '  20 


306  VOMITING.  [book   II. 

ligature  forcibly  applied  for  a  few  seconds,  the  constiiction  of  the 
cardiac  orifice  remained  permanent  ;  dilation  of  the  cardiac  orifice, 
and  in  consequence  vomiting,  became  impossible.  He  therefore 
regards  the  dilation  as  cai;sed  by  the  active  contraction  of  these 
fibres,  and  not  as  due  to  inhibition  of  the  normally  contracted  circular 
fibres.  In  order  that  the  contraction  of  the  radiating  fibres  should 
cause  dilation,  their  ends  distal  from  the  cesophagus  must  be  fixed. 
This  is  provided  by  the  stomach  being  supported  by  the  descent  of 
the  diaphragm.  The  support  afforded  to  the  oesophagus  by  the 
diaphragm  as  it  passes  through  that  muscle  must  also  be  of  advantage, 
and  the  longer  the  portion  of  oesophagus  between  the  diaphragm  and 
the  stomach,  the  greater  will  be  the  effect  of  the  radiating  muscles  in 
pulling  down  the  oesophagus  instead  of  dilating  its  orifice.  This  is 
possibly  the  reason  why  the  horse  and  other  herbivorous  animals  vomit 
with  such  difficulty. 


The  nervous  mechanism  of  vomiting  is  complicated  and  in 
many  aspects  obscure.  The  efferent  impulses  which  cause  the 
expiratory  effort  must  come  from  the  respiratory  centre  in  the 
medulla ;  with  these  we  shall  deal  in  speaking  of  respiration. 
The  dilation  of  the  cardiac  orifice  is  caused,  in  part  at  least,  by- 
efferent  impulses  descending  the  vagi,  since  when  these  are  cut 
real  vomiting  widi  discharge  of  the  gastric  contents  is  difficult, 
through  want  of  readiness  in  the  dilation.  The  sympathetic 
abdominal  nerves  coming  from  the  cceliac  ganglia  and  the 
splanchnic  nerves  seem  to  have  no  share  in  the  matter.  The 
efferent  impulses  which  cause  the  flow  of  saliva  in  the  introductory- 
nausea  descend  the  facial  along  the  chorda  tympani  branch. 
These  various  impulses  may  best  be  considered  as  starting  from  a 
vomiting  centre  in  the  medulla,  having  close  relations  with  the 
respiratory  centre.  This  centre  may  be  excited,  may  be  thrown 
into  action,  in  a  reflex  manner,  by  stimuli  applied  to  peripheral 
nerves,  as  when  vomiting  is  induced  by  tickling  the  fauces,  or  by 
irritation  of  the  gastric  membrane,  or  by  obstruction  due  to 
ligature,  hernia,  etc.,  of  the  intestine.  That  the  vomiting  in  the 
last  instance  is  due  to  nervous  action,  and  not  to  any  regurgitation 
of  the  intestinal  contents,  is  shewn  by  the  fact  that  it  will  take 
place  when  the  intestine  is  perfectly  empty  and  may  be  prevented 
by  section  of  the  mesenteric  nerves.  The  vomiting  attending 
renal  and  biliary  calculi  is  apparently  also  reflex  in  origin.  The 
centre  however  may  be  affected  directly,  as  probably  in  the  cases 
of  some  poisons,  and  in  some  instances  of  vomiting  from  disease 
of  the  medulla  oblongata.  Lastly,  it  may  be  thrown  into  action 
by  impulses  reaching  it  from  parts  of  the  brain  higher  up  than 
itself,  as  in  cases  of   vomiting  produced  by  smells,  tastes  and 


ClIAI'.   I.]  DIGESTION.  307 

emotions,  and  by  the  memory  of  past  occasions,  and  in  some 
cases  of  vomiting  from  cerebral  disease. 

Many  emetics,  such  as  tartar  emetic,  appear  to  act  directly  on 
the  centre,  since,  introduced  into  the  blood,  they  will  produce 
vomiting  even  when  a  bladder  is  substituted  for  the  stomach. 
Others  again,  such  as  mustard  and  water,  act  in  a  refle.x  manner 
by  irritation  of  the  gastric  mucous  membrane.  With  others, 
again,  which  cause  vomiting  by  developing  a  nauseous  taste,  the 
refle-K  action  involves  paits  of  the  brain  higher  than  the  centre 
itself. 

Since  the  vagus  acts  as  an  efferent  nerve  in  causing  the  dilation  of 
the  cardiac  orifice  so  essential  to  the  act,  it  is  difficult  to  eliminate  the 
share  taken  by  the  vagus  as  an  afferent  nerve  carrying  up  impulses 
from  the  stomach  to  the  vomiting  centre.  The  remarkable  fact  that, 
by  giving  tartar  emetic,  vomiting  may  in  dogs  be  sometimes  induced, 
even  after  section  of  the  vagi,  shews  that  the  dilation  of  the  cardiac 
orifice,  though  normally  effected  through  the  vagus,  may  be  carried 
out  by  means  of  some  local  mechanism,  and  that  the  emetic  may  also 
stimulate  that  local  mechanism  at  the  same  time  that  it  is  alTe^tingthe 
general  centre. 


Sec.  4.     The  Changes  which  the  Food  undergoes  in  the 
Alimentary  Canal. 

Having  studied  the  properties  of  the  digestive  juices,  and  the 
various  mechanisms  by  means  of  which  the  food  is  brought  under 
their  influence,  we  have  now  to  consider  what,  as  matters  of  fact, 
are  the  actual  changes  which  the  food  does  undergo  in  passing 
along  the  alimentary  canal,  what  are  the  steps  by  which  the  food 
is  converted  into  faeces. 

In  the  mouth  the  presence  of  the  food,  assisted  by  the 
movements  of  the  jaw,  causes,  as  we  have  seen,  a  flow  of  saliva. 
By  mastication,  and  by  the  addition  of  mucous  saliva,  the  food  is 
broken  into  small  pieces,  moistened,  and  gathered  into  a  con- 
venient bolus  for  deglutition.  In  man  some  of  the  starch  is,  even 
during  the  short  stay  of  the  food  in  the  mouth,  converted  into 
su.ar  ;  for  if  boiled  starch  free  from  sugar  be  even  momentarily 
held  in  the  mouth,  and  then  ejected  into  water  (kept  boiling  to 
destroy  the  ferment),  it  will  be  found  to  contain  a  decided  amount 
of  sugar.  In  many  animals  no  such  change  takes  place.  The 
viscid  saliva  of  the  dog  serves  almost  solely  to  assist  in  deglu- 
tition ;  and  even  the  longer  stay  which  food  makes  in  the  mouth 
of  the  horse  is  insufficient  to  produce  any  marked  conversion   of 

20 — 2 


308  CHANGES  OF  FOOD  IN  THE  STOMACH.      [BOOK  H. 

the  starch  it  may  contain.     During  the  rapid  transit  through  the 
oesophagus  no  appreciable  change  takes  place. 

In  the  stomach,  the  arrival  of  the  food,  the  reaction  of 
which  is  either  naturally  alkaline,  or  is  made  alkaline,  or  at  least 
is  reduced  in  acidity,  by  the  addition  of  saliva,  causes  a  flow  of 
gastric  juice.  This  already  commencing  while  the  food  is  as  yet 
in  the  mouth,  increases  as  the  food  accumulates  in  the  stomach, 
and  as,  by  the  churning  gastric  movements,  unchanged  particles 
are  continually  being  brought  into  contact  with  the  mucous 
membrane.  A-loreover  (see  p.  276),  the  absorption  of  the  earlier 
digested  portions  gives  rise  to  a  further  increase  of  secretion  and 
especially  of  pepsm.  The  secretion  of  acid  appears  to  continue 
at  a  fairly  constant  rate;  and  consequently,  unless  neutralized  by 
fresh  alkaline  food,  the  reaction  of  the  gastric  contents  becomes 
more  and  more  distinctly  acid  as  digestion  proceeds.  The  change 
of  starch  into  sugar  is  lessened  or  perhaps  arrested.  The  fats 
themselves  remain  unchanged ;  but,  through  the  conversion  of 
proteids  into  peptone,  not  only  are  the  more  distinctly  proteid 
articles  of  food,  such  as  meat,  broken  up  and  dissolved,  but  the 
proteid  framework,  in  which  the  starch  and  fats  are  frequently 
imbedded,  is  loosened,  the  starch-granules  are  set  free,  and  the 
fats,  melted  for  the  most  part  by  the  heat  of  the  stomach,  tend  to 
run  together  in  large  drops,  which  in  turn  are  more  or  less  apt  to 
be  broken  up  into  an  imperfect  emulsion.  The  collagenous 
tissues  are  dissolved  ;  and  hence  the  natural  bundles  of  meat  and 
vegetables  fall  asunder ;  the  muscular  fibre  splits  up  into  discs, 
and  the  protoplasm  is  dissolved  from  the  vegetable  cells.  While 
these  changes  are  proceeding,  the  thick  turbid  greyish  liquid  or 
chyme,  formed  by  the  imperfectly  dissolved  food,  is  from  time  to 
time  ejected  through  the  pylorus,  accompanied  by  even  large 
morsels  of  solid  less-digested  matter.  This  may  occur  within  a 
few  minutes  of  food  having  been  taken,  but  the  larger  escape 
from  the  stomach  probably  does  not  begin  till  from  one  to  two, 
and  lasts  from  four  to  five,  hours  after  the  meal,  becoming  more 
rapid  towards  the  end,  such  pieces  as  most  resist  the  gastric  juice 
being  the  last  to  leave  the  stomach. 

Busch'  saw  in  the  case  of  a  duodenal  fistula,  portions  of  food  pass 
into  the  duodenum  within  15  or  20  minutes  from  the  beginning  of  the 
meal.  Beaumont^  gives  a  very  full  statement  of  the  time  during 
which  various  articles  of  food  remained  in  the  stomach  of  Alexis  St. 
Martin.     The  length  of  stay,  however,  of  the  same  substance  varied 

'  Virchow's  Archiv,  Bd.  14  (1858),  p.  140. 
^  Exps.  and  obs.  on  gastric  juice,  1834. 


CHAP.    I.]  DIGESTION.  309 

very  much  under  vairious  circumstances.  Moreover  it  would  be  very 
hazardous  to  make  a  fistulous  stomach  the  canon  of  what  takes  place 
in  a  healthy  organ.  In  animals  the  stay  of  the  food  in  the  stoma  h  is 
very  variable.  Meidcniiain'  found  food  in  the  stomacli  of  dogi  16  to 
24  hrs.  after  a  meal,  and  as  is  well  known  the  stomachs  of  rabbits  are 
never  empty  but  always  more  or  less  filled  with  food. 

In  tlie  presence  of  healthy  gastric  juice,  and  in  the  absence  of 
any  nervous  interference,  the  question  of  the  digestibility  of  any 
food  is  determined  chietly  by  mechanical  conditions.  The  more 
linely  divided  the  material,  and  the  less  the  proteid  constituents 
are  sheltered  by  not  easily  soluble  envelopes,  such  as  those  of 
cellulose,  the  more  rapid  the  solution.  So  also  pieces  of  hard- 
boiled  egg,  which  have  to  be  gradually  dissolved  from  the  outside, 
are  less  easily  digested  than  the  more  friable  muscular  fibre,  the 
repeated  transverse  cleavage  of  which  increases  the  surface  exposed 
to  the  juice.  Unboiled  white  of  egg  again,  unless  thoroughly 
beaten  up  and  mixed  with  air,  is  less  digestible  than  the  same 
boiled.  The  unboiled  white  forms  a  viscid  clotted  mass,  of  low 
dilTusibility,  into  which  the  juice  permeates  with  the  greatest 
difficulty.  And  so  with  other  mstances.  Beyond  this  mechanical 
aspect  of  digestibility,  it  is  to  be  remembered  that  different  sub- 
stances may  differently  affect  the  gastric  membrane,  promoting  or 
checking  the  secretion  of  the  juice.  Hence  a  substance,  the  mass 
of  which  is  readily  dissolved  by  gastric  juice,  and  which  offers  no 
mechanical  ob.stacles  to  digestion,  may  yet  prove  indigestible  by 
so  affecting  the  gastric  membrane  through  some  special  con- 
stituent (or  possibly  in  other  ways)  as  to  inhibit  the  secretion  of 
the  juice. 

That  substances  can  be  absorbed  from  the  cavity  of  the 
stomach  into  the  circulation  is  proved  by  the  fact  that  food  when 
introduced  disappears  very  largely  from  the  stomach  of  an  animal, 
the  pylorus  of  which  has  been  ligatured.  But  we  cannot  speak 
with  certainty  as  to  what  extent  in  ordinary  life  gastric  absorption 
takes  place,  or  by  what  mechanism  it  is  carried  out.  The  pre- 
sumption is,  that  the  diffusible  sugars  and  peptone  pass  by  osmosis 
direct  ir^to  the  capillaries,  and  so  into  the  gastric  veins.  The 
filtrate  of  chyme  taken  from  a  stomach  in  full  digestion  contains 
jxnrapeptone,  but  scarcely  any  peptone.  From  this  it  may  fairly 
be  inferred  that  the  peptone  has  been  absorbed. 

In  the  act  of  swallowing,  no  inconsiderable  quantity  of  air  is 
carried  down  into  the  stomach,  entangled  in  the  saliva,  or  in  the 
food.  This  is  returned  in  eructations.  When  the  gas  of  eructa- 
tion or  that  obtained  directly  from  the  stomach  is  examined,  it  is 

'  Pfluger  s  Archiv,  Xix.  (1879),  p.   148. 


3IO  DIGESTION   OF   FATS.  [BOOK   II. 

found  to  consist  chiefly  of  nitrogen  and  carbonic  acid,  the  oxygen 
of  the  atmospheric  air  having  been  largely  absorbed.  In  most 
cases  the  carbonic  acid  is  derived  by  simple  diffusion  from  the 
blood,  or  from  the  tissues  of  the  stomach,  which  similarly  take  up 
the  oxygen.  In  many  cases  of  flatulency,  however,  it  may  arise 
from  a  fermentative  decomposition  of  the  sugar  which  has  been 
taken  as  such  in  food,  or  which  has  been  produced  from  the 
starch. 

In  the  latter  case,  however,  hydrogen  ought  also  to  make  its 
appearance ;  thus  CgH^gOe  =  2  C4H6O3  (lactic  acid)  =  CgHgOa 
(butyric  acid)  +  2  CO2  +  H^,  whereas  hydrogen  has  only  been  found 
in  the  small  intestine.  In  the  dog.  Planer'  found  in  the  stomach 
after  a  meat  diet  a  small  amount  of  gas  of  the  composition  CO  25*20, 
N  68-68,  O  6*i2,  after  a  meal  of  bread,  CO2  32'9i,  N  66-30,  O  -79. 

The  enormous  quantity  of  gas  which  is  discharged  through  the 
mouth  in  cases  of  hysterical  flatulency,  even  on  a  perfectly  empty 
stomach,  and  which  seems  to  consist  largely  of  carbonic  acid,  presents 
difficulties  in  the  way  of  explanation ;  it  is  possible  that  it  may  be 
simply  diffused  from  the  blood. 

In  the  small  intestine,  the  semi-digested  acid  food,  or 
chyme,  as  it  passes  over  the  biliary  orifice,  causes  gushes  of  bile, 
and  at  the  same  time,  as  we  have  seen  (p.  278),  the  pancreatic 
juice,  which  flowed  freely  into  the  intestine  at  the  taking  of  the 
meal,  is  secreted  again  with  renewed  vigour,  when  the  gastric 
digestion  is  completed.  These  two  alkaline  fluids  tend  to  neutra- 
lize the  acidity  of  the  chyme,  but  the  contents  of  the  duodenum 
do  not  become  distinctly  alkaline  until  some  distance  from  the 
pylorus  is  reached.  Even  in  the  lower  part  of  the  ileum  the 
chyme  may  be  acid^;  possibly  however  in  such  cases  it  has  been 
reacidified.  The  conversion  of  starch  into  sugar,  which  may  have 
languished  in  the  stomach,  is  resumed  with  great  activity  by  the 
pancreatic  juice,  though  portions  of  undigested  starch  may  be 
found  in  the  large  intestine  and  even  at  times  in  the  f^ces. 

The  pancreatic  juice,  as  we  have  seen,  emulsifies  fats,  and  also 
sphts  them  into  their  respective  fatty  acids  and  glycerine.  The 
fatty  acids  thus  set  free  become  converted  by  means  of  the  alka- 
line contents  of  the  intestine  into  soaps ;  but  to  what  extent 
saponification  thus  takes  place  is  not  exactly  known.  Undoubt- 
edly soaps  have  to  a  small  extent  been  found  both  in  portal  blood 
and  in  the  thoracic  duct  after  a  meal ;  but  there  is  no  proof  that 

'   Wien.  Sitzungsberichte,  XLII.  p.  307. 

^  Losnitzer,  Henle  and  Mei-sner's  Bericht,  1864,  p.  250. 


ClIAK   l.j  DIGESTION.  3II 

any  large  quantity  of  fat  is  introduced  in  this  form  into  the  circula- 
tion. On  tlie  other  hand,  tiie  presence  of  neutral  ftts,  both  in 
portal  blood,  and  especially  in  the  lacteals,  is  a  consi)icuous  result 
of  the  digestion  of  fatty  matters  ;  and  in  all  probability  saponifica- 
tion in  the  inte^ine  is  a  subsidiary  process,  intended  rather  to 
facilitate  the  emulsion  of  neutral  fats  than  to  introduce  soaps  as 
such  into  the  blood.  For  the  presence  of  soluble  soaps  favours 
the  emulsion  of  neutral  fats.  Thus  a  rancid  fat,  i.e.  a  fat  con- 
taining a  certain  amount  of  free  fatty  acid,  forms  an  emulsion 
with  an  alkaline  fluid  more  readily  than  a  neutral  fat.  A  drop  of 
rancid  oil  let  fall  on  the  surface  of  an  alkaline  fluid,  such  as  a 
solution  of  sodium  carbonate  of  suitable  strength,  rapidly  forms  a 
broad  ring  of  emulsion,  and  that  even  witiiout  the  least  agitation. 
'  As  saponii'ication  takes  place  at  the  junction  of  the  oil  and  alka- 
line fluid  currents  are  set  up,  by  which  globules  of  oil  are  detached 
from  the  main  droj)  and  driven  out  in  a  centrifugal  direction.  The 
intensity  of  the  currents  and  the  consequent  amount  of  emulsion 
depend  on  the  concentration  of  the  alkaline  medium  and  on  the 
solubility  of  the  soaps  which  are  formed  ;  hence  some  fats  such  as 
cod-liver  oil  are  much  more  easily  emulsionized  in  this  way  than 
others.  Now  the  bile  and  pancreatic  juice  supply  just  such  con- 
ditions as  the  above  for  emulsionizing  fats  :  they  both  together 
afford  an  alkaline  medium,  the  pancreatic  juice  supplies  an  ade- 
quate amount  of  free  fatty  acid,  and  the  bile  renders  duly  soluble 
the  soaps  thus  formed.  So  that  we  may  speak  of  the  emulsion  of 
fats  in  the  small  intestine  as  being  carried  on  by  both  bile  and 
pancreatic  juice '  ;  and  as  a  matter  of  fact  the  bile  and  pancreatic 
juice  do  largely  emulsify  the  contents  of  the  small  intestine,  so  that 
the  greyish  turbid  chyme  is  changed  into  a  creamy-looking  fluid, 
•which  has  been  sometimes  called  chyle.  It  is  advisable  however 
to  reserve  this  name  for  the  contents  of  the  lacteals. 

This  mutual  help  of  bile  and  pancreatic  juice  in  producing  an 
emulsion,  explains  to  a  certain  extent  the  controversy  which  long 
existed  between  those  who  maintained  that  the  bile  and  those  who 
maintained  that  the  pancreatic  juice  was  necessary  for  the  diges- 
tion and  absorption  of  fatty  food.  That  the  pancreatic  juice  does 
produce  in  the  intestine  such  a  change  as  favours  the  transference 
of  neutral  fats  from  the  intestine  into  the  lacteals,  is  shewn  by  the 
fact  that  in  diseases  affecting  the  pancreas,  much  fatty  food  fre- 
quently passes  through  the  intestine  undigested,  and  great  wasting 

'  Cf.  Briicke,  Witn.  Sitzun^sbericht,  Bd.  61  (1870),  p.  362  ;  Sleincr,  Archiv 
f.  Auat.  u.  Physiol.,  1874,  p.  286;  Gad,  ibid.,  1S78,  p.  181  ;  Quincke, 
Pfliiger's  y^rr^rt/,  XIX.  (1879),  p.  129. 


312  DIGESTION   OF   FATS.  [BOOK   II. 

ensues.  On  the  other  hand,  that  the  bile  is  of  use  in  the  digestion 
of  fat  is  shewn  by^the  prevalence  of  fatty  stools  in  cases  of  obstruc- 
tion of  the  bile-ducts ;  and  though  the  operation  of  ligaturing  the 
bile-ducts,  and  leading  all  the  bile  externally  through  a  biliary 
fistula,  is  open  to  objection,  since  it  so  exhausts  the  animal  as  in- 
directly to  affect  digestion,  still  the  results  of  Bidder  and  Schmidt, 
in  which  the  resorption  of  fat  was  distinctly  lessened  (the  quantity 
of  fat  in  the  lacteals  falling  from  3*2  to  *o2  p.  c.)  by  the  ligature 
and  fistula,  obviously  point  to  the  same  conclusion.  Thus  while 
'the  view  that  the  bile  alone,  or  the  view  that  the  pancreatic  juice 
alone,  is  the  agent  in  the  digestion  of  fat,  is  contradicted  by  facts, 
the  conflicting  experiments  are  reconciled  in  the  conclusion  that 
both  help  towards  the  same  end;  a  conclusion  which  is  in  harmony 
with  the  properties  of  the  juices,  as  seen  when  studied  out  of  the  ' 
body,  and  which  is  supported  by  the  observation  of  Busch,  in  a 
case  where  the  duodenum  opened  on  the  surface  by  a  fistula  in 
such  a  way  that  the  lower  part  of  the  intestine  could  be  kept  free 
from  the  contents  of  the  upper  part  containing  the  bile  and  pan- 
creatic juice.  Fats  introduced  into  the  lower  part,  where  they 
could  not  be  acted  upon  either  by  the  bile  or  by  the  pancreatic 
juice,  were  but  slightly  digested.  The  succus  entericus  may  have 
a  slight  emulsifying  power,  but  one  wholly  insufficient  to  meet  the 
needs  of  the  economy. 

We  have  seen  that  bile,  when  added  to  a  digesting  mixture, 
first  precipitates  and  then  re-dissolves  the  parapeptone  and  pep- 
tone, the  pepsin  being  carried  down  with  them.  The  object  of 
this  precipitation  is  probably  to  render  inert  the  pepsin  and  thus 
prevent  it  from  impairing  the  pancreatic  trypsin,  as  well  as  perhaps 
to  hinder  the  too  rapid  passage  of  the  semi-digested  liquids  along 
the  intestine.  The  granular  material  which  is  found  lining  the 
duodenum  is^possibly  the  result  of  such  a  precipitation.  We  have 
seen  that  bile,  while  it  stops  gastric  digestion,  favours  rather  than 
hinders  the  pancreatic  digestion  of  proteids.  As  a  matter  of  fact, 
since  the  contents  of  the  stomach  as  they  issue  from  the"  pylorus 
consist  very  largely  of  undigested  proteids,  these  must  be  digested 
by  the  pancreatic  juice  (with  or  without  the  assistance  of  the  succus 
entericus),  since  the  pepsin  of  the  gastric  juice  is  either  precipi- 
tated by  the  bile,  or  rendered  inert  by  the  increasing  alkalinity  of 
the  intestinal  contents.  To  what  stage  the  pancreatic  digesdon  is 
carried,  whether  peptone  is  chiefly  formed,  and  when  formed  at 
once  absorbed,  or  to  what  extent  the  pancreatic  juice  in  the  body, 
as  out  of  the  body,  carries  on  its  work  in  the  more  destructive 
form,  whereby  the  proteid  material  subjected  to  it  is  broken  down 
largely  into   leucin  and  tyrosin,  is  at  present  not  exactly  known. 


CHAP.    I.]  DIGESTION.  3 13 

Lencin  and  tyrusin  arc  found  in  the  intestinal  contents,  and  are 
therefore  formed  during  normal  digestion,  but  whether  a  large 
quantity  or  a  small  <iu  inlity  of  liie  protcid  material  of  food  is  thus 
hurried  into  a  crystalline  form  cannot  be  defmitcly  stated.  Possibly 
where  large  quantities  of  proteids  are  taken  at  a  meal,  the  excess 
is  at  once  got  rid  of  by  this  form  of  so-called  '  luxus  consumption  ; ' 
and  possibly  also,  in  the  intestine  as  in  the  laboratory,  this  pan- 
creatic digestion  of  proteids  in  excess  is  accompanied  by  a  con- 
siderable develoi)ment  of  bacteria  and  other  organized  bodies, 
which  create  trouble  by  inducing  fermentative  changes  in  the 
accompanying  saccharine  constituents  of  the  chyme. 

That  fermentative  changes  do  occur  in  the  small  intestine  is 
indicated  by  tlic  fact  that  the  gas  present  there  does  contain  free 
hydrogen.  Planer'  found  the  gas  from  the  small  intestine  of  a  dog 
fed  on  a  meat  diet  to  consist  of  CO._,  40-1,  H  13-86,  N  45 "5-)  ^^idi  only 
a  trace  of  oxygen.  In  a  dog  fed  on  vegetable  diet  the  composition  of 
the  gas  was  c6o  47 "34,  H  48-69,  N  3-97.  Chyme  after  removal  from 
the  intestine  continues  at  the  temperature  of  the  body  to  produce 
carbonic  acid  and  hydrogen  in  equal  volumes.  As  was  staled  above 
(p.  246),  during  butyric  acid  fermentation  from  sugar,  carbonic  acid 
and  hydrogen  are  evolved  in  equal  volumes.  Th^se  facts  suggest  the 
way  in  which  the  carbo-hydrate  constituents  of  food  may  become 
converted  into  fat,  for  by  this  butyric  acid  fermentation  the  sugar  is 
converted  into  a  member  of  the  fatty  acid  series  ;  and  it  is  at  least 
within  the  bounds  of  possibility  that,  by  fermentative  changes  of  some 
sort  or  other,  the  lower  members  of  the  series  may  be  raised  to  the 
higher.  But  did  butyric  acid  fermentations  occur  largely  in  the 
intestine,  we  should  expect  to  find  a  large  quantity  of  free  hydrogen 
discharged  from  the  system  by  the  bowel  or  lungs.  As  a  matter  of 
fact  it  is  discharged  in  small  qumtities  only.  Hence,  unless  we 
suppose  that  the  nascent  hydrogen  is  used  up  in  some  contemporaneous 
processes  of  reduction,  we  must  regard  butyric  acid  fermentation  as 
slight  and  unimportant.  Indeed  the  quantity  of  gas  on  which  Planer 
worked  was  small.  It  is  probable  however  that  by  fermentative 
changes  a  considerable  quantity  of  sugar  is  converted  into  lactic  acid, 
since  this  acid  is  found  in  increasing  quantities  as  the  food  descends 
the  intestine. 

Thus  during  its  transit  through  the  small  intestine,  by  tlie 
action  of  the  bile  and  pancreatic  juice  assisted  possibly  to  some 
extent  by  the  succus  cntericus,  the  proteids  are  largely  dissolved 
and  converted  into  peptone  and  other  products,  the  starch  is 
changed  into  sugar,  the  sugar  possibly  being  in  part  further  con- 
verted into  lactic  acid,  and  the  fats  are  largely  emulsified,  andjo 

'  Op.  cit 


314        CHANGES  OF  FOOD  IN  LARGE  INTESTINE.    [BOOK.  II. 

some  extent  saponified.  These  products,  as  they  are  formed,  pass 
into  either  the  lacteals  or  the  portal  blood-vessels,  so  that  the  con- 
tents of  the  small  intestine,  by  the  time  they  reach  the  ileo-caecal 
valve,  are  largely  but  by  no  means  wholly  deprived  of  their 
nutritious  constituents.  As  far  as  water  is  concerned,  the  secretion 
into  the  small  intestine  is  about  equal  to  the  absorption  from  it,  so 
that  the  intestinal  contents  at  the  end  of  the  ileum,  though  much 
more  broken  up.  are  about  as  fluid  as  in  the  duodenum. 

In  the  large  intestine,  the  contents  become  once  more  dis- 
tinctly acid.  This,  however,  is  not  caused  by  any  acid  secretion 
from  the  mucous  membrane ;  the  reaction  of  the  intestinal  walls  in 
the  large  as  in  the  small  intestine  is  alkaline.  It  must  therefore 
arise  from  acid  fermentations  going  on  in  the  contents  themselves; 
as  indeed  is  shewn  by  the  composition  of  the  gases  which  make 
their  appearance  in  this  portion  of  the  alimentary  canal.  In  car- 
nivora  the  contents  of  the  caecum  are  said  to  be  alkaline^,  and 
naturally  the  amount  of  fermentation  will  depend  largely  on  the 
nature  of  the  food. 

Ruge^  found  the  gas  of  the  large  intestine,  collected  per  anum,  to 
have  the  following  composition  ; 


Mixed  diet. 

Leguminous  diet 

Meat  diet. 

C02 

40-54 

21  05 

8-45 

N 

17-50 

18-96 

64-41 

CH4 

19-77 

55*94 

26-45 

H 

22-22 

5'o3 

•69 

SH2  a  trace  only. 

Of  the  particular  changes  which  take  place  in  the  large  intes- 
tine we  have  no  definite  knowledge  ;  but  it  is  exceedingly  probable 
that  in  the.  voluminous  csecum  of  the  herbivora,  a  large  amount  of 
digestion  of  a  peculiar  kind  goes  on.  We  know  that  in  herbivora 
a  considerable  quantity  of  cellulose  disappears  in  passing  through 
the  canal,  and  even  in  man  some  is  probably  digested.  We  are 
driven  to  suppose  that  this  cellulose  digestion  is  carried  on  in  the 
large  intestine,  though  we  know  nothing  of  the  nature  of  the 
agency  by  which  it  is  effected.  The  other  digestive  changes  are 
probably  of  a  fermentative  kind. 

Be  this  as  it  may,  whether  digestion,  properly  so  called,  is  all 
but  complete  at  the  ileo-c?ecal  valve,  or  whether  important  changes 
still  await  the  chyme  in  the  large  intestine,  the  chief  characteristic 
of  the  work  done  in  the  colon  is  absorption.     By  the  abstraction 

^  Bernard,  Liquides  de  T  Organisme. 
'    Wien.  Siiztmgsberichte,  1862,  p.  729. 


CHAP.   I.]  DIGESTION.  315 

of  all  the  soluble  constituents,  and  especially  by  the  withdrawal  of 
water,  the  liquid  chyme  becomes  as  it  approaches  the  rectum  con- 
verted into  the  firm  solid  feces,  and  the  colour  shifts  from  the  bright 
orange,  which  the  grey  chyme  gradually  assumes  after  admixture 
with  bile,  into  a  darker  anil  dirtier  brown. 

In  the  faeces  there  are  found  in  the  first  place  the  indigestible 
and  undigested  constituents  of  the  meal :  shreds  of  elastic  tissue, 
hairs  and  other  corneous  elements,  much  cellulose  and  chlorophyll 
from  vegetable,  and  some  connective  tissue  from  animal  food,  frag- 
ments of  disintegrated  muscular  fibre,  fat-ceils,  and  not  unfre- 
quently  undigested  starch-corpuscles.  The  amount  of  each  must 
of  course  vary  very  largely,  according  to  the  nature  of  the  food, 
and  the  digestive  powers,  temporary  or  permanent,  of  the  indivi- 
dual. In  the  second  place,  to  tiiese  must  be  added  substances, 
not  introduced  as  food,  but  arising  as  part  of,  or  as  products  of, 
the  digestive  secretions.  The  fceces  contain  a  ferment  similar  to 
pepsin,  and  an  amylolytic  ferment  similar  to  that  of  saliva  or  pan- 
creatic juice.  They  also  contain  mucus  in  variable  amount, 
sometimes  albumin,  cholesterin,  hydrobilirubin,  butyric  and  other 
fatty  acids,  lime  and  magnesia  soaps,  exc/etin  (a  non-nitrogenous 
crystalline  body,  containing  sulphur,  obtained  by  Marcet),  and 
salts,  especially  those  of  magnesia.  Cholalic  acid  (and  dyslysin) 
are  found  in  very  small  quantities  only,  thus  indicating  that  the 
bile-salts  have  been  in  part  at  least  destroyed  (they  may  have  been 
in  part  reabsorbed,  see  p.  292),  the  less  stable  taurocholic  acid  (of 
the  dog)  disappearing  more  readily  than  the  glycocholic  acid  (of 
the  cow).  The  fact  that  the  faeces  become  'clay-coloured'  when 
the  bile  is  cut  off  from  tlie  intestine  shews  that  the  bile-pigment  is 
at  least  tlie  mother  of  the  fascal  pigment;  and  the  special  pigment, 
which  has  been  isolated  and  called  stercobilin,'  is  said  to  be 
identical  with  urobilin,  i.e.  with  hydrobilirubin.  We  have  already 
seen  that  during  artificial  pancreatic  digestion,  a  distinctly  faecal 
odour  due  to  the  presence  of  indol  is  generated  ;  and  the  fact  that 
the  presence  of  bacteria,  or  other  similar  organisms,  is  essential  to 
the  production  of  this  body,  does  not  preclude  the  possibility  of 
it,  with  its  derivatives,  being  the  chief  cause  of  the  natural  odour 
of  faeces,  for  undoubtedly  bacteria  may  exist  throughout  the  whole 
length  of  the  intestinal  canal.  At  the  same  time  it  is  quite  possible, 
if  not  probable,    that    specific    odoriferous   substances    may  be 

'  Vauliir  and  Masius,   Cmtrbt.  f.  vnd.    Wiss.  1S71,  No.  24.     JafTe,  ibid.^ 
No.  3T. 


3l6  CHYLE.  {book  II. 

secreted  directly  from  the  intestinal  wall,  especially  from  that  of 
the  large  intestine, 

Brieger '  finds  in  human  excrement  a  small  quantity  only  of  indol, 
but  a  considerable  quantity  of  a  similar  body  which  he  calls  skatol, 
possessing  an  intense  faecal  odour. 


Sec.  5.     Absorption  of  the  Products  of  Digestion, 

We  have  seen  that  absorption  does,  or  at  least  may,  take  place 
from  the  stomach.  We  have  also  stated  that  a  large  absorption, 
especially  of  water,  occurs  along  the  whole  large  intestine. 

Absorption  from  the  large  intestine  after  injection  per  aman  or 
through  a  fistula  has  been  observed  not  only  in  the  case  of  soluble 
peptone  and  sugar,  but  also  in  that  of  starch,  white  of  egg,  and  casein  ; 
but  the  exact  changes  undergone  by  the  latter  previous  to  absorption 
are  unknown  ^ 

Nevertheless  the  largest  and  most  important  part  of  the  digested 
material  passes  away  from  the  canal,  during  the  transit  of  food 
along  the  smiall  intestine,  partly  into  the  lacteals,  partly  into  the 
portal  vessels. 

Digestion  being,  broadly  speaking,  the  conversion  of  non- 
diffusible  proteids  and  starch  into  highly  diffusible  peptone  and 
sugar,  and  the  emulsifying,  or  division  into  minute  particles,  of 
various  fats,  it  is  natural  to  suppose  that  the  diffusible  peptone  and 
sugar  pass  by  osmosis  into  the  blood-vessels,  and  that  the  emulsified 
fats  pass  into  the  lacteals.  That  a  large  part  of  the  fat  which  enters 
the  body  from  the  intestine  does  pass  through  the  lacteals,  there 
can  be  no  doubt ;  and  there  can  be  but  little  doubt  that  a  con- 
siderable quantity  of  peptone  and  sugar  does  pass  into  the  portal 
blood.  But  we  are  unable  to  say  at  present  how  far  the  fat  in  its 
difficult  passage  into  the  lacteal  is  accompanied  by  soluble  peptone 
or  by  less  diffusible  forms  of  proteids  arising  as  subsidiary  products 
of  proteolytic  digestion  or  by  carbohydrate  products. 

Characters  of  Chyle.  In  a  fasting  animal  the  contents  of 
the  thoracic  duct  are  clear  and   transparent  ;  shortly  after  a  meal 

'  Ber.  deutsch.  Chem.  Geselhch.  x.  (1877),  p.  1027. 
=  Bauer,  Zeitschft.  f  Biol.,  V.  536. 


CHAP.   I.]  DIGESTION.  317 

they  become  milky  and  opaque,  the  change  being  entirely  clue  to  a 
difference  in  the  cjuantity  of  the  fluid  brought  to  the  duct  by  the 
lactcals,  that  fluid  also  being,  as  seen  by  inspection  of  the  mesen- 
tery, transparent  during  fasting,  and  becoming  milky  and  opaque 
after  a  meal,  especially  after  one  containing  much  fat.  The  con- 
tents of  the  thoracic  duct  therefore  after  a  meal  may  be  taken  as 
illustrative  of  the  nature  of  the  chyle  present  in  the  lactcals,  though 
strictly  speaking  the  chyle  of  the  thoracic  duct  is  mixed  with 
lymph  coining  from  the  intestines  and  from  the  rest  of  the  body. 
During  fasting  the  contents  of  the  lacteals  agree  in  their  general 
character  with  lymph  obtained  from  other  structures. 

The  contents  of  the  thoracic  duct  may  be  obtained  by  laying  bare 
the  junction  of  the  subclavian  and  jugular  veins  and  introducing  a 
cannula  into  the  duct  as  it  enters  into  the  venous  system  at  that  point. 
The  operation  is  not  unattended  with  difficulties. 

Chyle  obtained  from  the  thoracic  duct,  after  a  meal,  is  a  white 
milky-iooking  fluid,  which  after  its  escape  coagulates,  forming  a  not 
very  firm  clot.  The  nature  of  the  coagulation  seems  to  be  exactly 
the  same  as  that  of  blood.  The  surface  of  the  clot  after  exposure 
to  air  becomes  pink,  even  though  no  blood  be  artificially  mixed 
with  the  chyle  during  the  operation  ;  the  colour  is  due  to  immature 
red  corpuscles  proper  to  the  chyle.  Examined  microscopically, 
the  coagulated  chyle  consists  of  fibrin,  a  large  number  of  white 
corpuscles,  a  small  number  of  developing  red  corpuscles,  an 
abundance  of  oil-globules  of  various  sizes  but  all  small,  and  a 
quantity  of  fatty  granules,  too  minute  to  be  recognised  under  the 
microscope  as  fatty  in  nature,  forming  the  so-called  '  molecular 
basis.'  Each  oil  globule  is  invested  with  an  albuminous  envelope  ; 
this  may  be  dissolved  by  the  aid  of  alkalis,  whereupon  the  globules 
run  together.  The  fibrin  and  white  corpuscles  are  very  scanty 
(and  the  red  corpuscles  entirely  absent)  in  lymph,  or  chyle  taken 
from  peripheral  vessels ;  but  they  increase  in  quantity  as  the 
lymph  passes  through  the  lymphatic  glands. 

The  composition  of  chyle  varies  considerably  not  only  in 
different  animals  but  in  the  same  animal  at  different  times.  The 
average  percentage  of  solids  may  perhaps  be  put  down  as  about 
0,  that  of  proteid  material  as  about  4  or  5,  and  that  of  fat  as 
about  3  or  4,  the  remainder  being  extractives  and  salts.  The  fats 
occur  chiefly  in  the  form  of  neutral  fats,  though  some  soaps  or 
fatty  acids  are  present. 


3l8  CHYLE.  [book   II. 

The  perc;entages  of  solid  matters  vary  in  the  different  analyses 
from  3  to  ii,  of  proteids  from  2  to  7,  of  fats  from  less  than  I  to  4'  ; 
but  Zawilski  ^  finds  that  in  dogs  after  a  meal  rich  in  fat,  the  percentage 
of  fat  in  the  chyle  may  vary  from  I4'6  to  o'25.  The  proteids  consist 
chiefly  of  serum-albumin,  with  a  globulin  or  alkali-albumin  precipitable 
by  acidSj  and  a  variable  but  small  quantity  of  fibrin.  Among  the  ex- 
tractives have  been  found  sugar,  urea,  and  leucin  ;  cholesterin  is  also 
frequently  present  in  considerable  quantity.  Since  these  extractives 
are  found  in  lymph  as  well  as  chyle  they  cannot  be  regarded  as  derived 
exclusively  from  the  intestinal  contents.  The  amount  of  peptone  is 
very  small  indeed.  The  gas  which  can  be  extracted  from  chyle  or 
lymph  consists  almost  entirely  of  carbonic  acid,  there  being  only  a 
small  quantity  of  nitrogen,  and  no  satisfactory  evidence  of  the  presence 
of  any  free  oxygen  at  all.  Hammarsten^  obtained  from  the  100  vols. 
of  lymph  of  the  dog  about  1"5  (I'l?)'*  vols,  nitrogen,  and  about  53 
(40"36)  vols,  carbonic  acid.  The  ash  is  remarkable  for  the  abundance 
of  sodium  chloride  and  the  scantiness  of  phosphates.  Iron  is  present 
in  greater  quantity  than  can  be  accounted  for  by  the  presence  of  red 
corpuscles. 

The  nature  of  the  fat  is  supposed  to  vary  with  that  of  the 
food,  but  this  has  not  been  conclusively  shewn. 

The  lymph  taken  from  the  duct  during  fasting  differs  chiefly 
from  that  taken  after  a  meal,  in  the  much  smaller  quantity  of  fat, 
the  microscope  shewing  white  corpuscles  with  very  few  oil-globules, 
and  in  the  almost  entire  absence  of  the  molecular  basis.  Lymph 
in  fact  is,  broadly  speaking,  blood  minus  its  red  corpuscles,  and 
chyle  is  lymph  plus  a  very  large  quantity  of  minutely  divided 
neutral  fat. 

It  has  been  calculated  that  a  quantity  equal  to  that  of'the 
whole  blood  may  pass  through  the  thoracic  duct  in  24  hours,  and 
of  this  it  is  supposed  that  about  half  comes  from  food  through  the 
lacteals  and  the  remainder  from  the  body  at  large ;  but  these 
calculations  are  based  on  uncertain  data. 

Entrance  of  the  Chyle  into  the  Lacteals.  The  lacteal 
begins  as  a  club-shaped  (or  bifurcate)  lymphatic  space  lying  in  the 
centre  of  the  villus,  and  connected  with  the  smaller  lymphatic 
spaces  of  the  adenoid  tissue  around  it ;  it  opens  below  into  the 
submucous  lymphatic  plexus  from  which  the  lacteal  vessels  spring. 

'  Cf.  Hensen,  Pfliiger's  Archiv,  x.  (1874),  p.  94. 

^  Ludwig's  Arbeiten,  1876,  p.  147. 

3  Ludwig's  ^r^J^/^w,  1871,  p.  121. 

*•  The  larger  figures  are  the  measurements  obtained  at  o''  C.  and  a  pressure  of 
760  nun.  mercury,  the  smaller  figures  in  brackets  the  measurements  according  to 
the  prevalent  German  method  .it  0°  C.  and  i  metre  of  mercury  pressure. 


CHAP.   I.]  DIGESTION.  3^9 

The  adenoid  tissue  of  the  surrounding  cryptS  of  Liebjrkiihn  is  by 
its  lymphatic  spaces  connected  with  the  same  lymphatic  plexus. 
That  the  finely-divided  fat  does  pass  from  the  intestine,  through 
the  epithelial  envelope  of  the  villus,  into  the  adenoid  tissue,  and 
so  into  the  lacteal  chamber,  is  certain,  but  much  discussion  has 
arisen  as  to  the  exact  mechanism  of  the  transit.  The  passage  is 
probably  assisted  by  the  movements  of  the  intestine,  though  even 
in  the  contractions  of  strong  peristaltic  movements  the  pressure 
within  the  intestine  is  never  very  great.  Of  more  obvious  use  is 
the  contraction  of  the  villus  itself.  The  longitudinal  muscular 
fibre-cells,  in  contracting,  pull  down  the  villus  on  itself;  the 
contents  of  the  lacteal  chamber  are  thus  forced  into  the'  under- 
lying lymphatic  plexus.  When  the  fibre-cells  relax,  the  empty 
lacteal  chamber  is  expanded  ;  the  chyle  cannot  flow  back  from 
the  lymphatic  channels  by  reason  of  the  valves  present  in  them, 
and  in  consequence  the  lacteal  chamber  is  filled  from  the 
substance  of  the  villus,  and  thus  the  entrance  into  the  villus  of 
material  from  the  intestine  is  facilitated.  The  villus  in  fact  acts  as 
a  kind  of  muscular  suction-pump. 

Merunowicz  '  finds  the  flow  of  lymph  increased  by  muscarin  poison- 
ing, and  attributes  the  increase  of  flow  to  the  coincident  increase  of  the 
peristaltic  movements  of  the  intestine. 

After  a  meal  the  epithelium  cells  of  the  villus  are  found  crowded 
with  fat.  Since  the  striation  of  the  hyaline  border  of  the  cells  is  not 
due  to  pores,  as  was  once  thought,  the  particles  must  have  entered  into 
the  cells  very  much  as  foreign  particles  enter  the  body  of  an  amoeba. 
The  epithelium  may  in  fact  be  said  to  eat  the  fat.  Since  the  (frequently) 
branched  ruid  protoplasmic  base  of  the  cell  is  in  intimate  connexion 
with  the  spaces  of  the  adenoid  tissue  of  the  villus,  the  fat  could  more 
readily  pa-^s  from  the  cell  in  this  direction  than  from  the  intestine  into 
the  cell.  There  would  thus  be  a  stream  of  fatty  particles  through  the 
cell  from  without  inwards,  a  stream  in  the  causation  of  which  the  cell 
took  an  active  part.  In  fact,  under  this  view,  absorption  by  the  cell 
might  be  regarded  as  a  sort  of  inverted  secretion,  the  cell  taking  much 
material  from  the  chyme  and  secreting  it,  with  little  or  no  change,  into 
the  villus.  The  observations  of  Watncy-  have  led  him  to  believe  that 
the  fit  passes  not  through  but  between  the  epithelium-cells,  being  taken 
up  by  the  inter-epithclium  processes  of  the  peculiar  cpithcloid-cclls, 
described  by  him  as  forming  a  continuous  protoplasmic  reticulum,  the 
epithelium-cells  themselves  therefore  hiving  no  active  share  in  absorp- 
tion. It  is  difficult  on  this  view  however  to  explain  the  almost  unani- 
mous opinion  of  previous  observers,  that  the  fat  may  be  seen  in  the 

'  Ludwig's  .^r3<r//<'«,  1S76,  p.  117. 
'  Phil.  Trans.,  1876,  p.  451. 


32C  MOVEMENTS   OF   CHYLE  AND   LYMPH.     [BOOK    II. 

substance  of  the  cell  itself,  though  Watney  argues  that  particles  of  fat 
adhering  to  the  outside  of  the  cell  have  been  erroneously  supposed  to 
be  really  within  the  cells. 

Movements  of  the  Chyle.  Having  reached  the  lym- 
phatic channels  the  onward  progress  of  the  chyle  is  determined 
by  a  variety  of  circumstances.  Putting  aside  the  pumping  action 
of  the  villi,  the  same  events  which  cause  the  movement  of  the 
lymph  generally  also  further  the  flow  of  the  chyle  ;  and  these  are 
briefly  as  follows.  In  the  first  place,  the  wide-spread  presence  of 
valves  in  the  lymphatic  vessels  causes  every  pressure  exerted  on 
the  tissues  in  which  they  lie,  to  assist  in  the  propulsion  forward  of 
the  lymph.  Hence  all  muscular  movements  increase  the  flow. 
If  a  cannula  be  inserted  in  one  of  the  larger  lymphatic  trunks  of 
the  limb  of  a  dog,  the  discharge  of  lymph  from  the  cannula  will 
be  more  distinctly  increased  by  movements,  even  passive  move- 
ments, of  the  limb  than  by  anything  else.  In  addition  to  the 
valves  along  the  course  of  the  vessels,  the  embouchement  of  the 
thoracic  duct  into  the  venous  system  is  guarded  by  a  valve,  so  that 
every  escape  of  lymph  or  chyle  from  the  duct  into  the  veins 
becomes  itself  a  help  to  the  flow.  In  the  second  place,  consider- 
ing the  whole  lymphatic  system  as  a  set  of  branching  tubes 
passing  from  the  extra  vascular  regions  just  outside  the  small 
arteries,  veins  and  capillaries,  to  the  large  venous  trunks,  it  is 
obvious  that  the  mean  pressure  of  the  blood  in  the  subclavian 
vein,  at  its  junction  with  the  jugular,  must  be  considerably  less 
than  that  of  the  lymph  in  the  lymphatic  spaces  around  the  small 
blood-vessels,  even  though  the  pressure  in  the  tissues  outside  the 
small  blood-vessels  is  distinctly  less  than  that  of  the  blood  within 
the  same  vessels.  In  other  words,  there  is  a  distinct  fall  of 
pressure  in  passing  from  the  beginning  to  the  end  of  .  the 
lymphatics  ;  this  of  course  would  alone  cause  a  continuous  flow. 
Further,  this  flow,  caused  by  the  lowness  of  the  mean  venous 
pressure  at  the  subclavian,  will  be  assisted  at  every  respiratory 
movement,  since  at  every  inspiration  the  pressure  in  the  venous 
trunks  becomes  negative,  and  thus  lymph  will  be  sucked  in  from 
the  thoracic  duct,  while  the  increase  of  pressure  in  the  great  veins 
during  expiration  is  warded  off  from  the  duct  by  the  valve  at  its 
opening.  In  the  third  place,  the  flow  may  be  increased  by  rhyth- 
mical contractions  of  the  muscular  walls  of  the  lymphatics  them- 
selves ;  but  this  is  doubtful,  since  it  is  not  clear  whether  the 
rhythmic   variations   seen   by  Heller^   in  the   mesentery   of  the 

'  Cbt.  Med.  Wiss.,  1869,  p.  545. 


CHAP.   l]  DIGESTION.  321 

guinea-pig  were  active  or  simply  passive,  i.e.  caused  by  the 
rhythmic  peristaltic  action  of  the  intestine,  each  contraction  of  the 
intestine  filling  the  lymph  channels  more  fully.  Lastly,  it  is  quite 
open  for  us  to  suppose  that  just  as  osmosis  may  give  rise  to 
increased  pressure  on  one  side  of  a  diffusion  septum,  so  the 
diffusion  of  substances  from  the  intestines  into  the  lacteals,  or 
from  the  tissues  into  the  lympliatics,  may  be  itself  one  of  the 
causes  of  the  flow  of  lymph.  We  have  at  least,  under  all 
circumstances,  one  or  other  of  these  causes  at  work  promoting  a 
continual  How  from  the  lymi)hatic  roots  to  the  great  veins.  We 
have  no  very  satisfactory  evidence  that  the  flow  of  lymph  is  in  any 
way  directly  governed  by  the  nervous  system. 

In  frogs  and  some  other  animals  the  centripetal  flow  of  lymph 
from  the  limbs  is  assisted  by  rhythmically  pulsating  muscular  lymph- 
hearts. 

The  observations  of  Paschutin '  and  Emminghaus^  failed  to  shew 
any  direct  connection  between  the  nerv'ous  system  and  the  lymph-flow. 
Section  of  the  sciatic,  leading  to  arterial  dilation  and  consequent  in- 
creased pressure  in  the  capillaries  and  small  veins,  had  verj'  little  effect, 
whereas  ligature  of  the  veins  led  to  a  very  marked  increase.  Active 
movements  of  the  limb,  caused  by  stimulation  of  the  sciatic,  produced 
no  greater  flow  than  did  passive  movements.  Goltz  =  has  recorded  an 
interesting  observation,  bearing  on  the  influence  of  the  nervous  system 
on  absorption.  Of  two  frogs  placed  underihe  influence  of  urari  so  as  to 
do  away  with  muscular  movements  and  the  action  oP  the  lymph-hearts, 
the  brain  and  spinal  cord  of  one  are  destroyed,  but  in  the  other  are  left 
intact.  Both  animals  are  suspended  by  the  lower  jaw  ;  chloride  of 
sodium  solution  (75  per  cent.)  is  poured  into  the  dorsal  lymphatic  sacs 
of  both  ;  and  in  both  the  aorta  is  cut  across.  In  the  one  where  the 
nervous  system  is  intact,  absorption  from  the  lymphatic  sac  takes  place 
copiously,  and  the  heart  pumps  out  large  quantities  of  fluid  by  the 
aorta.  In  the  other,  absorption  does  not  occur  ;  the  heart,  though 
beating,  remains  empty,  and  the  skin  becomes  dry.  The  result  how- 
ever shews  rather  the  influence  of  the  nerv^ous  system  in  maintaining 
the  tonicity  of  the  blood-vessels  and  keeping  up  the  connection  of  the 
heart  with  the  peripheral  vessels,  than  any  distinct  connection  between 
absorption  proper  and  the  nervous  system.  When  the  nervous  system 
is  destroyed,  dilation  of  the  splanchnic  vascular  area  causes  all  the 
blood  to  remain  stagnant  in  the  portal  vessels,  so  that  little  or  none 
reaches  the  heart,  and  with  the  enfeebled  circulation  the  absorption 
from  the  lymphatic  sac  is  slight.  So  long  as  the  nervous  system  is  still 
intact  this  stagnation  does  not  occur,  the  blood  reaches  the  heart,  and 
with  the  more  vigorous  circulation  absorption  from  the  lymphatic  sac 
goes  on  rapidly.    As  the  blood  is  pumped  away  its  place  is  renewed  by 

'  'LmAwi^^  Arbeiten,  1872,  p.  197.  '  Ibid.,  1S73,  p,  51. 

•■'  Pfluger's  Archiv,  V.  {1S72),  p.  53. 

F.  P.  21 


322  ABSORPTION   OF   FATS.  [BOOK    II. 

the  lymph,  supplied  by  the  fluid  in  the  sac,  and  thus  the  heart  may  be 
made  for  a  long  time  to  pump  away  the  fluid  poured  into  the  sac.  Still, 
though  we  cannot  prove  any  direct  connection  between  the  nervous 
system  and  absorption,  the  phenomena  of  disease  render  such 
a  connection  at  least  probable. 

The  course  taken  by  the  several  products  of  digestion. 

The  digested  contents  of  the  intestine  pass  into  the  blood 
either  directly  by  the  portal  system  or  indirectly  by  means  of  the 
lymphatics.  It  cannot  be  a  matter  of  indifference  which  course 
is  taken  by  the  particular  digestive  products  ;  for  in  the  latter  case, 
they  pass  into  the  general  blood-current  with  only  such  changes  as 
they  may  undergo  in  the  lymphatic  system,  while  in  the  former 
they  are  subjected  to  the  powerful  influences  of  the  liver  before 
they  find  their  way  to  the  right  side  of  the  heart.  What  those 
influences  are  we  shall  study  in  a  future  chapter. 

Fats.  As  we  have  seen,  a  special  mechanism  is  provided 
for  the  passage  of  fats  into  the  lacteals.  On  the  other  hand,  it 
is  difficult  to  suppose  that  solid  particles  of  fat  can  pass  into  the 
interior  of  the  blood  capillaries.  So  that  we  are  led  i  priori  to 
the  view  that  the  whole  of  the  fat  takes  the  course  of  the  lacteals. 
But  we  cannot  say  that  this  is  definitely  proved.  On  the  contrary, 
a  deficit  is  observed  when  the  quantity  of  fat  disappearing  after  a 
meal  from  the  alimentary  canal  is  compared  with  that  flowing  into 
the  thoracic  duct ;  and  if  it  be  true,  as  is  stated,  that  the  blood  of 
the  portal  vein  contains  during  digestion  more  fat  than  the  general 
venous  blood,  some  of  this  deficit  may  be  explained  by  the  fat 
passing  into  the  blood  capillaries,  difficult  as  that  passage  may 
appear.  The  portal  blood,  moreover,  during  digestion  contains  a 
small  but  appreciable  quantity  of  soaps. 

Zawilski '  finds  that  in  a  dog  after  a  meal  rich  in  fat  the  stream  of 
fat  from  the  thoracic  duct  into  the  venous  system  becomes  rapid  at 
about  the  second  hour,  but  does  not  reach  its  maximum  till  after  the 
fifth  hour.  This  it  maintains  till  about  the  twentieth  hour,  after  which 
it  sinks  till  about  the  thirtieth  hour,  at  which  time,  and  not  before,  has 
all  the  fat  of  the  food  disappeared  from  the  alimentary  canal.  In  dogs 
weighing  about  14  or  15  kilos,  and  fed  with  a  meal  containing  150  grm. 
fat,  the  maximum  discharge  of  fat  from  the  thoracic  duct  into  the 
venous  system  was  about  100  mgrm.  a  minute.  When  the  total 
amount  of  fat  passing  through  the  thoracic  duct  was  compared  with 
the  total  amount  of  fat  which  had  disappeared  from  the  alimentary 

'  Ludwig's  Arbeiten,  1876,  p.  147. 


CHAP.  I.]  DIGESTION.  323 

canal,  it  was  found  that  about  one-half  of  the  fat  could  not  be  .thus 
accounted  for.  Tiiis  missing  quantity  could  not  be  considered  as  the 
portion  still  ///  transitu  on  its  w.iy  from  the  intestines  to  the  mouth  of 
the  thoracic  duct,  since  it  was  quite  as  marked  when  the  experiment 
was  carried  on  until  the  percentage  of  fat  in  tiie  chyle  had  sunk  to 
its  lowest  limit.  Some  fat  therefore,  and  indeed  a  large  quan'.ity, 
must  have  cither  passed  into  the  portal  blood  or  have  been  removed 
from  the  lympliatic  vessels  on  its  course  between  the  villi  of  the 
intestine  and  the  thoracic  duct,  or  have  been  disposed  of  in  some 
other  unknown  way.  The  fat  thus  entering  the  blood  either  directly 
or  indirectly  is  rapidly  got  rid  of  in  some  way  or  other,  for  the  per- 
centage of  fat  in  the  blood  of  a  dog  after  a  meal  rich  in  fat,  did  not, 
at  the  lapse  of  10  hours  from  the  swallowing  of  the  food,  differ  materi- 
ally whether  the  fat  had  been  during  the  wliolc  time  shut  off  from  the 
blood  by  being  allowed  to  flow  out  of  a  cannula  placed  in  the  thoracic 
duct,  or  had  been  allowed  to  pass  into  the  venous  system  in  the 
usual  way. 

Proteids.  The  question  as  to  the  course  taken  by  the  digested 
proteids  is  complicated  by  the  insufficiency  of  our  knowledge 
concerning  the  exact  stages  to  which  the  digestion  of  proteids  is 
naturally  carried  in  the  alimentary  canal.  If  we  take  it  for  granted 
that  the  proteids  taken  as  food  are  reduced  at  least  to  the  condi- 
tion of  soluble  and  ditfusible  peptone,  it  seems  easy  to  suppose 
that  the  proteids  of  food  pass  by  diffusion  as  peptone  into  the 
portal  capillaries,  though  even  under  this  view  it  is  open  for  us  to 
imagine  that  all  the  peptone  which  passes  through  the  epithelium 
of  a  villus  is  not  intercepted  by  the  blood  capillaries,  but  that 
some  reaches  and  is  absorbed  by  the  more  centrally  placed  lacteal. 
On  the 'other  hand,  while  it  is  difficult  to  imagine  how  proteids 
can  pass  through  the  walls  of  the  capillaries  in  any  other  form 
than  that  of  diffusible  peptone.,  the  normal  passage  of  the  natural 
proteids  of  the  blood  being  exactly  in  the  opposite  direction, 
from  the  interior  of  the  capillaries  into  the  extravascular  elements 
of  the  tissues,  still  it  is  open  for  us  to  ask  the  question,  If  solid 
particles  of  fat  can  pass  from  the  interior  of  the  alimentary  canal 
into  the  lacteals,  why  should  not  various  forms  of  proteids  pass 
in  the  same  way  into  the  lacteals,  either  in  solution  or  even  as 
solid  particles  ? 

Briicke'  observed  that  after  a  meal  of  milk,  the  contents  of  the 
villus  after  death  were  loaded  with  a  granular  deposit  of  protcid  nature, 
and  of  an  acid  reaction.  He  infers  from  this  that  together  with  the 
fat  there  passes  into  the  villus  a  quantity  of  the  proteid  material  of  food 
m  the  form  of  alkali-albumin,  precipitable  by  weak  acids ;  and  argues 

'    Wien.  SiizuHgsba-'ichte,  xxxvii.,  iix. 

21 — 2 


324  ABSORPTION   OF   PROTEIDS.  [BOOK   II. 

from  this  and  other  facts  that  a  considerable  quantity  of  the.proteids 
of  food  thus  obtains  entrance  into  the  blood  without  suffering  the 
change  into  peptone. 

It  would  thus  seem  possible  for  some  of  the  proteids  to  pass 
into  the  lacteals  and  so  into  the  system  in  a  less  digested  form 
than  peptone  ;  and  it  is  further  possible  that  the  proteids  thus 
entering  into  the  system  in  different  forms  may  play  different  parts 
in  the  nutritive  labours  of  the  economy. 

But  in  all  these  considerations  the  fact  must  be  borne  in  mind 
that  the  intestinal  walls  undoubtedly  possess  a  selective  power  of 
absorption,  which  overrides  the  laws  of  diffusion  and  solubility. 
This  is  shewn  for  instance  by  the  results  of  Tappeiner ',  who 
found  that  the  fairly  soluble  and  diffusible  salts,  sodium  taurocho- 
late  and  glycocholate,  were  not  absorbed  by  the  duodenum  and 
upper  jejunum  even  at  a  time  when  fat  was  being  rapidly  absorbed 
in  those  regions,  but  did  disappear  in  the  ileum  or  lower  jejunum, 
the  glycocholate  apparently  being  absorbed  by  both  the  ileum 
and  lower  jejunum,  while  the  taurocholate  passed  away  in  the 
ileum  alone. 

We  cannot  judge  therefore  of  the  course  taken  by  the  proteids, 
or  of  the  form  in  which  they  are  absorbed,  by  deductions  based 
on  solubility  and  diffusion.  The  problems  we  are  discussing  can 
only  be  satisfactorily  settled  by  direct  experiment.  And  here  we 
meet  with  difficulties.  If  all  proteids  are  converted  into  peptone, 
and  so  pass  into  the  lacteals  or  into  the  blood  capillaries,  we 
might  expect  to  find  a  quantity  of  peptone  in  the  chyle  or  in 
portal  blood  or  in  both  after  a  proteid  meal.  But  neither  in  the 
portal  blood,  nor  in  the  chyle,  nor  in  the  general  blood  during 
digestion,  is  there  any  appreciable  quantity  of  peptone.  Of  course 
the  quantity  of  peptone  passing  into  the  portal  blood  at  any 
moment  might  be  small,  and  yet  a  considerable  quantity  might  so 
pass  during  the  hours  of  digestion.  We  may  suppose  moreover 
that  that  which  does  pass  is  immediately  converted,  possibly  by 
some  ferment  action,  into  one  or  other  of  the  natural  proteids  of 
the  blood,  or  otherwise  disposed  of;  and  Plosz  and  Gyergyai" 
have  shewn  that  peptone  injected  carefully  into  a  vein  disappears 
from  the  blood,  though  little  or  even  none  passes  out  by  the 
kidney.  Hence  the  failure  to  find  peptone  in  the  blood  (and  the 
same  may  be  said  of  the  chyle)  does  not  disprove  the  view  which 
seems  to  follow  legitimately  from  the  results  of  artificial  digestion, 

^    Wien.  Siizungsberichte,  Bd.  77,  Ap.  1878. 
=  Pfliiger's  Archiv,  X.  (1875)  536. 


CHAP.   I.]  DIGESTION.  325 

that  proteid  food  is  converted  into  peptone  before  passing  from 
the  alimentary  canal  into  the  system  ;  and  we  know  that  artificially- 
formed  peptone  is  availal)le  for  nutrition  ;  for  Plosz "  and  P16sz 
and  Ciyergyai  ^  found  liuit  dogs  fed  on  i)eptone  and  non-nitro- 
genous food  actually  put  on  flesh  and  gained  weight  3. 

On  the  other  hand,  that  the  proteids  pass  by  the  portal  blood 
(and  if  so  probably  in  the  form  of  peptone)  is  indicated  by  the 
experiments  of  Schmidt-Miilheim  •♦,  who  hnds  that  when  the  chyle 
is  entirely  prevented  from  entering  the  blood,  not  only  arc  jjroteids 
absorbed,  but  that  they  are  so  metal)oli/ed  in  the  body, that  the 
quantity  of  urea  which  in  consequence  makes  its  appearance  in 
the  urine  is  the  same  as  when  the  chyle  flows  into  the  venous 
system  as  usual.  Except  therefore  on  the  very  improbable  view 
that  proteids  absorbed  into  the  lacteals  of  the  villi  escape  (rgm 
the  lymphatic  system  before  they  reach  the  thoracic  duct,  we 
must  infer  that  they  are  absorbed  by  the  blood  capillaries. 

Sugar.  With  regard  to  the  path  taken  by  the  sugar,  the 
careful  inquiries  of  v,  Mcrings  shew  that  the  percentage  of  sugar 
both  in  chyle  and  in  general  blood  is  fairly  constant,  being  to  no 
marked  extent  increased  by  even  amylaceous  meals ;  but  that  a 
meal  of  sugar  or  starch  does  temporarily  increase  the  quantity  of 
sugar  in  the  portal  blood.  From  this  we  may  infer  that  such 
portions  of  the  sugar  of  the  intestinal  contents  as  are  absorbedas 
sugar  pass  exclusively  by  the  portal  vein.  But  it  must  be  re" 
membered  that  at  present  we  have  no  accurate  information  as  to 
how  large  a  proportion  of  the  sugar  resulting  from  a  meal  passes 
in  this  way  unchanged  until  it  reaches  the  liver,  and  how  much 
undergoes  the  lactic  acid  or  analogous  fermentation.  Nor  do  we 
know  as  yet  how  much  of  the  starch  taken  as  food  is  removed 
from  the  alimentary  canal  in  the  form  not  of  sugar  but  of 
dextrin. 

When  a  solution  of  sugar  is  injected  inio  an  empty  isolated  loop  of 
intestine  a  large  quantity  disappears,  without  the  contents  of  the 
loop  becoming  acid".  In  such  a  case  it  may  fairly  be  inferred  that 
the  sugar  is  .directly  absorbed  without  undergoing  any  change.  And 
where  sugar  is  introduced  in  large  quantities  into  the  alimentary  canal, 
the  percentage  of  sugt^r  in  the  blood  may  be  temporarily  increased  ; 
to   such    an   extent   indeed   that  sugar  may  appear  in  the   urine ', 

'  Pfliiger's  .4;r^;Y',  IX.  (1S74),  325,  "  Op.  cit. 

3  Cf.  Adamkiewicz,  Die  Naur  und  der  Sdhrwerth  da  Peptons,  1877. 

*  Anhivf.  Atiat.  11.  Physiol ,  1677,  p.  549.  s  Ibid.,  p.  379. 

*  Fuiike,  Ltlnb.  6tli  Aufl.  I.  p.  235. 

">  C.  Schmidt  und  v.  Becher,  quoted  in  Funke,  op.  cit.  p.  236. 


326  ABSORPTION   BY   DIFFUSION.  [BOOK   II. 

But  neither  of  these  facts  prove  that  the  sugar  of  an  ordinary  meal, 
passing  as  it  does  along  the  intestine  with  the  other  portions  of  the 
food,  and  produ:ts  of  digestion,  and  appearing  as  ic  does  in  most 
cases  in  comparatively  small  quantities  at  a  time  owing  to  the  more  or 
less  gradual  conversion  of  the  starch  of  the  meal,  is  similarly  absorbed 
unchanged  ;  while  in  order  that  the  marked  acidity  of  the  contents  of 
the  lower  intestine  should  be  kept  up,  a  considerable  quantity  of  sugar 
must  suffer  lactic  acid  fermentation,  if  the  acidity  be  due  as  stated  to 
lactic  acid. 

To  sum  up,  the  evidence  is  distinctly  in  favour  of  the  fats 
passing  largely  by  the  chyle,  and  of  the  proteids  and  sugar  pass- 
ing largely  by  the  portal  vein ;  but  there  still  remains  much 
doubt  as  to  the  course  and  fate  of  a  not  inconsiderable  portion  of 
the  fat,  and  the  question  as  to  the  exact  form  in  which  proteids 
arid  carbohydrates  leave  the  alimentary  canal,  cannot  be  answered 
in  a  perfectly  definite  manner. 

Absorption  by  diffusion.  It  is  evident,  from  the  discus- 
sion just  concluded,  that  simple  diffusion  is  far  from  explaining 
the  whole  transit  of  the  digested  food  from  the  intestine  into  the 
blood.  Nevertheless,  it  must  not  be  supposed  that  the  great  and 
general  property  of  diffusion  does  not  make  itself  felt  in  the  pro- 
cess of  absorption,  however  much  it  may,  in  the  case  of  various 
substances,  be  subordinated  and  held  in  check  by  more  potent 
influences.  Thus  the  passage  of  water  from  the  alimentary  cavity 
into  the  blood,  or  from  the  blood  into  the  alimentary  cavity,  and 
the  behaviour  of  various  inoi"ganic  salts,  when  taken  as  food  or 
medicine,  illustrate  very  clearly  the  influence  of  osmosis.  When 
the  intestine  contains  a  large  quantity  of  watery  matter,  the 
surplus  water  passes  by  diffusion  into  the  blood,  just  as  it  passes 
through  the  membrane  of  a  dialyser,  with  blood  or  serous  fluid  on 
the  one  side,  and  water  on  the  other.  When  an  albuminous  fluid 
of  the  specific  gravity  of  blood-serum  is  exposed  in  a  dialyser  to 
water,  about  200  parts  of  water  pass  through  the  membrane  of 
the  dialyser  from  the  water  into  the  albuminous  fluid  for  every 
one  part  of  albumin  which  passes  from  the  fluid  into  the  water. 
Moreover,  in  the  living  body,  the  blood  in  the  mesenteric 
capillary,  thus  diluted  by  diffusion  from  the  intestinal  contents,  is 
continually  beirig  replaced  by  fresh  blood  concentrated  by  its 
passage  through  the  skin,  lung,  or  kidney.  By  the  help  of  the 
circulation  an  almost  unlimited  quantity  of  water  can  be  absorbed 
from  the  alimentary  canal 

It  is  a  matter  of  common  experience  that  such  inorganic  and 
organic  salts  as  are   readily  diffusible,  pass  with  great  rapidity 


CHAP.  I.]  DIGESTION.  327 

into  the  blood  (and  thus  into  the  urine)  when  taken  by  the  mouth  ; 
and  the  rapidity  with  which  they  arc  absorbed  is  in  large  measure 
l^roportionate  to  their  dilTiisihiHty.  Of  course,  coincident  with 
tills  passage  of  the  salt  from  the  intestine  into  the  blood,  there  is 
a  proportionate  current  of  water  in  the  contrary  direction  from 
the  blood  into  the  intestine  ;  but  this,  though  opposed  to,  is, 
under  ordinary  circumstances,  too  small  to  diminish  to  any  serious 
extent  the  passage  of  water  from  the  intestine  into  the  blood,  of 
which  we  spoke  just  now,  as  caused  by  the  osmotic  influence  of 
the  albuminous  constituents  of  tlie  blood.  But,  under  certain 
circumstances,  the  former  may  overcome  the  latter.  Thus,  when 
a  concentrated  solution  of  a  highly  diffusible  salt,  such  as  mag- 
nesium suli)hate,  is  introduced  into  the  alimentary  canal,  the  flow 
of  water  from  the  blood  into  the  intestine  accompanying  the 
osmotic  transit  of  the  salt  from  the  intestine  into  the  blood,  is  so 
great  as  largely  to  exceed  the  current  in  the  contrary  direction  ; 
and  the  intestine  becomes  filled  with  water  at  the  expense  of  the 
blood.  Tiiis  is  probably  the  cause  of  the  purgative  action  of 
large  doses  of  many  sahne  matters.  And  even  the  purgative 
action  of  more  dilute  solutions  may  be  explained  in  the  same  way, 
since  in  the  case  of  some  salts  at  least  the  transit  of  water  as 
compared  with  the  transit  of  the  salt  is  relatively  more  rapid  with 
very  dilute  solutions  than  with  more  concentrated  solutions. 
Salts  such  as  these,  which,  when  introduced  into  the  intestine, 
produce  diarrhoea,  bring  about  a  contrary  condition  when  injected 
directly  into  the  blood  ;  and  magnesium  sulphate,  with  its  higher 
endosmotic  equivalent,  is  more  purgative  in  its  action  than 
sodium  chloride  with  its  lower  equivalent. 

Our  knowledge  of  the  physiology  of  digestion  is  the  accumulated 
gain  of  many  labours,  some  dating  back  from  very  old  times.  To 
Reaumur,  Spallanzani,  Tiedcmann  and  Gmelin,  Eberle  (who  first  ob- 
tained artificial  digestion  witn  gastric  mucus  and  an  acid),  Prout, 
Schwann  (who  first  introduced  the  idea  of  pepsin ',  though  Wasmann 
first  obtained  it  in  a  comparatively  pure  state),  Berzelius  and  other 
chemists,  we  owe  much.  The  observations  of  Dr.  Beaumont-',  carried 
on  by  means  of  the  accidental  gastric  fistula  of  Alexis  St.  Martin,  not 
only  added  largely  to  our  positive  knowledge,  but  were  also  of  great 
indirect  use  as  indicating  a  method  of  investigation  which  has  since 
proved  so  fruitful.    The  labours  of  Bidder  and  Schmidt^  and  Frerichs* 

'  Miilier's  Archiv,  1836,  p.  90. 

'  Exps.  atidObs.  on  the  Gaslric  Juia  and  Phys.  of  Digestion.    Boston,  U  S., 
1834. 
3  Die  Verdauungssd/le,  &c.,  1852. 
■*  Art.  '  Verdauung.'  W^z.-rncv's  Handivortcrbiic/i,  1846. 


328  DIGESTION.  [BOOK   II. 

were  of  great  value.  The  publication  of  Bernard's  work  on  pancreatic 
juice'  marked  a  distinct  step  in  advance  ;  but  of  far  greater  impor- 
tance was  the  same  illustrious  physiologist's  discovery  of  the  vaso- 
motor action  of  the  sympathetic  (see  p.  223),  followed  up  as  that  was  by 
Ludvvig's  demonstration  ==  of  the  secretory  activity  of  the  chorda  tym- 
pani,  and  enlarged,  as  this  has  been  in  turn,  as  well  by  the  labours  of 
Ludwig  a-nd  his  school,  as  by  those  of  Bernard,  Eckhard,  Wittich, 
Heidenhain  and  others.  To  the  importance  of  Heidenhain's  later 
observations  we  have  called  attention  in  the  text.  The  proofs  offered 
by  Corvisart3  and  ampHfied  by  Kiihnc*,  of  the  proteolytic  action  of  the 
pancreatic  juice  opened  out  a  line  of  inquiry  of  great  importance, 
which  is  as  yet  far  from  being  exhausted. 

'  Mem.  sur  I.  Pancreas,  1S56. 

=  Zt.f.  rat.  Med.,  N.  F.  i.  p.  255,  1851. 

3  Sur  une  FoncHon  p'U  conmte  dti  Pancreas,  1857. 

->  Yirchow'' s  Arckiv,  XXXIX.  (1867),  p.  130. 


CIIAPTKF    11. 

THE  TISSUES  AND  MECHANISMS   OF    RESPIRATION. 

We  have  already  seen  (Introduction,  p.  3)  tliat  one  particular  item 
of  the  body's  income,  viz.  oxygen,  is  peculiarly  associated  with  one 
particular  item  of  the  body's  waste,  viz.  carbonic  acid,  the  means 
which  are  applied  for  the  introduction  of  the  former  being  also 
used  for  the  getting  rid  of  the  latter.  Both  are  gases,  and  in  con- 
sequence the  ingress  of  the  one  as  well  as  the  egress  of  the  other 
is  far  more  dependent  on  the  simple  physical  process  of  diffusion 
than  on  any  active  vital  processes  carried  on  by  means  of  tissues. 
Oxygen  passes  from  the  air  into  the  blood  mainly  by  diffusion, 
and  mainly  by  diffusion  also  from  the  blood  into  the  tissues ;  in 
the  same  way  carbonic  acid  passes  mainly  by  diffusion  from  the 
tissues  into  the  blood,  and  from  the  blood  into  the  air.  Whereas, 
as  we  have  seen,  in  the  secretion  of  the  digestive  juices  the 
epithelium-cell  plays  an  all-important  part,  in  respiration  the 
entrance  of  oxygen  from  the  lungs  into  the  blood,  and  from  the 
blood  into  the  tissue,  and  the  passage  of  carbonic  acid  in  the 
contrary  direction,  are  affected  if  at  all,  in  a  wholly  subordinate 
manner,  by  the  behaviour  of  the  pulmonary,  or  of  the  capillary 
epithelium.  What  we  have  to  deal  with  in  respiration  then  is  not  so 
much  the  vital  activities  of  any  particular  tissue,  as  the  various 
mechanisms  by  which  a  rapid  interchange  between  the  air  and  the 
blood  is  effected,  the  means  by  which  the  blood  is  enabled  to  carry 
oxygen  and  carbonic  acid  to  and  from  the  tissues,  and  the  manner 
in  which  the  several  tissues  take  oxygen  from  and  give  carbonic 
acid  up  to  the  blood.  We  have  reasons  for  thinking  that  oxygen 
can  be  taken  into  the  blood,  not  only  from  the  lungs,  but  also  from 
the  skin,  and,  as  we  have  seen,  occasionally  from  the  alimentary 
canal  also  ;  and  carbonic  acid  certainly  passes  away  from  the  skin, 
and  through  the  various  secretions,  as  well  as  by  the  Jungs.  Still 
the  lungs  are  so  eminently  the  channel  of  the  interchange  of  gases 
between  the  body  and  the  air,  that  in  dealing  at  the  present  with 


330  INSPIRATION    AND   EXPIRATION.         [BOOK   II. 

respiration,  we  shall  confine  ourselves  entirely  to  pulmonary  re- 
spiration, leaving  the  consideration  of  the  subsidiary  respiratory 
processes  till  we  come  to  study  the  secretions  of  which  they 
respectively  form  part. 

Sec.   I.     The  Mechanics  of  Pulmonary  Respiration. 

The  lungs  are  placed,  in  a  semi-distended  state,  in  the  air-tight 
thorax,  the  cavity  of  which  they,  together  with  the  heart,  great 
blood-vessels  and  other  organs,  completely  fill.  By  the  contraction 
of  certain  muscles  the  cavity  of  the  thorax  is  enlarged ;  in  conse- 
quence the  pressure  of  the  air  within  the  lungs  becomes  less  than 
that  of  the  air  outside  the  body,  and  this  difference  of  pressure 
causes  a  rush  of  air  through  the  trachea  into  the  lungs  until  an 
equilibrium  of  pressure  is  established  between  the  air  inside  and 
that  outside  the  lungs.  This  constitutes  inspiration.  Upon  the 
relaxation  of  the  inspiratory  muscles  (the  muscles  whose  contraction 
has  brought  about  the  thoracic  expansion),  the  elasticity  of  the 
chest-walls  and  lungs,  aided  perhaps  to  some  extent  by  the  con- 
traction of  certain  muscles,  causes  the  chest  to  return  to  its 
original  size ;  in  consequence  of  this  the  pressure  within  the  lungs 
now  becomes  greater  than  that  outside,  and  thus  air  rushes  out  of 
the  trachea  until  equilibrium  is  once  more  established.  This  con- 
stitutes expiration  ;  the  inspiratory  and  expiratory  act  together 
forming  a  respiration.  The  fresh  air  introduced  into  the  upper 
part  of  the  pulmonary  passages  by  the  inspiratory  movement  con- 
tains more  oxygen  and  less  carbonic  acid  than  the  old  air  previously 
present  in  the  lungs.  By  diffusion  the  new  or  tidal  air,  as  it  is 
frequently  called,  gives  up  its  oxygen  to,  and  takes  carbonic  acid 
from,  the  old  or  stationary  air,  as  it  has  been  called,  and  thus 
when  it  leaves  the  chest  in  expiration  has  been  the  means  of  both 
introducing  oxygen  into  the  chest  and  of  removing  carbonic  acid 
from  it.  In  this  way,  by  the  ebb  and  flow  of  the  tidal  air,  and  by 
diffusion  between  it  and  the  stationary  air,  the  air  in  the  lungs 
is  being  constantly  renewed  through  the  alternate  expansion  and 
contraction  of  the  chest. 

In  ordinary  respiration,  the  expansion  of  the  chest  never  reaches 
its  m.aximum  ;  by  more  forcible  muscular  contraction,  by  what  is 
called  laboured  inspiration,  an  additional  thoracic  expansion  can 
be  brought  about,  leading  to  the  inrush  of  a  certain  additional 
quantity  of  air  before  equilibrium  is  established.  This  additional 
quantity  is  often  spoken  of  as  coiiiplemenial  air.  In  the  same  way, 
in  ordinary  respiration,  the  contraction  of  the  chest  never  reaches 
its   maximum.      By   calling  into   use   additional   muscles,  by   a 


ClIAr.    II.]  RESPIRATION.  331 

laboured  expiration,  an  additional  quantity  of  air,  the  so-called 
reserve  or  suf^pUntental  air,  may  be  driven  out.  Bui  even  after  the 
most  forcible  expiration,  a  considerable  quantity  of  air,  the  r^/i///^/ 
air,  still  remains  in  the  lungs.  Tlic  natural  condition  of  the  lungs 
in  the  chest  is  in  fact  one  of  partial  distension.  The  elastic  pul- 
monary tissue  is  always  to  a  certain  extent  on  the  stretch  ;  it  is 
always,  so  to  speak,  striving  to  pull  asunder  the  pulmonary  from 
the  parietal  pleura  ;  but  this  it  cannot  do,  because  the  air  can  have 
no  access  to  the  pleural  cavity.  When  however  the  chest  ceases 
to  be  air-tight,  when  by  a  puncture  of  the  chest- wall  or  diaphragm, 
air  is  introduced  into  the  pleural  chamber,  the  elasticity  of  the 
lungs  pulls  the  pulmonary  away  from  the  parietal  pleura,  and  the 
lungs  collapse,  driving  out  by  the  windpipe  a  considerable  quantity 
of  the  residual  air.  Even  then,  however,  the  lungs  are  not  com- 
pletely emptied,  some  air  still  remaining  in  the  air-cells  and 
j)assages.  It  need  hardly  be  added  that  when  the  pleura  is 
punctured,  and  air  can  gain //r^r  admittance  from  the  exterior  into 
the  pleural  chamber,  the  effect  of  the  respiratory  movements  is 
simply  to  drive  air  in  and  out  of  that  chamber,  instead  of  in  and 
out  of  the  lung.  There  is  in  consequence  no  renewal  of  the  air 
within  the  lungs  under  those  circumstances. 

In  man  the  pressure  exerted  by  the  elasticity  of  the  lungs  alone 
amounts  to  about  5  mm.  of  mercury.  This  is  estimated  by  tying  a 
manometer  into  the  windpipe  of  a  dead  subject  and  observing  the  rise 
of  mercury  which  takes  place  when  the  chest-walls  are  punctured.  If 
the  chest  be  forcibly  distended  beforehand,  a  much  larger  rise  of  the 
mercury,  amounting  to  30  mm.  in  the  case  of  a  distension  corre- 
sponding to  a  very  forcible  inspiration,  is  observed.  In  the  living 
body  this  mechanical  elastic  force  of  the  lungs  is  assisted  by  the 
contraction  of  the  plain  muscular  fibres  of  the  bronchi ;  the  pressure 
however  which  can  be  exerted  by  these  probably  does  not  e.xceed  i  or 
2  mm. 

When  a  manometer  is  introduced  into  a  lateral  opening  of  the 
windpipe  of  an  animal,  the  mercury  will  fall,  indicating  a  negative 
pressure  as  it  is  called,  during  inspiration,  and  rise,  indicating  a 
positive  pressure,  during  expiration,  the  former  or  negative  pressure 
amounting  to  about  3  mm.,  and  the  latter  or  positive  pressure  to  2  mm. 
of  mercury.  When  a  manometer  is  fitted  with  air-tight  closure  into 
the  mouth,  or  better,  in  order  to  avoid  the  suction-action  of  the  mouth, 
into  one  nostril,  the  other  nostril  and  the  mouth  being  closed,  and 
efforts  of  inspiration  and  expiration  are  made,  the  mercury  falls  or 
undergoes  negative  pressure  with  inspiration,  and  rises,  or  undergoes 
positive  pressure  during  expiration.  Bonders  found  in  this  way  that 
the  negative  pressure  of  a  strong  inspiratory  effort  varied  from  30  to 
74  mm.,  wliile  the  positive  pressure  of  a  strong  expiration  varied  from 
62  to  100  mm. 


332 


RHYTHM   OF   RESPIRATION. 


[book   II. 


The  total  amount  of  air  which  can  be  given  out  by  the  most 
forcible  expiration  following  upon  a  most  forcible  inspiration, 
that  is,  the  sum  of  the  complemental,  tidal  and  reserve  airs,  was 
called  by  Hutchinson  'the  vital  capacity;'  'extreme  differential 
capacity '  is  a  better  phrase.  It  may  be  measured  by  a  modifica- 
tion of  a  gas-meter  called  a  spiroineter.  The  medium  vital  capacity 
may  be  put  down  at  3 — 4000  c.c.  (200  to  250  cubic  inches). 

Independent  of  other  causes  of  variation,  Hutchinson  found  the 
vital  capacity  to  be  decidedly  dependent  on  stature,  the  taller  persons 
having  the  greater  capacity. 

Of  the  whole  measure  of  vital,  capacity,  about  500  c.c.  (30  c. 
inch)  may  be  put  down  as  the  average  amount  of  tidal  air,  the 
remainder  being  nearly  equally  divided  between  the  complemental 
and  reserve  airs.  The  quantity  left  in  the  lungs  after  the  deepest 
expiration  amounts  to  about  1400 — 2000  c.c. 

Since  the  respiratory  movements  are  so  easily  affected  by  various 
circumstances,  the  simple  fact  of  attention  being  directed  to  the 
breathing  being  sufficient  to  cause  modifications,  both  of  the  rate  and 
depth  of  the  respiration,  it  becomes  very  difficult  to  fix  the  volume  of 
an  average  breath.  Thus  various  authors  have  given  figures  varying 
from  53  c.c.  to  792  c.c.  The  statement  made  above  is  that  given 
by  Vierordt  as  the  mean  of  observations  varying  from  177  to 
699  c.c. 

The  Rhythm  of  Respiration.  If  the  movements  of  the 
column  of  tidal  air,  or  the  movements  of  expansion  and  contrac- 
tion, or  the  fall  and  rise  of  the  diaphragm,  be  registered,  some 
such  curve  as  that  represented  in  Fig.  46  is  obtained. 


Fig.  45.    Tracing  of  Thoracic  Respiratory  Movements   obtained   by   means  of 

Marey's  Pneumograph. 

(To  be  read  from  left  to  right.) 

A  whole  respiratory  phase  is  comprised  between  a  and  a  ;  inspiration,  during  which  the  lever 
descends,  extending  from  a  to  6,  and  expiration  from  i  to  a.  The  undulations  at  ;  are 
caused  by  the  heart's  beat. 


l"i<;.  47.    Apparatus  fok  taking  Tkacings  of  th 


The  recordinij  apparatus  shewn  is  the  ordinary  cylinder  recording  apparatus.    The 
by  the  spring  clock-'vorkin  C  regulated  by  Foucault  s  regulator  D.     By  means 
may  be  increased  or  diminished.   .  .       ,  ,  ■    _  „„:„.,i   :c  rnnnpcfpd  bv  indi; 

The  tracheotomy  tube  t  fixed  in  .the  trachea  °f/"  ^"'"^=^' .'V°;"^'"7be  Ju^^^ 
of  the  T  piece  proceeds  a  second  piece  of  '>''?'"g  ^V*^^  t"    tambour    "(serfV 
proceeds  a  third  piece  of  tubing  rf  connected  with  a  Marey  s  t^-^bour  j/^see  r^     2 
he  animal  breathes  freely  through  this,  and  ^^e  movements  in  the   air  ot  O  ana  c 
the  air  contained  in  the  jar,  and  the  movements  of  '^e  lever  of    he  tambour  bec^^^^^ 

Below  the  lever  is  seen  a  small  time-marker  w  connected  with  an  electro  magncc, 
by  a  clock-work  or  metronome. 


To  face  page  333. 


lEXTs  OF  JHE  Column  of  Air  in  Respiration 


A.  covered  with  smoked  paper  is  by  means  of  the  friction-plate  B  put  into  revolution 
E,  the  cylinder  can  be  raised  or  lowered  and  by  means  of  the  screw  F  its  speed 

ubin?  a  with  a  glass  T  piece  inserted  into  the  large  jar  G.  From  the  other  end 
r  partially  obstructed  at  pleasure  by  means  of  the  screw  clamp  c.  From  the  jar 
the  lever  of  which  /  writes  on  the  recording  surface.  When  the  tube  b  is  open 
ly  in  the  tambour  are  slight.  On  closing  the  clamp  c,  the  animal  breathes  only 
ly  much  more  marked. 
It  through  which  coming  from  a  battery  by  the  wires  x  and  y  is  made  and  broken 


334  THE   RESPIRATORY   MO\EMENTS.         [BOOK   II. 

respiration  becomes  infrequent,  pauses  of  considerable  length  may- 
be observed. 

In  what  may  be  considered  as  normal  breathing,  the  respiratory 
act  is  repeated  about  17  times  a  minute  ;  and  the  duration  of  the 
inspiration  as  compared  with  that  of  the  expiration  (and  such 
pause  as  may  exist)  is  about  as  ten  to  twelve. 

The  rate  of  the  respiratory  rhythm  varies  very  largely,  and  in  this 
as  in  the  volume  it  is  very  difficult  to  fix  a  satisfactory  average. 
While  Hutchinson  places  it  at  20  a  minute,  Vierordt  puts  it  at  irg, 
and  Funke  at  I3'5.  The  frequency  is  greater  in  children  than  in 
adults,  but  rises  again  somewhat  after  30  years  of  age.  Quetelet 
gives  the  rate  of  respiration  of  new-born  infants  at  44  ;  from  i  to  5 
years,  26,  from  25  to  30,  16,  from  30  to  50,  i8"i  per  minute.  The  rate 
is  infiuenced  by  the  position  of  the  body,  being  quicker  in  standing 
than  in  lying,  and  in  lying  than  in  sitting.  Ivluscular  exertion  and 
emotional  conditions  affect  it  deeply.  In  fact,  almost  every  event 
which  occurs  in  the  body  may  influence  it.  We  shall  have  to  consider 
in  detail  hereafter  the  manner  in  which  this  influence  is  brought  to 
bear. 

When  the  ordinary  respiratory  movements  prove  insufficient  to 
effect  the  necessary  changes  in  the  blood,  their  rhythm  and  cha- 
racter become  changed.  Normal  respiration  gives  place  to 
laboured  respiration,  and  this  in  turn  to  dyspnoea,  which,  unless 
some  restorative  event  occurs,  terminates  in  asphyxia.  These 
abnormal  conditions  we  shall  study  more  fully  hereafter. 


The  Respiratory  Movements. 

When  the  movements  of  the  chest  during  normal  breathing 
are  watched,  it  is  seen  that  during  respiration  an  enlargement  takes 
place  in  the  antero-posterior  diameter,  the  sternum  being  thrown 
forwards,  and  at  the  same  time  moving  upward.  The  lateral  width 
of  the  chest  is  also  increased.  The  vertical  increase  of  the  cavity 
is  not  so  obvious  from  the  outside,  though  when  the  movements 
of  the  diaphragm  are  watched  by  means  of  an  inserted  needle, 
the  upper  surface  of  that  organ  is  seen  to  descend  at  each  inspira- 
tion, the  anterior  walls  of  the  abdomen  bulging  out  at  the  same 
time.  In  the  female  human  subject,  the  movement  of  the  upper 
part  of  the  chest  is  very  conspicuous,  the  breast  rising  and  falling 
with  every  lespiration ;  in  the  male,  however,  the  movements  are 
almost  entirely  confined  to  the  lower  part  of  the  chest.  In 
laboured  respiration  all  parts  of  the  chest  are  alternately  expanded 
and  contracted*,  the  breast  rising  and  falling  as  well  in  the  male  as 
in  the  female.     We  have  now  to  consider  these  several  movements 


CHAP.    II.]  RESPIRATION.  335 

in  greater  detail,  and  to  study  the  means  by  which  they  are  carried 
out. 

Inspiration.  There  are  two  chief  means  by  which  the  chest 
is  enlarged  in  normal  inspiration,  viz.  the  descent  of  the  diaphragm 
and  tlie  elevation  of  the  ribs.  The  former  causes  that  movement 
in  the  lower  part  of  the  chest  and  abdomen  so  characteristic  of 
male  breathing,  which  is  called  diaphragmatic  ;  the  latter  causes 
the  movement  of  the  upper  chest  characteristic  of  female  breath- 
ing, which  is  called  costal.  These  two  main  factors  are  assisted 
by  less  important  and  subsidiary  events. 

The  descent  of  the  diaphragm  is  effected  by  means  of  the 
contraction  of  its  muscular  fibres.  When  at  rest  the  diaphragm 
presents  a  convex  surface  to  the  thorax  ;  when  contracted  it  be- 
comes much  flatter,  and  in  consequence  the  level  of  the  chest-floor 
is  lowered,  the  vertical  diameter  of  the  chest  being  proportionately 
enlarged.  In  descending,  tlie  diaphragm  presses  on  the  abdominal 
viscera,  and  so  causes  a  projection  of  the  tlaccid  abdominal  walls. 
From  its  attachments  to  the  sternum  and  the  false  ribs,  the  dia- 
phragm, while  contracting,  naturally  tends  to  jniU  the  sternum  and 
the  ujjper  f;il$e  ribs  downwards  and  inwards,  and  the  lower  false 
ribs  upwards  and  inwards,  towards  the  lumbar  spine.  In  normal 
breathing,  this  tendency  produces  litde  effect,  being  counteracted 
by  the  accompanying  general  costal  elevation,  and  by  certain  special 
muscles  to  be  mentioned  presently.  In  forced  inspiration  how- 
ever, and  especially  where  there  is  any  obstruction  to  the  entrance 
of  air  into  the  lungs,  the  lower  ribs  may  be  so  much  drawn  in  by 
the  contraction  of  the  diaphragm,  that  the  girth  of  the  trunk  at 
this  point  is  obviously  diminished. 

The  elevation  of  the  ribs  is  a  much  more  complex  matter  than 
the  descent  of  the  diaphragm.  If  we  examine  any  one  rib,  such 
as  the  fifth,  and  observe  that  while  it  moves  freely  on  its  vertebral 
articulation,  it  descends  when  in  the  position  of  rest  in  an  oblique 
direction  from  the  spine  to  the  sternum,  it  is  obvious  that  when 
the  rib  is  raised,  its  sternal  attachment  must  not  only  be  carried 
upward,  but  also  thrown  forwards.  The  rib  may  in  fact  be  regarded 
as  a  radius,  moving  on  the  vertebral  articulation  as  a  centre,  and 
causing  the  sternal  attachment  to  describe  an  arc  of  a  circle  in  the 
vertical  plane  of  the  body  ;  as  the  rib  is  carried  upwards  from  an 
oblique  to  a  more  horizontal  position,  the  sterna'  attachment  must 
of  necessity  be  carried  farther  away  in  front  of  the  spine.  Since 
all  the  ribs  have  a  downward  slanting  direction,  they  must  all  tend, 
when  raised  towards  the  horizontal  position,  to  thrust  the  sternum 
forward,  some  more  than  others  according  to  their  slope  and  length. 


336  MOVEMENTS   OF   INSPIRATION.  [BOOK   II. 

The  elasticity  of  the  sternum  and  costal  cartilages,  together  with 
the  articulation  of  the  sternum  to  the  clavicle  above,  permit  the 
front  surface  of  the  chest  to  be  thus  thrust  forwards  as  well  as 
upwards,  when  the  ribs  are  raised.  By  this  action,  the  antero- 
posterior diameter  of  the  chest  is  enlarged. 

According  to  A.  Ransome^,  the  forward  movement  in  inspiration, 
especially  of  the  upper  ribs,  is  so  great  that  it  can  only  be  accounted 
for  by  an  expiratory  bending  in  and  inspiratory  straightening  of  the 
ribs. 

Since  the  ribs  form  arches  which  increase  in  their  sweep  as 
one  proceeds  from  the  first  downwards  as  far  at  least  as  the  seventh, 
it  is  evident  that  when  a  lower  rib  such  as  the  fifth  is  elevated  so 
as  to  occupy  or  to  approach  towards  the  position  of  the  one  above 
it,  the  chest  at  that  level  will  become  wider  from  side  to  side, 
in  proportion  as  the  fifth  arch  is  wider  than  the  fourth.  Thus 
the  elevation  of  the  rib  increases  not  only  the  antero-posterior  but 
also  the  transverse  diameter  of  the  chest.  Further,  on  account  of 
the  resistance  of  the  sternum,  the  angles  between  the  ribs  and  their 
cartilages  are,  in  the  elevation  of  the  ribs,  somewhat  opened  out, 
and  thus  also  the  transverse  as  well  as  the  antero-posterior  diameter, 
somewhat  increased.  In  several  ways,  then,  the  elevation  of  the 
ribs  enlarges  the  dimensions  of  the  chest. 

The  ribs  are  raised  by  the  contraction  of  certain  muscles.  Of 
these  the  external  intercostals  are  the  most  important.  Even  in 
the  case  of  two  isolated  ribs  such  as  the  fifth  and  sixth,  the  con- 
traction of  the  external  intercostal  muscle  of  the  intervening 
space  raises  the  two  ribs,  thus  bringing  them  towards  the  position 
in  which  the  fibres  of  the  muscle  have  the  shortest  length,  viz.  the 
horizontal  one.  This  elevating  action  is  further  favoured  by  the 
fact  that  the  first  rib  is  less  moveable  than  the  second,  and  so 
affords  a  comparatively  fixed  base  for  the  action  of  the  muscles 
between  the  two,  the  second  in  turn  supporting  the  third  and  so 
on,  while  the  scaleni  muscles  in  addition  serve  to  render  fixed, 
or  to  raise,  the  first  two  ribs.  So  that  in  normal  respiration,  the 
act  begins  probably  by  a  contraction  of  the  scaleni.  The  first  two 
ribs  being  thus  fixed,  the  contraction  of  the  series  of  external 
intercostal  muscles  acts  to  the  greatest  advantage. 

While  the  elevating  i.e.  inspiratory  action  of  the  external  inter- 
costals is  admitted  by  all  authors,  the  function  of  the  internal 
intercostals  has  been  much  disputed. 

Haller  may  be  regarded  as  the  leader  of  those  who  regard  the 
internal  intercostals  as  inspiratory,  while  Hamberger  was  the  first  wha 

^  On  Stethometry,  1876,  p.  96. 


CHAP.    II.]  RESPIRATION  337 

suc'-cssfully  advocntcd  the  perhaps  more  commonly  adopted  view  that 
while  those  parts  of  thcai  whioh  lie  between  the  sternal  cartilajjes  act 
like  t!ic  external  intercostal  as  elevators, />.  as  inspirato/y  in  function, 
thoic  parts  which  lie  between  the  osseous  ribs  act  as  depressors,  i.e.  as 
expiratory  in  function. 

In  the  well-kn  )wn  model  invented  by  Bernoulli  and  adopted  by 
Hambergcr,  consisting  of  two  rigid  bars,  representing  the  ribs,  moving 
vertically  by  means  of  their  articulations  witli  an  upright  representing 
the  spine  and  connected  at  their  free  ends  l)y  a  piece  representing  the 
sternum,  it  is  undoubtedly  true  that  stretched  elastic  bands  attached  to 
the  birs  in  such  a  way  as  to  represent  respectively  the  external  and 
internal  interlocals,  viz.  sloping  in  the  one  case  downwards  and 
forwards  a-nd  in  the  other  downwards  and  backwards,  do,  on  being  left 
free  to  contract,  in  the  former  case  elevate  and  in  the  latter  depress  the 
ribs.  Such  a  model  however  does  not  fairly  represent  the  natural 
conditions  of  the  ribs,  which  are  not  straight  and  rigid,  but  peculiarly 
curved  and  of  varying  elasticity,  capable  moreover  of  rotation  on  their 
own  a.xes,  and  having  their  movements  determined  by  the  characters 
of  tiieir  vertebral  articulations.  On  the  other  hand,  not  only  do  the 
direction  and  attachments  of  the  internal  intercostals  between  the 
sternal  cartilages  suggest  an  elevating  inspiratory  action,  but  the 
absence  of  the  external  muscles  in  front  and  the  internal  behind  seems 
to  point  to  both  sets  of  muscles  acting  towards  the  same  end.  The 
mechanical  conditions  however  are  in  the  case  of  these  muscles  so 
complex,  that  a  deduction  of  their  actions  from  simple  mechanical 
principles,  or  from  the  direction  of  the  fibres,  must  be  exceedingly 
difficiilt  and  dangerous.  Newell-Martin  and  Hartwell'  have  shewn 
by  an  ingenious  experiment  that  in  the  cat  and  the  dog,  the  internal 
intercostals,  along  their  whole  length,  contract,  even  in  the  early  stages 
of  dyspnoea,  alternately  with  the  diaphragm,  and  are  therefore  to  be 
regarded  as  expiratory  in  function. 

Next  in  importance  to  the  external  intercostals  come  the  leva- 
tores  costaruni,  which,  though  small  muscles,  are  able,  from  the 
nearness  of  their  costal  insertions  to  the  fulcrum,  to  produce 
considerable  movement  of  the  sternal  ends  of  the  ribs.  The 
external  intercostals  and  the  levatores  costarum  with  the  scaleni 
may  foirly  be  said  to  be  the  elevators  of  the  ribs,  i.e.  the  chief 
muscles  of  costal  inspiration  in  normal  breathing. 

Additional  space  in  the  transverse  diameter  is  afforded  probably  by 
the  rotation  of  the  ribs  on  an  antero-posterior  axis ;  but  this  movement 
is  quite  subsidiaiy  and  unimportant.  When  the  chest  is  at  rest,  the 
ribs  are  somewhat  inclined  with  their  lower  borders  directed  inwards 
as  well  as  downwards.  When  they  are  drawn  up  by  the  action  of  the 
intercostal  muscles,  their  lower  borders  are  everted.  Thus  their  flat 
sides  are  presented  to  the  thoracic  cavity,  which  is  thereby  slightlj 
increased  in  width. 

■   Jourtt.  /VirstW.,  II.  (1S79)  p.  24.   . 
F.  P.  '  22 


33^  LABOURED   INSPIRATION.  [EOOK   II. 

Laboured  Inspiration.  When  respiration  becomes  laboured, 
other  muscles  are  brought  into  play.  The  scaleni  are  strongly 
contracted,  so  as  to  raise  or  at  least  give  a  very  fixed  support  to 
the  first  and  second  ribs.  In  the  same  way  the  serratus  posticus 
superior,  which  descends  from  the  fixed  spine  in  the  lower  cervical 
and  upper  dorsal  regions  to  the  second,  third,  fourth  and  fifth  ribs, 
by  its  contractions  raises  those  ribs.  In  laboured  breathing  a 
function  of  the  lower  false  ribs,  not  very  noticeable  in  easy 
breathing,  conies  into  play.  They  are  depressed,  retracted,  and 
fixed,  thereby  giving  increased  support  to  the  diaphragm,  and 
directing  the  whole  energies  of  that  muscle  to  the  vertical  en- 
largement of  the  chest.  In  this  way  the  serratus  posticus  inferior, 
which  passes  upward  from  the  lumbar  aponeurosis  to  the  last  four 
ribs,  by  depressing  and  fixing  those  ribs  becomes  an  adjuvant 
inspiratory  muscle.  The  quadi-atits  himboru7?t  and  lower  portions 
of  the  sacio-lumbalis  may  have  a  similar  function. 

All  these  muscles  may  come  into  action  even  in  breathing 
which,  deeper  than  usual,  can  hardly  perhaps  be  called  laboured. 
When  however  the  need  for  greater  inspiratory  eff'orts  becomes 
urgent,  all  the  muscles  which  can,  from  any  fixed  point,  act  in 
enlarging  the  chest,  come  into  play.  Thus  the  arms  and  shoulder 
being  fixed,  the  serratus  magjius  passing  from  the  scapula  to  the 
middle  of  the  first  eight  or  nine  ribs,  the  pectoralis  minor  passing 
from  the  coracoid  to  the  front  parts  of  the  third,  fourth  and  fifth 
ribs,  the  pectoralis  major  passing  from  the  humerus  to  the  costal 
cartilages,  from  the  second  to  the  sixth,  and  that  portion  of  the 
latissi7niis  dorsi  which  passes  from  the  humerus  to  the  last  three 
ribs,  all  serve  to  elevate  the  ribs  and  thus  to  enlarge  the  chest. 
The  sterno-mastoid  and  other  muscles  passing  from  the  neck  to 
the  sternum,  are  also  called  into  action.  In  fact,  every  muscle 
which  by  its  contraction  can  either  elevate  the  ribs  or  contribute 
to  the  fixed  support  of  muscles  which  do  elevate  the  ribs,  such  as 
the  trapezius,  levator  anguli  scapulse  and  rliomboidei  by  fixing  the 
scapula,  may,  in  the  inspiratory  efforts  which  accompany  dyspnoea, 
be  brought  into  play. 

Expiration.  In  normal  easy  breathing,  expiration  is  in  the 
main  a  simple  effect  of  elastic  reaction.  By  the  inspiratory  effort 
the  elastic  tissue  of  the  lungs  is  put  on  the  stretch  ;  so  long  as  the 
inspiratory  muscles  continue  contracting,  the  tissue  remains 
stretched,  but  directly  those  muscles  relax,  the  elasticity  of  the 
lungs  comes  into  play  and  drives  out  a  portion  of  the  air  contained 
in  them.  Similarly  the  elastic  sternum  and  costal  cartilages  are 
by  the  elevation  of  the  ribs  put  on  the  stretch :  they  are  driven 


CHAP.    II.]  RESPIRATION.  339 

into  a  position  which  is  unnatural  to  thera.  When  the  intercostal 
and  other  elevator  musrles  cease  to  contract,  the  elasticity  of  the 
sternum  and  costal  cartilages  causes  them  to  return  to  their  pre- 
vious position,  thus  depressing  the  ribs,  and  diminishing  the 
dimensions  of  the  chest.  Wlien  the  diaphragm  descends,  in  push- 
ing down  the  abdominal  viscera,  it  puts  the  abdominal  walls  on 
the  stretch ;  and  hence,  when  at  the  end  of  inspiration  the 
diaphragm  relaxes,  the  abdominal  walls  return  to  their  place,  and 
by  pressing  on  the  abdominal  viscera,  push  the  diaphragm  up 
again  into  its  position  of  rest.  Expiration  then  is,  in  the  main, 
simple  elastic  reaction  ;  but  it  is  obvious  that  since  external  work 
has  been  effected  by  the  respiratory  act,  viz.  the  movement  of  the 
column  of  air,  the  reaction  of  exjiiration  must  fall  short  of  the 
action  of  inspiration  ;  there  must  be  some,  though  it  may  be  a 
very  slight,  additional  expenditure  of  energy  to  bring  the  chest 
completely  to  its  former  condition.  This  is,  as  we  have  seen, 
supposed  by  many  to  be  afforded  by  the  internal  intercostals 
acting  as  depressors  of  the  ribs.  If  these  do  not  act  in  this  way, 
we  may  suppose  that  the  elastic  return  of  the  abdominal  walls  is 
accompanied  and  assisted  by  a  contraction  of  the  abdominal 
muscles.  The  triangularis  sterni,  the  effect  of  whose  contraction 
is  to  pull  down  the  costal  cartilages,  may  also  be  regarded  as  an 
expiratory  muscle. 

When  expiration  becomes  laboured,  the  abdominal  muscles 
become  important  expiratory  agents.  By  pressing  on  the  con- 
tents of  the  abdomen,  they  thrust  them  and  the  diaphragm  up 
into  the  chest,  the  \ertical  diameter  of  which  is  thereby  lessened, 
and  by  pulling  down  the  sternum  and  the  middle  and  lower  ribs 
they  lessen  also  the  cavity  of  the  chest  in  its  aniero-posterior  and 
transverse  diameters.  They  are  in  fact  the  chief  expiratory 
muscles,  though  they  are  doubtless  assisted  by  the  serratus 
posticus  inferior  and  portions  of  the  sacro-Iumbalis,  since  when  the 
diaphragm  is  not  contracting,  the  depression  of  the  lower  ribs 
which  the  contraction  of  these  muscles  causes,  serves  only  to 
narrow  the  chest.  As  expiration  becomes  more  and  more  forced, 
every  muscle  in  the  body  which  can  either  by  contracting  depress 
the  ribs,  or  press  on  the  abdominal  viscera,  or  afford  fixed  support 
to  muscles  having  those  actions,  is  called  into  play. 

Facial  and  Laryngeal  Respiration.  The  thoracic  respiratory  move- 
ments are  accompanied  by  associated  respiratory  movements  of  other 
pans  ot   the  body,  more  particularly  of  the  face  and  of  the  glottis. 

In  normal  healthy  respiration  the  current  of  air  which  passes 
in  and  out  of  the  lungs,  travels,  not  through  the  mouth  but  through 
the  nose,  viz.,  chietly  through  the  lower  nasal  meatus.     The  ingoing 

22—2 


340  >  CHANGES   OF   THE   AIR.  [BOOK   II, 

air,  by  exposure  to  the  vascular  mucous  membrane  of  the  narrow  and 
winding  nasal  passages,  is  more  efficiently  warmed  than  it  would  be  if 
it  passed  through  the  mouth  ;  and  at  the  same  time  the  mouth  is 
thereby  protected  from  the  desiccating  effect  of  the  continual  inroad 
of  comparatively  dry  air. 

During  each  inspiratory  effort  the  nostrils  are  expanded,  probably 
by  the  action  of  the  dilatores  naris,  and  thus  the  entrance  of  air  facili- 
tated. The  return  to  their  previous  condition  during  expiration  is 
effected  by  the  elasticity  of  the  nasal  cartilages,  assisted  perhaps  by  the 
compressores  naris.  This  movement  of  the  nostrils,  perceptible  in 
many  people,  even  during  tranquil  breathing,  becomes  very  obvious  in 
laboured  respiration. 

When  the  mouth  is  closed,  the  soft  palate  which  is  held  somewhat 
tense,  is  swayed  by  the  respiratory  current,  but  entirely  in  a  passive 
manner,  and  it  is  not  until  the  larynx  is  reached  by  the  ingoing  air  that 
any  active  movements  are  met  with.  When  the  larynx  is  examined  with 
the  laryngoscope,  it  is  frequently  seen  that,  while  during  inspiration  the 
glottis  is  widely  open,  with  each  expiration  the  arytenoid  cartilages  ap- 
proach each  other  so  as  to  narrow  tJtie  glottis,  the  cartilages  of  Santorini 
projecting  inwards  at  the  same  time.  Thus,  synchronous  with  the 
respiratory  expansion  and  contraction  of  the  chest,  and  the  respiratory 
elevation  and  depression  of  the  alas  nasi,  there  is  a  rhythmic  widening 
and  narrowing  of  the  glottis.  Like  the  n^ovements  of  the  nostril,  this 
respiratory  action  of  the  glottis  is  much  more  evident  in  laboured  than 
in  tranquil  breathing.  Indeed  in  the  latter  case  it  is  frequently  absent. 
The  manner  in  which  this  rhythmic  opening  and  narrowing  is  effected 
will  be  described  when  we  come  to  study  the  production  of  the  voice. 
Whether  there  exists  a  rhythmic  contraction  and  expansion  of  the 
trachea  and  bronchial  passages  effected  by  means  of  the  plain  muscular 
tissue  of  those  organs  and  synchronous  with  the  respiratory  movements 
of  the  chest,  is  uncertain '. 

Sec.  2.     Changes  of  the  Air  in  Respiration. 

During  its  stay  in  the  lungs,  or  rather  during  its  stay  in  the 
bronchial  passages,  the  tidal  air  (by  means  of  diffusion  chiefly) 
effects  exchanges  with  the  stationary  air  ;  in  consequence 
the  expired  air  differs  from  inspired  air  in  several  important 
particulars. 

1.  The  temperature  of  expired  air  is  variable,  but  under 
ordinary  circumstances  is  higher  than  that  of  the  inspired  air.  At 
an  average  temperature  of  the  atmosphere,  for  instance  at  about 
20°  C,  the  temperature  of  expired  air  is,  in  the  mouth  33"y°,  in 
the  nose  35*3°.  When  the  external  temperature  is  low,  that  of  the 
expired  air  sinks  somewhat,  but  not  to  any  great  extent,  thus  at 
-6'3°  C.  it  is  29*8°  C.  When  the  external  temperature  is  high, 
the  expired  air  may  become  cooler  than  the  inspired,  thus  at  41 '9* 

^  Cf.  Horvath,  PflLiger's  ArcMv,  xiii.  {1876)  p.  508. 


CIIAr.    II.]  RESPIRATION.  34! 

it  was  found  by  Valentin  to  be  38 'i^  Tlie  exact  temperature  in 
lact  (lepcnds  on  the  relative  temperature.s  of  the  blood  and 
inspired  air,  and  on  the  depth  and  rate  of  breathing, 

2.  The  expired  air  is  loaded  with  aqueous  vapour.  The 
point  of  saturation  of  any  gas,  that  is,  the  utmost  quantity  of 
water  which  any  given  volume  of  gas  can  take  up  as  aqueous 
vapour,  varies  with  the  temperature,  being  higher  with  the  higher 
temperature.  For  its  own  temperature  expired  air  is  according 
to  most  observers  saturated  with  acpieous  vapour.  According  to 
Edward  Smith  it  is,  when  lasting,  only  half  saturated. 

3.  When  the  total  quantity  of  tidal  air  given  out  at  any 
expiration  is  compared  with  that  taken  in  at  the  corresponding 
insiiiraiion,  it  is  found  that,  both  being  dried  and  measured  at  the 
same  pressure,  the  expired  air  is  less  in  volume  than  the  inspired 
air,  the  difference  amounting  to  about  ^^^^th  or  -.'(j^th  of  the  volume 
of  the  latter.  Hence,  when  an  animal  is  matle  to  breathe  in  a 
confined  space,  the  atmosphere  is  absolutely  diminished,  as  was 
observed  so  long  ago  as  1674  by  Mayow.  The  approximate 
equivalence  in  volume  between  inspired  and  expired  air  arises 
from  the  fact  that  the  volume  of  any  given  quantity  of  carbonic 
acid  is  equal  to  the  volume  of  the  oxygen  consumed  to  produce  it ; 
the  slight  falling  short  of  the  expired  air  is  due  to  the  circumstance 
that  all  the  oxygen  inspired  does  not  reappear  in  the  carbonic 
acid  expired,  some  having  formed  other  combinations. 

4.  The  expired  air  contains  about  4  or  5  p.c.  less  oxygen, 
and  about  4  p.c.  more  carbonic  acid  than  the  inspired  air,  the 
quantity  of  nitrogen  suffering  but  little  change.     Thus 

oxygen.  nitrogen.         carbonic  acid. 

Inspired  air  contains  2081  79'i5  '04 

Expired     „         „        16033       "      79'557  4'3^° 

The  quantity  of  nitrogen  in  the  expired  air  is  sometimes  found 

to  be  greater,  as  in  the  table  above,  but  sometimes  less,  than  that 

of  the  inspired  air. 

W.  Edwards  thought  that  nitrogen  was  absorbed  in  cold,  and 
thrown  out  in  warm  weather.  W.  Miillcr  observed  that  in  an  atmo- 
sphere consisting  entirely  of  nitrogen,  an  absorption,  and  in  one  devoid 
of  nitrogen  or  containing  little  nitrogen,  an  escape  of  nitrogen  took 
place  ;  a  result  which  appears  probable. 

In  a  single  breath  the  air  is  richer  in  carbonic  acid  (and  poorer 
in  oxygen),  at  the  end  than  at  the  beginning.  Hence  the  longer  the 
breath  is  held,  the  greater  the  pause  between  inspiration  and  expira- 
tion, the  higher  the  percentage  of  carbonic  acid  in  the  expired  air 


342  CHANGES   OF   THE   AIR.  [BOOK   II. 

Thus  Becher  found  that  by  increasing  the  pause  from  o  to  loo  seconds, 
the  percentage  was  raised  from  3 '6  to  7 "5.  The  rate  of  increase 
however  continually  diminishes,  being  greatest  at  the  beginning  of 
the  period. 

When  the  rate  of  breathing  remains  the  same,  by  increasing  the 
depth  of  the  breathing  the  percentage  of  carbonic  acid  in  each  breath 
is  lowered,  but  the  total  quantity  of  carbonic  acid  expired  in  a  given 
time  is  increased.  Similarly  when  the  depth  of  breath  remains 
the  same,  by  quickening  the  rate  the  percentage  of  carbonic  acid  in 
each  breath  is  lowered,  but  the  quantity  expired  in  a  given  time  is 
increased. 

The  variations  in  both  the  consumption  of  oxygen  and  production 
of  carbonic  acid,  due  to  variations  in  pressure,  will  be  considered  in 
connection  with  the  respiratory  changes  of  blood. 

Taking,  as  we  have  done,  at  500  c.c.  the  amount  of  tidal  air 
passing  in  and  out  of  the  chest  of  an  average  man,  such  a  person 
will  expire  about  22  c.c.  of  carbonic  acid  at  each  breath;  this, 
reckoning  the  rate  of  breathing  at  17  a  minute,  would  give  over 
500  litres  of  carbonic  acid  for  the  day's  production.  By  actual 
experiment,  however,  Pettenkofer  and  Voit,  of  whose  researches 
we  shall  have  to  speak  hereafter,  determined  the  total  daily 
excretion  of  carbonic  acid  in  an  average  man  to  be  800  grms., 
i.e.  rather  more  than  400  litres  (406),  containing  2i8'i  grms. 
carbon,  and  581  "9  grms.  oxygen,  the  oxygen  actually  consumed 
at  the  same  time  being  about  700  grms.  This  amount  represents 
the  gases  given  out  and  taken  in,  not  by  the  lungs  only,  but  by 
the  whole  body ;  but  the  amount  of  carbonic  acid  given  out  by 
the  skin  is,  as  we  shall  see,  very  slight  (10  grms,  or  even  less), 
so  that  800  grms.  may  be  taken  as  the  average  production  of 
carbonic  acid  by  an  average  man.  The  quantity  however,  both  of 
oxygen  consumed  and  of  carbonic  acid  given  out,  is  subject  to 
very  wide  variations ;  thus  in  Pettenkofer  and  Voit's  observations, 
the  daily  quantity  of  carbonic  acid  varied  from  686  to  1285  grms., 
and  that  of  the  oxygen  from  594  to  1072  grms.  These  variadons 
and  their  causes  will  be  discussed  when  we  come  to  deal  with  the 
problems  of  nutrition. 

The  quantity  of  carbonic  acid  produced  and  oxygen  consumed 
increases  in  man  from  birth  up  to  about  thirty  years,  and  after  that 
diminishes.  In  the  female,  the  quantity,  always  less  than  that  of 
man,  increases  up  to  puberty,  remains  during  the  menstrual  life  at 
a  standstill,  and  after  the  climacteric  declines. 

5.  Besides  carbonic  acid,  expired  air  contains  various  im- 
purities, many  of  an  unknown  nature,  and  all  in  small  amounts. 


CHAT.    II.]  RESri RATION.  343 

Ammonia  has  been  detected  in  expired  air,  even  in  that  taken* 
directly  from  the  tracliea,  in  which  case  its  presence  could  not  be 
due  to  decomposing  food  lingering  in  the  mouth.  Accordmg  to 
Losscn,  the  amount  given  off  in  ordinary  respiration  in  24  hours 
is  '014  grm.  When  the  expired  air  is  con<lensed  by  being  con- 
veyed into  a  cooled  receiver,  the  aqueous  product  is  found  to 
contain  organic  matter,  and  rapidly  to  putrefy.  The  organic  sub- 
stances thus  shewn  to  be  present  in  the  expired  air  are  the  cause 
in  part  of  the  odour  of  breath.  It  is  probable  that  many  of 
them  are  of  a  poisonous  nature ;  for  an  atmosphere  containing 
simply  I  p.c.  of  carbonic  acid  (with  a  corresponding  diminution  of 
oxygen)  has  very  little  effect  on  the  animal  economy,  whereas  an 
atmosphere  in  which  the  carbonic  acid  has  been  raised  to  i  p.c. 
by  breathing,  is  highly  injurious.  In  fact,  air  rendered  so  far 
impure  by  breathing  that  the  carbonic  acid  amounts  to  '08  p.c.  is 
distinctly  unwholesome,  not  so  much  on  account  of  the  carbonic 
acid,  as  of  the  accompanying  impurities.  Since  these  impurities 
are  of  unknown  nature  and  cannot  be  estimated,  the  easily 
determined  carbonic  acid  is  usually  taken  as  the  measure  of  their 
presence.  We  have  seen  that  the  average  man  loads,  at  each 
breath,  500  c.c.  of  air  with  carbonic  acid  to  the  extent  of  4  p.c. 
He  will  accordingly  at  each  breath  load  2  litres  to  the  extent  of 
I  p.c,  and  in  one  hour,  if  he  breathe  17  times  a  minute,  will 
load  rather  more  than  2000  litres  to  the  same  extent.  At  the 
very  least  then  a  man  ought  to  be  supplied  with  this  quantity  of 
■air  hourly  ;  and  if  the  air  is  to  be  kept  fairly  wholesome,  that  is 
with  the  carbonic  acid  reduced  to  'i  p.c,  he  should  have  ten 
times  as  much. 


Sec.  3.     The  Respiratory  Changes  in  the  Blood. 

While  the  air  in  passing  in  and  out  of  the  lungs  is  thus  robbed 
of  a  portion  of  its  oxygen,  and  loaded  with  a  certain  quantity  of 
carbonic  acid,  the  blood  as  it  streams  along  the  pulmonary  capil- 
laries undergoes  important  correlative  changes.  As  it  leaves  the 
right  ventricle  it  is  venous  blood  of  a  dark  purple  or  maroon 
colour  ;  when  it  falls  into  the  left  auricle,  it  is  arterial  blood  of  a 
/bright  scarlet  hue.  In  passing  through  the  capillaries  of  the  body 
from  the  left  to  the  right  side  of  the  heart,  it  is  again  changed 
from  the  arterial  to  the  venous  condition.  We  have  to  inquire, 
What  are  the  essential  differences  between  arterial  and  venous 
blood,  by  what  means  is  the  venous  blood  changed  into  arterial  in 
the  lung:;,  and  the  arterial  into  venous  in  the  rest  of  the  body,  and 


344  CHANGES   IN   THE   BLOOD.  [BOOK  II. 

what  relations  do  these  changes  in  the  blood  bear  to  the  changes 
in  the  air  which  we  have  already  studied  ? 

The  facts,  that  venous  blood  at  once  becomes  arterial  on  being 
exposed  to  or  shaken  up  with  air  or  oxygen,  and  that  arterial 
blood  becomes  venous  when  kept  for  some  little  time  in  a  closed 
vessel,  or  when  submitted  to  a  current  of  some  indifferent  gas 
such  as  nitrogen  or  hydrogen,  prepare  us  for  the  statement  that 
the  fundamental  difference  between  venous  and  arterial  blood  is 
in  the  relative  proportion  of  the  oxygen  and  carbonic  a:cid  gases 
contained  in  each.  From  both,  a  certain  quantity  of  gas  can  be 
extracted  by  means  which  do  not  otherwise  materially  alter  the 
constitution  of  the  blood;  and  this  gas  when  obtained  from 
arterial  blood  is  found  to  contain  more  oxygen  and  less  carbonic 
acid  than  that  obtained  from  venous  blood.  This  is  the  real 
differential  character  of  the  two  bloods ;  all  other  differences  are 
either,  as  we  shall  see  to  be  the  case  with  the  colour,  dependent 
on  this,  or  are  unimportant  and  fluctuating. 

If  the  quantity  of  gas  which  can  be  extracted  by  the 
mercurial  air-pump  from  loo  vols,  of  blood  be  measured  at  o°C., 
and  a  pressure  of  760  mm.,  it  is  found  to  amount,  in  round 
numbers,  to  60  vols^ 

The  vacuum  produced  by  the  ordinary  mechanical  air-pump  is 
insufficient  to  extract  all  the  gas  from  blood.  Hence  it  becomes 
necessary  to  use  either  a  large  Torricellian  vacuum  or  a  Sprengel's 
pump.  In  the  former  (Fig.  48)  case  two  large  globes  of  glass,  one  ■ 
fixed  and  the  other  moveable,  are  connected  by  a  flexible  tube  ;  the 
fixed  globe  is  made  to  communicate  by  means  of  air-tight  stopcocks 
alternately  with  a  receiver  containing  the  blood,  and  with  a  receiver 
to  collect  the  gas.  When  the  moveable  globe  filled  with  mercury  is 
raised  above  the  fixed  one,  the  mercury  from  the  former  runs  into  and 
completely  fills  the  latter,  the  air  previously  present  being  driven  out. 
After  adjusting  the  cocks,  the  moveable  globe  is  then  depressed  thirty 
inches  below  the  fixed  one,  in  which  the  consequent  fall  of  the  mercury 
produces  an  almost  complete  vacuum.  By  turning  the  proper  cock 
this  vacuum  is  put  into  connection  with  the  receiver  containing  the 
blood,  which  thereupon  becomes  proportionately  exhausted.  By  again 
adjusting  the  cocks  and  once  more  elevating  the  moveable  globe,  the 
gas  thus  extracted  is  driven  out  of  the  fixed  globe  into  a  receiver. 
The  vacuum  is  then  once  more  established  and  the  operation  repeated 
as  long  as  gas  continues  to  be  given  off  from  the  blood.  This  form 
of  pump,  introduced  by  Ludwig,  or  a  modifica,tion  of  it,  with  drying 
apparatus,  employed  by  Pfliiger,  is  the  one  which  has  been  hitherto 
most  extensively  used ;  but  a  Sprengel's  pump-  is  preferred  by 
some 

'  Or,  at  a  pressure  of   l  metre,  about  50  vols. 


CHAP.   II.]  RESl'IKATION.  345 

The  average  composition  of  fliis  gas  is  in  the  two  kinds  of 
blood  as  follows : 

From  100  vols.  may  be  obtained 

Of  oxyjjeii,  of  carbonic  acid,      of  nitrogen. 

Of  Arterial  Blood,  20  ('^')  vols.  39  (3°)  vols.  i  to  2  vols. 
Of  Venous  Blood,  8  to  12  (^^  '"  '°)  vols.  46  (35)  vols.  i  to  2  vols, 
all  measured  at  760  mm.  and  0°  C 

It  will  be  convenient  to  consider  the  relations  of  each  of  these 
gases  separately. 

I'he  relations  of  Oxy^^cn  in  the  Blood. 

When  a  liquid  such  as  water  is  e.xposed  to  an  atmosphere 
containing  a  gas  such  as  o.xygen,  some  of  the  oxygen  will  be  dis- 
solved in  the  watjr,  that  is  to  say  will  be  absorbed  from  the 
atmosphere.  The  quantity  which  is  so  absorbed  will  depend  on 
the  quantity  of  oxygen  which  is  in  the  atmosphere  above;  that  is 
to  say  on  tiie  pressure  of  the  oxygen  ;  the  greater  the  pressure  of 
the  oxygen,  the  larger  the  amount  which  will  be  absorbed.  If  on 
the  other  hand  water,  already  containing  a  good  deal  of  oxygen 
dissolved  in  it,  be  exposed  to  an  atmosphere  containing  little  or 
no  oxygen,  the  oxygen  will  escape  from  the  water  into  the  atmo- 
sphere. The  oxygen  in  fact  which  is  dissolved  in  the  water  is  in 
a  state  of  tension,  the  degree  of  tension  depending  on  the  quantity 
dissolved  ;  and  when  water  containing  oxygen  dissolved  in  it  is 
exposed  to  any  atmosphere,  the  point  whether  the  oxygen  escapes 
from  the  water  into  the  atmosphere,  or  passes  from  the  atmo- 
sphere into  the  water,  depends  on  whether  the  tension  of  the 
oxygen  in  the  water  is  greater  or  less  than  the  pressure  of  the 
oxygen  in  the  atmosphere.  Hence  when  water  is  exposed  to 
oxygen,  the  oxygen  either  escapes  or  is  absorbed  until  equilibrium 
is  established  between  the  pressure  of  t!ie  oxygen  in  the  atmosphere 
above  and  the  tension  of  the  oxygen  in  the  water  below.  This 
result  is,  as  far  as  mere  absorption  and  escape  are  concerned, 
quite  independent  of  what  other  gases  are  present  in  the  water 
or  in  the  atmosphere.  Suppose  a  half-litre  of  water  were  lying  at 
the  bottom  of  a  two-litre  flask,  and  that  the  atmosphere  in  the 
flask  above  the  water  was  one-third  oxygen ;  it  would  make  no 
difl'erence,  as  far  as  the  absorption  of  oxygen  by  the  water  was 
concerned,  whether  the  remaining  two-thirds  of  the  atmosphere 
was  carbonic  acid,  or  nitrogen,  or  hydrogen,  or  whether  the  space 
above   the    water    was  a  vacuum  filled    to    one-third   with    pure 

'  Tlie  numbers  in  brackets  represent  in  ruund  numbers  the  same  amounts 
mea'iured,  according  to  the  present  German  method,  at  a  pressure  of  i  metre. 


34^ 


[book  II. 


Fig.  48.    DiAGKAMMATic  Illustration  of  Ludwig's  Mekcurial  Gts  Pump. 

A  and  B  are  two  glass  globes,  connected  by  strong  india-rubber  tubes,  a  and  i,  with  two 
similar  glass  globes  A'  and  B'.  A  is  further  connected  by  means  of  the  stopcock  c  with  the 
receiver  C  containing  the  blood  (or  other  fluid)  to  be  analysed,  and  B  by  means  of  the  stop, 
cock  d  and  the  tube  e  with  the  receiver  D  for  receiving  the  gases.  A  and  B  are  also 
connected  with  each  other  by  means  of  the  stopcocks y"  and.?",  the  iatter  being  so  arranged 
that  B  also  communicates  with  B'  by  the  passage  g'.  A'  and  B'  being  full  of  mercury  and  the 
cocks  /i,  f.  g,  and  d  being  open  but  c  and  g'  closed,  on  raising  A'  by  means  of  the  pulley  / 
the  mercury  of  A'  fills  A,  driving  out  the  air  contained  in  it,  mto  B,  and  so  out  throtigh  e. 
When  the  mercuiy  has  risen  abjve^f,  _/is  closed,  and^'  being  opened,  B'  is  in  turn  raised  til! 
B  is  completely  filled  with  mercury,  all  the  air  previously  in  it  being  driven  cut  through  e. 
Upon  closing  d,  and  lowering  B'.  the  whrde  of  the  mercury  in  B  falls  in  B',  and  a  vacuum 
consequently  is  established  in  B.  On  closing^',  but  opening^,  y,  and  k  and  lowering  A', 
a  vacuum,  is  similarly  established  in  A  and  in  the  junctiLn  between  A  and  B.  If  the  cock 
c  be  now  opened  the  gases  of  the  blood  in  C  escape  into  the  vacuum  of  A  and  B.  By  raising 
A',  after  the  closure  of  c.  and  opening  of  d,  the  gases  so  set  free  are  driven  from  A  into  B, 
and  by  the  raising  of  B'  from  B,  through  e  into  the  receiver  D,  standing  over  mercury. 


CHAP.    II.]  RESPIRATION.  347 

oxyi;>.'n.  Hence  is  said  that  the  absorption  of  any  gas  depends 
on  lUc  /lar/ia/ //rss///r  of  that  gas  in  the  atniospliere  to  which  tht 
liquid  is  exposed.  'I'liis  is  true  not  only  of  oxygen  and  water, 
but  of  all  gases  and  liiiuids  which  do  not  enter  into  chemical 
combination  with  eu  h  other.  DilTerent  liquids  will  of  course 
absorb  dilVerent  gases  witli  ililTering  readiness,  but  with  the  same 
gas  and  the  same  li(|uid,  llie  amount  absorbed  will  depend 
tlirectly  on  the  partial  |)ressiire  of  the  gas.  It  should  be  added 
that  the  process  is  much  influenced  by  temperature.  Hence,  to 
state  tlie  matter  generally,  the  absorption  of  any  gas  by  anyli(juid, 
will  dejiend  on  the  nature  of  the  gas,  the  nature  of  the  licjuid, 
the  pressure  of  the  gas,  and  the  temi)erature  at  which  both  stand. 

Now  it  might  bj  supposed,  and  indeed  was  once  supposed, 
that  the  oxygen  in  the  blood  was  simply  dissolved  by  the  blood. 
If  this  were  so,  then  the  amount  of  oxygen  present  in  any  given 
quantity  of  blood  exposed  to  any  given  atmosphere,  ought  to  rise 
and  fall  steadily  and  regularly  as  the  partial  pressure  of  oxygen  in 
that  amosphere  is  increased  or  diminished.  IJut  this  is  found  not 
to  be  the  case.  If  we  expose  blood  containing  little  or  no  oxygen 
to  a  succession  of  atmospheres  containing  increasing  quantities 
of  oxygen,  we  find  that  at  first  there  is  a  very  rapid  absorption  ol 
the  available  oxygen,  and  then  this  somewhat  suddenly  ceases  or 
becomes  very  small ;  and  if  on  the  other  hand  we  submit  arterial 
blood  to  successively  diminishing  pressures,  we  find  that  for  a 
long  time  very  little  is  given  off,  and  then  suddenly  the  escape 
becomes  very  rapid.  The  absorption  of  oxygen  by  blood  does 
not  follow  the  general  law  of  absorption  according  to  pressure. 
The  phenomena  on  the  other  hand  suggest  the  idea  that  the  oxygen 
in  the  blood  is  in  some  particular  combination  with  a  substance 
or  some  substances  present  in  the  blood,  the  combination  being 
of  such  a  kind  that  dissociation  readily  occurs  at  certain  pressures 
and  certain  temperatures.  What  is  that  substance  or  what  are 
those  substances  ? 

If  serum,  free  from  red  corpuscles,  be  used  in  such  absorp>- 
tion  experiments,  it  is  found  ihac  as  compared  with  the  entire 
blood,  very  little  oxygen  is  absorbed,  about  as  much  as  would  be 
absorbed  by  the  same  quantity  of  water;  but  such  as  is  absorbed 
does  follow  the  law  of  pressures.  In  natural  arterial  blood  the 
quantity  of  oxygen  which  can  be  obtained  from  serum  is  e.xceed- 
ingly  small  ;  it  docs  not  amount  to  half  a  volume  in  one  hundred 
volumes  of  the  entire  blov.d  to  which  the  serum  belonged.  It  is 
evident  that  the  oxygen  which  is  present  in  blood  is  in  some  way 
or  other  peculiarly  connected  with  the  red  corpuscles.  Now  the 
distinguishing  feature  of   the  retl  corpuscles  is   the  presence  of 


343  HEMOGLOBIN.  [BOOK   II. 

•haemoglobin.  We  have  already  seen  (p.  33)  that  this  constitutes 
90  per  cent,  of  the  dried  red  corpuscles.  There  can  be  a  priori 
iittle  doubt  that  this  must  be  the  substance  with  which  the 
oxygen  is  associated  ;  and  to  the  properties  of  this  body  we  must 
therefore  direct  our  attention. 

Hce^noglobin  ;  its  properties  and  derivatives. 

When  separated  from  the  other  constituents  of  the  serum, 
haemoglobin  appears  as  a  substance,  either  amorphous  or  crystal- 
line, readily  soluble  in  water  (especially  in  warm  water)  and  in 
serum. 

Since  it  is  soluble  in  serum,  and  since  the  identity  of  the  crystals 
observed  occasionally  within  the  corpuscles  with  those  obtained  in 
other  ways  shews  that  the  hsemoglobm  as  it  exists  in  the  corpuscle  is 
the  same  thing  as  that  which  is  artificially  prepared  from  blood,  it  is 
evident  that  some  peculiar  relationship  between  the  stroma  and  the 
haemoglobin  must,  in  natural  blood,  keep  the  latter  from  being  dis- 
solved by  the  serum.  Hence  in  preparing  hsemoglobin  it  is  necessary 
first  of  all  to  break  up  the  corpuscles.  This  may  be  done  by  the 
addition  of  chloroform  or  of  bile  salts,  or  by  repeatedly  freezing  and 
thawing.  It  is  also  of  advantage  previously  to  remove  the  alkaline 
serum,  ■sO  as  to  operate  only  on  the  red  corpuscles.  The  corpuscles 
being  thus  broken  up,  an  aqueous  solution  of  haemoglobin  is  the  result. 
The  alkalinity  of  the  solution,  wdien  present,  being  reduced  by  the 
cautious  addition  of  dilute  acetic  acid,  and  the  solvent  power  of  the 
aqueous  medium  being  diminished  by  the  addition  of  one  fourth  its 
bulk  of  alcohol,  the  mixture,  set  aside  in  a  temperature  of  0°  C.  still 
further  to  reduce  the  solubility  of  the  haemoglobin,  reaJily  crystallizes, 
when  the  blood  used  is  that  of  the  dog,  cat,  horse,  rat,  guinea-pig,  &c. 
The  crystals  may  be  separated  by  filtration,  redissolved  in  water  and 
recrystallized. 

Haemoglobin  from  the  blood  of  the  rat,  guinea-pig,  squirrel, 
hedgehog,  horse,  cat,  dog,  goose,  and  some  other  anim^ds,  crystal- 
lizes readily,  the  crystals  being  generally  slender  four-sided 
prisms,  belonging  to  the  rhombic  system,  and  often  appearing 
quite  acicular.  The  crystals  from  the  blood  of  the  guinea-pig  are 
octahedral,  but  also  belong  to  the  rhombic  system  ;  those  of  the 
squirrel  are  six-sided  plates.  The  blood  of  the  ox,  sheep,  rabbit, 
pig,  and  man,  crystallizes  \vith  difficulty.  Why  these  differences 
exist  is  not  known  ;  but  the  composition,  and  the  amount  of 
water  of  crystallization,  vary  somewhat  in  the  crystals  obtained 
from  different  animals.  In  the  dog,  the  percentage  composition 
of  the  crystals  is,  according  to  Hoppe-Seyler  ^,  C.  53 '85,  H.  7*32, 
N.  i6t7,  O.  21-84,  S.  0-39,  Fe  -43,  with  3  to  4  per  cent,  of  water 

'   Untersuch,  ill.  (1868)  p.  370, 


350  HEMOGLOBIN.  [BOCK   II. 

Fig.  49.    The  Spectra    of    Hemoglobin  and  some   of   its   Derivatives    shewn   in 

REFEUENCE  TO    FrAUENHOFEr's    LiNES. 

The  first  spectrum  of  oxyhsemogljbin  is  that  of  an  exceedingly  dilute  solution.  That  of 
a  solution  intermediate  between  the  first  and  secoad  spectra  would  resemble  in  the 
i7i.tensity  i^i  its  absorption  bands  the  spectrum  given  as  that  of  carbonlic  oxide  haemoglobin. 

of  crystallization.  It  will  thus  be  seen  that  haemoglobin  contains 
iron,  in  addition  to  the  other  elements  usually  present  in  proteid 
substances. 

The  crystals,  when  seen  under  the  microscope,  have  the  same 
bright  scarlet  colour  as  arterial  blood  has  to  the  naked  eye  ;  when 
seen  in  a  mass  they  naturally  appear  darker.  An  aqueous 
solution  of  haemoglobin,  obtained  by  dissolving  purified  crystals 
in  distilled  water,  has  also  the  same  bright  arterial  colour,  A 
tolerably  dilute  solution  placed  before  the  spectroscope  is  found 
to  absorb  certain  rays  of  light  in  a  peculiar  and  characteristic 
manner.  A  portion  of  the  red  end  of  the  spectrum  is  absorbed, 
as  is  also  a  much  larger  portion  of  the  blue  end  ;  but  what  is 
most  striking  is  the  presence  of  two  strongly  marked  absorption 
bands,  lying  between  the  solar  lines  D  and  E.  (See  Fig.  49.) 
Of  these  the  one  a,  towards  the  red  side,  is  the  thinnest,  but  the 
most  intense  and  in  extremely  dilute  solutions  is  the  only  one 
visible ;  its  middle  lies  at  some  little  distance  to  the  blue  side  of 
D.  The  other,  /3,  much  broader,  lies  a  little  to  the  red  side  of  E, 
its  blue-ward  edge,  even  in  moderately  dilute  solutions,  coming 
close  up  to  that  line.  Each  band  is  thickest  in  the  middle,  and 
gradually  thins  away  at  the  edges.  These  two  absorption  bands 
are  extremely  characteristic  of  a  solution  of  haemoglobin.  Even 
in  very  dilute  solutions  both  bands  are  visible  (they  may  be  seen 
in  a  thickness  of  1  cm,  in  a  solution  containing  i  grm.  of  haemo- 
globin in  10  litres  of  water),  and  that  when  scarcely  any  of  the 
extreme  red  end,  and  very  little  of  the  blue  end,  is  cut  off.  They 
then  appear  not  only  faint  but  narrow.  As  the  strength  of  the 
solution  is  increased,  the  bands  broaden,  and  become  more 
intense ;  at  the  same  lime  both  the  red  end,  and  still  more  the 
blue  end,  of  the  whole  spectrum,  are  encroached  upon.  This 
may  go  on  until  the  two  absorption  bands  become  fused  together 
into  one  broad  band.  The  only  rays  of  light  which  then  pass 
through  the  haemoglobin  solution  are  those  in  the  green  between 
the  united  bands  and  the  general  absorption  at  the  blue  end,  and 
those  in  the  red  between  the  band  and  the  general  absorption  at 
the  red  end  (see  Fig.  49).  If  the  solution  be  still  further  in- 
creased in  strength,  the  interval  on  the  blue  side  of  the  band 
becomes  absorbed  also,  so  that  the  only  rays  which  pass  through 
are  the  red  rays  lying  to  the  red  side  of  D  ;  these  are  the  last  to 
disappear,  and   hence  the   natural   red  colour  of  the   solution  as 


CIIAr.    II.j  RESriRATION.  35 1 

seen  by  transmitted  light.  Exactly  the  same  appearances  are 
s*;en  when  crystals  of  hcumoglobin  arc  examined  with  a  micro- 
spcctrosco]ie.  They  are  also  seen  when  arterial  blood  itself 
(diluted  with  saline  solutions  so  that  the  corpuscles  remain  in  as 
natural  condition  as  ]iossible)  is  examined  with  the  spectroscope, 
as  well  as  when  a  droj)  of  blood,  which  from  the  necessary  ex- 
posure to  air  is  always  arterial,  is  examined  with  the  microspec- 
troscope.  In  fact,  the  spectrum  of  hemoglobin  is  the  spectrum 
of  normal  arterial  blood. 

When  crystals  of  heemoglobin,  prepared  in  the  way  described 
above,  are  subjected  to  the  vacuum  of  the  mercurial  air-pump, 
they  give  off  a  certain  quantity  of  oxygen,  and  at  the  same  time 
they  change  in  colour.  The  quantity  of  oxygen  given  off  is 
definite,  i  grm.  of  the  crystals  giving  off  i  76  '  c.cm.  of  oxygen  *. 
In  other  words,  the  crystals  of  haemoglobin  over  and  above  the 
oxygen  which  enters  intimately  into  their  composition,  (and  which 
alone  is  given  in  the  elementary  composition  stated  on  p.  348,) 
contain  another  quantity  of  oxygen,  which  is  in  loose  combination 
only,  and  which  may  be  dissociated  from  them  by  establishing 
a  sufficiently  low  pressure.  The  change  of  colour  which  ensues 
when  this  loosely  combined  oxygen  is  removed,  is  characteristic; 
the  crystals  become  darker  and  more  of  a  purple  hue,  and  at  the 
same  time  dichroic,  so  that  while  the  thin  edges  appear  green,  the 
thicker  ridges  are  purple. 

An  ordinary  solution  of  haemoglobin,  like  the  crystals  from 
which  it  is  formed,  contains  a  definite  quantity  of  oxygen  in  a 
similarly  peculiar  loose  combination  ;  this  oxygen  it  also  gives  up 
at  a  sufiiciently  low  pressure,  becoming  at  the  same  time  of  a 
purplish  hue.  This  loosely  combined  oxygen  may  also  be  re- 
moved by  passing  a  stream  of  hydrogen  or  other  indifferent  gas 
through  the  solution,  whereby  dissociation  is  effected.  It  may 
also  be  got  rid  of  by  the  use  of  reducing  agents.  Thus  if  a  few 
drops  of  ammonium  sulphide  or  of  an  alkaline  solution  of  ferrous 
sulphate,  kept  from  precipitation  by  the  presence  of  tartaric  acid  3, 
be  added  to  a  solution  of  haemoglobin,  or  even  to  an  unpurified 
solution  of  blood  corpuscles  such  as  is  afforded  by  the  washings 
from  a  blood  clot,  the  oxygen  in  loose  combination  with  "he 
haemoglobin  is  immediately  seized  upon  by  the  reducing  agent. 
This  may  be  recognised  at  once,  without  submitting  the  fluid  to 
the  air-pump,  by  a  characteristic  change  of  colour;  from  a 
bright  scadet  the  solution   becomes  of  a  purplish  claret  colcur, 

'  Or,  I  34  iiieasureil  at  a  pressure  of  I  metre. 

»  Cf.  Iliifner,  Zt.f.  Plnsiol.  Chem.  i.  (1S77)  P-  317- 

3  Stoke<,  Proc.  Roy.  Soc.  XII I.  (1864^  p.  355. 


352  H/EMOGLOBIN.  [BOOK   II. 

when  seen  in  any  thickness,  but  green  when -sufficiontly  thin: 
the  colour  of  the  reduced  solution  is  exactly  like  that  of  the 
crystals  from  which  the  loose  oxygen  has  been  removed  by  the 
air-pump. 

Examined  by  the  spectroscope,  this  reduced  solution,  or 
solution  of  reduced  hemoglobin  as  we  may  now  call  it,  offers  a 
spectrum  (Fig.  49)  entirely  different  from  that  of  the  unreduced 
solution.  The  two  absorption  bands  have  disappeared,  and  in 
their  place  there  is  seen  a  single,  much  broader,  but  at  the  same 
time  much  fainter  band  a,  whose  middle  occupies  a  position  about 
midway  between  the  two  absorption  bands  of  the  unreduced 
solution,  though  the  red-ward  edge  of  the  band  shades  away 
rather  farther  towards  the  red  than  does  the  other  edge  towards 
the  blue.  At  the  same  time  the  general  absorption  of  the  spec- 
trum is  dififerent  from  that  of  the  unreduced  solution  ;  less  of  the 
blue  end  is  absorbed.  Even  when  the  solutions  become  tolerably 
concentrated,  many  of  the  bluish  green  rays  to  the  blue  side  of 
the  single  band  still  pass  through.  Hence  the  difference  in  colour 
between  haemoglobin  which  retains  the  loosely  combined  oxygen  ^, 
and  hgemoglobm  which  has  lost  its  oxygen  and  become  reduced. 
In  tolerably  concentrated  solutions,  or  tolerably  thick  layers,  the 
former  lets  through  the  red  and  the  orange-yellow  rays,  the  latter 
the  red  and  the  bluish-green  rays.  Accordingly,  the  one  appears 
scarlet,  the  other  purple.  In  dilute  solutions,  or  in  a  thin  layer, 
the  reduced  haemoglobin  lets  through  so  much  of  the  green  rays 
that  they  preponderate  over  the  red,  and  the  resulting  impression 
is  one  of  green.  In  the  unreduced  haemoglobin  or  oxyhaemoglobin, 
the  potent  yellow  which  is  blocked  out  in  the  reduced  haemoglobin 
makes  itself  felt,  so  that  a  very  thin  layer  of  haemoglobin,  as 
in  a  single  corpuscle  seen  under  the  microscope,  appears  yellow 
rather  than  red. 

When  the  haemoglobin  solution  (or  crystal)  which  has  lost  its 
oxygen  by  the  action  either  of  the  air-pump  or  of  a  reducing 
agent  or  by  the  passage  of  an  indifferent  gas,  is  exposed  to  air 
containing  oxygen,  an  absorption  of  oxygen  at  once  takes  place. 
If  sufficient  oxygen  be  present,  the  whole  of  the  haemoglobin 
seizes  upon  its  complement,  each  gramme  taking  up  in  combi- 
nation 176  (^'34)  c.cm.  of  oxygen;  if  there  be  an  insufficient 
quantity  of  oxygen,  a  part  only  of  the  haemoglobin  gets  its 
allowance  and  the  remainder  continues  reduced.     If  the  amount 

*  For  brevitj''s  sake  we  may  call  the  hteinoglobiii  containing  oxygen  in  loose 
combination,  oxyhcemoglubin,  and  the  hoemo^lobin  from  which  this  loosely 
combined  oxygen  has  been  removed,  reduced  haemoglobin  or  simply  hsemo- 
globin. 


CHAP.   II.]  RESPIRATION.  353 

of  oxygen  be  sufficient,  the  solution  (or  crystal),  as  it  takes  up  the 
oxygen,  regains  its  bright  scarlet  colour,  and  its  characteristic 
absorption  spectrum,  the  single  band  being  replaced  by  the  two. 
Thus  if  a  solution  of  oxyhaimoglobin  in  a  test-tube  after  being 
reduced  by  the  ferrous  .salt,  and  shewing  the  purple  colour  and 
the  single  band,  be  shaken  up  with  air,  the  bright  scarlet  colour 
at  once  returns,  and  when  the  fluid  is  ])laced  before  the  spec- 
troscope, it  is  .seen  that  the  single  faint  broad  band  of  the 
reduced  haemoglobin  has  wholly  disappeared,  and  that  in  its 
place  are  the  two  sharp  thinner  bands  of  the  oxyhaemoglobin. 
if  left  to  stand  in  the  test-tube  the  quantity  of  reducing  agent  still 
present  is  generally  sufficient  again  to  rob  the  haemoglobin  of  the 
oxygen  thus  newly  acquired,  and  soon  the  scarlet  hue  fades  back 
again  into  the  purple,  the  two  bands  giving  place  to  the  one. 
Another  shake  and  exposure  to  air  will  however  again  bring  back 
the  scarlet  hue  and  the  two  bands ;  .nnd  once  more  these  may 
disappear.  In  fact,  a  few  drops  of  the  reducing  fluid  will  allow 
this  game  of  taking  oxygen  from  the  air  and  giving  it  up  to  the 
reducer  to  be  played  over  and  over  again,  and  at  each  turn  of 
the  game  the  colour  shifts  from  scarlet  to  purple,  and  from  purple 
to  scarlet,  while  the  two  bands  exchange  for  the  one,  and  the  one 
for  the  two. 


Colour  of  venous  and  arterial  Blood.  Evidently  we 
have  in  these  properties  of  haemoglobin  an  explanation  of  at  least 
one-half  of  the  great  respiratory  process,  and  they  teach  us  the 
meaning  of  the  change  of  colour  which  takes  place  when  venous 
blood  becomes  arterial  or  arterial  venous.  In  venous  blood,  as  it 
issues  from  the  right  ventricle,  the  oxygen  present  is  insufficient 
to  satisfy  the  whole  of  the  haemoglobin  of  the  red  corpuscles ; 
much  reduced  haemoglobin  is  present,  hence  the  purple  colour  of 
venous  blood. 

When  ordinary  venous  blood,  diluted  without  access  of  oxygen,  is 
brought  before  the  spectroscope,  the  two  bands  of  oxyhasmojjlobm  are 
seen.  This  is  explained  by  the  fact  that  in  a  mixture  of  oxyhemo- 
globin and  (reduced)  ha:moglobin,  the  two  sharp  bands  of  the  former 
are  always  much  more  readily  seen  than  the  much  fainter  band  of  the 
latter.  Now  in  ordinary  venous  blood  there  is  always  some  loose 
oxygen,  removable  by  diminished  pressure  or  otherwise;  there  is 
always  some,  indeed  a  considerable  quantity,  of  oxyha^moglobin  as 
»vell  as  (reduced)  haemoglobin.  It  is  only  in  the  last  stages  of  asphyxia 
that  all  the  loose  oxygen  of  the  blood  disappears  ;  and  then  the  two 
bands  of  the  oxyhoemoglobin  vanish  too.  So  distinct  are  the  two 
bands  of  even  a  small  quantity  of  oxyha^moglobin  in  the  midst  of  a 
F.  P.  23 


354  HEMOGLOBIN.  [BOOK   II. 

large  quantity  of  haemoglobin  that  a  solution  of  (completely  reduced) 
haemoglobin  may  be  used  as  a  test  for  the  presence  of  oxygen  \ 

As  the  blood  passes  through  the  capillaries  of  the  lungs,  this 
reduced  haemoglobin  takes  from  the  pulmonary  air  its  complement 
of  oxygen,  all  or  nearly  all  the  haemoglobin  of  the  red  corpuscles 
becomes  oxy-haemoglobin,  and  the  purple  colour  forthwith  shifts 
into  scarlet. 

The  haemoglobin  of  arterial  blood  is  saturated  or  nearly  saturated 
with  oxygen.  By  increasing  the  pressure  of  the  oxygen,  an  additional 
.quantity  may  be  driven  into  the  blood,  but  this  is  effected  by  simple 
absorption.  The  quantity  so  added  is  extremely  small  compared  with 
the  total  quantity  combined  with  the  hsemoglobin,  but  its  physiological 
importance  is  increased  by  its  being  present  at  a  high  tension. 

Passing  from  the  left  ventricle  to  the  capillaries,  some  of  the 
oxyhaemoglobin  gives  up  its  oxygen  to  the  tissues,  becomes 
reduced  haemoglobin,  and  the  blood  in  consequence  becomes 
once  more  venous,  with  a  purple  hue.  Thus  the  red  corpuscles 
by  virtue  of  their  haemoglobin  are  emphatically  oxygen-carriers. 
Undergoing  no  intrinsic  change  in  itself,  the  haemoglobin  combines 
in  the  lungs  with  oxygen,  which  it  carries  to  the  tissues  ;  these, 
more  greedy  of  oxygen  than  itself,  rob  it  of  its  charge,  and  the 
reduced  haemoglobin  hurries  back  to  the  lungs  in  the  venous 
blood  for  another  portion.  The  change  from  venous  to  arterial 
blood  is  then  in  part  (for  as  we  shall  see  there  are  other  events 
as  well)  a  pecuhar  combination  of  haemoglobin  with  oxygen,  while 
the  change  from  arterial  to  venous  is,  in  part  also,  a  reduction 
of  oxyhaemoglobin  ;  and  the  difference  of  colour  between  venous 
and  arterial  blood  depends  almost  entirely  on  the  fact  that  the 
reduced  haemoglobin  of  the  former  is  of  purple  colour,  while  the 
oxyhaemoglobin  of  the  latter  is  of  a  scarlet  colour. 

There  may  be  other  causes  of  the  change  of  colour,  but  these  are 
■wholly  subsidiary  and  unimportant.  When  a  corpuscle  swells,  its  re- 
fractive power  is  diminished,  and  in  consequence  the  number  of  rays 
■which  pass  into  and  are  absorbed  by  it  are  mcreased  at  the  expense  of 
those  reflected  from  its  surface  ;  anything  theretore  which  swells  the 
corpuscles,  such  as  the  addition  of  water,  tends  to  darken  blood,  and 
anything,  such  as  a  concentrated  saline  solution,  which  causes  the 
corpuscles  to  shrink,  tends  to  brighten  blood.  Carbonic  acid  has 
apparently  some  influence  in  swelling  the  corpuscles,  and  therefore  may 
aid  in  darkening  the  venous  blood. 

We  have   spoken   of  the   combination   of  haemoglobin  with 
oxygen  as  being  a  peculiar  one.     The  peculiarity  consists  in  the 
*  Hoppe-Seyler,  Zt.f.  Physiol.  Chem.  i.  {1877)  p.  121. 


CilAr.   II.]  RF.SPIRATION.  35, 

facts  that  the  oxygen  may  be  associated  and  dissociated,  without 
any  general  disturbance  of  the  molecule  of  hcemoglobin,  and  that 
dissociation  may  be  brought  about  very  readily.  Haemoglobin 
combines  in  a  wholly  similar  manner  with  other  gases.  If  carbonic 
oxide  be  passed  through  a  solution  of  haemoglobin,  a  change  of 
colour  takes  place,  a  peculiar  bluish  tinge  making  its  appearance. 
At  the  same  time  the  spectrum  is  altered  ;  two  bands  are  still 
visible,  but  on  accurate  measurement  it  is  seen  that  they  are 
placed  more  towards  the  blue  end  than  are  the  otherwise  similar 
bands  of  oxyhemoglobin  (see  Fig.  49).  When  a  known  quantity 
of  carbonic  oxide  gas  is  sent  through  a  hcemoglobin  solution,  it 
will  be  fountl  on  examination  that  a  certain  amount  of  the  gas  has 
been  retained,  an  equal  volume  of  oxygon  appearing  in  its  place 
in  the  gas  which  issues  from  the  solution.  If  the  solution  so 
treated  be  crystallized,  the  crystals  will  have  the  same  charac- 
teristic colour,  and  give  the  same  absorption  spectrum  as  the 
solution  ;  when  subjected  to  the  action  of  the  mercurial  pump, 
they  will  give  off  a  defmite  quantity  of  carbonic  oxide,  i  grm.  of. 
the  crystals  affording  i  76  ('34)  c.cm.  of  the  gas.  In  fact, 
haemoglobin  combines  loosely  with  carbonic  oxide  just  as  it 
does  with  oxygen  ;  but  its  affinity  with  the  former  is  greater 
than  with  the  latter.  While  carbonic  oxide  readily  turns  out 
oxygen,  o.xygen  cannot  so  readily  turn  out  carbonic  oxide. 
Indeed,  carbonic  oxide  has  been  used  as  a  means  of  driving  out 
and  measuring  the  quantity  of  oxygen  present  in  any  given  blood. 
This  property  of  carbonic  oxide  explains  its  poisonous  nature. 
When  the  gas  is  breathed,  the  reduced  and  the  unreduced 
haemoglobin  of  the  venous  blood  unite  with  the  carbonic  oxide, 
and  hence  the  peculiar  bright  cherry  red  colour  observable  in  the 
blood  and  tissues  in  cases  of  poisoning  by  this  gas.  The  carbonic 
oxide  haemoglobin,  however,  is  of  no  use  in  respiration  ;  it  is  not 
an  oxygen-carrier,  nay  more,  it  will  not  readily,  though  it  does 
so  slowly  and  eventually,  give  up  its  carbonic  oxide  for  oxygen, 
when  the  gas  no  longer  enters  the  chest  and  pure  air  is  supplied, 
The  organism  is  killed  by  suffocation,  by  want  of  oxygen,  in  spite 
of  the  blood  not  assuming  any  dark  venous  colour.  As  Bernard 
phrased  it,  the  corpuscles  are  paralysed. 

Hasmoglobin  similarly  forms  a  compound,  having  a  characteristic 
spectrum  with  nitric  oxide,  more  stable  than  that  with  carbonic  oxide, 
I  grm.  of  hajmoglobin  uniting  with  176  (•"34)  c.cm.  of  the  gas.  In  all 
these  compounds,  in  fact,  the  same  volume  of  gas  unites  with  the  same 
quantity  of  the  substance,  and  all  three  compounds  are  isomorphous. 
Compounds  also  exist  between  haemoglobin  and  hydrocyanic  acid. 
Nitrous  oxide  reduces  haemoglobin. 

23 — 2 


356  H/EMOGLOBIN.  [BOOK   II. 

Haemoglobin  is  a  so-called  ozone-carrier.  If  to  a  mixture  of  ozonized 
turpentine  (turpentine  kept  for  some  time)  and  tincture  of  guaiacum,  a 
drop  of  blood  or  haemoglobin  solution  be  added,  the  turpentine  at  once 
oxidises  the  guaiacum  and  produces  a  blue  colour  ;  this,  before  the 
addition  of  the  haemoglobin,  it  is  unable  to  do.  If  a  drop  of  tincture 
of  guaiacum  (the  experiment  fails  with  many  specimens  of  tincture)  be 
spread  out  and  allowed  to^dry  on  a  piece  of  white  filtering  paper,  and  a 
drop  of  blood  or  haemoglobin  solution  be  placed  on  it,  a  blue  ring  is 
developed.  This  was  held  by  A.  Schmidt  to  indicate  that  the  oxygen 
in  combination  with  haemoglobin  was  in  an  active,  or  ozonic  condition. 
Since  however  the  experiment  fails  when  glass  or  even  smooth  paper  is 
used  instead  of  filtering  paper,  it  is  more  than  probable  that  the  result 
is  caused  by  a  decomposition  of  the  hsemoglobin  due  to  the  porous 
nature  of  the  paper'. 

Although  a  crystalline  body,  haemoglobin  diffuses  with  great 
difificulty.  This  arises  from  the  fact  that  it  is  in  part  a  proteid 
body ;  it  consists  of  a  colourless  proteid,  associated  with  a 
coloured  compound  named  hcetnatifi.  All  the  iron  belonging  to 
the  haemoglobin  is  in  reality  attached  to  the  haematin.  A  solution 
of  haemoglobin,  when  heated,  coagulates,  the  exact  degree  at 
which  the  coagulation  takes  place  depending  on  the  amount  of 
dilution ;  at  the  same  time  it  turns  brown  from  the  setting  free  of 
the  haematin.  If  a  strong  solution  of  haemoglobin  be  treated  with 
acetic  (or  other)  acid,  the  same  brown  colour,  from  the  appearance 
of  haematin,  is  observed.  The  proteid  constituent  however  is  not 
coagulated,  but  by  the  action  of  the  acid  passes  into  the  state  of 
acid-albumin.  On  adding  ether  to  the  mixture,  and  shaking,  the 
haematin  rises  into  the  supernatant  ether,  which  it  colours  a  dark 
red,  and  which,  examined  with  the  spectroscope,  is  found  to  possess 
a  well-marked  spectrum,  the  spectrum  of  the  so-called  acid 
haematin  of  Stokes  (Fig.  49).  The  proteid  in  the  water  below  the 
ether  appears  in  a  coagulated  form.  In  a  somewhat  similar  man- 
ner alkalis  split  up  haemoglobin  into  a  proteid  constituent  and 
haematin.  The  exact  nature  of  the  proteid  constituent  has  not  as 
yet  been  clearly  determined  ;  it  was  supposed  to  be  globulin,  hence 
the  name  haematoglobulin  contracted  into  haemoglobin.-  The 
proteid  which  is  precipitated  when  a  solution  of  haemoglobin  is 
exposed  to  the  air,  though  belonging  to  the  globulin  family,  has 
characters  of  its  own.  It  has  been  named  by  Vx&ytx'^  globin.  It 
is  free  from  ash.  Haematin  when  separated  from  its  proteid 
fellow,  and  purified,  appears  as  a  dark-brown  amorphous  powder, 
or  as  a  scaly  mass  with  a  metallic  lustre,  having  the  probable  com- 
position of  C32,  Hg^,  N4,  Fe,  O5.     It  is  readily  soluble  in  dilute 

'  Pfliiger,  Pflilger's  Archiv,  X.  (1875)  p.  252. 
»  Die  Blut-Krystalle,  187 1. 


CHAl'.    II.]  KESriKATloN.  357 

alkaline    solutions,    and    then    gives    a    characteristic    spectrum 

(i'^'g-  49)- 

An  interesting  feature  in  hccmatin  is  that  its  alkaline  solution  is 
capable  of  bcinj,'  reduced  by  reducing  agents,  tl'.e  spectrum  changing 
at  the  same  time,  and  that  the  reduced  solution  will,  like  the 
hicmoglobin,  take  up  oxygen  again  on  being  brought  into  contact 
with  air  or  oxygen.  This  would  seem  to  indicate  that  the  oxygen- 
holding  power  of  ha:mo;.;lobin  is  connected  exclusively  with  its 
luem.itin  constituent.  By  the  action  of  strong  sulphuric  acid  ha^matin 
may  be  robbed  of  all  its  iron.  It  still  retains  the  feature  of  possessing 
colour,  the  solution  of  iron- free  haimatin  being  a  dark  rich  brownish 
red ;  but  is  no  longer  capable  of  combining  loosely  with  oxygen. 
This  indicates  that  the  iron  is  in  some  way  associated  with  the 
peculiar  respiratory  functions  of  hcEmoglobin  ;  though  it  is  obviously 
an  error  to  suppose,  as  was  once  supposed,  that  the  change  from 
venous  to  arterial  blood  consists  essentially  in  a  change  from  a  ferrous 
to  a  ferric  salt. 

Though  not  crystallizable  itself,  ha^matin  forms  with  hydro- 
chloric acid  a  compound,  occurring  in  minute  rhombic  crystals,  the 
so-called  hcemin  crystals. 

The  spectrum  of  hzematin  in  an  alkaline  solution  (Fig.  49)  gives  one 
broad  band  to  the  red  side  of  the  line  D.  The  blue  end  of  the  spec- 
trum suffers  much  absorption,  and  since  the  characteristic  single  band 
is  faint,  and  only  seen  in  concentrated  solutions,  the  whole  appearance 
of  the  spectrum  of  hoematin  is  far  less  striking  than  that  of  haemo- 
globin. The  solutions  are  dichroic,  of  a  reddi^h  brown  in  a  thick,  and 
of  an  olive  green  in  a  thin  layer.  The  spectrum  of  reduced  hamatin  is 
marked  by  two  faint  bands  to  the  blue  side  of  the  single  band  of  the 
unreduced  hcEmatin  ;  there  is  at  the  same  time  less  absorption  of  the 
blue  end.  The  spectrum  of  the  so-called  acid  hsematin,  i.e.  of  hcematin 
prepared,  as  spoken  of  above,  by  treatment  with  acetic  acid  and  ether, 
is  marked  by  a  very  characteristic  and  easily  seen  band,  a,  in  the  red, 
to  the  blue  side  of  C  (Fig.  49),  the  other  bands  (i3,  y,  8)  shewn  in  the 
figure  being  less  easily  seen.  This  so-called  hasmatin  band  readily 
appears  when  haemoglobin  is  acted  upon  by  weak  acids,  and  hence  is 
seen  when  carbonic  acid  is  passed  for  sometime  through  haemoglobin. 
A  wholly  similar  band,  however,  makes  its  appearance  when  blood  is 
acted  upon  for  some  time  by  ammonium  sulphide,  or  when  blood  is 
allowed  to  stand  for  any  length  of  time,  or  after  the  action  of  weak 
alkalis  ;  in  these  cases  it  is  supposed  to  indicate  the  existence  of  a 
hypothetical  body  mcthaemoglobin,  an  intermediate  stage  which 
haemoglobin  is  supposed  to  pass  through  on  its  way  to  be  split  up 
into  baematin  and  the  proteid  body.  When  haeniatin  or  haemoglobin 
is  dissolved  in  concentrate  1  sulphuric  acid,  a  spectrum  is  obtained,  on 
diluting  with  the  acid,  resembling  but  in  some  points  differing  from 
that  of  acid  haematin  as  given  in  Fig.  41.  The  iron-free  haematin, 
obtained  by  precipitating  with  a  large  quantity  of  water  the  solution 


358  CARBONIC   ACID   IN   THE   BLOOD.         [BOOK   11. 

of  haemaiin  or  liEemoglobin  in  concentrated  sulphuric  acid,  also  gives 
in  ammoniacal  and  in  acetic  acid  solutions  spectra  differing  in  minor 
points  only  from  the  same  spectrum.  Preyer'  believes  that  Stokes' 
acid  haematin,  i.e.  the  substance  in  solution  in  the  ether  added  to  blood 
treated  with  acetic  acid,  is  in  reality  iron-free  hsematin,  or,  as  he  pre- 
fers to  call  it,  hcEinatoiit.  Haematin  also  forms  a  special  compound 
with  a  characteristic  spectrum,  when  acted  on  by  potassium  cyanide. 
Hoppe-Seyler^ by  treating  reduced  hsemoglobin  with  acids  or  alkalis, 
in  the  total  absence  of  oxygen,  obtained  a  colouring  body,  with  a 
characteristic  spectrum,  to  which  he  gave  the  name  of  hsemochromogen, 
regarding  it  as  the  substance,  forming  part  of  haemoglobin,  which  by 
oxidation  passes  into  haematin. 

In  conclusion,  the  condition  of  oxygen  in  the  blood  is  as 
follows.  Of  the  whole  quantity  of  oxygen  in  the  blood,  only  a 
minute  fraction  is  simply  absorbed  or  dissolved,  according  to  the 
law  of  pressures  (the  Henry-Dalton  law).  The  great  mass  is  in  a 
state  of  combination  with  the  haemoglobin,  the  connection  being 
of  such  a  kind  that  while  the  haemoglobin  readily  combines  with 
the  oxygen  of  the  air  to  which  it  is  exposed,  dissociation  readily 
occurs  at  low  pressures,  or  in  the  presence  of  indifferent  gases,  or 
by  the  action  of  substances  having  a  greater  affinity  for  oxygen 
than  has  haemoglobin  itself.  The  difference  between  venous  and 
arterial  blood,  as  far  as  oxygen  is  concerned,  is  that  while  in  the 
latter  there  is  an  insignificant  quantity  of  reduced  haemoglobin,  in 
the  former  there  is  a  great  deal ;  and  the  characteristic  colours  of 
venous  and  arterial  blood  are  in  the  main  due  to  the  fact  that  the 
colour  of  reduced  haemoglobin  is  purple,  while  that  of  oxyhaemo- 
globin  is  scarlet. 

The  Relations  of  the  Carbonic  Acid  in  the  Blood. 

The  presence  of  carbonic  acid  in  the  blood  appears  to  be 
determined  by  conditions  more  complex  in  their  nature  and  at 
present  not  so  well  understood  as  those  which  determine  the 
presence  of  oxygen.  The  carbonic  acid  is  not  simply  dissolved 
in  the  blood ;  its  absorption  by  blood  does  not  follow  the  law  of 
pressures.  It  exists  in  association  with  some  substance  or  sub- 
stances in  the  blood,  and  its  escape  from  the  blood  is  a  process  of 
dissociation.  We  cannot  however  speak  of  it  as  being  associated 
like  the  oxygen  with  the  haemoglobin  of  the  red  corpuscles.  So 
far  from  the  red  corpuscles  containing,  as  is  the  case  with  the 
oxygen,  the  great  mass  of  the  carbonic  acid,  the  quantity  of  this 
gas  whicTi  is  present  in  a  volume  of  serum  is  actually  greater  than 

'  Die  Blut-Krystalle  {\%'ji)  p.  i8i. 
=  Untersuch.,  IV.  (1871)  540. 


CMAI'.    II.]  KESI'IRATION.  359 

that  which  is  present  in  an  equal  voUime  of  blood,  i.e.  an  ecjual 
volume  of  mixed  corpuscles  and  serum. 

When  serum  is  subjected  to  the  mercurftil  vacuum,  by  far  the 
greater  pait  of  the  carbonic  acid  is  given  off;  but  a  small  ad- 
ditional quantity  (2  to  5  vols,  per  cent )  may  be  extracted  by  the 
subsecpient  addition  of  an  acid,  'liiis  latter  portion  may  be 
spoken  of  as  *  fixed '  carbonic  acid  in  distinction  to  the  larger 
*  loose  '  portion  which  is  given  off  to  the  vacuum.  When  how- 
ever tlic  whole  blood  is  subjected  to  the  vacuum,  all  the  carbonic 
acid  is  given  off,  so  that  when  scrum  is  mixed  with  corpuscles 
all  the  carbonic  acid  may  be  spoken  of  as  '  loose  ' ;  and  according 
to  Fredericfj ',  the  excess  of  carbonic  acid  in  serum  over  that 
present  in  entire  blood,  corresponds  to  the  fixed  portion  in  serum 
which  has  to  be  driven  off  by  an  acid.  Moreover,  though  the 
quantity  of  carbonic  acid  in  blood  is  less  than  that  in  an  equal 
volume  of  serum,  the  tension  of  the  carbonic  acid  in  blood  is 
greater  than  in  serum. 

Putting  these  facts  together  it  seems  probable  that  the  carbonic 
acid  exists  associated  with  some  substance  or  substances  in  the 
serum,  but  that  the  conditions  of  its  association  (and  therefore  of 
its  dissociation)  are  determined  by  the  action  of  some  substance 
or  substances  present  in  the  corpuscles.  It  is  further  probable 
that  the  association  of  the  carbonic  acid  in  the  serum  is  with 
sodium  as  sodium  bicarbonate,  and  it  is  even  possible  that  the 
haemoglobin  of  the  corpuscles  plays  a  part  in  promoting  the  dis- 
sociation of  the  sodium  bicarbonate  or  even  the  carbonate,  and 
thus  keeping  up  thj  carbonic  acid  tension  of  the  entire  blood. 
But  further  investigations  arc  necessary  before  the  matter  can  be 
said  to  have  been  placed  on  a  wholly  satisfactory  footing. 


Gaule-  puts  forward  the  view  that  a  constituent  of  the  red  cor- 
puscles (probibly  the  haemoglobin)  possesses  an  affinity  for  sodium 
carbonate,  and  by  continually  withdrawing  this  from  the  serum,  pro- 
motes the  dissociation  of  the  bicarbonate  and  the  setting  free  of  car- 
bonic acid.  He  further  suggests  that  so  long  as  the  tension  of  the 
carbonic  acid  in  the  scrum  is  low,  the  haemoglobin  is  able  to  split  up 
even  the  simple  carbonate,  uniting  with  the  sodium,  and  setting  free 
carbonic  acid.  As  tiie  tension  in  the  scrum  increases,  however,  he 
supposes  this  pro:css  to  be  reversed,  and  thus,  by  a  constant  action 
and  reaction  of  haemoglobin  and  sodium  carbonate,  the  tension  ol 
carbonic  acid  in  the  blood  is  kept  constants 

•  Compt.  Rend.  t.  84  (1S77),  p.  661,  t.  85  (187S),  p.  29. 
'  Archivf.  Anat^  u.  P/iys.,  1878,  Phys.  yMith.,  p.  469. 
3  Cf.  however  Bert,  Compt.  Rend.  t.  87  (1878),  p.  628. 


360  •  THE   CHANGES  IN    THE   LUNGS.         [BOOK   II. 

The  Relations  of  the  Nitrogen  in  the  Blood. 

The  small  quantity  of  this  gas  which  is  present  in  both  arterial 
and  venous  blood  seems  to  exist  partly  in  a  state  of  simple  solu- 
tion, partly  in  some  loose  chemical  combination,  but  the  conditions 
of  the  association  are  unknown. 

Sec.  4.     The  Respiratory  Changes  in  the  Lungs. 

The  entrance  of  Oxygen.  We  have  already  seen  that  the 
blood  in  passing  through  the  lungs  takes  up  a  certain  variable 
quantity  (from  8  to  12  p.  c.  vols.)  of  oxygen.  We  have  further 
seen  that  the  quantity  so  taken  up,  putting  aside  the  insignificant 
fraction  simply  absorbed,  enters  into  direct  but  loose  combination 
with  the  haemoglobin.  We  have  also  seen  that  at  low  pressures 
the  oxygen  is  dissociated  from  the  haemoglobin  and  set  free,  but 
not  at  high  pressures.  If  the  tension  of  the  oxygen  in  the  lungs  is 
higher  than  the  tension  of  the  oxygen  in  the  venous  blood  of  the 
pulmonary  artery,  there  will  be  no  difficulty  in  the  reduced  hemo- 
globin of  that  blood  taking  up  oxygen  j  and  this  may  go  on  until 
the  haemoglobin  of  the  blood  in  the  pulmonary  capillaries  is  all 
converted  into  oxyhsemoglobin,  or  until  the  oxygen  tension  in  the 
blood  is  increased  so  as  to  be  equal  to  that  of  the  air  in  the  lungs. 
Now  the  oxygen  in  the  expired  air  amounts  to  about  i  6  p.  c, 
having  lost  4  or  5  p.  c.  in  the  lungs.  Of  course  the  air  at  the 
bottom  of  the  lungs  will  contain  still  less  oxygen.  How  much  less 
we  do  not  exactly  know,  but  we  may  probably  put  the  limit  of 
reduction  at  10  p.  c.  We  may  say  then  that  the  tension  of  the 
oxygen  in  the  pulmonary  air-cells  is  at  least  10  p.  c. — or,  .to 
measure  it  in  millimetres  of  mercury,  since  the  pressure  of  the ' 
one  entire  atmosphere  is  760  mm.,  ^^'^  of  that  will  amount  to 
76  mm. 

Now  the  tension  of  oxygen  in  the  arterial  blood  of  the  dog* 
amounts  to  3*9  p.  c.  (varying  from  5"6  to  2'8),  or  about  30  mm.  of 
mercury.  That  is  to  say,  the  arterial  blood  of  the  dog  exposed  to 
an  atmosphere  containing  3*9  p.  c.  of  oxygen  neither  gives  off  nor 
takes  up  any  oxygen.  The  tension  of  the  oxygen  in  the  average 
venous  blood  of  the  dog  amounts  to  2*9  p.  c.  (varying  from  4'6  to 
I  "4)^.  Both  these  numbers  are  far  below  10  p.  c.  ;  in  fact  we  may 
suppose  the  percentage  of  oxygen  in  the  pulmonary  alveoli  to  be 
less  than  half  the  amount  stated  above,  and  yet  see  no  difficulty 
in  ordinary  venous  blood  taking  up  oxygen  while  passing  through 

'  Strassbuig,  Pfluger's  Archiv,  VI.  (1872)  p.  65. 

"  Wolffberg,  Pfluger's  Archiv,  iv.  (1871)  465,  VI.  (1872)  23. 


CIl.vI'.   II.]  RESl'IKATION.  361 

the  lungs.  But  whai  takes  place  when  the  tension  of  the  oxygen 
in  the  air  is  lowered,  as  when  the  win(i|)i()e  is  obstructed,  and 
asphyxia  sets  in  ?  It  has  been  ascertained  that  in  the  dog,  in  the 
last  breath  given  out  in  such  an  asphyxia,  the  expired  air  has  an 
oxygen  tension  of  2*3  p.  c,  and  when  the  heart  ceases  to  beat,  the 
oxygen  of  the  pulmonary  air  sinks  to  '403  p,  c.  These  tensions  are 
of  course  lower  than  that  of  ordinary  venous  blood,  but  in  asphyxia 
the  blood  is  no  longer  ordinary  venous  blood  ;  instead  of  contain- 
ing a  comparatively  sm:.ll  amount,  it  contains  a  large  and  gradually 
increasing  amount,  of  reduced  hcemoglobin.  And  as  the  reduced 
haemoglobin  increases  in  amount,  the  oxygen  tension  of  the  venous 
blood  decreases  ;  it  thus  keeps  below  that  of  the  air  in  the  lungs  ; 
and  hence  even  the  last  traces  of  oxygen  in  the  lungs  are  taken 
up  by  the  blood,  and  carried  away  to  the  tissues.  Even  with  the 
last  heart's  beat,  when  the  oxygen  in  the  lungs  has  sunk  to  "403 
J),  c,  the  bands  of  oxyhaemoglobin  may  still  for  a  moment  be 
detected  in  the  blood  of  the  left  side  of  the  heart'. 

The  exit  of  Carbonic  Acid.  It  seems  natural  to  sup- 
pose that  the  carbonic  acid  would  escape  by  diffusion  from  the 
blood  of  the  alveolar  capillaries  into  the  air  of  the  alveoli.  But 
in  order  that  diffusion  should  thus  take  place,  the  carbonic  acid 
tension  of  the  air  in  the  pulmonary  alveoli  must  always  be  less 
than  that  of  the  \enous  blood  of  the  pulmonary  artery,  and  indeed 
ought  not  to  exceed  that  of  the  blood  of  the  pulmonary  vein. 
There  arc  however  many  practical  difficulties  in  the  way  of  an 
exact  determination  of  the  carbonic  acid  tension  of  the  pulmonary 
alveoli  (for  though  it  must  be  greater  than  that  of  the  expired  air, 
it  is  difficult  to  say  how  much  greater),  and  of  the  carbonic  acid 
tension  of  the  blood  at  the  same  time,  so  as  to  be  in  a  position  to 
compare  the  one  with  the  other.  Hence  though  the  balance  of 
evidence  is  in  favour  of  the  escape  of  carbonic  acid  being  sunply 
a  process  of  diffusion,  ai.d  against  it  being  effected  by  any  special 
action  taking  place  in  the  alveoli,  the  matter  can  hardly  be  said  at 
present  to  be  satisfactorily  cleared  up. 

An  experiment  distinctly  in  favour  of  the  process  being  simply  one 
of  diffusion  has  been  broin^ht  forward  by  Wolffberg'.  This  observer 
introduced  into  the  bronchus  of  the  lun^f  of  a  dog  a  catheter,  round 
whi  jh  was  arranged  a  small  bag,  by  the  inrtation  of  which  the  bronchus, 
whenever  desired,  could  be  comphtely  blocked  up.  Thus,  without  any 
disturbance  of  the  genentl  brer.thing,  and  therefore  without  any  chani;e 
in  the  normal  proportions  of  the  gases  of  the  blood,  he  was  able  to 
stop  the  ingress  of  fresh  air  into  a  limited  portion  of  the  lung.  The 
blood  passing  through  the  alveolar  capillaries  of  this  limited  portion 

»  Stroganow,  Trtuger's  Aiciiiz;  XII.  (1876)  p.  iS.         '  Wolff  berg,  of.cit. 


362  THE   CHANGES   IN   THE   LUNGS.  [BOOK  II 

would  naturally  possess  the  same  carbonic  acid  tension  as  the  rest  of 
the  venous  blood  flowing  through  the  pulmonary  artery,  a  tension 
which,  though  varying  slightly  from  moment  to  moment,  would  main- 
tain a  normal  average.  On  the  supposition  that  carbonic  acid  passes 
simply  by  diffusion  from  the  pulmonary  blood  into  the  air  oj"the  alveoli, 
because  the  carbonic  acid  tension  of  the  latter  is  normally  lower  than 
that  of  the  former,  one  would  expect  to  find  that  the  air  in  the  occluded 
portion  of  the  lung  would  continue  to  take  up  carbonic  acid  until  an 
equilibrium  was  established  between  it  and  the  carbonic  acid  tension 
of  the  venous  blood,  and  consequently  that  if  after  an  occlusion,  say  of 
some  minutes  (by  which  time  the  equilibrium  might  fairly  be  assumed 
to  have  been  established),  the  carbonic  acid  tension  of  the  air  of  the 
occluded  portion  were  determined,  it  would  be  found  to  be  equal  to,  and 
not  more  than  equal  to,  the  carbonic  acid  tension  of  the  venous  blood 
of  the  pulmonary  artery.  And  this  was  the  result  at  which  Wolffberg 
arrived  ;  he  found  that  the  carbonic  acid  of  the  occluded  air  and  of  the 
venous  blood  of  the  right  side  of  the  heart  were  just  about  equal  ; 
allowing  for  errors  of  observation,  the  tension  of  each  was  about 
3-5  P-c. 

The  carbonic  acid  tension  of  the  venous  blood  as  determined  by 
Wolffberg  was  decidedly  low.  Strassburg'  makes  it  (for  the  dog)  5  "4 
p.  c.  ;  and  the  assumption  that  the  limit  of  the  carbonic  acid  tension  in 
the  pulmonary  alveoli  is  only  3"5  p.c.  necessitates  that  the  carbonic  acid 
in  the  e.xpired  air  of  the  dog  is  less  than  this,  much  less  in  fact,  than 
that  in  the  expired  air  of  man.  Moreover  in  the  normal  condition  of 
the  lung  when  the  venous  blood  is  becoming  arterial  (which  of  course 
was  not  the  case  in  the  occluded  lung),  the  continuance  of  diffusion 
depends  on  the  carbonic  tension  of  the  alveoli  having  for  its  limits  the 
degree  of  carbonic  acid,  not  of  the  venous  but  of  the  arterial  blood,  and 
this  Wolffberg  puts  as  low  as  2"8  p.  c.  Consequently  the  expired  air 
(of  the  dog)  ought  to  contain  less  than  2'8  p.  c.  of  carbonic  acid,  a 
result  which  does  not  agree  with  those  of  other  observers. 

The  belief  that  some  local  action  in  the  pulmonary  alveoli  tempo- 
rarily raised  the  carbonic  acid  tension  of  the  blood,  as  it  passed  through 
the  alveolar  capillaries,  above  that  of  the  venous  blood  flowing  along 
the  trunk  of  the  pulmonary  artery,  was  originaUy  based  on  Becher's 
conclusion  (see  antea  p.  342)  that  in  man  at  least  the  carbonic  acid 
tension  of  the  pulmonary  alveoli  is  as  high  as  7*5  or  8  p.c,  a  degree  of 
tension  which  had  not  been  found  by  experiment  to  exist  in  the  normal 
venous  blood  of  any  animal.  Becher's  results  however  are  clearly  in- 
validated by  the  consideration  that  in  holding  his  breath  he  necessarily 
increased  beyond  the  normal  the  carbonic  acid  tension  of  his  blood  ; 
and  he  of  course  did  not  determine  the  gases  of  his  own  blood.  Hence 
though  Wolffberg  s  results  seem  to  require  repetition  they  probably 
giv£  a  more  correct  view  of  the  matter. 

On  the  supposition  that  the  carbonic  acid  tension  of  the  pulmonary 
alveoli  is  really  higher  than  that  of  the  venous  blood  and  that  therefore 
somiC  additional  process  is  nece^s-.ry  to  promote  the  escape  of  the 
carbonic  acid,   it  has  been,  suggested  that  the  act  of  absorption   of 

'  Op.  cit. 


CHAP.    II.]  RESriKATIOX.  363 

oxygen  by  the  hasmoj^lobin  in  some  way  or  olher  rai-.es  temporarily  at 
the  same  timctlu  carbonic  acid  lell^Iun  ot  the  blood,  tu".  .^t.  brings 
about  un  exaggeration  of  that  Uinction  of  the  cor|jiisties  of  which  we 
have  already  spoken  on  \).  359.  Ill  support  of  this  it  is  stated  tlial  the 
carbonic  acid  tciision  of  venous  biooii  is  greater  wiicn  deierinined  by 
the  agitation  of  tiie  blood  with  air  cont.iining  oxygen  than  \shen  a;r 
free  from  oxygen  is  used.  And  it  might  be  urged  against  WoUlberg's 
result  that  in  the  occluded  portion  of  the  lung  the  absorption  of  oxygen 
after  a  while  did  not  take  place,  as  usual,  "and  that  in  consequence  the 
limit  of  carbonic  acid  tension  in  the  occluded  portion  is  not  a  measure 
of  that  of  the  normal  lung. 

It  has  also  been  suggested  that  the  e.icape  of  carbonic  acid  is 
efi'ected  by  a  direct  activity  of  the  pulmonary  epithelium,  lh::t  the  cells 
of  the  alveoli  actively  excrete  in  fact,  c.irbonic  acid.  I'he  arguments 
in  favour  of  this  view  are  based  on  the  experiments  of  J.  J.  MijUer', 
who  found  th;;t  more  carbonic  aciil  was  given  off  when  venous  blood 
was  driven througli  the  pulmoniry  artery,  and  so  expired  to  air  in  u 
normal  manner  through  the  walls  of  the  alveoli  of  a  living  lung,  than 
when  it  was  simply  agitated  with  air. 

Sf.c.  5.     The   Respiratory  Changes  in  the  Tissues. 

In  passing  through  the  several  tissues  the  arterial  blood  be- 
comes once  more  venous.  A  considerable  quantity  of  the  o.xy- 
haimoglobin  becomes  reduced,  and  a  quantity  of  carbonic  acid 
passes  from  the  tissues  into  the  blood.  The  amount  of  change 
varies  in  the  various  tissues,  and  in  the  same  tissue  may  vary  at 
different  times.  Thus  in  a  gland  at  rest,  as  we  have  seen,  the 
venous  blood  is  dark,  sliewing  the  i)resence  of  a  large  quantity  of 
reduced  hccmoglobin  ;  when  the  gland  is  active,  the  venous  blood 
in  its  colour,  and  in  the  amount  of  ha:;moglobin  which  it  contains, 
resembles  closely  arterial  blood.  The  blood  therefore  which 
issues  from  a  gland  at  rest  is  more  '  venous '  than  that  from  an 
active  gland,  though  the  total  quantity  of  carbonic  acid  formed  in 
a  given  time  may  be  greater  in  the  latter.  The  blood,  on  the 
other  hand,  which  comes  from  a  contracting  muscle,  is  not  only 
richer  in  carbonic  acid,  but  also,  though  not  to  a  corresponding 
amount,  poorer  in  oxygen  than  the  blood  which  tlows  from  a 
muscle  at  rest. 

In  all  these  cases  the  great  question  which  comes  up  for  our 
consideration  is  this  :  Does  the  oxygen  pass  from  the  blood  into 
the  tissues,  and  does  the  oxidation  take  place  in  tiie  tissues,  giving 
rise  to  carbonic  acid,  which  passes  in  turn  away  from  the  tissues 
into  the  blood  ?  or  do  certain  oxidisablc  reducing  substances  pass 
from  the  tissues  into  the  blood,  and  there  become  oxidi/ed  inia 
'  Ludwig's  Arbeilen,  1869,  p.  37. 


364  THE  CHANGES   IN    THE   TISSUES.        [BOOK   II. 

carbonic  acid  and  other  products,  so  that  the  chief  oxidation  takes 
place  in  the  blood  itself? 

There  are,  it  is  true,  reducing  oxidisable  substances  in  the 
blood,  but  these  are  small  in  amount,  and  the  quantity  of  carbonic 
acid  to  which  they  give  rise  when  the  blood  containing  them  is 
agitated  with  air  or  oxygen,  is  so  small  as  scarcely  to  exceed  the 
errors  of  observation. 

The  conclusion  of  Estorand  St.  Pierre,  that  the  oxygen  diminishes 
even  in  the  great  arteries  fiora  the  heart  outwards,  has  been  shewn  by 
Pfliiger  to  be  based  on  erroneous  analyses. 

On  the  other  hand,  it  will  be  remembered  that  in  speaking  of 
muscle,  we  drew  attention  to  the  fact  that  a  frog's  muscle  removed 
from  the  body  (and  the  same  is  true  of  muscles  of  other  animals) 
contained  no  free  oxygen  whatever ;  none  could  be  obtained  from 
it  by  the  mercurial  air-pump.  Yet  such  a  muscle  will  not  only 
when  at  rest  go  on  producing  and  discharging  a  certain  quantity, 
but  also  when  it  contracts  evolve  a  very  considerable  quantity  of 
carbonic  acid.  Moreover  this  discharge  of  carbonic  acid  will  go 
on  for  a  certain  time  in  muscles  under  circumstances  in  which  it 
is  impossible  for  them  to  obtain  oxygen  from  without.  Oxygen, 
it  is  true,  is  necessary  for  the  life  of  the  muscle  :  when  venous 
instead  of  arterial  blood  is  sent  through  the  blood-vessels  of  a 
muscle,  the  irritability  speedily  disappears,  and  unless  fresh  oxygen 
be  administered  the  muscle  soon  dies.  The  muscle  may  however, 
during  the  interval  in  which  irritability  is  still  retained  after  the 
supply  of  oxygen  has  been  cut  off,  continue  to  contract  vigorously. 
The  presence  of  oxygen,  though  necessary  for  the  maintenance  of 
irritability,  is  not  necessary  for  the  manifestation  of  that  irritability, 
is  not  necessary  for  that  explosive  decomposition  which  developes 
a  contraction.  A  frog's  muscle  will  continue  to  contract  and  to 
produce  carbonic  acid  in  an  atmosphere  of  hydrogen  or  nitrogen, 
that  is  in  the  total  absence  of  free  oxygen  both  from  itself  and 
from  the  medium  in  which  it  is  placed.  And  a  considerable 
quantity  of  carbonic  acid  may  be  set  free  from  living  muscle  by 
simply  exposing  it  to  the  temperature  of  boiling  water^,  the 
quantity  being  largely  diminished  if  the  muscle  be  thrown 
immediately  before  into  a  violent  tetanus. 

Thus  on  the  one  hand  the  muscle  seems  to  have  the  property 
of  taking  up  and  fixing  in  some  way  or  other  the  oxygen  to  which 
it  is  exposed,  of  converting  it  into  intra-molecular  oxygen,  in  which 
condition  it  cannot  be  removed  by  simple  diminished  pressure, 
so  that  the  tension  of  oxygen  in  the  muscular  substance  may  be 

'  Stintzing,  Pfliiijer's  Archiv,  xvili.  (1878)  p.  388. 


CHAP.   II.]  RESPIRATION.  365 

considered  as  always  nil ;  while  on  the  other  hand  the  muscular 
substance  is  always  undergoing  a  decomposition  of  such  a  kind  th.it 
carbonic  acid  is  set  free,  sometimes,  as  when  the  muscle  is  at  rest, 
in  small,  sometimes,  as  during  a  contraction,  in  large  quantities. 
But  if  the  oxygen  tension  of  the  muscular  tissue  be  thus  always 
nil,  the  oxygen  of  the  blood-corpuscles,  in  which  it  is  at  a  com- 
paratively high  tension,  will  be  always  passing  over,  through  the 
plasma,  through  the  capillary  walls,  the  lymph  ^spaces  and  the 
sarcolemma,  into  the  muscular  substance,  and  as  soon  as  it  arrives 
there  will  be  hidden  away  as  intra-molecular  oxygen,  leaving  the 
oxygen  tension  of  the  muscular  substance  once  more  nil.  Con- 
versely, the  carbonic  acid  produced  by  the  decomposition  of  the 
muscular  substance  will  tend  to  raise  the  carbonic  acid  tension  of 
the  muscle  until  it  exceeds  that  of  the  blood  ;  whereupon  it  will 
JKTSS  from  the  muscle  into  the  blood,  its  ])lace  in  the  muscular 
substance  being  supplied  by  freshly  generated  carbonic  acid. 
Tliere  will  always  in  I'act  be  a  stream  of  oxygen  from  the  blood  to 
the  muscle  and  of  carbonic  acid  from  tlie  muscle  to  the  blood. 
The  respiration  of  the  muscle  then  does  not  consist  in  throwing 
into  the  blood  oxidizable  substances  there  to  be  oxidized  into 
carbonic  acid  and  other  matters  ;  but  it  does  consist  in  the 
assumption  of  oxygen  as  intra-molecular  oxygen,  in  the  building 
up  by  help  of  that  oxygen  of  explosive  decomposable  substances, 
and  in  the  occurrence  of  decompositions  wliereby  carbonic  acid 
and  other  matters  are  discharged  first  into  the  substance  of 
the  muscle  and  subsequently  into  the  blood.  We  cannot  as 
yet  trace  out  the  stejis  taken  by  the  oxygen  from  the  moment  it 
slips  into  its  intra-molecular  position  to  the  moment  when  it  issues 
united  with  carbon  as  carbonic  acid.  The  whole  mystery  of 
life  lies  hidden  in  the  story  of  that  progress,  and  for  the  i)resent 
we  must  be  content  witli  simply  knowing  the  beginning  and 
the  end. 

Our  knowledge  of  the  respiratory  changes  in  muscle  is  more 
complete  than  in  the  case  of  any  other  tissue  ;  but  we  have  no 
reason  to  suppose  the  phenomena  of  muscle  are  exceptional.  On 
the  contrary,  all  the  available  evidence  goes  to  shew  that  in  all 
tissues  the  oxidation  takes  place  in  the  tissue,  and  not  in  the 
adjoining  blood.  It  is  a  remarkable  fact,  that  lymph,  serous  fluids, 
bile,  urine,  and  milk '  contain  a  mere  trace  of  free  or  loosely  com- 
bined oxygen,  and  saliva  or  pancreatic  juice  a  very  small  quantity 
only. (about  '5  p.  c),  while  the  tension  of  carbonic  acid  in  peritoneal 
fluid  is  as  high  as  6  per  cent,  and  in  bile  and  urine  is  still  higher. 

*  PfliiRcr,  PnUger's  Archiv,    I.  (186S)  p.  686  ;  II.    (1869)  p.  156.     Hoppe- 
Seyler,  Zt.f.  Physio!.  C/ieni.,  I.  (1S77)  p.  137. 


366  THE   CHANGES   IN   THE   TISSUES.         [BOOK   II. 

The  tension  of  carbonic  acid  in  lymph,  while  higher  than  that  oi 
arterial  blood,  is  lower  than  that  of  the  general  venous  blood  ;  but 
this  probably  is  due  to  the  fact  that  the  lymph  in  its  passage 
onwards  is  largely  exposed  to  arterial  blood  in  the  connective  tissues 
and  in  the  lymphatic  glands,  where  the  production  of  carbonic 
acid  is  slight  as  compared  to  that  going  on  in  nmscles  Sirassburg^ 
has  attempted  to  determine  the  tension  of  carbonic  acid  in  the 
intestinal  walls  ;  the  experiment  is  perhaps  open  to  objection,  but 
the  result  is  worth  recording-  he  found  the  tension  to  be  77  per 
cent.,  ie.  higher  than  that  of  the  venous  blood  examined  at  the 
same  time.  All  these  facts  point  to  the  conclusion,  that  it  is  the 
tissues,  and  not  the  blood,  which  become  primarily  loaded  with 
carbonic  acid,  the  latter  simply  receiving  the  gas  from  the  former 
by  diffusion,  except  the  (probably)  small  quantity  which  results 
from  the  metabolism  of  the  blood-corpuscles  ;  and  that  the  oxygen 
which  passes  from  the  blood  into  the  tissues  is  at  once  taken  up  in 
some  combination,  so  that  it  is  no  longer  removable  by  diminished 
tension. 

As  a  matter  of  fact,  Oertmann  -  has  shewn  that  if  in  a  frog,  the  whole 
blood  of  the  body  be  replaced  by  normal  saline  solution,  the  total 
metabolism  of  the  body  is,  for  some  time,  unchanged.  The  saline 
medium  is  able,  owing  to  the  low  rate  of  metabolism,  and  large  re- 
spiratory surface  of  the  animal,  to  supply  the  tissues  with  ail  the  oxygen 
they  need,  and  to  remove  all  the  carbonic  acid  they  produce.  It  is 
difficult  to  believe  that,  in  sujh  an  experiment,  the  oxidation  took  place 
in  the  saline  solution  itself  while  circulating"  in  the  blood-vessels  and 
tissue-spaces  of  the  animal. 

We  may  add,  that  the  oxidative  power  which  the  blood  itself 
removed  from  the  body  is  able  to  exert  on  substances  which  are 
undoubtedly  oxidized  in  the  body  is  so  small  that  it  may  be 
neglected  in  the  present  considerations.  If  grape-sugar  be  added 
to  blood,  or  to  a  solution  of  ha:;moglobin,  the  mixture  may  be  kept 
lor  a  long  time  at  the  temperature  of  the  body,  without  undergoing 
oxidation  3. 

Almost  the  only  indication,  and  that  an  indirect  one,  that  blood  is 
capable  of  oxidizing  sugar  is  to  be  found  in  the  facf*,  that  when  the  sugar 
in  shed  blood  is  quantitatively  determined,  the  amount  is  greatest, 
when  the  blood  is  examined  immediately  on  leaving  the  blood-vessels, 
and   diminishes   afterwards.     Schememetjewski  =   found  that   sodium 

'  Pfliiger's  Archiv,  VI.  (1872)  p.  65. 

*  Pfliigei-'s  Archiv,  XV.  (1877)  p.  381. 

3  Hoppe-Seyler,  t/ntersuc'i.  i.  (1866)  p.  136.     See  also  Pfliiger's  ^;r/z?V,  vil. 
{1873)  p.  399. 

*  Bernard,  T.t^or"  sur  le  Diabete,  1S77.     Va.w'j,  Proc.  Roy.  Soc„'\.y.V\.  (1877) 
p.  346.  5  YjVidiW'x^i  Aibeiten,  1868,  p.  \\\. 


CHAl'.   II.J  RLSriRATlON.  jO/ 

lactate  injected  into  the  veins  increased  the  respiratory  interchange  ; 
but  that  the  increase  was  not  due  to  the  dire't  c<inil)uslion  of  the  >alt 
in  the  blond  seems  to  be  indicated  by  the  fact  tnat  no  oxidation  of  the 
salt  took  pla:e\vhen  it  was  simply  exposed  to  the  action  of  shed  blood  ; 
moreover  the  injection  of  sugar  did  not  even  increase  the  respiratory 
interchange. 

Even  within  the  body  a  slight  excess  of  sugar  in  the  blood  over 
a  certain  ]iercentage  wholly  escapes  oxidation,  and  is  discharged 
unchanged.  Many  easily  oxidi.'.cd  substances,  such  as  pyrogallic 
acid,  pass  largely  through  the  blood  of  a  living  body  without  being 
oxidized.  The  organic  acids,  such  as  citric,  even  in  combination 
with  alkaline  bases,  are  only  partially  oxidized  ;  when  administered 
as  acids,  and  not  as  salts,  they  are  hardly  oxitlized  at  all.  It  is  of 
course  quite  possible  that  the  changes  whicii  the  blood  undergoes 
when  shed  might  interfere  with  its  oxidative  action,  and  hence  the 
fact  that  slicd  blood  has  little  or  no  oxidizing  power,  is  not  a 
satisfactory  proof  that  the  unchanged  blood  within  the  living 
vessels  may  not  have  such  a  power.  But  did  oxidation  take  place 
largely  in  the  blood  itself,  one  would  expect  even  highly  diffusible 
substances  to  be  oxidized  in  their  transit ;  whereas  if  we  suppose 
the  oxidation  to  take  place  in  the  tissues,  it  becomes  intelligible 
why  such  difi'usible  substances  as  those  which  the  tissues  in  general 
refuse  to  take  up  largely,  should  readily  pass  unchanged  from  the 
blood  through  the  secreting  organs. 

We  have  seen  that  in  muscle  the  production  of  carbonic  acid  is 
not  directly  de])endent  on  the  consumption  of  oxygen.  The  muscle 
produces  carbonic  acid  in  an  atmosphere  of  hydrogen.  What  is 
true  of  muscle  is  true  also  of  other  tissues  and  of  the  body  at  large. 
Spallanzani  and  W.  Edwards  shewed  long  ago  that  animals  might 
continue  to  breathe  out 'carbonic  acid  in  an  atmosphere  of  nitrogen 
or  hydrogen  ;  and  recently  Prtiiger  '  has  shewn,  by  a  remarkable 
experiment,  that  a  frog  kept  at  a  low  temperature  will  live  for 
several  hours,  and  continue  to  produce  carbonic  acid,  in  an  atmo- 
sphere absolutely  free  from  oxygen.  The  carbonic  acid  produced 
during  this  period  was  made  by  help  of  the  oxygen  inspired  in  the 
hours  anterior  to  the  commencement  of  the  experiment.  The 
oxygen  then  absorbed  was  stowed  away  from  the  haemoglobin  into 
the  tissues,  it  was  made  use  of  to  build  up  the  explosive  com- 
pounds, whose  explosions  later  on  gave  rise  to  the  carbonic  acid ; 
or,  to  adopt  Pfliiger's  simile,  the  oxygen  helps  to  wind  up  the  vital 
clock  ;  but  once  wound  up  tlie  clock  will  go  on  for  a  period  without 
further  winding.  The  hog  will  continue  to  live,  to  move,  to ' 
produce  carbonic  acid  for  a  while  without  any  fresh  oxygen,  as  we 
'  Vflugcr'B.hr/iiv,  x.  (1S75)  \\  251. 


368  THE   CHANGES  IN   THE   TISSUES.        [BOOK   IT. 

know  of  old  it  will  without  any  fresh  food  ;  it  will  continue  to  do 
so  till  the  explosive  compounds  which  the  oxygen  built  up  are 
exhausted  ;  it  will  go  on  till  the  vital  clock  has  run  down. 

To  sum  up,  then,  the  results  of  respiration  in  its  chemical 
aspects.  As  the  blood  passes  through  the  lungs,  the  low  oxygen 
tension  of  the  venous  blood  permits  the  entrance  of  oxygen  from 
the  air  of  the  pulmonary  alveolus,  through  the  thin  alveolar  wall, 
through  the  thin  capillary  sheath,  through  the  thin  layer  of  blood- 
plasma,  to  the  red  corpuscle,  and  the  reduced  hccmoglobin  of  the 
venous  blood  becomes  wholly,  or  all  but  wholly,  oxy-hsmoglobin. 
Hurried  to  the  tissues,  the  oxygen,  at  a.  comparativdy  high  tension 
in  the  arterial  blood,  passes  largely  into  them.  In  the  tissues,  the 
oxygen  tension  is  always  kept  at  an  exceedingly  low  pitch,  by  the 
fact  that  they,  in  some  way  at  present  unknown  to  us,  pack  away 
at  every  moment  into  some  stable  combination  each  molecule  of 
oxygen  which  they  receive  from  the  l)lood.  With  much  but  not 
all  of  its  oxy-hffimoglobin  reduced,  the  blood  passes  on  as  venous 
blood.  How  much  haemoglobin  is  reduced  will  depend  on  the 
activity  of  the  tissue  itself.  The  quantity  of  haemoglobin  in  the 
blood  is  the  measure  of  limit  of  the  oxidizing  power  of  the  body 
at  large ;  but  within  that  limit  the  amount  of  oxidation  is 
determined  by  the  tissue,  and  by  the  tissue  alone. 

Though  the  quantity  of  carbonic  acid  expired  (p.  342)  may  be  tempo- 
rarily increased  by  an  increase  of  the  respiratory  movements,  this, 
according  to  Pfliiger,  is  to  be  regarded  as  the  result  of  increased  venti- 
lation rather  than  of  increased  metabolic  production.  This  physiolo- 
gist '  has  brought  forward  strong  evidence  in  favour  of  the  view  urged 
by  him,  that  neither  the  extent  of  the  respiratory  movements  nor  the 
velocity  of  the  flow  of  blood  are  to  be  regarded  as  prime  factors 
determining  the  amount  of  general  metabolism.  It  is  according  to 
him  the  quicker  metabolism  which  determines  the  more  active  circulation 
and  the  more  vigorous  respiration  ;  not  vice  versa. 

We  cannot  trace  the  oxygen  through  its  sojourn  in  the  tissue. 
We  only  know  that  sooner  or  later  it  comes  back  combined  in 
carbonic  acid  (and  other  matters  not  now  under  consideration). 
Owing  to  the  continual  production  of  carbonic  acid,  the  tension  of 
that  gas  in  the  extravascular  elements  of  the  tissue  is  always  higher 
than  that  of  the  blood  ;  the  gas  accordingly  passes  from  the  tissue 
into  the  blood,  and  the  venous  blood  passes  on  not  only  with  its 
haemoglobin  reduced,  i.e.  with  its  oxygen  tension  decreased,  but 
also  with  its  carbonic  acid  tension  increased.  Arrived  at  the  lungs, 
the  blood  finds  the  pulmonary  air  at  a  lower  carbonic  acid  tension 

'  Pfluger's  Archiv,  VI.    (1872)  p.  43  ;  x.    (1875)  p.   251  ;  xiv.  (1877)  p.  i. 
Finkler,  ibid.  X.  p.  368      Finkler  and  Oertmann,  ibid.  XIV.  p.  38. 


CHAP.    II.]  .  kESPIRATION.  369 

than  itself.  The  gas  accordingly  streams  through  the  thin  vascular 
and  alveolar  walls,  till  the  tension  without  the  blood-vessel  is 
equal  to  the  tension  within.  Tims  the  air  of  the  pulmonary 
alveoli,  having  given  up  oxygen  to  the  blood  and  taken  up 
carbonic  acid  from  the  blood,  having  a  higher  carbonic  acid  tension 
and  a  lower  oxygen  tension  than  the  tidal  air  iiT  the  bronchial 
passages,  mixes  rapidly  with  this  by  diffusion.  The  mixture  is 
furdier  assisted  by  ascending  and  descending  currents ;  and  the 
tidal  air  issues  from  the  chest  at  the  breathing  out  poorer  in  oxygen 
and  richer  in  carbonic  acid  than  the  tidal  air  which  entered  at  the 
breathing  in. 

Sec.  6.     The  Nervous  Mechanism  of  Respiration. 

Breathing  is  an  involuntary  act.  Though  the  diaphragm  and 
all  the  other  muscles  employed  in  respiration  are  voluntary  muscles, 
i.e.  muscles  which  can  be  called  into  action  by  a  direct  effort  of 
the  will,  and  though  respiration  may  be  modified  within  very  wide 
limits  by  the  will,  yet  we  habitually  breathe  without  the  intervention 
of  the  will :  the  normal  breathing  may  continue,  not  only  in  the 
absence  of  consciousness,  but  even  after  the  removal  of  all  the 
parts  of  the  brain  above  the  medulla  oblongata. 

We  have  already  seen  how  complicated  is  even  a  simple  respi- 
ratory act.  A  very  large  number  of  muscles  are  called  into  play. 
Many  of  these  are  very  far  apart  from  each  other,  such  as  the 
diaphragm  and  the  nasal  muscles ;  yet  they  act  in  harmonious 
sequence  in  point  of  time.  If  the  lower  intercostal  muscles  con- 
tracted before  the  scaleni,  or  if  the  diaphragm  contracted  while 
the  other  chest-muscles  were  enjoying  an  interval  of  rest,  the 
satisfactory  entrance  and  exit  of  air  would  be  impossible.  These 
muscles  moreover  are  coordinated  also  in  respect  of  the  amount  of 
their  several  contractions  ;  a  gentle  and  ordinary  contraction  of 
the  diaphragm  is  accompanied  by  gentle  and  ordinary  contractions 
of  the  intercostals,  and  these  are  preceded  by  gentle  and  ordinary 
contractions  of  the  scaleni.  A  forcible  contraction  of  the  scaleni, 
followed  by  simply  a  gentle  contraction  of  the  intercostals,  would 
hinder  rather  than  assist  inspiration.  Further,  the  whole  complex 
inspiratory  effort  is  often  followed  by  a  less  marked  but  still 
comjilex  expiratory  action.  It  is  impossible  that  all  these  so 
carefully  coord-inated  muscular  contractions  should  be  brought 
about  in  any  other  way  than  by  coordinate  nervous  impulses 
descending  along  efferent  nerves  from  a  coordinating  centre.  By 
experiment  we  find  this  to  be  the  case. 

When  in  a  rabbit  the  trunk  of  a  phrenic  nerve  is  cut,  the 
F.  \  24 


370  NERVOUS   MECHANISM.  [BOOK   II. 

diaphragm  on  that  side  remains  motionless,  and  respiration  goes 
on  without  it.  When  both  nerves  are  cut,  the  whole  diaphragm 
remains  quiescent,  though  the  respiration  becomes  excessively 
laboured. 

The  occasional  slight  rhythmic  movements  of  the  diaphragm  ob- 
served by  Brown-Sequard,  after  section  of  the  phrenic,  interesting 
from  another  point  of  view,  do  not  militate  against  the  above 
statement. 

When  an  intercostal  nerve  is  cut  no  active  respiratory  move- 
ment is  seen  in  that  space,  and  when  the  spinal  cord  is  divided 
below  the  origin  of  the  seventh  cervical  spinal  nerve,  costal  respira- 
tion ceases,  though  the  diaphragm  continues  to  act  and  that  with 
increased  vigour.  When  the  cord  is  divided  just  below  the  medulla, 
all  thoracic  movements  cease,  but  the  respiratory  actions  of  the 
nostrils  and  glottis  still  continue.  These  however  disappear  when 
the  facial  and  recurrent  laryngeal  are  divided.  We  have  already 
stated  that  after  removal  of  the  brain  above  the  medulla,  respira,- 
tion  still  continues  very  much  as  usual,  the  modifications  which 
ensue  from  loss  of  the  brain  being  unessential.  Hence,  putting 
all  these  facts  together,  it  is  clear  that  in  respiration,  coordinated 
impulses  do,  as  we  suggested,  descend  from  the  medulla  along  the 
several  efferent  nerves.  The  proof  is  completed  by  the  fact  that 
the  removal  or  injury  of  the  medulla  alone  at  once  stops  all  respi- 
ratory movements,  even  though  every  nmscle  and  every  nerve 
concerned  be  left  intact.  Nay  more,  if  only  a  small  portion  of 
the  medulla,  a  tract  whose  limits  are  not  as  yet  exactly  fixed,  but 
which  lies  below  the  vaso-motor  centre,  between  it  and  the  calajnus 
scriptorws,  be  removed  or  injured,  respiration  ceases  for  ever, 
though  every  other  part  of  the  body  be  left  intact'.  When  this 
spot  is  excised  or  injured,  breathing  at  once  ceases,  and  since  the 
inhibitory  vagus  centre  is  generally  at  the  same  time  stimulated, 
and  the  heart's  beat  arrested,  death  ensues  instantaneously.  Hence 
this  portion  of  the  nervous  system  was  called  by  Flourens  the 
vital  knot,  or  ganglion  of  life,  nceud  vital.  We  shall  speak  of  it  as 
the  respiratory  centre.  The  nature  of  this  centre  must  be  ex- 
ceedingly complex ;  for  while  even  in  ordinary  respiration  it  gives 
rise  to  a  whole  group  of  coordinate  nervous  impulses  of  inspiration 
followed  in  due  sequence  by  a  smaller  but  still  coordinate  group 
of  expiratory  impulses,  in  laboured  respiration  fresh  and  larger 
impulses   are  generated,    though   still   in   coordination   with   the 

^  Strieker,  Wien.  Sitzimgsbericht,  Bd.  75  (1877)  P-  ^>  ^^.s  seen  in  dogs 
poisoned  by  antiarin,  respiratory  efforts  after  division  of  the  medulla 
oblongata. 


CIIAP.    II.]  RESPIRATION.  37I 

normal  ones,  the  expiratory  events  being  especially  augmented  ; 
and  in  the  more  extreme  cases  of  dyspncea  and  asphyxia  impulses 
overtlow,  so  to  speak,  from  it  in  all  directions,  tliou^^h  only 
gradually  losing  their  coordination,  until  almost  every  muscle  in 
the  body  is  thrown  into  contractions. 

The  first  question  we  have  to  consider  is,  Are  we  to  regard 
the  rhythmic  action  of  this  respiratory  centre  as  due  essentially  to 
cliangcs  taking  place  in  itself,  or  as  duo  to  aff-'rent  nervous 
imjjulses  or  other  stimuli  which  atfect  it  in  a  rhythmic  manner 
from>A'ithout  ?  In  other  words,  Is  the  action  of  the  centre  auto- 
matic or  purely  reflex?  We  kno\V  tliat  the  centre  may  be  influenced 
by  impulses  proceeding  from  without,  and  that  the  breathing  may 
be  aft'ected  by  the  action  of  the  will,  or  by  an  emotion,  or  by  a 
dash  of  cold  water  on  the  skin,  or  in  a  hundred  other  ways  ;  but 
the  fact  that  the  action  of  the  centre  may  be  thus  modified  from 
without,  is  no  proof  that  the  continuance  of  its  activity  is  depen- 
dent on  extrinsic  causes. 

In  attempting  to  decide  this  question  we  naturally  turn  to  the 
pneumogastric  as  being  die  nerve  most  likely  to  serve  as  the 
channel  of  afferent  impulses  setting  in  action  the  respiratory 
centre.  If  both  vagi  be  divided,  respiration  still  continues  though 
in  a  modified  form.  This  proves  distinctly  that  afferent  impulses 
ascending  those  nerves  are  not  t!.e  efficient  cause  of  the  respiratory 
movements.  We  have  seen  that  when  the  spinal  cord  is  divided 
below  the  medulla,  the  facial  and  laryngeal  movements  still 
continue.  This  proves  that  the  respiratory  centre  is  still  in  action, 
though  its  activity  is  unable  to  manifest  itself  in  any  thoracic 
movement.  But  when  the  cord  is  thus  divided  the  respiratory 
centre  is  cut  off"  from  all  sensory  impulses,  save  those  which  may 
pass  into  it  from  the  cranial  nerves ;  and  the  division  of  these 
cranial  nerves  in  no  way  destroys  respiration.  Hence  it  is  clear 
that  the  respiratory  impulses  proceeding  from  the  respiratory 
centre  are  not  simply  afferent  impulses  reaching  the  centre  along 
aff'erent  nerves  and  transformed  by  reflex  action  in  that  centre. 
They  evidently  start  de  novo  from  tlie  centre  itself,  however  much 
their  characters  may  be  aff"ected  by  afferent  impulses  reaching  that 
centre  at  the  time  of  their  being  generated.  The  action  of  the 
centre  is  automatic,  not  simply  reflex. 

Among  the  afferent  impulses  which  aff'ect  the  automatic  action 
of  the  centre,  the  most  important  are  those  which  ascend  along 
the  vagi.  If  one  vagus  be  divided,  the  respiration  becomes 
slower;  if  both  be  oivided,  it  becomes  very  slow,  the  piuses 
between  expiration  and  inspiration  being  excessively  prolonged. 
The    character   of    the   respiratory   movement   too   is   markedly 

24 — 2 


372  NERVOUS  mzj:tL\xism.  [book  n. 

r^iangpri^  eatdk  respiiaticMi  is  tiiiier  and  dee^fsr^  so  mndi  so  that 
what  is  lost:  in  late  is  gaiaed  in  estenL  die  amount  of  carbonic 
acid  produced  and  osjgen  ronsnmed  in  a  g^ven  pmod  raa[iaining 
after  'drnsioo  of  die  litres  aboot  die  same  as  when  diey  weie 
intact.  It  is  evident  from  diis,  in  the  fiist  place,  diat  during  life 
aSoent  impulses  aie  continually  ascending  tbe  vagi  and  modifying 
tbe  actioa  of  die  les^rabxj  centre,  and  in  the  second  place,  that 
the  modificatiai  beais  ampfy  on  the  distribution  in  time  of  the 
e&renf  le^iatxxy  impulses,  and  not  at  all  on  the  amount  to 
vfaicfa  dier  aie  generated.  These  afferent  impulses  aie  piob^Idy 
staited  in  the  longs  by  the  conditicm  of  die  blood  in  die  pnlmraiaiy 
„-.-._,.  icting  as  a  stimulus  to  the  peiipheial  hidings  of  die 
zt  izh  possil^  the  altoed  air  in  the  air-cells  may  also 

3.^:  ^  :.       J -'.IS  <Mi  the  nerfe-endnLTS. 


ted  that  the  mer 
;erre  as  a  sti::- 
-  rr^Tiicalh-  dr. 

1       tn  air  is  dr; 


3    n; 
7  al 

r.  the 
i  die 
ses  be 


of  proiloogc 


.'xejakoad's  Artim,  1S75,  p.  jQOk 


CHAP.   II.]  RESPIRATION.  373 

severed  or  not,  a  slowing  of  the  respiration  takes  place,  and  this 
may  by  proper  stimulation  be  carried  so  far  that  a  complete  stand- 
still of  respiration  in  the  phase  of  rest  is  brought  about,  i.e.  the 
respiratory  apparatus  remains  in  the  condition  which  obtains  at 
the  dose  of  an  ordinary  expiration,  the  diaphragm  being  com- 
pletely relaxed.  In  other  words,  the  superior  laryngeal  nerve 
contains  fibres,  the  stimulation  of  which  produces  afferent  im- 
pulses whose  effect  is  to  inhibit  the  action  of  the  respiratory 
centre;  while  the  main  trunk  of  the  vagus  contains  fibres,  the 
stimulation  of  which  produces  afferent  impulses  whose  effect  is  to 
accelerate  or  augment  the  action  of  the  respiratory  centre.  In 
some  cases  stimulation  of  the  main  trunk  of  the  vagus  also  causes 
a  slowing  or  even  standstill  of  the  respiration,  especially  when  the 
nerve  has  become  exhausted  by  previous  stimulation.  We  may, 
for  the  present  at  least,  ex[»lain  these  results  by  supposing  that 
while  the  superior  laryngeal  contains  only  inhibitorj^  fibres,  the 
main  trunk  of  the  vagus  contains  both  accelerating  and  inhibitory 
fibres,  the  former  however  greatly  preponderating,  ^^'hi!e,  from 
the  results  of  simple  section  of  the  main  trunk,  it  is  clear  that  the 
accelerating  fibres  are  continually  at  work,  it  is  not  so  clear  that 
the  inhibitory  fibres  are  always  in  action,  since  section  even  of 
both  superior  larjngeals  does  not  necessarily  quicken  respiration. 

The  statement  made  above,  if  not  wholly  satisfactorv-,  has  at  least 
the  merit  of  recoaciiing  conflicting  statements.  For  a  long  time  a 
controversy  was  carried  on  between  those  authors  who  maintained 
that  stimulation  of  the  central  end  of  the  vagus,  when  the  ner;e  was 
divided  in  the  neck,  brought  about  a  tetanic  contraction  of  the 
diaphragm  and  so  had  an  inspiratory  effect,  and  those  who  observed 
a  complete  relaxation  to  follow  upon  stimulation,  and  so  regarded 
the  effect  as  expiratorv*.  We  are  indebted  to  Rosenthal'  for  pointing 
out  the  contrast  between  the  action  of  the  main  trunk  of  the  vagus 
and  that  of  the  superior  larv-ngeal  branch  :  and  the  view  just  put 
forward  in  the  text  is  in  the  main  that  of  Rosenthal,  except  that  he 
denies  the  existence,  admitted  by  most  other  observers  -,  of  any 
inhibitory-  fibres  in  the  main  trunk.  We  further  owe  to  Rosenthal  a 
consistent  theory  of  the  manner  in  which  the  vagus  acts  on  the  re- 
spiratory centre.  According  to  him  we  may  regard  the  respiratory 
centre  as  the  seat  of  two  conflicting  forces,  one  tending  to  generate 
respiratory  impulses,  and  the  other  offering  resistance  to  the  generation 
of  these  impulses,  the  one  and  the  other  alternately  gaining  the  victory 
and  thus  leading  to  a  rhythmic  discharge.  The  afferent  impulses, 
passing  upward  along  the  main  trunks  of  the  vagi  are  further  to  be 
looked  upon  as  acting  not  on  the  generation  of  impulses  but  on  t'^e 

'  Die  Alhembezvi^ung'n,  1S62,  and  du  Bois-Reymond's ^/Titrp,  1S64.  p  450; 
1S65,  p.  191  ;   1S70,  p.  423. 
'  Cf.  Burkart,  Pdiiger's  Archiv,  xvi.  (1S78)  p.  427. 


374  NERVOUS   MECHANISM.  [BOOK   II. 

resistance  offered  by  the  centre,  diminishing  that  resistance  in  pro- 
portion to  their  intensity.  Hence  when  the  vagi  are  divided,  the 
central  resistance  is  increased,  owing  to  the  absence  of  the  usual 
afferent  impulses  tending  to  diminish  that  resistance  ;  in  consequence, 
the  respiratory  impulses  take  a  longer  time  in  gathering  head  sufficient 
to  overcome  the  increased  resistance,  and  therefore  are  less  frequent, 
though  the  discharge  when  it  does  occur  is  proportionately  more 
forcible.  Stimulation  of  the  divided  vagi  on  the  other  hand,  by  in- 
creasing the  afferent  impulses  and  so  diminishing  the  central  resistance, 
renders  the  discharges  more  frequent.  The  impulses  which  ascend  to 
the  medulla  along  the  superior  laryngeal  branches  may  in  like  manner 
be  regarded  as  increasing  the  central  resistance,  and  thus  as  inhibitory 
of  the  respiratory  discharge. 

It  is  obvious  that  this  theory,  though  constructed  chiefly  with  the 
view  of  explaining  inspiratory  impulses  and  their  inhibition,  must,  in 
order  to  be  satisfactory,  also  include  the  consideration  of  distinctly 
expiratory  impulses.  For  in  laboured  respiration  we  must  in  some 
way  or  other  admit  the  existence  of  specific  expiratory  impulses,  and 
if  Hering  and  Breuer's  view  be  correct,  the  vagus  must  even  in 
ordinary  breathing  be  the  channel  of  stimuli  which  excite  expiratory 
impulses.  Many  writers  regard  the  standstill  which  is  produced  by 
stimulation  of  the  superior  laryngeal  nerve  as  an  expiratory  effect,  and 
indeed  frequently  speak  of  it  as  an  '  expiratory  standstill.'  But  it  is 
obvious  that  a  distinction  ought  to  be  made  between  a  state  of  things 
in  which  there  is  a  complete  absence  of  all  respiratory  muscular  activity 
and  in  which  the  chrst  remains  in  a  condition  of  passive  rest,  and  one 
in  which  the  chest  is  maintained  in  a  fixed  condition  by  the  continued 
contraction  of  certain  expiratory  muscles  ;  it  is  the  latter  Avhich  is  the 
true  expiratory  standstill,  the  antithesis  of  the  inspiratory  standstill,  in 
which  the  diaphragm  remains  in  tetanic  contraction.  The  inhibition 
of  inspiratory  impulses  is,  however,  the  natural  precursor  of  expiratory 
impulses,  and  it  would  seem  that  the  same  impulses  which  bring  about 
a  standstill  of  inspiration,  may  when  increased  in  strength  give  rise  to 
movements  of  a  distinctly  expiratory  character.  Thus  stimulation  of 
the  superior  laryageal  branch  when  carried  beyond  the  strength 
necessary  to  inhibit  inspiration,  may  give  rise  to  contraction  ot  the 
abdominal  muscles  indicative  of  expiratory  efforts.  We  may  therefore 
complete  the  hypothesis  of  the  respiratory  centre,  by  supposin^j  it  to 
consist  of  an  inspiratory  part  and  an  expiratory  part,  so  disposed  'in 
reference  to  each  other,  that  the  impulses  which  tend  to  excite  the  one 
part  tend  at  the  same  time  to  inhibit  the  other  part,  and  vice  versci, 
the  expiratory  tract  however  being  less  irritable  than  the  inspiratory 
tract,  so  that  the  latter  is  thrown  into  action  first,  and  the  former 
comes  into  play  to  any  very  appreciable  effect  only  wnen  comparatively 
strong  stimuli  are  brought  to  bear  upon  it^ 

Stimulation  of  the  central  end  of  the  inferior  recurrent  laryngeal  is 
said  to  have  an  inhibitory  effect  like  that  of  the  superior  laryngeal, 
but  much  slighter  ^ 

*  Rosenthal,  Automat.  Nerveti- Centra,  1875. 
'  Rosenthal,  oj).  cit. 


CHAP.    II.]  RESPIRATION.  375 

This  double  or  alternate  respiratory  action  of  the  vaf,'i  may  be 
taken  as  in  a  general  way  illustrative  of  the  manner  in  which  other 
afferent  nerves  and  various  parts  of  the  cerebrum  are  enabled  to 
influence  respiration,  this  or  that  afferent  impulse,  started  by  a 
stimulus  applied  to  the  skin  or  elsewhere,  or  by  an  emotion  and 
the  Jike,  playing,  according  to  circumstances,  now  an  inhibitory 
now  an  accelerating  part.  As  we  know  from  daily  experience,  of 
all  the  apsychical  nervous  centres,  the  respiratory  centre  is  the 
one  which  is  most  frequently  and  most  deeply  affected  by  nervous 
impulses  from  various  quarters. 

According  to  Langendorff',  weak  stimulation  of  any  sensory  nerve 
produces  acceleration,  st'ong  stimulation  inhibition  or  slowing  of 
respiration.  It  is  absurd  to  suppose  that  every  sensory  nerve  contains 
distinct  acclcratmg  and  inhibitory  fibres  connected  with  the  respiratory 
centre.  And  the  existence  of  two  classes  of  respiratory  Jibres  \x\  the 
va.;us  or  its  branches  must  he  regarded  in  the  same  provisional  sense 
as  the  existence  of  distinct  vaso  dilator  and  vaso-conscrictor  fibres. 

The  one  thing,  however,  which  above  others  affects  the 
respiratory  centre,  is  the  condition  of  the  blood  in  respect  to  its 
respiratory  changes ;  the  n)ore  venous  (less  arterial)  the  blood,  the 
greater  is  the  activity  of  the  respiratory  centre.  When  by  reason 
either  of  any  hindrance  to  the  entrance  of  air  into  the  chest,  or  of 
a  greater  respiratory  activity  of  the  tissues,  as  during  muscular 
exertion,  the  blood  becomes  less  arterial,  more  venous,  i.e.  with  a 
smaller  charge  of  oxyhoemoglobin  and  more  heavily  laden  with 
carbonic  acid,  the  respiration  from  being  normal  becomes  laboured. 
This  effect  of  deficient  arterialization  of  blood  is  very  different 
from  that  of  section  of  the  vagi ;  it  is  no  mere  change  in  the 
distribution  of  impulses;  the  breathing  is  quicker  as  well  as 
deeper,  there  is  an  increase  of  the  sum  of  efferent  impulses 
proceeding  from  the  centre,  and  the  expiratory  impulses,  which  in 
normal  respiration  are  very  slight,  acquire  a  pronounced  im- 
portance. As  the  blood  becomes,  in  cases  of  obstruction,  less 
and  .less  arterial,  more  and  more  venous,  the  discharge  from  the 
respiratory  centre  becomes  more  and  more  vehement,  and  instead 
of  confining  itself  to  the  usual  tracts,  and  passing  down  to  the 
ordinary  respiratory  muscles,  overflows-into  other  tracts,  puts  into 
action  other  muscles,  until  there  is  perhaps  hardly  a  muscle  in  the 
body  which  is  not  made  to  feel  its  effects.  And  this  discharge 
may,  as  we  shall  see  in  speaking  of  asphyxia,  continue  till  the 
nervous  energy  of  the  respiratory  centre  is  completely  exhausted. 
The  effect  of  venous  blood  then  is  to  augment  these  natural 
explosive   decompositions  of   the  nerve-cells   of   the   respiratory 

'  Millh.  a.  d.  Konigsbcr^cr physiol.  Lab.,  iSyS,  p.  33. 


3/6  NERVOUS  MECHANISM.        [BOOK  II. 

centre  wliich  give  rise  to  respiratory  impulses  ;  it  increases  their 
amount,  and  also  quickens  their  rhythm.  The  latter  change  how- 
ever is  always  much  less  marked  than  the  former,  the  respiration 
in  dyspnoea  being  much  more  deepened  than  hurried,  and  the 
several  respirator}-  acts  are  never  so  much  hastened  as  to  catch 
each  other  up,  and  so  to  produce  an  inspiratory  tetanus  like  that 
resulting  from  stimulation  of  the  vagus.  On  the  contrary,  espe- 
cially as  exhaustion  begins  to  set  in,  the  rhythm  becomes  slower 
out  of  proportion  to  the  weakening  of  the  indi%-idual  movements. 

There  seem  to  be  two  distinct  kinds  of  dyspncea.  In  one  with  in- 
creased depth  the  rhythm  is  not  proportionately  quickened  or  may 
even  be  diminished.  Thus  in  the  dyspnoea  caused  by  section  of  the 
phrenic  nerves,  the  rhythm  falls  notably  ^  In  the  other,  which  may  be 
called  the  asthmatic  type,  the  rhythm  is  hurried,  while  the  depth  of 
each  breath  is  not  increased  but,  in  many  cases  at  least,  diminished. 

On  the  other  hand,  the  blood  may  be  made  not  more  but  less 
venous  than  usual.  This  condition  may  be  brought  about  by  an 
animal  being  made  to  inspire  oxygen,  or  to  breathe  for  a  time 
more  rapidly  and  more  forcibly  than  the  needs  of  the  economy 
require.  If  in  a  rabbit  artificial  respiration  is  carried  on  very 
vigorously  for  a  while  and  then  suddenly  stopped,  the  animal  does 
not  immediately  begin  to  breathe.  For  a  variable  period  no 
respiration  takes  place  at  all,  and  when  it  does  begin  occtu's  gently 
and  normally,  only  passing  into  dyspncea  if  the  animal  is  unable 
to  breathe  of  itself,  and  then  quite  gradually.  Evidently  during 
this  period  the  respiratory  centre  is  in  a  state  of  complete  rest,  no 
explosions  are  taking  place,  no  respiratory  impulses  are  being 
generated,  and  the  quiet  transuion  from  this  condition  to  that  of 
normal  respiration  shews  that  the  subsequent  generation  of 
impulses  is  attended  by  no  great  disturbance.  The  cause  of  this 
state  of  things,  which  is  known  as  that  of  apticea,  is  to  be  sought 
for  in  the  condition  of  the  blood.  By  the  increased  vigour  of  the 
artificial  respiratory  movements  the  haemoglobin  of  the  arterial 
blood,  which  is  naturally  not  quite  saturated,  becomes  almost 
completely  so,  and  the  dissolved  oxygen  is  increased,  its  tension 
being  largely  augmented.  -  Respiration  is  arrested  because  the 
blood  is  more  highly  arterialized  than  usual.  Thus  we  have  in 
apncea  the  converse  to  dyspncea;  and  both  states  point  to  the 
same  conclusion,  that  the  activity  of  the  respiratory  centre  is 
dependent  on  the  condition  of  the  blood,  being  augmented  when 
the  blood  is  less  arterial  and  more  venous,  being  depressed  when 
it  is  more  arterial  and  less  venous  than  usual. 

^  Piukinje,  quoted  by  Hering  and  Breuer,  op.  cit. 


CMAP.    II.]  RESPIRATION.  *  377 

The  question  now  arises,  Does  this  condition  of  the  blood 
affect  the  respiratory  centre  directly,  or  does  it  produce  its  effect 
by  stimulating  tlic  periplieral  ends  of  afferent  nerves  in  various 
parts  of  the  body,  and,  by  the  creation  there  of  afferent  impulses, 
indirectly  modify  the  action  of  the  centre  ?  ^Vithout  denying  the 
possibility  that  the  latter  mode  of  action  may  help  in  the  matter, 
as  regards  not  only  the  vagi,  but  all  nliVrcnt  nerves,  it  is  clear  from 
the  following  reasons  that  the  main  effect  is  produced  by  the 
direct  action  of  the  blood  on  the  respiratory  centre  itself  If  the 
sjiinal  cord  be  divided  below  the  medulla  oblongata,  and  both 
vagi  be  cut,  want  of  proper  aeration  of  the  blood  still  produces 
an  increased  activity  of  the  respiratory  centre,  as  shewn  by  the 
increased  vigour  of  the  facial  respiratory  movements.  If  the 
supjily  of  blood  be  cut  off  from  the  medulla  by  ligature  of  the 
blood-vessels  of  the  neck,  dyspnoea  is  produced,  though  the 
operation  produces  no  change  in  the  blood  generally,  but  simply 
affects  the  respiratory  condition  of  the  medulla  itself,  by  cutting 
off  its  blood-suj)ply,  the  immediate  result  of  which  is  an  accu- 
mulation of  carbonic  acid  and  a  paucity  of  available  oxygen  in  the 
protoplasm  of  the  nerve-cells  in  that  region.  If  the  blood  in  the 
carotid  artery  in  an  animal  be  warmed  above  the  normal,  dyspnoea 
is  at  once  produced.  The  over-warm  blood  hurries  on  the 
activity  of  the  nerve-cells  of  the  respiratory  centre,  so  that  the 
normal  supply  of  blood  is  insufficient  for  their  needs.  The 
condition  of  the  blood  then  affects  respiration  by  acting  directly 
on  the  respiratory  centre  itself. 

Deficient  aeration  produces  two  effects  in  blood  :  it  diminishes 
the  oxygen,  and  increases  the  carbonic  acid.  Do  both  of  these 
changes  affect  the  respiratory  centre,  or  only  one,  and  if  so, 
which?  When  an  animal  is  made  to  breathe  an  atmosphere 
containing  nitrogen  only,  the  exit  of  carbonic  acid  by  diffusion  is 
not  affected,  and  the  blood,  as  is  proved  by  actual  analysis, 
contains  no  excess  of  carbonic  acid'.  Yet  all  the  phenomena  of 
dyspnoea  are  present  In  this  case  these  can  only  be  attributed  to 
the  deficiency  of  oxygen.  On  the  other  hand,  if  an  animal  be 
made  to  breathe  an  atmosphere  rich  in  carbonic  acid,  but  at  the 
same  time  containing  abundance  of  oxygen,  though  the  breathing 
becomes  markedly  deeper  and  also  somewhat  more  frequent,  there 
is  no  culmination  in  a  con\ulsive  asphyxia,  even  when  the 
quantity  of  carbonic  acid  in  the  blood,  as  shewn  by  direct  analysis, 
is  very  largely  increased^.  On  the  contrary  the  increase  in  the 
respiratory   movements   after   a   while   passes    off,     the    animal 

'  Pfluger,  Pfluger's  Archiv,  I.  (i8b8)  p.  61. 

*  Dohmen,  Untersu'ch.  a.  d.  Physiol.  Lab.  in  Bonn,  1S65.     Pfluger,  op.  cU. 


378  NERVOUS   MECHANISM.  [BOOK   II. 

becoming  unconscious,  and  appearing  to  be  suffering  rather  from 
a  narcotic  poison  than  from  simple  dyspnoea.  It  does  not  seem 
certain  that  the  increased  respiratory  movements  seen  at  first  are 
the  direct  result  of  the  action  of  the  carbonic  acid  on  the  respira- 
tory centre  •  it  is  possible  that  the  carbonic  acid  may  affect  the 
respiratory  centre  in  an  indirect  way,  by  stimulating  the  respiratory 
passages,  or  by  its  action  on  higher  parts  of  the  brain  ;  and  in  all 
cases  there  is  a  marked  contrast  between  the  slow  develppment  and 
evanescent  character  of  the  hyperpnoea  of  carbonic  acid  poisoning, 
and  the  rapid  onset  and  speedy  culmination  in  convulsions  and 
death  of  the  dyspnoea  due  to  the  absence  of  oxygen.  There  can 
in  fact  be  no  doubt  that  the  action  of  deficiently  arterialized  blood 
on  the  respiratory  centre,  as  manifested  in  an  augmentation  of  the 
respiratory  explosions,  is  due  primarily  to  a  want  of  oxygen,  and 
in  a  secondary  manner  only  to  an  excess  of  carbonic  acid. 

Cheyne- Stokes  Respiration.  A  remarkable  abnormal  rhythrrt  of 
respiration,  first  obseived  by  Cheyne  '  but  afterwards  more  fully 
studied  by  Stokes^  and  hence  called  by  their  combined  names,  occurs 
in  certain  pathological  cases.  The  respiratory  movements  gradually 
decrease  both  in  extent  and  rapidity  until  they  cease  altogether,  and  a 
condition  of  apncea,  lasting  it  may  be  for  several  seconds,  ensues. 
This  is  followed  by  a  feeble  respiration,  succeeded  in  turn  by  a  some- 
what stronger  one,  and  thus  the  respiration  returns  gradually  to.  the 
normal,  or  may  even  rise  to  hyperpnoea  or  slight  dyspnoea  after  which 
it  again  declines  in  a  similar  njianner.  A  secondary  rhythm  of  respi- 
ration is  thus  developed,  periods  of  normal  or  slightly  dyspnceic 
respiration  alternating  by  gradual  transitions  with  periods  of  apnoea. 
The  cause  of  the  phenomena  is  not  thoroughly  understood.  Stokes 
connected  it  with  a  fatty  condition  of  the  heart,  but  it  has  been  met 
with  in  various  maladies.  Schiff  ^  observed  it  as  the  result  of  com- 
pression of  the  medulla  oblongata  ;  and  closely  similar  phenomena 
have  been  observed  during  sleep,  under  perfectly  normal  conditions ''. 
It  presents  a  striking  analogy  with  the  '  groups  '  of  heart-beats  so 
frequently  seen  in  the  frog's  ventricle  placed  under  abnormal 
circumstances. 

Sec.  7.     The  Effects  of  Respiration  on  the  Circulation. 

We  have  seen,  while  treating  of  the  circulation,  that  the  blood- 
pressure  curves  are  marked  bv  undulations,  which,  since  their 
rhythm  is  synchronous  with  that  of  the  respiratory  movements,  are 
evidently  in  some  way  connected  with  respiration.     An  analysis  of 

^  Dublin  Hospital  Reports,  II.  (1816)  p.  21.  • 

'^  See  Diseases  of  Heart,  &c.,  1854,  p.  324. 

3  Lehrb.,  1858,  p.  324. 

♦  Cf.  Mosso,  Arch.  Anat.  u.  Phys.,  1878,  Phys.  Abth.  p.  441. 


CUM'.    II.  I  RESPIRATION  379 

these  undulations  sliews  that  their  causation  is  complex  ;  several 
events  apparently  may  combine  to  bring  them  about. 

When  the  brain  of  a  living  mammal  is  c.xjjosed  by  the  removal 
of  the  skull,  a  rhythmic  rise  and  fall  of  the  cerebral  mass,  a 
pulsation  of  the  brain,  quite  distinct  Irom  the  movements  caused 
by  the  pulse  in  tlie  arteries  of  the  brain,  is  observed  ;  and  upon 
examination  it  will  be  found  thai  these  movements  are  synchronous 
with  the  respiratory  movements,  the  brain  rising  up  during  expira- 
tion and  sinking  during  inspiration.  They  disappear  when  the 
arteries  going  to  the  brain  are  ligatured,  or  when  the  venous 
sinuses  of  the  dura  mater  are  laid  open  so  as  to  admit  of  a  free 
escape  of  the  venous  blood.  They  evidently  arise  from  the 
expiratory  movements  in  some  way  hindering  and  the  inspiratory 
movements  assisting  tiie  return  of  blood  from  the  brain.  We  have 
already  (p.  147)  stated  that  during  inspiration  the  pressure  of  blood 
in  the  great  veins  may  become  negative,  i.e.  sink  belov/  the  pressure 
of  the  atmosphere  ;  and  a  puncture  of  one  of  these  veins  may 
cause  immediate  deatli  by  air  being  actually  drawn  into  the  vein 
and  thus  into  tlie  heart  during  an  inspiratory  movement.  When 
the  veins  of  an  animal  are  laid  bare  in  the  neck  and  watched,  the 
so-called  pulsus  venosus  may  be  observed  in  them,  that  is,  they 
swell  up  during  expiration  and  diminish  again  during  inspiration. 
And  indeed  a  little  consideration  will  shew  that  the  expansion  and 
contraction  of  the  chest  must  have  a  decided  effect  on  the  flow  of 
blood  through  the  thoracic  portion  of,  and  thus  indirectly  through 
the  whole  of  the  vascular  system. 

The  heart  and  great  blood-vessels  are,  like  the  lungs,  placed  in 
the  air-tight  thoracic  cavity,  and  are  subject  like  the  lungs  to  the 
pumping  action  of  the  respiratory  movements.  Were  the  lungs 
entirely  absent  from  the  chest,  the  whole  force  of  the  expansion  of 
the  thorax  in  inspiration  would  be  directed  to  drawing  blood  from 
the  extra-thoracic  vessels  towards  the  heart,  and  conversely  the 
effect  of  the  contraction  of  the  thorax  in  expiration  would  be  to 
drive  the  blood  back  again  from  the  heart  towards  the  extra-thoracic 
vessels.  In  the  presence  of  the  lungs  however  the  free  entrance 
of  air  into  the  interior  of  the  chest  tends  to  maintain  the  pressure 
around  the  heart  and  great  vessels  within  the  thorax  equal  to  the 
ordinary  atmospheric  pressure  on  the  vessels  of  the  rest  of 
the  body  outside  the  thorax ;  but  it  is  unable  completely  to 
equalize  the  two  pressures.  Did  the  air  enter  as  freely  into  the 
lungs  as  it  does  into  the  pleural  cavities  when  wide  openings  are 
made  in  the  thoracic  walls,  the  respiratory  movements  would  have 
very  little  effect  indeed  on  the  flow  of  b.ood  to  and  from  the 
heart,  just  as  under  similar  circumstances  (p.  331)  they  would  be 


380  EFFECTS   ON   CIRCULATION.  [BOOK  II. 

ineffectual  in  promoting  the  entrance  and  exit  of  air  to  and  from 
the  lungs.  But  the  air  does  not  pass  into  the  pulmonary  alveoli  as 
freely  as  it  would  do  into  a  pleural  cavity  through  an  opening  in 
the  thoracic  wall.  Before  the  inspired  air  can  fill  a  pulmonary 
alveolus,  the  walls  of  the  alveolus  have  to  be  distended  at  the  expense 
of  the  pressure  which  causes  the  inspired  air  to  enter.  Part  of  the 
atmospheric  pressure  in  fact  which  causes  the  entrance  of  the  air 
into  the  lung  is  spent  in  overcoming  the  elasticity  of  the  pulmonary 
passages  and  cells.  Consequently,  any  structure  lying  within  the 
thorax  but  outside  the  lungs,  is  never,  even  at  the  conclusion  of  an 
inspiration  when  the  lungs  are  filled  with  air,  subject  to  a  pressure 
as  great  as  that  of  the  atmosphere.  The  pressure  on  such  a 
structure  always  falls  short  of  the  pressure  of  the  atmosphere  by 
the  amount  of  pressure  necessary  to  counterbalance  the  elasticity 
of  the  pulmonary  passages  and  cells.  And,  since  the  fraction  of  the 
atmospheric  pressure  which  is  thus  spent  in  distending  the  lungs 
increases  as  the  lungs  become  more  and  more  stretched,  it  follows 
that  the  fuller  the  inspiration  the  greater  is  the  difference  between 
the  pressure  en  structures  outside  the  lungs  but  within  the  thorax 
and  the  ordinary'  pressure  of  the  atmosphere.  Now  we  have  seen 
(p.  331)  that  the  pressure  necessary  to  counterbalance  the  elasticity 
of  the  lungs,  w^hen  they  are  completely  at  rest  (m  the  pause  between 
expiration  and  inspiration),  is  in  man  about  5  to  7  mm.  of  mercury, 
and  that  when  the  lungs  are  fully  distended,  as  at  the  end  of  a 
forcible  inspiration,  the  pressure  rises  to  as  much  as  30  mm.  of 
mercury.  Hence  at  the  height  of  a  forcible  inspiration  the  pressure 
exerted  on  the  heart  and  great  vessels  within  the  throax  is  30  mm. 
less  than  the  ordinary  atmospheric  pressure  of  760  mm.,  and  even 
when  the  chest  is  completely  at  rest,  at  the  end  of  an  expiration, 
the  pressure  on  the  heart  and  great  vessels  is  sHghtly  (^by  about  5 
ram.  mercury)  below  that  of  the  atmosphere. 

During  an  inspiration  then  the  pressure  around  the  heart  and 
great  blood-vessels  becomes  considerably  less  than  that  of  the 
atmosphere  on  the  vessels  outside  the  thorax.  During  expiration 
this  pressure  returns  towards  that  of  the  atmosphere,  but  in 
ordinary  breathing  never  quite  reaches  it.  It  is  only  in  forcible 
expiration  that  the  pressure  on  the  thoracic  vascular  organs 
exceeds  that  of  the  atmosphere.  But  if  during  inspiradon  the 
pressure  bearing  on  the  right  auricle  and  the  venae  cavae  becomes 
less  than  the  pressure  which  is  bearing  on  the  jugular,  subclavian, 
and  other  veins  outside  the  thorax,  this  must  result  in  an  increased 
flow  from  the  latter  into  the  former.  Hence,  during  each  in- 
spiration a  larger  quantity  of  blood  enters  the  right  side  of  the 
heart.     This  probably  leads  to  a  stronger  stroke  of  the  heart,  and 


CHAP.   II.]  RESPIRATION.  38 1 

at  all  events  cause  a  larger  quantity  to  be  ejected  by  the  right 
ventricle ;  this  causes  a  larger  quantity  to  escape  from  the  left 
ventricle,  and  thus  more  blood  is  thrown  into  the  aorta,  and  the 
artjrial  tension  proportionately  increased.  During  expiration  the 
converse  takes  place.  The  pressure  on  the  intra-thoracic  blood- 
vessels returns  to  the  normal,  the  flow  of  blood  from  the  veins 
outside  the  thorax  into  the  venae  cavae  and  right  auricle  is  no 
longer  assisted,  and  in  consequence  less  blood  passes  through 
the  heart  into  the  aorta,  and  arterial  tension  falls  again.  During 
forced  expiration,  the  intrathoracic  pressure  may  be  so  great  as 
to  afford  a  distinct  obstacle  to  the  flow  from  the  veins  into  the 
heart. 

The  effect  of  the  respiratory  movements  on  the  arteries  is 
naturally  different  from  that  on  the  veins.  During  inspiration  the 
diminution  of  pressure  in  the  thorax  around  the  aortic  arch  tends 
to  draw  the  blood  from  the  arteries  outside  the  thorax  back  to  the 
arch  of  the  aorta,  or  in  other  words,  tends  to  check  the  onward 
flow  of  blood.  At  the  same  time,  and  this  is  the  point  to  which 
we  wish  to  call  attention,  the  aortic  arch  itself  tends  to  expand ; 
in  consequence  the  pressure  of  blood  within  it,  i.e.  the  arterial 
tension,  tends  to  diminish.  During  expiration,  the  increase  of 
pressure  outside  the  aortic  arch  of  coarse  tends  to  increase  also 
the  blood-pressure  within  it,  acting  in  fact  just  in  the  same  way  as 
if  the  coats  of  the  aorta  themselves  contracted.  Thus  as  far  as 
arterial  blood-pressure  is  concerned  the  effects  of  the  respiratory 
movements  on  the  great  veins  and  great  arteries  respectively,  are 
antagonistic  to  each  other ;  the  effect  on  the  vems  being  to 
increase  arterial  tension  during  inspiration  and  to  diminish  it 
during  expiration,  while  the  effect  on  the  arteries  is  to  diminish 
arterial  tension  during  inspiration  and  to  increase  it  during  ex- 
piration. But  we  should  naturally  expect  the  effect  on  the  thin- 
walled  veins  to  be  greater  than  that  on  the  stout  thick-walled 
arteries,  so  that  the  total  effect  of  inspiration  would  be  to 
increase,  and  the  total  effect  of  expiration  to  diminish,  arterial 
tension. 

These  facts  seem  at  first  sight  to  afford  a  ready  explanation  of 
the  respiratory  undulations  of  the  blood-pressure  curve ;  the  rise 
of  pressure  in  each  undulation  might  be  supposed  to  be  due  to 
the  inspiratory,  the  fall  to  the  expiratory  movement  When  how- 
ever the.  respirator)'  undulations  of  the  blood-pressure  curve  are 
compared  carefully  with  the  variations  of  intra-thoracic  pressure, 
it  is  seen  that  neither  the  rise  nor  the  fall  of  the  former  are  exactly 
synchronous  with  either  diminution  or  increase  of  the  latter. 
Fig  50  shew-s  two  tracings  from  a  dog  taken  at  the  same  time, 


382 


EFFECTS   ON    CIRCULATION. 


[book  II. 


one,  a,  being  the  ordinary  blood-pressure  curve  from  the  carotid, 
and  the  other,  b,  representing  the  condition  of  the  intra-thoracic 
pressure  as  obtained  by  carefully  bringing  a  manometer  into  con- 
nection with  the  pleural  cavity.  On  comparing  the  two  curves,  it 
is  evident  that  neither  the  maximum  nor  the  minimum  of  arterial 
pressure  coincides  exactly  either  with  inspiration  or  with  expiration. 
At  the  beginning  of  inspiration  (/)  the  arterial  pressure  is  seen  to 
be  falhng ;  it  soon  however  begms  to  rise,  but  does  not  reach  the 
maximum  until  some  time  after  expiration  {e)  has  begun ;  the  fall 
continues  during  the  remainder  of  expiration,  and  passes  on  into 
the  succeeding  inspiration.  In  order  to  reconcile  the  facts  re- 
presented by  these  curves  with  the  mechanical  explanation  given 


'S^'i'l 


Fig.  50.    Comparison  op  Blood-Pressure  Curve  with    Curve  of  Intra-thoracic 
Pressure.      To  be  read  from  left  to  right. 

a  is  the  blood-pressure  curve,  with  its  respiratory  undulations,  the  slower  beats  on  the 
descent  being  very  marked,  b  is  the  curve  of  intra-thoracic  pressure  obtained  by  connecting 
one  limb  of  a  manometer  with  the  pleural  cavity.  Inspiration  begins  at  i,  expiration  at  e. 
The  intra-thoracic  pressure  rises  very  rapidly  after  the  cessation  of  the  inspiratory  effort,  and 
then  slowly  falls  as  the  air  issues  from  the  chest ;  at  the  beginning  of  the  inspiratory  effort  the 
fall  becomes  more  rapid. 

above,  we  must  suppose  that  the  beneficial  effects  of  the  inspi- 
ratory movement  in  the  larger  supply  of  blood  brought  to  the  heart, 
take  some  time  to  develope  themselves,  and  last  beyond  the  move- 
ment itself. 

But  there  are  phenomena  which  shew  that  in  the  production 
of  the  respiratory  undulation  other  influences  besides  those  just 
discussed  are  at  work. 

When,  as  for  instance  in  an  animal  under  urari,  artificial  is 
substituted  for  natural  respiration,  undulations  of  the  blood-pressure 
curve  are  observed  (Fig.  51,  i),  similar  in  character  to,  though  less 
in  extent  than,  those  seen  under  natural   conditions.     Now   in 


CHAP.    II.]  RESPIRATION.  383 

artificial  respiration,  the  meclianical  conditions,  under  which  the 
thoracic  viscera  are  placed  as  regards  pressure,  are  the  exact 
opposite  of  those  existing  during  natural  respiration  ;  for  when  air 
is  blown  into  thj  trachea  to  distend  the  lungs,  the  pressure  within 
the  chest  is  increased  instcail  of  diminished.  I'Aidently  the  ex- 
planation given  above  is  not  valid  for  the  resijuatoiy  untlulations 
of  blood-pressure  which  occur  during  artificial  respiration. 

But  another  ex|)lanation,  still  of  a  mechanical  nature,  suggests 
itself.  When  the  lung  is  expanticd,  wiiether  I)y  artificial  or  natural 
respiration,  i.e.  whether  by  means  of  a  tracheal  positive  pressure 
or  a  ])leural  negative  pressure,  the  increase  in  the  area  of  the  wall 
of  each  pulmonary  alveolus  tends  to  stretch  and  elongate  the 
capillaries  lying  in  the  alveolar  walls,  and  in  elongating  them  neces- 
sarily narrows  them,  just  as  an  india-rubber  tube  is  narrowed  when 
it  is  stretched  lengthways.  This  narrowing  of  the  capillaries  is  an 
obstacle  to  the  passage  of  blood  through  them ;  and  hence  the 
expansion  of  the  alveoli  in  inspiration,  other  things  being  equal, 
will  be  unfavourable  to  the  flow  of  blood  through  the  lungs.  In 
artificial  respiration  moreover  the  positive  pressure  on  the  alveolar 
walls  will  tend  as  well  to  compress  the  capillaries  and  still  further 
to  hinder  the  flow  of  blood  through  them  ;  and  direct  experiments 
shew  that  when  blood  is  driven  artificially  at  a  constant  rate 
through  the  pulmonary  artery,  the  outfiow  through  the  pulmonary 
veins  is  diminished  when  the  lungs  are  inflated  (by  tracheal  posi- 
tive pressure)  and  increases  again  when  the  lungs  are  allowed  to 
return  to  tiieir former  volume'.  The  diminished  or  increased  flow 
of  blood  through  the  lungs  will  naturally,  by  diminishing  or  in- 
creasing tlie  quantity  in  the  left  heart,  diminish  or  increase  the 
blood -pressure.  And  it  is  exceedingly  probable  that  the  respiratory 
undulations  seen  when  artificial  respiration  is  carried  on  are  thus 
brought  about  by  changes  in  the  calibre  of  the  pulmonary  capil- 
laries and  small  vessels.  The  case  of  natural  respiration  is 
somewhat  different  :  the  narrowing  of  the  capillaries  due  to  the 
increase  of  the  dimensions  of  the  pulmonary  alveoli  comes  into 
play  as  before,  but  instead  of  the  tracheal  positive  pressure  a 
pleural  negative  pressure  is  brought  to  bear  on  the  capillaries,  and 
this  probably  tends  to  widen  them  ;  but  the  problem  then  becomes 
very  complicated,  and  though  it  is  stated-  that  when  inspiration  is 
carried  out  by  means  of  a  negative  pleural  pressure,  tiie  artificial 
flow  through  the  lungs,  contrary  to  the  case  when  positive  trach  ea 
pressure  is  employed,  is  increased,  the  matter  is  too  unsettled  to 

'  Poiseuille,  Compt.  Rntd.,  T.  XLIV.  (1855)   p.  1072.     Quincke  u.  PfcilTe, 
Arch.f.  A  Hat.  u.  Fliys.,  1871,  p.  90. 
*  Quincke  u.  PfcifTer,  op.  cit. 


384  EFFECTS   ON    CIRCULATION.  [BOOK   II. 

enable  us  to  state  how  far  the  undulations  of  blood-pressure  during 
normal  respiration  are  brought  about  by  changes  in  the  pulmonary 
circulation. 

We  have  more  overevidence  of  other  influences,  not  mechanical 
but  nervous  in  nature,  having  at  least  some  share  in  producing  the 
phenomena  we  are  discussing.  One  striking  feature  of  the  re- 
spiratory undulation  in  the  blood  pressure  curve  of  the  dog  is  the 
fact  that  the  pulse-rate  is  quickened  during  the  rise  of  the  ur-du- 
lation  and  becomes  slower  during  the  fall,  The  quickening  of  the 
beat  might  be  considered  as  itself  partly  accounting  for  the  rise, 
were  it  not  for  two  facts.  In  the  rabbit,  the  respiratory  undu- 
lations, though  well  marked,  present  a  very  small  difference  of 
pulse-rate  in  the  rise  and  fall.  In  the  dog,  the  difference  is  at 
once  done  with,  without  any  other  essential  change  in  the  undu- 
lations, by  section  of  both  vagi.  Evidently  the  slower  pulse 
during  the  fall  is  caused  by  a  coincident  stimulation  of  the  cardio- 
inhibitory  centre  in  the  medulla  oblongata,  the  quicker  pulse 
during  the  rise  "being  due  to  the  fact  that,  during  that  interval,  the 
centre  is  comparatively  at  rest.  We  have  here  most  important 
indications  that,  while  the  respiratory  centre  in  the  medulla  oblon- 
gata is  at  work,  sending  out  rhythmic  impulses  of  inspiration  and 
expiration,  the  neighbouring  cardio-inhibitory  centre  is,  as  it  were 
by  sympathy,  thrown  into  an  activity  of  such  a  kind  that  its 
influence  over  the  heart  waxes  and  wanes  with  each  respiratory 
movement. 

But  if  the  cardio-inhibitory  centre  is  thus  synchronously 
affected,  ought  we  not  to  expect  that  the  vaso- motor  centre 
should  also  be  involved  in  the  action  ?  We  have  evidence  that 
it  is. 

When  artificial  respiration  is  stopped,  a  very  large  but  steady 
rise  of  pressure  is  observed.  This  may  be  in  part  due  to  the 
increased  force  of  the  cardiac  beat,  caused  by  the  increasingly 
venous  character  of  the  blood ;  but  only  in  part,  and  that  a  small 
part.  The  rise  so  witnessed  is  very  similar  to  that  brought  about 
by  powerfully  stimulating  a  number  of  vaso-constrictor  nerves  ; 
and  there  can  be  no  doubt  that  it  is  due  to  the  venous  blood 
stimulating  the  vaso-motor  centre  in  the  medulla,  and  thus  causing 
constriction  of  the  small  arteries  of  the  body,  particularly  those 
of  the  splanchnic  area.  We  say  '  stimulating  the  medullary  vaso- 
motor centre,'  because,  though  the  venous  blood  may  stimulate 
other  vaso-motor  centres  in  the  spinal  cord  '  and  possibly  even 
act  directly  on  local  peripheral  mechanisms,  or  on  the  muscular 
coats  of  the  small  arteries  themselves,  since  a  rise  of  pressure 
'  Luchsinger,  Pfliiger's  Archiv,  xvi.  (1878]  p.  510. 


CHAP.    11.] 


RESPIRATION. 


385 


follows  upon  dyspnoea  when  the  spinal  cord  has  been  previously 
divided  below  the  medulla,  yet  the  fact  that  it  is  much  less  under 
these  circumstances  shews  that  the  medullary  centre  plays  the 
chief  part.  Upon  the  cessation  of  the  artificial  respiration,  the 
respiratory  undulations  cease  also,  so  that  the  blood-pressure  curve 
rises  at  first  steadily  in  almost  a  straight  lin^ ;  yet  after  a  while 
new  undulations,  the  so-called  Traube's  curves,  make  their  ap- 
pearance (Fig.  51,  2,  3),  very  similar  to  the  previous  ones,  except 


A      \  i  \  '. 


I  I  /  \ 


■«  !  i 
!  I  i 
1  I  i 


\!    '., 


1 ;      I    I 


A 


.A  r^  i 

i  i  \l  1/ 

i  i    V    ^ 


<   i 

i  I 
i  i 
il 


\i\l  \l\ 


'•  '  1.' 


A 


'■    ■' 
I  1 1 


•'.    ! 


Fig.  si.     Traubl's  Curves.     To  be  read  froni  left  to  right. 

The  curves  i.  2,  3,  ^.  s  were  taken  at  intervals,  and  all  form  part  of  one  experiment. 
Each  curve  is  placed  in  its  proper  position  relative  to  the  base  line,  which,  to  save  space,  is 
omitted.  During  i.  anificial  respiration  was  kept  up.  the  undulations  visible  .ire  therefore  not 
due  to  the  mechanical  action  of  ihe  chest.  When  the  ar.ificial  respiration  was  suspended  these 
undulations  for  a  while  disappeared,  and  the  blood-pressure  ro?e  steadily  while  the  he.ir:-beats 
becaiic  slower.  Soon,  as  shewn  in  curve  2,  the  undulations  re-appeared.  A  little  la'er.  the 
blood-pressure  was  still  rising,  the  heart-beats  still  sliwcr.  but  the  undula'ions  still  obvious 
(curve  3).  Still  later  (curve  4)  the  p-essure  was  siill  higher,  but  the  hear:-bea"s  were  quicker, 
and  the  un  iuUtions  flatter.  The  pressure  then  began  10  fall  rapidly  (curve  5),  and  continued 
to  fall  until  some  time  af:cr  artificial  respiration  was  resumed. 


that  their  curves  are  larger  and  of  a  more  sweeping  character. 
These  new  undulations,  since  they  appear  in  the  absence  of  all 
thoracic  or  pulmonary  movements,  passive  or  active,  and  are 
witnessed  even  when  both  vagi  are  cut,  must  be  of  vaso-motorial 
F.  P.  25 


386  EFFECTS   ON   CIRCUI-ATION.  [BOOK   II. 

origin ;  the  rhythmic  rise  must  be  due  to  a  rhythmic  constriction 
of  the  small  arteries  due  to  a  rhythmic  discharge  from  vaso- 
motor centres  and  especially  from  the  medullary  vaso-motor  centre, 
smce  the  undulations  are  far  less  marked  when  the  spinal  cord  is 
divided.  They  are  maintained  as  long  as  the  blood-pressure  con- 
tinues to  rise.  With  the  increasing  venosity  of  the  blood,  however, 
both  the  vaso-motor  centre  and  the  heart  become  exhausted ;  the 
undulations  disappear,  and  the  blood-pressure  rapidly  sinks. 

We  have  then  experimental  evidence  that,  in  the  entire  absence 
of  all  mechanical  causes,  undulations  of  blood-pressure,  of  direct 
nervous  origin,  closely  simulating  those  accompanying  natural 
respiration,  may  be  brought  about  whenever  the  blood  becomes 
sufficiently  venous.  It  is  difficult  to  imagine  why  the  vaso-motor 
centre  should  exhibit  the  rhythmic  activity  shewn  in  Traube's 
curves,  and  why  that  rhythm  should  simulate  the  respiratory 
rhythm,  unless  the  vaso-motor  centre  had  been  previously  accus- 
tomed to  a  rhythmic  activity  synchronous  with  the  rhythmic 
activity  of  the  respiratory  centre.  It  is  impossible  to  give  direct 
expermiental  proof  that  in  natural  respiration  the  vaso-motor  centre 
is  stimulated  by  the  natural  venous  blood  to  a  rhythmic  activity 
like  that  shewn  in  Traube's  curves,  because  it  is  impossible  to 
eliminate  the  mechanical  factors  discussed  above.  And  the  argu- 
ment that  because  the  undulations  seen  in  artificial  respiration 
continue,  as  is  asserted,  after  division  of  the  medulla,  the  vaso- 
motor events  can  have  no  share  in  producing  the  undulations  of 
natural  respiration,  is  invalid,  since,  as  we  have  seen,  the  undula- 
tions of  artificial  respiration  have  a  distinctly  different  mechanical 
origin  from  those  of  natural  respiration.  On  the  other  hand,  if,  as 
is  stated  by  others,  the  undulations  even  of  artificial  respiration 
though  not  obliterated  are  diminished  by  section  of  the  medulla, 
these  too  must  be  in  part  of  vaso-motorial  origin ;  for  the  mere 
diminution  of  general  blood-pressure  which  results  from  section 
of  the  medulla  ought  not  to  influence  largely  the  respiratory 
undulations  if  these  are  entirely  of.  mechanical  origin. 

Mayer  '■  has  observed  in  perfect  quiet  normally  breathing  rabbits, 
without  urari,  curves  very  similar  to  Traube'  s  curves,  on  which  the 
respiratory  curves  may  be  seen  superimposed.  He  regards  these 
longer  curves  as  of  vaso-motorial  origin. 

We  may  conclude  then  that  the  respiratory  undulations  of 
blood-pressure  are  of  complex  origin,  being  partly  the  mechanical 
results  of  the  thoracic  movements,  possibly  also  produced  by  the 

*   Wien.  Sitzungsberichte,  Bd.  74,  1876. 


CHAP.    II.]  RESPIRATION.  387 

alternate  expansion  and  collapse  of  the  pulmonary  alveoli,  but 
probably  in  addition  brought  ai)out  by  a  rhytlnnic  variation  of  the 
vascular  porii)heral  resistance,  the  result  of  a  rhythmic  activity  of 
the  vaso-motor  centre. 

In  cslimaling  the  mechanical  effects  on  the  flow  of  blood  to  and 
from  the  hiart  ])roduccd  by  tlic  rcs|)iratory  movements,  attention  must 
be  paid,  not  only  to  ihc  action  ut  the  thorax,  but  al^o  to  that  of  the 
alKlomcn.  Thus  on  the  descent  of  the  diapiiragm,  thou^^di  the  flow  of 
blood  to  t'le  right  heart  from  the  upper  part  of  the  body  is  thereby 
undoubtedly  assi-^ted,  that  from  tiie  lower  part  of  the  body  and  abdo- 
men IS  diminished.  Conversely  in  expiration  the  compression  of  the 
abdomen  tends  at  first  to  drive  the  blood  onward  to  the  heart,  though 
subsequently,  especially  if  long  continued  and  laboured,  it  may  prove 
an  obstacle  both  to  the  flow  to  the  heart  along  the  vena  cava  and  to 
that  from  the  heart  along  the  aorta. 

Funke  and  Latschcnberger  ',  who  insist  on  the  expansion  and 
collapse  of  the  lungs  as  the  chief  factor  of  the  respiratory  undulations, 
point  out  that  while  the  main  effect  of  expansion  is,  by  lengthening 
and  narrowing  the  capillaries,  to  hinder  the  flow  through  the  lungs, 
yet  the  initial  result  is  to  drive  an  extra  quantity  of  blood  from  the 
capillaries  onwards,  and  that  similarly  the  initial  resu't  of  the  collapse 
is,  by  the  shortening  and  widening  ot'  the  same  capillaries,  to  retain  a 
certain  quantity  of  blood  for  a  wliile  in  the  lungs.  They  offer  by  help 
of  these  considerations  very  ingenious  explanations  of  the  variations 
in  the  character  of  the  respiratory  undulations  accompanying  variations 
in  the  rhythm  and  character  of  the  respiratory  movements.  And 
they  contend  that  their  explanations  are  valid,  not  only  in  artificial 
respiration,  but  also  in  natural  respiration,  even  when  the  negative 
pleural  pressure  bears  on  the  large  vessels  of  the  chest  as  well.  Kow- 
alewsky^,  on  the  other  hand,  explains  the  undulations  seen  in  artificial 
respiration,  by  reference  not  so  much  to  the  narrowing  and  widening 
of  the  capillaries  due  to  their  longitudinal  stretching  and  return,  as  to 
the  variations  of  pressure  in  the  air  of  the  pulmonary  alveoli  ;  but 
argues  in  opposition  to  Funke  and  Latschenbcrger,  that  m  natural 
respiration,  these  variations,  produced  by  pleural  negative  pressure  and 
not  by  tracheal  positive  pressure,  are  more  than  compensated  by 
the  simultaneous  effects  of  the  same  pleural  pressure  on  the  great 
vessels  3. 

It  has  been  suggested  that  the  increased  frequency  of  beat  during 
the  inspiratory  phase  may  be  due  to  the  mechanical  distension  of  the 
lungs,  whereby  afferent  impulses  are  transmitted  along  the  vagus, 
which  by  inhibiting  the  cardio-inliibi  ory  centre  cause  an  increased 
frequency  of  beat.  But  the  experiments  on  which  this  view  is  based 
are  not  conclusive. 

'  Pfliiger's  Archiv,  XV.  (1877)  p.  405  ;  ibid.  Xvil.  (1S78)  p.  54.7. 
'  Arcltiv  f.  Anat.  u.  PJiys.,  1S77,  I'hys.  Al)th.  p.  416. 
3  Cf.  Zuntz,  Pflugcr's  Archiv,    XVII.  (1878)  p.  374. 

25—2 


388  ASPHYXIA.  [BOOK    II. 

Sec.  8.     The  Effects  of  Changes  in  the  Air  Breathed. 
The  Effects  of  deficient  Air.     Asphyxia. 

When,  on  acconnt  of  occlusion  of  the  trachea,  or  by  breathing 
in  a  confined  space,  a  due  supply  of  air  is  not  obtained,  normal 
respiration  gives  place  through  an  intermediate  phase  of  dyspnoea 
to  the  condition  known  as  asphyxia  ;  this,  unless  remedial  measures 
be  taken,  rapidly  proves  fatal. 

Phenonema  of  Asphyxia.  As  soon  as  the  oxygen  in  the 
arterial  blood  sinks  below  the  normal,  the  respiratory  movements 
become  deeper  and  at  the  same  time  more  frequent ;  both  tlie 
inspiratory  and  expiratory  phases  are  exaggerated,  the  supple- 
mentary muscles  sjjoken  of  at  p.  338  are  brought  into  play,  and 
the  rate  of  the  rhythm  is  hurried.  In  this  respect,  dyspntea,  or 
hypcrpncea  as  this  first  stage  has  been  calUd,  contrasts  very 
stroni^ly  with  the  peculiar  respiratory  condition  caused  by  section 
of  the  vagi,  in  which  the  re.s|)imtory  movements,  while  much  more 
profound  than  the  normal,  are  diminishc*!  in  frequency. 

As  the  blootl  continues  to  become  more  and  more  venous  the 
respiratory  movements  continue  to  increase  both  in  force  and  fre- 
quency, a  larger  number  of  muscles  being  called  into  action  and 
that  to  an  increasing  extent.  Very  soon,  however,  it  may  be 
observed  that  the  expiratory  movements  are  becoming  more 
marked  th.in  the  inspiratory.  Kvcry  muscle  which  can  in  any 
way  assist  in  expiration  is  in  turn  brought  into  play ;  and  at  last 
almost  all  the  muscles  of  the  body  are  involved  in  the  struggle. 
The  orderly  expiratory  movcmtnls  cuhninale  in  expiratory  con- 
vulsions, the  or«ler  and  sequence  of  which  is  obscured  by  their 
violence  and  extent.  That  these  convulsions,  through  which 
dyspmca  merges  into  asphyxia,  are  due  to  a  stimulation  of  the 
medulla  oblongata  by  the  venous  blood,  is  proved  by  the  fact  that 
they  fail  to  make  their  appearance  when  the  spinal  cord  has  been 
previously  divided  below  the  medulla,  though  they  still  occur  after 
those  portions  of  the  brain  which  lie  above  the  niedulia  have  been 
removed.  It  is  usual  to  speak  of  a  'convulsive  centre '  in  the 
medulla,  the  stimulation  of  which  gives  rise  to  these  convulsions  ; 
but  if  wc  accept  the  existence  of  such  a  centre  we  must  at  the 
same  time  admit  tliat  it  is  connected  by  the  closest  ties  with 
the  normal  expiratory'  division  of  the  respiratory  centre,  since 
every  inter>ening  step  may  be  observed  between  a  simple  slight 
expiratory  movement  of  normal  respiration  and  the  most  violent 


CHAP.    II.]  RESPIRATION.  389 

convulsion  of  asphyxia.  An  additional  proof  that  these  convul- 
sions are  carried  out  by  the  agency  of  the  medulla  is  afforded  by 
the  fact  that  convulsions  of  a  wholly  similar  character  are  wit- 
nessed when  the  supply  of  blood  to  the  medulla  is  suddenly 
cut  off  by  ligaturing  the  blood-vessels  of  the  head.  In  this  case 
the  nervous  centres,  being  no  longer  furnished  with  fresh  blood, 
become  rapidly  asphyxiated  through  lack  of  oxygen,  and  expiratory 
convulsions  quite  similar  to  those  of  ordinary  asphyxia,  and  pre- 
ceded like  them  by  a  passing  phase  of  dyspnoea,  make  their 
appearance.  Similar  '  ansemic  '  convulsions  are  seen  after  a  sud- 
den and  large  loss  of  blood  from  the  body  at  large,  the  medulla 
being  similarly  stimulated  by  lack  of  arterial  blood. 

Such  violent  efforts  speedily  exhaust  the  nervous  system ;  and 
the  convulsions  after  being  maintained  for  a  brief  period  sud- 
denly cease  and  are  followed  by  a  period  of  calm.  The  calm 
is  one  of  exhaustion  ;  the  pupils,  dilated  to  the  utmost,  are 
unaffected  by  light  ■  touching  the  cornea  calls  forth  no  movement 
of  the  eyelids,  and  indeed  no  reflex  actions  can  anywhere  be  pro- 
duced by  the  stimulation  of  sentient  surfaces.  All  expiratory 
active  movements  have  ceased;  the  muscles  of  the  body  are 
flaccid  and  quiet;  and  though  from  time  to  time  the  respiratory 
centre  gathers  sufficient  energy  to  develope  respiratory  move- 
ments, these  resemble  those  of  quiet  normal  breathing,  in  being, 
as  far  as  muscular  actions  are  concerned,  almost  entirely  inspi- 
ratory. They  occur  at  long  intervals,  like  those  after  the  section 
of  the  vagi ;  and  Hke  them  are  deep  and  slow.  The  exhausted 
respiratory  centre  takes  some  time  to  develope  an  inspiratory 
explosion  ;  but  the  impulse  when  it  is  generated  is  proportionately 
strong.  It  seems  as  if  the  resistance  which  had  in  each  case 
to  be  overcome  was  considerable,  and  the  effort  in  consequences 
when  successful,  productive  of  a  large  effect. 

As  time  goes  on,  these  inspiratory  efforts  become  less  fre- 
quent ;  their  rhythm  becomes  irregular ;  long  pauses,  each  one  of 
which  seems  a  final  one,  are  succeeded  by  several  somewhat 
rapidly  repeated  inspirations.  The  pauses  become  longer,  and  the 
inspiratory  movements  shallower.  Each  inspiration  is  accom- 
panied by  the  contraction  of  accessory  muscles,  especially  of  the 
face,  so  that  each  breath  becomes  more  and  more  a  prolonged 
gasp.  The  inspiratory  gasps  spread  into  a  convulsive  stretching 
of  the  whole  body ;  and  with  extended  limbs,  and  a  straightened 
trunk,  with  the  head  thrown  back,  the  mouth  widely  open,  the 
face  drawn,  and  the  nostrils  dilated,  the  last  breath  is  taken  in. 

Thus  we  are  able  to  distinguish  three  stages  in  the  phenomena 
ivhich  result  from  a  continued  deficiency  of  air  : — (i)    A  stage  of 


390  ASPHYXIA.  [BOOK   II. 

dyspnoea,  characterized  by  an  increase  of  the  respiratory  move- 
ments both  of  inspiration  and  expiration.  (2)  A  convulsive 
stage,  characterized  by  the  dorhinance  of  the  expiratory  efforts, 
and  culminating  in  general  convulsions.  (3)  A  stage  of  ex- 
haustion, in  which  lingering  and  long-drawn  inspirations  gradually 
die  Out.  When  brought  about  by  sudden  occlusion  of  the  trachea 
these  events  run  through  their  course  in  about  4  or  5  minutes  in 
the  dog,  and  in  about  3  or  4  minutes  in  the  rabbit.  The  first 
stage  passes  gradually  into  the  second,  convulsions  appearing  at 
the  end  of  the  first  minute.  The  transition  from  the  second  stage 
into  the  third  is  somewhat  abrupt,  the  convulsions  suddenly 
ceasing  early  in  the  second  minute.  The  remaining  time  is 
occupied  in  the  third  stage. 

The  duration  of  asphyxia  varies  not  only  in  different  animals  but  in 
the  same  animal  under  different  circumstances.  Newly  borja  and 
young  animals  need  much  longer  immersion  in  water  before  death  by 
asphyxia  occurs  than  do  adults.  Thus  while  in  a  full-grown  dog 
recovery  from  drowning  is  unusual  after  i^  minutes,  a  new-born  puppy 
has  been  known  to  bear  an  immersion  of  as  much  as  50  minutes.  The 
cause  of  the  dififei'ence  lies  in  the  fact  that  in  the  young  animal  the 
respiratory  changes  of  the  tissues  are  much  less  active.  These  con- 
sume less  oxygen,  and  the  general  store  of  oxygen  in  the  blood  has  a 
less  rapid  demand  made  upon  it.  The  respiratory  activity  of  the 
tissues  may  also  be  lessened  by  a  deficiency  in  the  circulation;  hence 
bodies  in  a  state  of  syncope  at  the  time  when  the  deprivation  of 
oxygen  begins  can  endure  the  loss  for  a  much  longer  period  than  can 
bodies  in  which  the  circulation  is  in  full  swing.  There  being  the  same 
store  of  oxygen  in  the  blood  in  each  case,  the  quicker  circulation  must 
of  necessity  bring  about  the  speedier  exhaustion  of  the  store.  In 
many  cases  of  drownmg,  death  is  hastened  by  the  entrance  of  water 
into  the  lungs. 

By  training,  the  respiratory  centre  may  be  accustomed  to  bear  a 
scanty  supply  of  oxygen  for  a  much  longer  time  than  usual  before 
dyspncea  sets  in,  as  is  seen  in  the  case  of  divers. 

The  phenomena  of  slow  asphyxia,  where  the  supply  of  air 
is  gradually  diminished,  are  fundamentally  the  same  as  those 
resulting  from  a  sudden  and  total  deprivation.  The  same  stages 
are  seen,  but  their  development  takes  place  more  slowly. 

The  circulation  in  Asphyxia.  If  the  carotid  or  other 
artery  of  an  animal  be  connected  with  a  manometer  during  the 
development  of  the  asphyxia  just  described,  the  following  facts 
may  be  observed.  During  the  first  and  second  stages  the  blood- 
pressure  rises  rapidly,  attaining  a  height  far  above  the  normal. 
During  the  third  stage  it  falls  even  more  rapidly,  repassing  the 


CHAP.    II  ]  RESPIRATION.  39I 

normal  and  becoming  ////  as  death  en.sues.  The  respiratory  undu- 
lations of  the  pressure-curve  are  abrupt  and  somewhat  irregular, 
the  inspiratory  movements  being  accompanied  by  a  fall  of  pressure. 
When  the  animal  has  been  previously  placed  under  urari,  so  that 
the  respiratory  imjiulses  cannot  manifest  themselves  by  any  mus- 
cular movements,  the  rise  of  the  pressure  curve,  as  we  have 
already  said,  is  at  first  steady  and  unbroken,  but  after  a  variable 
period  Traube's  curves  make  their  appearance.  As  during  the 
third  stage  the  pressure  sinks,  these  undulations  pass  away. 

The  heart -beats  are  at  first  somewhat  quickened,  but  speedily 
become  slow,  while  at  the  same  time  they  acquire  great  force ;  so 
that  the  pulse-curves  on  the  tracing  are  exceedingly  bold  and 
striking,  Fig.  51.  Even  while  the  blood-pressure  is  sinking,  the 
pulse-curves  still  maintain  somewhat  these  characters  ;  and  the 
heart  continues  to  beat  for  some  seconds  after  the  respiratory 
movements  have  ceased,  the  strokes  at  last  rapidly  failing  in 
frequency  and  strength. 

If  the  chest  of  an  animal  be  opened  under  artificial  respira- 
tion, and  asphyxia  brought  on  by  cessation  of  the  respiration,  it 
will  be  seen  that  the  heart  during  the  second  and  third  stages 
becomes  completely  gorged  with  venous  blood,  all  the  cavities  as 
well  as  the  large  veins  being  distended  to  the  utmost.  If  the 
heart  be  watched  to  the  close  of  the  events,  it  will  be  seen  that 
the  feebler  strokes  which  come  on  towards  the  end  of  the  third 
stage  are  quite  unable  to  empty  its  cavities  ;  and  when  the  last 
beat  has  passed  away  its  parts  are  still  choked  with  blood.  The 
veins  spirt  out  when  pricked  :  and  it  may  frequently  be  observed 
that  the  beats  recommence  when  the  over-distension  of  the  heart's 
cavities  is  relieved  by  puncture  of  the  great  vessels.  When  rigor 
mortis  sets  in  after  death  by  asphy.xia,  the  left  side  of  the  heart 
is  more  or  less  emptied  of  its  contents  ;  but  not  so  the  right  side. 
Hence  in  an  ordinary  post-mortem  examination  in  cases  of  death 
by  asphyxia,  while  tlie  left  side  is  found  comparatively  empty,  the 
right  appears  gorged. 

These  various  phenomena  are  probably  brought  about  in  the 
following  way. 

The  increasingly  venous  character  of  the  blood  augments  the 
action  of  the  general  vaso-motor  centre,  and  thus  leads  to  a  general 
constriction  of  the  small  arteries.  This  is  the  cause  of  the  mark- 
edly increased  blood-pressure  ;  though,  as  we  have  already  said, 
the  venous  blood  may  also  act  directly  on  the  other  spinal  vaso-motor 
centres  and  possibly  on  peripheral  vaso-motor  mechanisms  or  on 
the  muscular  arterial  coats,  or  may  even  affect  the  peripheral  resist- 
ance by  modifying  the  changes  in  the  capillary  regions,  see  p.  229. 


39?'  ASPHYXIA.  [BOOK   II. 

This  increased  peripheral  resistance,  while  indirectly  (p.  198) 
helping  to  augment  the  force  of  the  heart's  beat,  is  a  direct 
obstacle  to  the  heart  emptying  itself  of  its  contents.  On  the 
other  hand,  the  increased  respiratory  movements  favour  the  flow 
of  venous  blood  towards  the  heart,  which  in  consequence  becomes 
more  and  more  full.  This  repletion  is  moreover  assisted  by  the 
marked  infrequency  of  the  beats.  This  in  turn  depends  in  part 
on  the  cardio-inhibitory  centre  in  the  medulla  being  stimulated 
by  the  venous  blood ;  since  when  the  vagi  are  divided  the 
infrequency  is  much  less  pronounced.  It  does  not  however 
disappear  altogether;  and  we  are  therefore  driven  to  suppose 
it  is  in  part  due  to  the  venous  blood  acting  in  an  inhibitory 
manner  directly  on  the  heart  itself.  The  increased  resistance 
in  front,  the  augmented  supply  from  behind,  and  the  long  pauses 
between  the  strokes,  all  concur  in  distending  the  heart  more 
and  more. 

When  the  large  veins  have  become  full  of  blood  the  inspiratory 
movements  can  no  longer  have  their  usual  effect  in  increasing  the 
blood-pressure.  The  whole  force  of  the  chest  movement,  as  far 
as  the  circulation  is  concerned,  is  spent  in  diminishing  the  pres- 
sure around  the  large  arteries ;  and  hence  the  sinking  of  the 
blood-pressure  during  each  inspiratory  movement. 

The  distension  of  the  cardiac  cavities,  at  first  favourable  to 
the  heart-beat,  as  it  increases  becomes  injurious.  At  the  same 
time  the  cardiac  tissues,  which  at  first  probably  are  stimulated, 
after  a  while  become  exhausted  by  the  action  of  the  venous 
blood ;  and  the  strokes  of  the  heart  become  feebler  as  well  as 
slower. 

On  account  of  this  increasing  slowness  and  feebleness  of  the 
heart's  beat,  the  blood-pressure,  in  spite  of  the  continued  arterial 
constriction,  begins  to  fall,  since  less  and  less  blood  is  pumped 
into  the  arterial  system ;  the  boldness  of  the  pulse-curves  at 
this  stage  being  chiefly  due  to  the  infrequency  of  the  strokes. 
As  the  quantity  which  passes  from  the  heart  into  the  arteries 
becomes  less  second  by  second,  the  pressure  gets  lower  and  lower, 
the  descent  being  assisted  by  the  exhaustion  of  the  vaso-motor 
centre,  until  almost  before  the  last  beats  it  has  sunk  to  zero. 
Thus  at  the  close  of  asphyxia,  while  the  heart  and  venous  system 
are  distended  with  blood,  the  arterial  system  is  less  than  normally 
full. 

The  Effects  of  an  increased  su;pply  of  Air.      Apnoea. 

It  is  a  matter  of  common  experience  that  after  several 
inspiratory  efforts  of  greater  force  than  ordinary,  the  breath  can 


CIIAl'.    II.]  R INSPIRATION.  393 

be  held  for  a  much  longer  lime  than  usual.  In  other  words,  by 
an  increaseil  respiratory  action,  the  Mood  can  be  brought  into 
such  a  condition  liiat  the  generation  of  the  respiratory  impulses 
in  tlie  medulla  is  delayed  beyond  the  usual  time  ;  the  d,esire  to 
breathe  can  then  be  resisted  for  a  longer  time  than  usual.  This 
state  of  tilings,  which  we  can  easily  produce  in  ourselves,  is  the 
beginning  of  that  peculiar  condition  brought  about  by  a  too 
vigorous  respiration,  or  by  the  inhalation  of  oxygen,  to  which 
we  have  already  (p.  376)  referred  under  the  name  of  'apncea',' 
The  essential  feature  of  apnoca  consists  in  the  blood  containing 
for  the  time  being  more  oxygen  than  usual.  In  consequence  of 
this  a  longer  time  is  needed  before  the  deficiency  of  oxygen  in 
the  blood  of  the  capillaries  of  the  medulla  oblongata,  or  rather  in 
the  nerve  cells  constituting  the  respiratory  centre,  reaches  the  limit 
which  determines  the  discharge  of  a  respiratory  impulse.  The 
molecular  processes  of  these  cells  are  so  arranged,  that  whenever 
the  oxygen  which  is  available  for  their  use  sinks  below  a  certain 
level,  respiratory  explosions  occur  whereby  a  fresh  supply  of 
oxygen  is  gained.  By  increasing  their  available  oxygen,  the 
explosive  action  of  the  cells  is  deferred  and  diminished  ;  that 
is,  apncea  is  established.  Similarly  when  the  supply  of  oxygen 
is  diminished,  the  explosions  are  hastened  and  increased,  that  is, 
dyspnoea  is  brought  about.  The  different  conditions  of  the 
respiratory  centre  during  apnoea,  normal  breathing  or  eupnoea, 
and  dyspnoea,  are  well  shewn  by  the  different  effects  produced  by 
stimulating  the  afferent  fibres  of  the  trunk  of  the  vagus  with  the 
same  stimulus  during  the  three  stages.  If  the  current  chosen  be 
of  such  a  strength  as  will  gently  increase  the  rhythm  of  normal 
breathing,  it  will  be  found  to  have  no  effect  at  all  in  apnoea, 
while  in  dyspnoea  it  may  produce  almost  convulsive  movements. 
Indeed  in  well-marked  apnoea  even  strong  stimulation  of  the 
vagus  may  produce  no  effect  whatever. 

.According  to  Ewald'  the  haemoglobin  of  the  blood  during  apnoea 
becomes  perfectly  or  almost  perfectly  saturated  with  oxygen.  The 
absolute  increase  does  not  seem  great,  from  "i  to  "9  p.  c.  vol.  The 
tension  at  which  this  increment  exists  is  however  very  great.  The 
venous  blood,  if  the  artificial  respiration,  used  to  produce  the  apncea, 
be  carefully  carried  out,  contains  more  oxygen  than  the  normal  and 
appears  of  a  bright  red  colour.  In  cases  where  the  artificial  respira- 
tion   interferes  with  the  pulmonary  circulation   and    so   reduces   the 

'  It  is  to  be  regretted  that  this  name  is  used  by  some  medical  authorities  in  a 
sense  almost  identical  \\  itli  asphyxia.  In  its  physiological  sense,  as  here  used, 
it  is  the  very  opposite  of  asphyxia. 

•  Pflii'^er  s //rr///V,  vrr.  (1S73)  575- 


394  EFFECTS   OF   CHANGES   IN    THE   AIR.      [BOOK   II. 

rapidity  of  the  general  flow  of  blood,  the  venous  blood  may  be  even 
darker  than  usual  ^ 

The  Effects  of  changes  iii  the  Composition  of  the  Air  breathed  ^. 

We  have  already  discussed  the  effects  of  such  changes  as  are 
produced  by  the  act  of  respiration  itself,  viz.  a  deficiency  of 
oxygen  and  an  excess  of  carbonic  acid.  We  have  only  to  add, 
that  the  result  of  an  access  of  oxygen,  except  in  the  cases  of 
extreme  pressure  to  be  mentioned  immediately,  is  simply  apnoea, 
and  that  variations  in  amount  of  nitrogen  have  of  themselves  no 
effect,  this  gas  being  eminently  an  indifferent  gas  as  fur  as 
physiological  processes  are  concerned. 

Poisonous  gases.  Carbonic  oxide  produces  the  same 
effects  as  deficiency  of  oxygen,  inasmuch  as  it  preoccupies  the 
haemoglobin  and  so  prevents  the  blood  from  becoming  properly 
oxygenated,  see  p.  355.  Sulphuretted  hydrogen  produces  similar 
effects,  but  in  a  different  manner ;  it  acts  as  a  reducing  agent,  see 
p.  352.  Some  gases  are  irrespirable,  on  account  of  their  causing 
spasm  of  the  glottis,  and  this  is  said  to  be,  to  a  certain  extent,  the 
case  with  carbonic  acid. 

The  Effects  of  changes  in  the  Pj'essure  of  the  Air  breathed  ^. 

Gradual  Diminution  of  Pressure.  The  symptoms  are 
those  of  deficiency  of  oxygen  ;  the  animals  die  of  asphyxia.  The 
blood  contains  less  and  less  oxygen  as  the  pressure  is  reduced, 
the  quantity  present  in  the  arterial  blood  soon  becoming  less  than 
that  in  normal  venous  blood.  The  quantity  of  carbonic  acid  in 
the  blood  is  also  diminished.  The  increasing  dyspnrea  is  accom- 
panied by  great  general  feebleness;  and  convulsions  though 
frequent  are  not  invariable.  The  occurrence  of  these  seems  to 
depend  on  the  suddenness  with  which  the  oxygen  of  the  blood 
is  diminished. 

Sudden  Diminution.  Death  in  these  cases  ensues  from 
the  Hberation  of  gases  within  the  blood-vessels  and  the  consequent 
mechanical  interference  with  the  circulation.  The  gas  which  is 
found  in  the  blood-vessels  on  examination  after  death  consists 
chiefly  of  nitrogen. 

Increase  of  Pressure.  Up  to  a  pressure  of  several 
atmospheres    of    air,    merely   symptoms   of   narcotic    poisoning, 

'  Finkler  and  Oertrmnn.     Pfliiger's  Archiv,  xiv.  (1877)  38. 
*  Paul  Bert,  Rech.  Exp.  sur  la  Prtssion  Baromel.  1874. 


CHAP.    II.]  RESPIRATION.  395 

altogether  like  those  of  breathing  an  excess  of  carbonic  acid,  are 
developed,  and  there  can  be  littlj  doul)t  that  tiicy  originate  from 
the  same  cause,  vi^.  the  excess  of  carbonic  acid  in  the  blood. 
At  a  pressure  however  of  4  atmospheres  of  oxygen,  corresponding 
to  2D  atmos|;heres  of  air,  and  upwards,  a  very  remarkable  pheno- 
menon presents  itself.  The  animals  die  of  asphyxia  and  con- 
vulsions, exactly  in  the  same  wny  as  when  oxygen  is  d^-'ficient. 
Ci)rresponding  with  this  it  is  found  that  the  production  of  carbonic 
acid  is  diminislied.  That  is  to  say,  when  the  pressure  of  the 
oxygen  is  increased  beyond  a  certain  limit,  the  oxidations  of  the 
body  are  diminished,  and  wiUi  a  still  furdier  increase  of  the 
oxygen  are  arrested  altogether.  The  oxidation  of  jjliosphorus 
is  quite  analogous ;  at  a  high  pressure  of  oxygen  phosphorus 
will  not  burn.  IJert  has  further  shewn  that  plants,  bacteria,  and 
organizjd  ferments,  are  similarly  killed  by  a  too  great  pressure 
of  oxygen. 


Sec.  9.    Modified  Respir.-vtory  Movements. 

The  respiratory  mechanism  with  its  adjuncts,  in  addition  to  its 
respiratory  function,  becomes  of  service,  especially  in  the  case  of 
man,  as  a  means  of  expressing  emotions.  The  respiratory  columa 
of  air,  moreover,  in  its  exit  from  the  chest,  is  frequently  made  use 
of  in  a  mechanical  way  to  expel  bodies  from  the  upper  air-passagos. 
Hence  arise  a  number  of  peculiarly  raoditied  and  more  or  less 
complicated  respiratory  movements,  sighing,  coughing,  laughter, 
&c.  adapted  to  secure  special  ends  which  are  not  distmctly 
respiratory.  They  are  all  essentially  rellex  in  character,  the 
stimulus  determining  each  movement,  sometimes  affecting  a  peri- 
pheral afferent  nerve  as  in  the  case  of  coughing,  sometimes 
working  through  the  higher  parts  of  the  brain  as  in  laughter  and 
crying,  sometimes  possibly,  as  in  yawning  and  sighing,  acting  on 
the  respiratory  centre  itself.  Like  the  simple  respiratory  act,  they 
may  wuh  more  or  less  success  b-  carried  out  by  a  direct  effort 
of  the  will. 

Sighing  is  a  deep  and  long-drawn  inspiration  chiefly  through 
the  nose  followed  by  a  somewhat  shorter,  but  correspondingly 
large  expiration. 

Yawning  is  similarly  a  deep  inspiration,  deeper  and  longer 
continued  than  a  sigh,  drawn  through  the  widely  open  mouth,  and 
accompanied  by  a  i)eculiar  depression  of  the  lower  jaw  and 
frequently  by  an  elevation  of  the  shoulders. 


39^  COUGHING,   ETC.  [BOOK  II. 

Hiccough  consists  in  a  sudden  inspiratory  contraction  of  the 
diaphragm,  in  the  course  of  which  the  glottis  suddenly  closes,  so 
that  the  further  entrance  of  air  into  the  chest  is  prevented,  while 
the  impulse  of  the  column  of  air  just  entering,  as  it  strikes  upon 
the  closed  glottis,  gives  rise  to  a  well-known  accompanying  sound. 
The  afferent  impulses  of  the  reflex  act  are  conveyed  by  the  gastric 
branches  of  the  vagus.  The  closCire  of  the  glottis  is  carried  out  by 
means  of  the  inferior  laryngeal  nerve.     See  Voice. 

In  sobbing  a  series  of  similar  convulsive  inspirations  follow 
each  other  slowly,  the  glottis  being  closed  earlier  than  in  the  case 
of  hiccough,  so  that  little  or  no  air  enters  into  the  chest. 

Coughing  consists  in  the  first  place  of  a  deep  and  long- 
drawn  inspiration  by  which  the  lungs  are  well  filled  with  air.  This 
is  followed  by  a  complete  closure  of  the  glottis,  and  then  comes  a 
sudden  and  forcible  expiration,  in  the  midst  of  which  the  glottis 
suddenly  opens,  and  thus  a  blast  of  air  is  driven  through  the 
upper  respiratory  passages.  The  afferent  impulses  of  this  reflex 
act  are  in  most  cases,  as  when  a  foreign  body  is  lodged  in  the 
larynx  or  by  the  side  of  the  epiglottis,  conveyed  by  the  superior 
laryngeal  nerve  ;  but  the  movement  may  arise  from  stimuli  applied 
to  other  afferent  branches  of  the  vagus,  such  as  those  supplying 
the  bronchial  passages  and  stomach  (.?)  and  the  auricular  branch 
distributed  to  the  meatus  externus.  Stimulation  of  other  nerves 
also,  such  as  those  of  the  skin  by  a  draught  of  cold  air,  may 
develope  a  cough. 

In  sneezing  the  general  movement  is  essentially  the  same, 
except  that  the  opening  from  the  pharynx  into  the  mouth  is  closed 
by  the  contraction  of  the  anterior  pillars  of  the  fiiuces  and  tb.e 
descent  of  the  soft  palate,  so  that  the  force  of  the  blast  is  driven 
entirely  through  the  nose.  The  afferent  impulses  here  usually 
come  from  the  nasal  branches  of  the  fifth.  When  sneezing  however 
is  produced  by  a  bright  light,  the  optic  nerve  would  seem  to  be 
the  afferent  nerve. 

Laughing  consists  essentially  in  an  inspiration  succeeded, 
not  by  one,  but  by  a  whole  series,  often  long  continued,  of  short 
spasmodic  expirations,  the  glottis  being  freely  open  during  the 
whole  time,  and  the  vocal  cords  being  thrown  into  characteristic 
vibrations. 

In  crying,  the  respiratory  movements  are  modified  in  the 
same  way  as  in  laughing ;  the  rhythm  and  tlie  accompanying  facial 
expressions  are  however  different,  though  laughing  and  crying 
frequently  become  indistinguishable. 


CHAP,    n.]  RESPIRATION.  39/ 

Our  real  knowledge  of  the  physiology  of  respiration  dates  back  from 
1777,  when  Lavoi^icr  shewed  the  true  n:itine  of  comtDUitidn,  following 
close  as  this  di  1  upon  Priestley's  demonstration  of  the  identity  of  re- 
spiration and  combuiiion  (1771)  and  discovery  of  oxygen  (1774).  IJcfore 
th.it  time  the  c'lief  steps  of  progress  were,  the  discovery  by  Van 
Hclmont  (164S)  that  gas  sylvestre  (jarbonic  acid  gas)  wai  untit  for 
respiration,  the  demonstration  by  Hook  (1664)  of  the  effects  of  arti- 
ficial respiration,  by  Lower  ( 1 669)  of  the  connection  with  respiration 
of  the  difference  in  colour  between  venous  and  arterial  blood,  by 
Boyle  (1670)  of  the  necessity  for  respiratory  purposes  of  the  a  r  dis- 
solved in  water,  tlie  obbcrvations  and  reflections  of  Mayow  (1674)  on 
the  bpiritus  nitro-aereus  (oxygen),  in  whi:h  he  narrowly  missel  antici- 
pating Livoisier  by  a  century,  and  the  discovery  by  Bl.ick  (1757)  of 
carbonic  acid  in  air.  Lavoisier  however  held  that  the  respiratory 
combustion  took  place  in  tlie  bronchial  tube-;,  a  hydro-carbonous  sub- 
stance being  secreted  for  that  purpose  from  the  blood  :  and  though 
Lagrange  suggested  that  the  oxygen  might  be  absorbed  into  and  the 
carbonic  acid  exhaled  from  the  blood,  the  combustion  occurring  in  the 
blood  or  tissues,  and  Spallanzani  (1803)  and  \V.  F.  Edwards  (1823) 
shewed  that  snails,  frogs  and  young  mammals  continued  to  produce 
cirbonic  acid  in  an  atmosphere  of  hydrogen,  w'lereby  direct  combus- 
tion in  the  lungs  vas  rendered  impossible,  Lavoisier's  view  held  its 
ground,  owing  to  the  difficulty  of  extracting  gases  from  the  blood, 
until  in  1837  iVIagnu;  used  the  mercurial  air-jjump  and  proved  that 
both  venous  and  arterial  blood  contained  both  oxygen  and  carbonic 
acid.  His  researches  and  those  of  Lothar  Meyer  and  Fernet,  which 
r-JIowcd  soon  after,  form  the  basis  of  our  pre-ent  knowledge.  The 
labours  of  Ludwig  and  his  school,  of  Pfliiger  and  his  pupils,  and 
of  others,  have  advanced  this  subject  to  its  present  condition.  The 
spectroscopic  discoveries  of  Hoppe-Seyler  and  Siokes  have  proved 
of  great  and  increasing  impoitance  ;  and  we  are  indebted  to 
Rosenthal  for  a  clear  exposition  of  the  nervous  mechanism  of 
respiration. 


CHAPTER   III. 

SECRETION  BY  THE  SKIN. 

We  have  traced  the  food  from  the  alimentary  canal  into  the  blood, 
and,  did  the  state  of  our  knowledge  permit,  the  natural  course  of 
our  study  would  be  to  trace  the  food  from  the  blood  into  the 
tissues,  and  then  to  follow  the  products  of  the  activity  of  the  tissues 
back  into  the  blood  and  so  out  of  the  body.  This  however  we 
cannot  as  yet  satisfactorily  do  ;  and  it  will  be  more  convenient  to 
study  first  the  final  products  of  the  metabolism  of  the  body,  and 
the  manner  in  which  they  are  eliminated,  and  afterwards  to  return 
to  the  discussion  of  the  intervening  steps. 

Our  food  consists  of  certain  food-stuffs,  viz.  proteids,  fats  and 
carbohydrates,  of  various  salts,  and  of  water.  In  their  passage 
through  the  blood  and  tissues  of  the  body,  the  proteids,  fats  and 
carbohydrates  are  converted  into  urea  {or  some  closely  allied  body), 
carbonic  acid  and  water,  the  nitrogen  of  the  urea  being  furnished 
by  the  proteids  alone.  Many  of  the  proteids  contain  sulphur,  and 
also  have  phosphorus  attached  to  them  in  some  combination  or 
other,  and  some  of  the  fats  taken  as  food  contain  phosphorus  ; 
these  elements  ultimately  suffer  oxidation  into  phosphates  and 
sulphates,  and  leave  the  body  in  that  form  in  company  with  the 
other  salts. 

Broadly  speaking  then,  the  waste  products  of  the  animal 
economy  are  urea,  carbonic  acid,  salts  and  water.  Of  these  a  large 
portion  of  the  carbonic  acid,  and  a  considerable  quantity  of  water, 
leave  the  body  by  the  lungs  in  respiration  ;  while  all  (or  nearly  al!) 
the  urea,  the  greater  portion  of  the  salts,  and  a  large  amount  of 
water,  with  an  insignificant  quantity  of  carbonic  acid,  pass  away 
by  the  kidneys.  The  work  therefore  of  the  remaining  excretory 
tissue,  the  skin,  is  confined  to  the  elimination  of  a  comparatively 
small  quantity  of  salts,  a  little  carbonic  acid,  and  a  variable  but  on 
the  whole  large  quantity  of  water  in  the  form  of  perspiration.  The 
actual  excretion  by  the  bowel,  that  is  to  say,  that  portion  of  the 


CHAP.    Ill]  CUTANEOUS   SECRETION.  399 

feces  which  is  not  simply  undigested  matter,  we  have  seen  to  be 
very  small. 

The  nature  and  amount  of  Perspiration. 

The  quantity  of  matter  which  leaves  the  human  body  by  way 
of  the  skin  is  very  considerable.  Thus  Sequin'  estimated  that, 
while  7  grains  passed  away  through  the  lungs  per  minute,  as  much 
as  II  grains  escaped  througii  the  skin.  The  amount  varies 
extremely ;  Funke^  calculated,  from  data  gained  by  enclosing 
the  arm  in  a  caoutchouc  bag,  that  the  total  amount  of  perspiration 
from  the  whole  body  in  24  hours  might  range  from  2  to  20  kilos  ; 
but  such  a  mode  of  calculation  is  obviously  open  to  many  sources 
of  error. 

Of  the  whole  amount  thus  discharged,  part  passes  away  at  once 
as  watery  vapour  containing  volatile  matters,  while  part  may  remain 
for  a  time  as  a  fluid  on  the  skin  ;  the  former  is  frequently  spoken  of 
as  insensible,  the  latter  2.%  sensible  perspiration.  The  proportion  of 
the  insensible  to  the  sensible  perspiration  will  depend  on  the 
rapidity  of  the  secretion  in  reference  to  the  dryness,  temperature, 
and  amount  of  movement,  of  tlie  surrounding  atmosphere.  Thus, 
supposing  the  rate  of  secretion  to  remain  constant,  the  drier  and 
hotter  the  air,  and  the  more  rapidly  the  strata  of  air  in  contact  with 
the  body  are  renewed,  the  greater  is  the  amount  of  sensible 
perspiration  which  is  by  evaporation  converted  into  the  insensible 
condition ;  and  conversely  when  the  air  is  cool,  moist,  and 
stagnant,  a  large  amount  of  the  total  perspiration  may  remain  on 
the  skin  as  sensible  sweat.  Since,  as  the  name  implies,  we  are 
ourselves  aware  of  the  sensible  perspiration  only,  it  may  and 
frequently  does  happen  that  we  seem  to  ourselves  to  be  perspiring 
largely,  when  in  reality  it  is  not  so  much  the  total  perspiration 
which  is  being  increased  as  the  relative  proportion  of  the  sensible 
perspiration.  The  rate  of  secretion  may  however  be  so  much 
increased,  that  no  amount  of  dryness,  or  heat,  or  movement  of  th-e 
atmosphere,  is  sufficient  to  curry  out  the  necessary  evaporation, 
and  thus  the  sensible  perspiration  may  become  abundant  in  a  hot 
dry  air.  And  practically  this  is  the  usual  occurrence,  since  certainly 
a  high  temperature  conduces,  as  we  shall  point  out  presently,  to  an 
increase  of  the  secretion,  and  it  is  possible  that  mere  dryness  of  the 
air  has  a  similar  effect. 

The  total  amount  of  perspiration  is  affected  not  only  by 
the  condition  of  the  atmosphere,  but   also  by  the   nature  and 

'  Ann.  d.  Chivi,,  xc.  pp.  52,  403. 
'  Moleschott's  Untersuch.,  I  v.  p.  36. 


400    SENSIBLE  AND  INSENSIBLE  PERSPIRATION.    [BOOK  XL 

quantity  of  food  eaten,  by  the  amount  of  fluid  drunk,  and  by  the 
amount  of  exercise  taken.  It  is  also  inriuenced  by  mental 
conditions,  by  medicines  and  poisons,  by  diseases,  and  by  the 
relative  activity  of  the  other  excreting  organs,  more  particularly  of 
the  kidney. 

The  fluid  perspiration,  or  sweat,  Avhen  collected,  is  found  to  be 
a  clear  colourless  fluid,  with  a  strong  and  distinctive  odour  varying 
according  to  the  part  of  the  body  from  which  it  is  taken.  Besides 
accidental  epidermic  scales,  it  contains  no  structural  elements. 
The  reaction  of  the  secretion  of  the  sweat-glands,  apart  from  that 
of  the  sebaceous  glands,  appears  to  be  alkaline.  This  is  well  seen 
when  the  sweat  becomes  abundant.  An  admixture  of  sebaceous 
secretion  may,  when  the  sweat  itself  is  scanty,  give  rise  to  an 
acid  reaction  %  probably  from  the  sebaceous  fats  becoming  con- 
verted into  fatty  acids.  The  average  amount  of  solids  is  about 
i'8  [  p.  c.^,  of  which  about  two-thirds  consist  of  organic  substances. 
The  chief  normal  constituents  are:  (i)  Sodium  chloride  with 
small  quantities  of  other  inorganic  salts.  (2)  Various  acids  of  the 
fatty  series,  such  as  formic,  acetic,  butyric,  with  probably  propionic, 
caproic,  and  caprylic.  The  presence  of  these  latter  is  inferred 
from  the  odour  ;  it  is  probable  that  many  various  volatile  acids  are 
present  in  small  quantities.  Lactic  acid,  which  Berzelius  reckoned 
as  a  normal  constituent,  is  stated  not  to  be  present  in  health. 
(3)  Neutral  fats,  and  cholesterin  ;  these  have  been  detected  even 
in  places,  such  as  the  palms  of  the  hand,  where  sebaceous  glands 
are  absent.  (4)  Ammonia  (urea),  and  possibly  other  nitrogenous 
bodies. 

Funke^  detected  a  very  considerable  amount  of  urea  in  the  sweat 
gained  by  his  method,  so  much  so  that  he  calculated  the  total  amount 
given  off  by  the  skin  in  24  hours  at  about  10  grms.  Ranke'*  on  the 
other  hand,  who  collected  some  of  the  sweat  given  off  when  the  body 
was  exposed  in  a  large  space  to  an  abundant  atmosphere,  found  no 
evidence  whatever  of  urea.  This  striking  contradiction  has  not  yet 
been  explained,  though,  as  will  be  seen  in  dealing  with  nutrition,  the 
satisfactory  results  which  are  gained  by  supposing  that  under  normal 
conditions  all  the  urea  passes  out  by  the  kidneys,  render  it  probable 
that  Funke's  result  is  essentially  an  abnormal  one.  In  various  forms 
of  disease  the  sweat  has  been  found  to  contain,  sometimes  in  consider- 
able quantities,  blood  (in  bloody  sweat),  albumin,  urea  (particularly  in 
cholera),  uric  acid,  calcium  oxalate,  sugar,  lactic  acid,  indigo,  bile  and 
other  pigments.  Iodine  and  potassium  iodide,  succinic,  tartaric,  and 
benzoic  (partly  as  hippuric)  acids  have  been  found  in  the  sweat  when 
taken  internally  as  medicines. 

^  Cf.  Triimpy  and  Luchsinger,  Pfluger's  Archiv,    xvili.  {1878)  p.  494- 
==  Funke,  op.  cit.  ^  Op.  cit.  '■  Tetanus,  p.  247. 


CHAP.    Ill]  CUTANEOUS   SECRETION.  4OI 

Cutaneous  Respiration. 

A  frog,  the  lungs  of  which  have  been  renioverl,  will  continue 
to  live  for  some  time  ;  and  during  that  period  will  continue  not 
only  to  produce  carbonic  acid,  but  also  to  consume  oxygen.  In 
other  words,  the  frog  is  able  to  breathe  without  lungs,  respiration 
being  carried  on  etticiently  by  means  of  the  skin.  In  mammals 
and  in  man  this  cutaneous  respiration  is,  by  reason  of  the  thickness, 
of  the  epidermis,  restricted  to  within  very  narrow  limits  ;  neverthe- 
less, when  the  body  remains  for  some  time  in  a  closed  chamber  to 
which  the  air  passing  in  and  out  of  the  lungs  has  no  access  (as 
when  the  body  is  enclosed  in  a  large  air-tight  bag  fitting  tightly 
round  the  neck,  or  where  a  tube  in  the  trachea  carries  air  to  and 
from  the  lungs  of  an  animal  placed  in  an  air-tight  bo.\),  it  is  found 
that  the  air  in  the  chamber  loses  oxygen  and  gains  carbonic  acid. 
The  amount  of  carbonic  acid  which  is  thus  thrown  off  by  the  skia 
of  an  average  man  in  24  hours  amounts  according  to  Scharling  to 
no  more  than  about  10  grms.,  according  to  Aubert'  to  about 
4  grms.,  increasing  with  a  rise  of  temperature,  and  being  very 
markedly  augmented  by  bodily  exercise.  Regnault  and  Reiset 
state  that  the  amount  of  oxygen  consumed  is  about  equal  in 
volume  to  that  of  the  carbonic  acid  given  off,  but  Gerlach"  makes 
it  rather  less.  It  is  evident  therefore  that  the  loss  which  the  body 
suffers  through  the  skin  consists  chiefly  of  water. 

The  thickness  of  the  mammalian  or  human  epidermis  must  afford  a 
great  obstruction  to  any  diffusion  between  the  blood  in  the  cutaneous 
capillaries  anJ  the  external  air.  It  has  been  suggested  that  the  car- 
bonic acid  makes  its  exit  in  the  form  of  carbonates  present  in  the 
sweat,  and  that  these  being  de:omposed  by  the  acids  also  present  in 
sweat,  their  carbonic  acid  is  set  free. 

When  an  animal,  such  as  a  rabbit,  is  covered  over  with  an 
impermeable  varnish  such  as  gelatine,  so  that  all  exit  or  entrance 
of  gases  or  liquids  by  the  skin  is  prevented,  death  shortly  ensues. 
This  result  cannot  be  due,  as  was  once  thought,  to  arrest  of 
cutaneous  respiration,  seeing  how  insignificant  is  the  gaseous 
interciiange  by  the  skin  as  compared  with  that  by  the  lungs.  Nor 
are  the  symptoms  those  of  asphyxia,  but  rather  of  some  kind  of 
poisoning,  marked  by  a  very  great  fall  of  temperature,  which  how- 
ever does  not  seem  to  be  the  result  of  diminished  production  of 
heat,  since  according  to  BurdonSanderson  it  is  coincident  with  an 
actual  increase  of  the  discharge  of  heat  from  the  surface.     The 

'  Pfliiger's  Archiv,  vi.  (1S72)  539. 
"  Miller's  Archiv,  1851,  p.  431. 
F.  P.  26 


402  THE   SECRETION   OF   PERSPIRATION,      [BOOK   II. 

animal  may  be  restored,  or  at  all  events  its  life  may  be  prolonged 
with  abatement  of  the  symptoms,  if  the  great  loss  of  heat  which 
is  evidently  taking  place  be  prevented  by  covering  the  body 
thickly  with  cotton  avooI,  or  keeping  it  in  a  warm  atmosphere. 
The  symptoms  have  not  as  yet  been  clearly  analysed,  but  they 
seem  to  be  due  in  part  to  a  pyrexia  or  fever  possibly  caused  by  the 
retention  within  or  re-absorption  into  the  blood  of  some  of  the 
constituents  of  the  sweat,  or  by  the  products  of  some  abnormal 
metabolism,  and  in  part  to  a  dilation  of  the  cutaneous  vessels 
which  causes  an  abnormally  large  loss  of  heat,  even  through  the 
varnish. 

According  to  Rohrig'  the  injection  of  fresh  filtered  human  sweat 
into  the  veins  of  a  rabbit  causes  pyrexia,  and  albuminuria,  and  thus 
produces  some  of  the  effects  of  'varnishing.' 


The  Secretion  of  Perspiration. 

The  skin  contains,  besides  the  ordinary  sudoriparous  glands, 
the  sebaceous  glands,  and  thie  special  odoriferous  glands  of  the 
axilla,  anus,  and  other  regions.  With  regard  to  the  various  volatile 
and  odoriferous  substances  peculiar  to  sweat,  and  especially  with 
regard  to  those  peculiar  to  the  sweat  of  particular  regions  of  the 
skin,  there  can  be  no  doubt  that  these  are  secreted  by  the  epithe- 
lium of  the  appropriate  glands.  There  can  be  equally  no  doubt 
that  the  fats  which  come  to  the  surface  of  the  skin  from  the 
sebaceous  glands  arise  from  a  metabolism  of  the  cells  of  those 
glands.  And  we  shall  probably  not  go  far  wrong  in  regarding  the 
sweat  as  a  whole  as  supplied  by  the  sweat-glands  alone.  For 
though  it  seems  evident  that  some  amount  of  fluid  must  pass  by 
simple  transudation  through  the  ordinary  epidermis  of  the  portions 
of  skin  intervening  between  the  mouths  of  the  glands,  yet  on  the 
whole  it  is  probable  that  the  portion  which  so  passes  is  a  small 
fraction  only  of  the  total  quantity  secreted  by  the  skin  ;  and 
Erismann^  finds  that  even  the  simple  evaporation  of  water  is  much 
greater  from  those  parts  of  the  skin  in  which  the  glands  are 
abundant  than  from  those  in  which  they  are  scanty. 

The    nervous    mechanism    of    Perspirations.      The 

secreting  activity  of  the  skin,  like  that  of  other  glands,  is  usually 
accompanied  and  aided  by  vascular  dilation.    In  one  of  Bernard's 

*  Jahrb.f.  Bain.,  I.  I.  *  Zeitschrift f.  Biol.,  XI.  I. 

3  Luchsinger  and  Kendall,  Pfliigei-'s  Archiv,  Xiii.  (1876)  p.  212.  Luchsinger, 
ibid.,  XIV.  (1877)  p.  369;  XV.  (1877)  p.  482;  XVI.  (1878)  p.  545;  xviu. 
(1878)    p.    178,   p.   483.        Ostroumoff,   Moskauer    drztlicher  Anzeiger,    1876. 


CHAP     III.]  CUTANEOUS   SECRETION.  4O3 

early  experiments  on  division  of  the  cervical  sympathetic,  it  was 
observeil  that  in  the  case  of  the  horse,  the  vascular  dilation  of 
tile  face  on  the  side  operated  on  was  accompanied  by  increased 
perspiration.  Indeed  the  connection  between  the  .state  of  the 
cutaneous  blood-vessels  and  the  amount  of  perspiration  is  a  matter 
of  daily  observation.  When  the  vessels  of  the  skin  are  contracted, 
tlie  secretion  of  the  skin  is  dimmished  ;  when  tiiey  are  dilated  it 
becomes  abundant.  And  in  this  way,  as  we  shall  later  on  point 
out,  the  temperature  of  the  body  is  largely  regulated.  When  the 
surrounding  atmosphere  is  warm,  the  cutaneous  vessels  are  dilated, 
the  amount  of  sweat  secreted  is  increased,  and  the  consequently 
augmented  evaporation  tends  to  cool  down  the  body.  On  the 
other  hand,  when  the  atmosphere  is  cold,  the  cutaneous  vessels 
are  constricted,  perspiration  is  scanty,  and  less  heat  is  lost  to  the 
body  by  evaporation. 

The  analogy  with  the  other  secreting  organs  which  we  have 
already  studied  leads  us  however  to  infer  that  there  are  special 
nerves  directly  governing  the  activity  of  the  sudoriparous  glands, 
independent  of  variations  in  the  vascular  supply.  And  not  only 
is  this  view  supported  by  many  pathological  facts,  such  as  the 
profuse  perspiration  of  the  death  agony,  of  various  crises  of 
disease,  and  of  certain  mental  emotions,  ai:d  the  cold  sweats 
occurring  in  phthisis  and  other  maladies,  in  all  of  which  the  skin 
is  anemic  rather  than  hyper^mic;  but  we  have  direct  experimental 
evidence  of  a  nervous  mechanism  of  perspiration  as  complete  as 
the  vaso-motor  mechanism. 

If  in  the  dog  or  cat  (the  latter  animal  bjing  especially  suitable 
for  these  purposes)  the  periplieral  stump  of  the  divided  sciatic 
nerve  be  stimulated  with  tlie  interrupted  current,  a  profuse  sweat 
breaks  out  in  the  foot,  and  may  readily  be  observed  in  the  balls 
of  the  toes.  Not  only  may  the  secretion  be  observed  when  the 
cutaneous  vessels  are  thrown  into  a  state  of  constriction  by  the 
stimulus,  but  it  also  appears  when  the  aorta  or  crural  artery  is 
clamped  previous  to  the  stimulation,  or  indeed  when  the  leg  is 
amputated.  Moreover  when  atropin  has  been  injected,  the  stimu- 
lation produces  no  sweat,  though  vaso-motor  effects  follow  as 
usual.  The  analogy  between  the  sweat-glands  of  the  foot  and 
such  a  gland  as  the  subma.villary  is  in  fact  very  close,  and  we  are 
justitiecl  in  speaking  of  the  sciatic  nerve  as  containing  secretory 
fibres  distributed  to  the  sudoriparous  glands  of  the  hind  limb. 

Xawrocki,  Cbt.f.  tried.  IViss.,  1878,  pp.  2,  17,  721.  Acl.imkiewicz,  Die  Secrf 
tion  iLs  SchWi-issa,  1S7S.  Vulpian,  Cjinpl.  RenJ.,  T.  86  (187S),  i^p.  1233, 
1308,  1438;  r.  87  (1S78),  pp.  311,  350,  471.  Coyne,  ibid.,  T.  86  (1S78), 
p.  1276. 

26 2 


404  NERVOUS   MECHANISM.  [BOOK   II. 

Similar  results  may  be  obtained  with  the  nerves  of  the  fore  limb 
and  of  other  parts  of  the  body.  And  in  ourselves  a  copious 
secretion  of  sweat  may  be  induced  by  tetanizing  through  the  skin 
the  nerves  of  the  limbs  or  the  face. 

If  a  cat  in  which  the  sciatic  nerve  has  been  divided  on  one 
side  be  exposed  to  a  high  temperature  in  a  heated  chamber,  the 
limb  the  nerve  of  which  has  been  divided  remains  dry,  while  the 
whole  of  the  rest  of  the  skin  sweats  freely.  This  result  shews  that 
the  sweating  which  is  caused  by  exposure  of  the  body  to  high 
temperatures  is  brought  about  not  by  a  local  action  on  the  sweat- 
glands  but  by  the  agency  of  the  central  nervous  system.  A  high 
temperature  up  to  a  certain  limit  increases  the  irritability  of  the 
epithelium  of  the  sweat-glands  as  it  does  that  of  other  forms  of 
protoplasm  :  thus  stimulation  of  the  sciatic  in  the  cat  produces  a 
much  more  abundant  secretion  in  a  limb  exposed  to  a  temperature 
of  35°  or  somewhat  above,  than  in  one  which  has  been  exposed 
to  a  distinctly  lower  temperature,  and  in  a  limb  which  has  been 
placed  in  ice-cold  water  hardly  any  sjcretion  at  all  can  be  gained ; 
but  apparently  mere  rise  of  temperature  without  nerve-stimulation 
will  not  give  rise  to  a  secretory  activity  of  the  glands.  The 
sweating  caused  by  a  dyspnoeic  condition  of  blood,  and  such 
appears  to  be  the  sweat  of  the  death  agony,  is  similarly  brought 
about  by  the  agency  of  the  central  nervous  system.  When  an 
animal  with  the  sciatic  nerve  divided  on  one  side  is  made  dysp- 
noeic, no  sweat  appears  in  the  hind  limb  of  that  side,  though 
abundance  is  seen  in  other  parts  of  the  body. 

Sweating  may  be  brought  about  as  a  reflex  act.  Thus  when 
the  central  stump  of  the  divided  sciatic  is  stimulated  sweating 
is  induced  in  the  other  limbs,  and  the  introduction  of  pungent 
substances  into  the  mouth  will  frequently  give  rise  to  a  copious 
perspiration  over  the  side  of  the  face.  We  are  thus  led  to  speak 
of  sweat  centres,  analogous  to  the  vaso-motor  centres,  as  existing 
in  the  central  nervous  system ;  and  as  in  the  case  of  vaso-motor 
centres,  a  dispute  has  arisen  as  to  whether  there  is  a  dominant 
sweat  centre  in  the  medulla  oblongata  or  whether  such  centres 
are  more  generally  distributed  over  the  whole  of  the  spinal  cord. 

It  does  not  at  present  appear  certain  whether  the  sweating 
caused  by  heat  is  carried  out  by  direct  action  on  the  sweat  centres, 
or  by  the  higher  temperature  affecting  the  skin  and  so  producing 
its  effect  in  a  reflex  manner ;  but  in  the  case  of  dyspnoea  at  least 
we  may  fairly  suppose  that  the  action  of  the  venous  blood  is 
chiefly  if  not  exclusively  on  the  nerve  centres.  Drugs,  such  as 
pilocarpin,  which  cause  sweating  appear  to  act  locally  on  the 
glands  (though  pilocarpin  at  least  has  as  well  some  action  on  the 


CHAP.   III.J  CUTANEOUS  SECRETION.  405 

nerve  centres),  and  the  antagonistic  action  of  atropin  is  similarly 
local.  Nicotin  a|)pears  to  produce  its  sweating  action  chiefly  by 
acting  on  the  central  nervous  system. 

The  sweat  fibre;  for  the  hind  foot  (in  the  cat),  according  to  Nawrocki 
and  Lujhsingcr",  leave  the  spinal  cord  by  the  roots  of  the  last  dorsal 
and  first  two  lumbnr  or  last  two  dorsal  and  first  four  lumbar  nerves, 
pass  along  the  rami  ioiniiunticantes  to  the  abdominal  syinpatheti:,  and 
thus  rea.h  the  sci  '.ic  nerve.  Similarly  the  sweat-nervci  for  the  for^; 
fjiit  leave  the  spinal  cord  by  the  roots  of  the  fourth  (or  fourth,  filth, 
and  sixth)  dorsal  nerves,  pass  into  the  thoraij  s\mpatheti:,  thcn.e  into 
the  ganglion  stcUatum,  and  t!ius  join  the  brajhi  d  ple\us  ;  the  course 
to  the  foot  is  finally  along  the  median  and  ulnar  nerves  respectively. 
Accordmg  to  them,  when  tlic  abdominal  sympatlietic  below  the  junction 
with  the  se:ond  or  fourth  lumbar  root  is  divided  swelling  cannot  be 
induced  by  nervous  agency  in  the  hind  foot  ;  and  section  of  the  thor- 
a.ic  sympatheti,:  above  the  junction  with  the  fourth  dorsal  root  or 
removal  or  the  ganglion  stellatum  similarly  prevents  the  sweating  of 
the  fore-foot.  Vulpian ',  on  the  other  hand,  finds  that  the  swea.t-fibres 
pass  in  a  direct  course  along  the  roots  of  the  sciatic  or  brachial  plexus, 
and  sees  reason  to  believe  that  the  sympathetic  tracts  contain  inhibi- 
tory fibres,  since  he  has  been  able  to  check  perspiration  by  stimulating 
these  nerves. 

Nawrojki '  found  that  the  reflex  excitation  of  sweat  by  stimulation 
of  the  central  sciatic  failed  when  the  spinal  cord  was  divided  below 
the  medulla.  Hence  he  believed  that  a  general  sweat  centre  was  situate 
in  the  medulla  oblongata.  Sweating  in  the  hind  limbs  may  however 
be  produced  after  section  of  the  cord  in  the  dorsal  region  either  by 
dyspnoea  or  by  heating,  and  these  act  as  we  have  seen  through  a  nerve 
centre.  Lujhsinger'  indeed  found  that  so  long  as  a  portion  of  the  cord 
in  the  lower  dorsal  ar.d  upper  lumbar  region  was  left  intact,  sweating 
could  thus  be  induced  in  the  hind  limbs  even  when  all  the  nerve- roots 
had  been  divided,  except  those  springing  from  the  intact  portion  of  the 
cord  ;  but  that  the  etl'ect  entirely  ceased  when  this  portion  of  the  cord 
was  destroyed.  He  accordingly  inferred  that  a  sweat  centre  for  tVe 
hind  limbs  existed  in  this  part  of  the  cord. 

Absorption  by  the  Skin. 

Although  under  normal  circumstances  the  skin  serves  only  as 
a  channel  of  loss  to  the  body,  there  are  facts  which  sceni  to  shew 
that  it  may,  under  particular  circumstances,  be  a  means  of  gain. 
Cases  are  on  record  where  bodies  have  been  ascertained  to  have 
gaii  cd  in  weight  by  immersion  in  a  bath,  or  by  exposure  to  a 
moist  attnosphere  during  a  given  period,  in  which  no  food  or 
drink  was  taken,  or  to  have  gained  more  than  the  weight  of  tl  e 
lood  or  dni.k  taken.     The  gain  in  such  cases  must  have  been  due 

'  Op.  cil. 


40O  .^SORPTIOX  BY  THE   SKIN.  [bOOK   II. 

is  intact  the  evidence  ZS^^-  "^V^"^ ''^^'' '^^  ^P^^'^^^^is 
absorption  t^kes  W^c^  y^r.^l^f^'^'  ^''""Scomr^dictory ;  but 
even  solid  partid£  ^bb^  i'T^'  ^°™  .^^^^"^^  ^""^^es,  and 
when  appuSTa  fiS-  the  £  J  ''"'^  '^^°  u"^>"-  ^^^P^-'^^>' 
n.e.cu,,-o.^en.  find  a.el^^:::;\ro  ^e  ^IdeJu^  Iv^p^i^r 

not  absorbed,  and  tha^  vo  a   le  .ubstn  °"."°^^""^"  substancel  are 

be  detected  in  the  sv.tem  Ser  a  tr^'^  '^-'^  as  lodme  which  n-.av 
not  by  the  skin  bat  bV  the  mu  L?  ^^^u"^T§  '^^™  ^^  absorled 

'  Gattmann,    Virchow's  ^r  ife    Rd     -    /rS/;-. 
F  'OS-   i.oriiag.>^^^.^^*g;  -^^   \\fj>J^   p.  451  ;    Bd.  41  (XS67), 


CHAPTER   IV. 
SECRETION  BY  THE  KIDNEYS. 

The  epithelium  of  the  kidney,  like  that  of  the  alimentary  canal 
is  a  secretins  tissue.     The  protoplasmic  cells  which  Ime  at  least  a 
lar-xe  portion  of  the  tubuli  urinif^ri  elaborate  from  the  blood,  m  a 
ma'nner  which  we  shah  presently  disoass,  certain  substances,  and 
ditchige  tl.em  into  the  channels  of  the  tubules.     Besides  these 
disdnctly  active  secreting  structures,  however,  the  kidney  exhibit 
in  its  M'alpighian  bodies  an  arrangement  very  analogous  to  that 
which  obtains  in  the  lungs.     Just  as  in  the  latter  the  tanctions  of 
the   alveolar   epithelium   are   reduced   to   a   mmiraum    and   the 
entrance  and  egress  of  the  gases  of  respiration  are  mamly  earned 
on   by  diffusion,  so  in  the  former   the  epitliehum  covering  the 
glomeruli  can  have  but  htrie  secreting  activit>%  aad  the  passage  of 
material  from  the  interior  of  the  convoluted  blood-vessels  into  the 
cav-ides  of  die  tubules  must  be  chiefly  a  matter  of  simple  titration. 
What   substances   pass   in   this   way,   and  what    substances   are 
secreted  by  the  direct  action  of  the  epidiehum  of  tiie  secretmg 
tXules,   we    shall    shortiy   consider.      The   various    substances 
passing  in  either  die  one  or  the  odier  way    m  company  with 
Td  amount  of  water,  into  the  ducts  of  the  gland,  constitu^ 
the  secretion  called  urine.     And  since  none  ot  die  substances 
so  dirown  out  are  of  any  further  use  in  die  economy,  bat  are  at 
once  earned  away,  urine  is  generally  spoken  of  as  an  excretion. 
Sec.  I.     Composition  of  Ukine. 

The  healthy  urine  of  man  is  a  clear  yellowish  fluorescent  fluid, 
of  a  peculiar  odour,  sahne  taste,  and  acid  reaction,  having  a  mean 
speofic  gravit.-  of  i-o.o.  and  generaUy  holdmg  m  s^^P^^^^^^^ 
little  mucus.  The  nonnal  constituents  may  be  arranged  m  .everai 
classes. 

I.     Water. 

2  Inorganic  salts.  These  for  the  most  part  exist  in 
urine  in  natural  solution,  die  composition  of  die  ash  almost 
exactly  corresponding  widi  tl.e  results  ^^  ^lie  direct  analv-si^ot 
the  fluid  •  in  diis  respect  urine  contrasts  torcibly  widi  blood,  the 


408  COMPOSITION.  [book  II. 

jish  of  which  is  largely  composed  of  inorganic  substances,  which 
previous  to  the  combustion  existed  in  peculiar  combination  with 
proteid  and  other  complex  bodies.  Iji  the  ash  of  urine  there  is 
.rather  more  sulphur  than  corresponds  to  the  sulphuric  acid 
directly  determined  ;  this  indicates  the  existence  in  urine  of  some 
sulphur-holding  complex  body.  And  there  are  traces  of  iron, 
pointing  to  some  similar  iron-holding  substance.  But  otherwise, 
all  the  substances  found  in  the  ash  exist  as  salts  in  the  natural 
fluid.  The  most  abundant  and  important  is  sodium  chloride. 
There  are  found  in  smaller  quantities,  calcium  chloride,  potassium 
and  sodium  sulphates,  sodium,  calcium  and  magnesium  phosphates, 
with  traces  of  silicates.  Alkaline  carbonates  are  frequently  found, 
and  nitrates  in  small  quantity  are  also  said  to  be  sometimes  present. 
The  phosphates  are  derived  partly  from  the  phosphates  taken 
as  such  in  food,  partly  from  the  phosphorus  or  phosphates 
peculiarly  associated  with  the  proteids,  and  partly  from  the 
phosphorus  of  certain  complex  fats  such  as  lecithin.  When  urine 
becomes  alkaline,  the  calcic  and  magnesic  phosphates  are  pre- 
cipitated, the  sodium  phosphates  remaining  in  solution.  The 
sulphates  are  derived  partly  from  the  sulphates  taken  as  such  in 
food  and  partly  from  the  sulphur  of  the  proteids.  The  carbonates, 
when  occurring  in  large  quantity,  generally  have  their  origin  in  the 
oxidation  of  such  salts  as  citrates,  tartrates,  &c.  The  bases 
present  depend  largely  on  the  nature  of  the  food  taken.  Thus 
with  a  vegetable  diet,  the  excess  of  the  alkalis  in  the  food 
reappears  in  the  urine  ;  with  an  animal  diet,  the  earthy  bases  in  a 
similar  way  come  lo  the  front. 

3.  Nitrogenous  crystalline  bodies,  derivatives  of  the 
metabolism  of  the  proteids  of  the  body  and  food.  First  and 
foremost  come  urea  and  its  immediate  ally,  uric  acid.  These  will 
be  considered  in  detail  hereafter  ;  they  are  the  typical  products  of 
the  metabolism  of  proteids.  Existing  in  much  smaller  quantities 
are  a  number  of  bodies  more  or  less  closely  related  to  urea,  which 
may  for  the  most  part  be  regarded  as  less-completely  oxidised  pro- 
ducts of  metabolism.  Such  are  :  kreatmin,  xanthin,  hypoxanthin, 
and  occasionally  allantoin.  To  these  may  be  added  hippuric  acid, 
ammonium  oxalurate,  and,  at  times,  taurin,  cystin,  leucin,  and  ■ 
tyrosin.  These  too  we  shall  have  to  consider  in  dealing  with  the 
metabolism  of  the  body. 

4.  Non-nitrogenous  bodies.  These  exist  in  very  small 
quantities,  and  many  of  them  are  probably  of  uncertain  occur- 
rence. They  are  organic  acids,  such  as  lactic,  succinic,  formic, 
oxalic,    phenylic,    &c.     It    has     been    maintained    that    minute 


CHAP.   IV.]  RENAL   SECRETION.  •  4C9 

quantities  of  sugar  are  invariably  present  in  even  healthy 
urine ;  this  however  has  not  as  yet  been  placed  beyond  all 
doubt. 

5.  Pigments.  Tliose  are  at  present  very  imperfectly  under- 
stood. WIicUrt  the  natural  y<llo\v  colour  of  urine  be  due  to  a 
single  pigment,  the  ///w/zriw/t' of  Tluidichum,  or  to  more  than  one, 
and  what  is  the  ex:ict  nature  of  these  pigments,  must  he  left  un- 
decided? As  was  stated  above  (p.  39),  the  urine  frecjMently  contains 
urobilin  ;  and  the  ])eculiar  red  colour  of  some  rheumatic  urines  is 
due  to  the  jiresence  of  a  body  called  by  Prout ////////v// and  by 
Heller  uroerythrin.  The  urine  of  man  and  of  many  animals, 
es[)ecially  of  the  dog,  contains  i/iduaii,  whicii  under  certain  cir- 
cumstances may  give  rise  to  the  production  of  indigo-blue. 

6.  Other  bodies.  Urine  treated  with  many  times  its 
volume  of  alcohol  gives  a  precipitate.  In  this  precipitate  is  found 
a  body,  giving  proieid  reactions;  and  an  aqueous  solution  of  the 
precipitate  is  i)oth  amylolylic  and  proteolytic,  i.e.  appears  to  con- 
tain some  of  both  the  salivary  (pancreatic)  ferment  and  pepsin. 

7.  Gases.  Those  gases  which  can  be  ex'racted  from  urine 
by  the  mercurial  pump  are  chijfly  nitrogen  and  carbonic  acid, 
oxygen  occurring  in  very  small  quantities  or  being  wholly  absent. 

The  quantities  in  which  these  multifarious  constituents  are 
present  vary  within  very  wide  limits,  being  dependent  on  the 
nature  of  the  food  taken,  and  on  the  circumstances  of  the  body. 
These  points  will  be  considered  in  the  succeeding  chapter.  What 
may  be  called  the  average  composition  of  human  urine  is  sliewn 
in  the  following  table. 

AMOUNTS    OF   Till-:    .SEVERAL    URINARY   CONSTITUENTS 
I'ASSKD   LN   TWENTV-1-OUR    HOURS.     (After   Parkes.) 


Cy  .in  average 

Per  1  kilo. 

man  of  66  kilos. 

of  BoJy  Weight. 

Water 

1500'0"0  grammes 

23'OOOJ  tjra;imics 

Total  Solids 

72 '000 

I"  1000 

Urea 

33'iSo 

•5CX)0 

Uric  Acid 

■555 

•0084 

Uippuric  Acid 

•400 

•og6o 

Krcatinin 

■910 

•0140 

PigiiL-nt,  and 

other  substances 

lO'OOO 

•i5[o 

Sulphuric  Acid 

2*OI2 

0.S05 

Pli  )sph<)ric  Acid 

3"i64 

•04150 

Chlorine 

70CX3  (8-21) 

■1260 

Amaaonia 

•770 

Potxs-ium 

2"5CO 

Sodium 

1 1  "090 

Calcium 

•260 

Magnesium 

•207 

410  CONSTITUENTS   OF   URINE,  [BOOK   II. 

Aciditj'  of  Urine.  The  healthy  urine  of  man  is  acid,  the 
amount  of  acidity  being  about  equivalent  to  2  grms.  of  oxalic  acid 
in  twenty-four  hours.  It  is  due  to  the  presence  of  acid  sodium 
phosphate,  the  absence  of  free  acid  being  shewn  by  the  fact  that 
sodium  hyposulphite  gives  no  precipitate.  The  amount  of  acidity 
varies  much  during  the  twenty-four  hours,  being  in  an  inverse  ratio 
to  the  amount  of  acid  secreted  by  the  stomach  ;  thus  it  decreases 
after  food  is  taken,  and  increases  as  gastric  digestion  becomes  com- 
plete. It  varies  with  the  nature  of  the  food  ;  with  a  vegetable  diet 
the  excess  of  alkalis  secreted  leads  to  alkalinity,  or  at  least  to 
diminished  acidity,  whereas  this  effect  is  wanting  with  an  animal 
diet,  in  which  the  earthy  bases  preponderate.  Hence  the  urine  of 
carnivora  is  generally  very  acid,  while  that  of  herbivora  is  alkaline. 
The  latter,  when  fasting,  are  for  the  time  being  carnivorous,  living 
entirely  on  their  own  bodies,  and  hence  their  urine  becomes  under 
these  circumstances  acid. 

The  natural  acidity  increases  for  some  time  after  the  urine  has 
been  discharged,  owing  to  the  formation  of  fresh  acid,  apparently 
by  some  kind  of  fermentation.  This  increase  of  acid  frequently 
causes  a  precipitation  of  urates,  which  the  previous  acidity  has 
been  insufficient  to  throw  down.  After  a  while  however  the  acid 
reaction  gives  way  to  alkalinity.  This  is  caused  by  a  conversion 
of  the  urea  into  ammonium  carbonate  through  the  agency  of  a 
specific  ferment.  This  ferment  as  a  general  rule  does  not  make  its 
appearance  except  in  urine  exposed  to  the  air ;  it  is  only  in  un- 
healthy conditions  that  the  fermentation  takes  place  w^ithin  the 
bladder. 

Abnormal  constituents  of  Urine.  The  structural  ele- 
ments found  in  the  urine  under  various  circumstances  are  blood, 
pus  and  mucous  corpuscles,  epithelium  from  the  bladder  and 
kidney,  and  spermatozoa.  Serum-albumin,  fibrin  (frequently  as 
*  casts '),  alkali-albumin,  globulin,  a  peculiar  form  of  albumin, 
(discovered  by  Bence-Jones  in  mollifies  ossium,  characterised  by 
being  soluble  at  high  temperatures,  and  re-discovered  by  Kiihne 
as  a  product  of  digestion),  fats,  cholesterin,  sugar,  leucin,  tyrosin, 
oxalic  acid,  bile  acids  and  bile  pigment,  may  be  enumerated  as  the 
most  important  metabolic  products  abnormally  present  in  urine.- 
Besides  these  the  urine  serves  as  the  chief  channel  of  elimination 
for  various  bodies,  not  proper  constituents  of  food,  which  may 
happen  to  have  been  taken  into  the  system.  Thus  various 
minerals,  alkaloids,  salts,  pigmentary  and  odoriferous  matters,  may 
be  passed  unchanged.  Many  substances  thus  occasionally  taken 
suffer  changes  in  passing  through  the  body  ;  tb.e  most  important 
of  these  will  be  considered  in  a  succeeding  chapter. 


CHAP.    IV.]  RENAL   SECRETION.  4I I 

Sec.  2.     The  Secretion  of  Urine. 

We  have  already  called  attention  to  the  fact  that  the  kidney, 
unlike  the  other  secreting  organs  which  we  have  hitherto  studied, 
cnnsists  of  two  distinct  parts  :  of  an  actively  secreting  part,  the 
cpilhelium  of  the  secreting  tubules,  and  of  what  may  be  called  a 
filtering  part,  the  Malpighian  bodies.  Corresponding  to  this 
dcnible  structure  we  find  that,  of  the  various  urinary  constituents 
enumerated  in  the  preceding  section,  some,  such  as  sodium 
chloride,  are  known  to  be  present  in  the  blood  independently  of 
any  activity  of  the  kidney  ;  others,  such  as  the  urinary  pigments, 
appear  to  be  absent  from  the  blood  ;  while  of  others,  such  as 
urea,  it  is  probable  that  their  occurrence  in  the  blood  is  in  part 
the  result  of  some  previous  renal  action,  or  at  least  it  is  not 
certain  that  this  is  not  the  case.  The  first  of  these  we  may  fairly 
suppose,  as  Bowman*  long  ago  suggested,  to  be  in  large  part  at 
least  simply  filtered  through  the  renal  glomeruli ;  the  others  we 
may  regard  provisionally  as  the  products  of  the  activity  of  the 
renal  epithelium.  Since  the  pas.sage  of  fluids  and  dissolved 
substances  through  membranes  is  in  large  part  directly  de])endent 
on  pressure,  the  extent  and  rapidity  of  that  part  of  the  whole 
process  of  the  secretion  of  urine  which  is  a  mere  filtration,  will 
be  directly  affected  by  the  amount  of  arterial  pressure  in  the  renal 
arteries,  while  the  effect  of  variations  of  arter'al  pressure  on  that 
])art  of  the  process  which  is  a  real  active  secretion,  will  be  an 
indirect  one  only.  Since,  then,  the  discharge  of  urine  by  the 
kidneys  must  be  to  a  much  greater  extent  than  is  the  case  with 
the  secretion  of  saliva  or  of  gastric  juice  a  mere  matter  of 
]iressure,  it  will  be  more  convenient  to  study  the  relations  of 
urinary  secretion  to  blood-pressure  before  we  enter  upon  the 
discussion  of  the  active  secretion  itself. 

The  relation  of  the  Secretion  of  Urine  to  Arterial  Pressure. 

The  circumstance  to  which  we  have  to  direct  our  attention  is 
the  extent  of  jiressure  present  in  the  small  vessels  of  the  renal 
glomeruli.  The  more  the  pressure  of  the  blood  in  these  exceeds 
the  pressure  of  the  fluid  in  the  channels  of  the  uriniferous  tubules, 
the  more  rapid  and  extensive  will  be  the  filtration  from  the  one 
into  the  other. 

This  local  blood-pressure  in  the  small  vessels  of  the  glomeruli 
may  be  increased — 

I.  By  an  increase  of  the  general  blood-pressure,  brought 
about — {a)   by  an  increased  force,  frequency,  &c.  of  the  heart's 

'  PliiL   Trans.,  184:^. 


412  RELATIONS   TO   BLOOD-PRESSURE.       [BOOK   IL 

beat,  [b)  by  the  constriction  of  the  small  arteries  supplying  areas 
other  than  the  kidney  itself. 

2.  By  a  relaxation  of  the  renal  arter}',  which,  as  we  have 
previously  pointed  out  (p.  225),  while  diminishing  the  pressure  in 
the  artery  itself,  increases  the  pressure  in  the  capillaries  and  small 
veins  which  the  artery  supplies.  It  need  hardly  be  added  that 
this  local  relaxation  must  either  be  accompanied  by  constriction  in 
other  vascular  areas,  or  at  all  events  must  not  be  accompanied  by 
a  sufficiently  compensating  dilation  elsewhere. 

The  same  local  pressure  may  similarly  be  diminished — 

■  I.  By  a  constriction  of  the  renal  artery,  which,  while  in- 
creasing the  pressure  on  the  cardiac  side  of  the  artery,  diminishes 
the  pressure  in  the  capillaries  and  veins  which  are  supplied  by  the 
artery.  This  again  must  either  be  accompanied  by  dilation  in 
other  vascular  areas,  or  at  least  not  accompanied  by  a  com- 
pensating constriction. 

2.  By  a  lowering  of  the  general  blood-pressure,  brought  about 
—{a)  by  diminished  force  &c.  of  the  hearts  beat,  {b)  by  a  general 
dilation  of  the  small  arteries  of  the  body  at  large,  or  by  a  dilation 
of  vascular  areas  other  than  the  kidneys. 

Bearing  these  facts  in  mind,  it  becomes  easy  to  explain  many 
of  the  instances  in  which  an  increase  or  diminution  of  urine  is 
produced  by  natural  ©r  artificial  means.  Thus  section  of  the 
spinal  chord  below  the  medulla  causes  a  great  diminution,  and 
indeed  in  most  cases  a  complete  or  almost  complete  arrest  of  the 
secreiion  of  urine.  This  operation,  by  cutting  off  so  many 
vascular  areas  from  the  medullary  vaso-motor  centre  (and  possibly 
also  by  giving  rise  to  a  condition  of  shock  in  the  spinal  cord) 
leads  to  a  very  general  vascular  dilation,  in  consequence  of  which 
there  ensues  a  great  fall  of  the  general  blood- pressure.  Although 
the  renal  arteries  suffer  with  the  rest  in  this  dilation,  still  this  is 
insufficient  to  compensate  the  greatly  diminished  pressure ;  and 
when  the  g:jneral  blood-pressure  fills  sufficiently  low  (below 
30  mm.  mercury  in  the  dog)  the  secretion  of  urine  is  totally 
arrested. 

Stimulation  of  the  spinal  cord  below  the  medulla,  though 
acting  in  the  converse  direction,  brings  about  the  same  result, 
arrest  of  the  secretion.  By  the  stimulation  the  action  of  the 
vaso-motor  nerves  is  augmented,  and  constriction  of  the  renal 
arteries  as  well  as  of  other  arteries  in  the  body  is  brought 
about.     The  increase  of  general  blood-oressure  thus  produced  is 


CHAP.   IV.J  RENAL   SKCRETION.  413 

insufficient  to  compensate  for  the  increased  resistance  in  the  renal 
artt-rics ;  and  as  a  consequence  the  flow  of  blood  into  the 
glomeruli  is  largely  reduced.  Indeed  on  inspection  the  kidneys 
are  seen  during  the  stimulation  to  become  paL*  and  bloodless. 

Section  of  the  renal  nerves  is  followed  by  a  most  copious 
secretion,  by  what  has  been  called  hydruria  or  polyuria,  the  urine 
at  the  same  time  frequently  becoming  albuminous.  The  section 
of  the  nerves,  by  interrupting  the  vaso-motor  tracts,  leads  to 
dilation  of  the  renal  arteries,  and  this  to  increased  pressure  ///  the 
small  vessels  of  the  glomeruli.  If  after  section  of  the  lenal  nerves 
the  cord  be  divided  below  the  medulla,  the  polyuria  disappears ; 
for  the  diminution  of  general  blood-pressure  thus  produced  more 
than  comi)ensates  for  the  special  dilation  of  the  renal  arteries. 
Conversely,  if  after  section  of  the  renal  nerves  the  cord  be  stimu- 
lated, the  flow  of  urine  is  still  further  increased,  since  the  rise  or 
general  blootl-pressure  due  to  the  general  arterial  constriction 
caused  by  tiie  stimulation  tends  to  throw  still  more  blood  into  the 
renal  arteries,  on  wiiich,  owing  to  the  division  of  their  nerves,  the 
spinal  stimulation  is  powerless. 

Section  of  the  splanchnic  nerves,  along  which  apparently  the 
vaso-motor  tracts  from  the  spinal  cord  to  the  kidneys  run,  produces 
also  an  increased  flow  of  urine.  But  the  augmentation  in  this  case 
is  smaller  and  less  certain  than  in  the  case  of  section  of  the 
renal  nerves  themselves,  since  the  splanchnic  nerves  govern  the 
whole  splanchnic  area,  and  hence  a  large  portion  of  the  increased 
supply  of  blood  is  diverted  from  the  kidney  to  other  abdominal 
organs.  Conversely,  stimulation  of  the  splanchnic  nerves 
arrests  the  flow  of  urine  by  producing  constriction  of  the  renal 
arteries. 

We  shall  have  occasion  in  the  succeeding  chapter  to  call 
atteiilion  to  tiie  fact  that  puncture  of  the  fourth  ventricle,  or 
mechanical  irritation  of  the  first  thoracic  ganglion,  gives  rise 
to  the  appearance  of  a  large  quantity  of  sugar  in  the  urine,  and 
at  the  same  time  causes  a  more  copious  flow  of  that  fluid  ;  the 
condition  of  body  thus  brought  about  is  known  as  artificial 
diabetes.  The  increased  flow  of  urine  in  this  case  cannot  be 
accoimted  for  by  supposing  that  the  increased  quantity  of  sugar  in 
the  blood  in  passing  out  by  the  ki(iney  leads  in  some  way  or  other 
to  an  increased  excretion  of  water ;  for  the  same  operation,  or  a 
similar  injury  to  certain  parts  of  the  cerebellum',  may  give  rise  to 
an  excessive  secretion  of  urine  without  any  sugar  being  present. 
It  is  probable,  but  not  as  yet  cleaily  proved,  that  the  increase  of 
urine  is  ^wq  to  the  dilation  of  the  renal  arteries  ;  and  this  view  is 
»  Eckhard,  Beilrdge,  v.  (1870)  153;  vi.  i,  51,  117,  175. 


414  ACTIVITY  OF   THE   EPITHELIUM.         [BOOK   II. 

supported  by  the  fact  that  the  increase  is  temporarily  prevented 
(as  is  also  a  similar  diabetic  increase  of  flow  in  carbonic-  oxide 
poisoning)  by  stimulation  of  the  splanchnic  nerves. 

Irritation  of  the  central  end  of  the  vagus  causes  an  increased  flow 
of  urine.  This  may  be  explained  by  supposing  that  the  afferent 
impulses  ascending  the  vagus  inhibit  the  vaso-motor  centre  which 
governs  the  renal  arteries,  and  so  produce  dilation  of  those  arteries. 
Possibly  at  the  same  time,  as  in  the  case  of  the  rabbit's  ear  (p.  210), 
some  amount  of  general  constriction  is  brought  about. 

The  experimental  phenomena  recorded  above  are  thtis  seen  to 
receive  a  fairly  satisfactory  explanation  when  they  are  referred 
exclusively  to  variations  in  blood-pressure.  And  many  of  the 
natural  variations  in  the  flow  of  urine  may  be  interpreted  in  this 
way.  No  fact  in  the  animal  economy  is  oftener  or  more  strikingly 
brought  home  to  us  than  the  correlation  of  the  skin  and 
the  kidneys  as  far  as  their  secretions  are  concerned  ;  and  this 
seems  to  be  maintained  by  means  of  the  vaso-motor  nervous 
mechanism.  Thus  when  the  skin  is  cold,  its  blood-vessels  are,  as 
we  know,  constricted.  This  by  causing  an  increase  of  general 
blood-pressure,  accompanied  possibly  by  a  dilation  of  the  renal 
arteries,  will  augment  the  flow  through  the  kidneys.  Conversely, 
the  dilated  condition  of  the  arteries  of  a  warm  skin,  with  the 
consequent  diminution  of  general  blood-pressure,  accompanied 
possibly  with  a  corresponding  constriction  of  the  renal  arteries, 
will  give  rise  to  a  diminished  renal  discharge.  The  eff^ects  of 
emotions  may  possibly  be  explained  in  a  similar  way  as  essentially 
vaso-motor  phenomena. 

The  increase  of  urine  observable  after  taking  fluids  cannot  be 
explained  by  reference  to  any  direct  increase  of  blood-pressure  due  to 
an  augmentation  of  the  quantity  of  blood,  for,  as  we  have  seen  (p.  230), 
an  increase  of  the  quantity  of  blood  does  not  raise  the  general  blood- 
pressure.  The  increased  filtration  may  be  due  simply  to  the  more 
diluted  condition  of  the  blood,  though  possibly  the  introduction  of  the 
fluid  into  the  alimentary  canal  may  cause  a  dilation  of  the  splanchnic 
or  renal  areas,  either  directly  or  indirectly,  in  a  reflex  manner  by  the 
help  of  the  vagi.  This  observation  refers  of  course  to  inert  fluids  such 
as  water  ;  the  introduction  of  various  substances  in  an  ordinary  meal 
may  affect  the  flow  of  urine  in  other  ways  to  be  presently  stated. 

Secretion  by  the  Renal  Epithelium. 

While  thus  recognizing  the  importance  of  the  relations  of  the 
flow  of  urine  to  blood-pressure,  we  must  not  be  led  into  the  error 
of  supposing  that  the  work  of  the  kidney  is  wholly  a  matter  of 


CHAP.   IV.J  RENAL   SECRETION.  415 

filtration.  The  glomerular  mechanism,  so  specially  fitted  for  filtra- 
tion is  after  all  a  small  portion  only  of  the  whole  kidney,  and 
the  epithelium  over  a  large  part  of  the  course  of  the  tubuli  uri/ii/cri 
boars  most  distinctly  the  characters  of  an  active  secreting  epithe- 
lium. These  facts  would  lead  us  a  priori  to  suppose  that  the 
flow  of  urine  is  in  part  the  result  of  an  active  secretion  compar- 
able to  that  of  the  salivary  or  other  glands  which  we  have  already 
studieil.  And  we  have  experimental  evidences  that  such  is 
the  case. 

For  a  flow  of  urine  may  be  artificially  excited  even  when  the 
natural  llovv  has  been  arrested  by  diminution  of  blood-pressure. 
Thus  if,  when  the  urine  has  ceased  to  fiow  in  consequence  of  a 
section  of  the  medulla  oblongata,  certain  substances,  such  as 
urea,  urates,  &c.,  be  injected  into  the  blood,  a  copious  secretion  is 
at  once  set  up.  This  secretion  is  unaccompanied  by  any  rise  of 
blood-pressure  sufticient  to  account  for  the  flow  on  any  filtration 
hypothesis'.  The  most  natural  way  of  explaining  the  phenomena 
is  to  suppose  that  the  presence  of  these  substances  in  the  blood 
excites  the  renal  epithelium  to  an  unwonted  activity,  causing  them 
to  pour  into  the  mterior  of  the  tubules  a  copious  secretion,  just  as 
the  presence  of  pilocarpin  in  the  blood  will  cause  the  salivary  cells 
to  pour  forth  their  secretion  into  the  lumen  of  their  ducts.  This 
explanation  of  course  supposes  that  in  the  ordinary  state  of  the 
blood  the  epithelium  cells  are  quiescent,  or  at  least  do  not  secrete 
any  appreciable  quantity  of  fluid,  otherwise  the  mere  interference 
of  the  pressure  arrangements  due  to  the  section  of  the  medulla 
oblongata  would  not  arrest  the  flow.  And  indeed  this  abnormal 
activity  of  the  epithelium  is  in  itself  no  sufticient  proof  that  any 
large  part  of  the  normal  flow  of  urine  is  due  to  a  normal  action  of 
the  epithelium.  There  remains  however  the  fact  that  in  the 
absence  of  the  usual  blood-pressure,  a  considerable  quantity  of 
fluid  may,  under  the  influence  of  suitable  stimuli,  be  secreted 
into  the  interior  of  the  tubuli  uriniferi  and  so  give  rise  to  even  a 
copious  flow  of  urine.  And  this  warns  us  to  be  cautious  in 
acceptnig  in  all  cases,  even  in  the  instances  quoted  previously,  a 
vaso-motor  explanation  of  increased  or  dnninished  activity  of 
tiie  kidney,  simple  and  straightforward  as  that  explanation  may 
seem.  It  may  be  that  in  some  cases  what  appjars  to  be  simply 
a  vaso-motor  action  is  after  all  a  direct  action  of  nerves  on 
secreting  cells  accompanied  by  adjuvant  but  not  indispensable 
vascular  changes. 

That  it  is  the  epithelium,  and  not  any  other  portion  of  the 
renal  api)aratus,  which  gives  rise  to  the  flow  of  urine,  when  urea 
'  Cf.  Ustimowitsch,  Ludwig's  Arbciten,  1870,  p.  199. 


41 6  ACTIVITY  OF   THE   EPITHELIUM.         [BOOK   II. 

or  urates  are  injected  into  the  blood-vessels  of  animals  in  which 
the  normal  secretion  has  been  arrested  by  section  of  the  medulla, 
appears  probable  from  the  following  considerations. 

Heidenhain  ^  has  brought  forward  distinct  experimental  evi- 
dence that,  with  regard  to  one  substance  at  least,  the  renal 
epithelium  does  exercise  a  distinct  secreting  activity,  independent 
of  and  distinct  from  the  relations  of  blood-pressure.  Into  the 
veins  of  animals  in  which  the  urinary  flow,  had  been  arrested  by 
section  of  the  spinal  cord  below  the  medulla,  Heidenhain  injected 
the  sodium  suiphindigotate,  or  so-called  indigo-carmine.  By 
killing  the  animals  at  appropriate  times  and  examining  the  kidneys 
microscopically  and  otherwise,  he  was  enabled  to  ascertain  that 
the  pigment  so  injected  passed  from  the  blood  into  the  renal 
epithelium,  and  from  thence  into  the  channels  of  the  tubules, 
wliere  it  was  precipitated  in  a  solid  form.  There  being  no  stream 
of  fluid  through  the  tubules,  owing  to  the  arrest  of  urmary  flow  by 
means  of  the  preliminary  operation,  the  pigment  travelled  very 
little  way  down  the  interior  of  the  tubules,  and  remained  very 
much  where  it  was  cast  out  by  the  epithelium  cells.  There  Were 
no  traces  whatever  of  the  pigment  having  passed  by  the  glo- 
meruli ;  and  the  cells  which  could  be  seen  distinctly  to  take  up 
and  eject  it,  were  those  lining  such  portions  of  the  tubules  {viz. 
the  so-called  secreting  tubules,  intercalated  tubules  and  portions 
of  the  loops  of  Henle)  as  from  their  microscopic  features  have 
been  supposed  to  be  the  actively  secreting  portions  of  the  entire 
tubules.  By  varying  the  quantity  injected  and  the  time  which 
was  allowed  to  elapse  between  the  injection  and  subseqiient  in- 
speciion,  Heidenhain  was  able  to  trace  the  material  step  by  step 
into  the  cells,  out  of  the  cells  into  the  interior  of  the  tubules, 
and  for  some  little  distance  along  the  tubules.  The  advantage  of 
the  absence  of  a  large  flow  of  urine  is  obvious  •  had  this  been 
present,  the  pigment  would  have  been  rapidly  carried  off  imme- 
diately that  it  issued  from  the  cells  into  the  interior  of  the  tubules. 
One  observation  he  made  of  a  peculiarly  interesting  character. 
After  injecting  a  certain  quantity  of  pigment,  and  allowing  such 
a  time  to  elapse  as  he  knew  from  previous  experiments  would 
suffice  for  the  passage  of  the  material  through  the  epithelium  to 
be  pretty  well  completed,  he  injected  a  second  quantity.  He 
found  that  the  excretion  of  this  second  quantity  was  most  incom- 
plete and  imperfect.  It  seemed  as  if  the  cells  were  exhausted  by 
their  previous  efforts,  just  as  a  muscle  which  has  been  severely 
tetanized  will  not  respond  to  a  renewed  stimulation. 

As  far  as  indigo-carmine  is  concerned,  then,  we  are  justified 
^  Pfliiger's  Archiv,  ix.  (1874)  i. 


CHAP.   IV.]  KKNAL   SECRETION.  417 

in  speaking  of  an  active  though  not  a  formative  secretion,  an  ex- 
rrelion  rather  than  a  secretion,  by  means  of  the  renal  epithelium, 
the  cells  taking  up  the  pigment  out  of  the  blood  and  passing  it 
on  into  the  channel  of  the  tubules. 

This  activity  of  the  epithelium  cells  cannot  be  shewn  in  the 
same  way  with  natural  constituents  of  urine,  with  urea  or  urates, 
for  instance,  as  with  indigo-carmine,  for  the  very  reason  that  these 
substances  give  rise,  as  we  have  seen,  to  such  a  copious  flow  of 
urine  that  the  contents  of  the  tubules  are  swept  away,  and  the 
evidences  of  local  activity  arc  thus  lost.  But  we  have  evidence 
of  another  kind  that  the  urea  which  appears  in  urine  passes  from 
the  blood  into  the  ret.al  ducts  through  the  epithelium  of  the 
iul)uli  uriniferi  and  not  through  the  glomeruli  ;  and  if  so  it  can 
hardly  be  doubted  that  the  flow  of  urine  which  follows  the  in- 
jection of  urea  into  the  blood-vessels  after  section  of  the  medulla, 
is  caused  by  the  efforts  of  the  epithelium  to  carry  off  from  the 
blood  the  excess  of  urea,  though  why  the  passage  of  urea  should 
thus  necessitate  the  concomitant  secretion  of  fluid  while  the 
indigo-carmine  is  carried  through  without  any  such  accompanying 
fluid  is  at  present  a  matter  of  obscurity.  The  evidence  that  urea 
passes  by  the  epithelium  of  the  tubules  and  not  by  the  glomeruli 
is  of  the  following  kind. 

In  the  amphibia,  the  kidney  has  a  double  vascular  supply  ;  it 
receives  arterial  blood  from  the  renal  artery,  but  there  is  also 
poured  into  it  venous  blootl  from  another  source.  The  femoral 
vein  divides  at  the  top  of  the  thigh  into  two  branches,  one  of 
which  runs  along  the  front  of  the  abdomen  to  meet  its  fellow  in 
the  middle  line  and  form  the  anterior  abdominal  vein,  while  the 
other  passes  to  the  outer  border  of  the  kidney  and  branches  in 
the  substance  of  that  organ,  forming  the  so-called  renal  portal 
system.  Now  the  glomeruli  are  supplied  exclusively  by  the 
branches  of  the  renal  artery,  the  renal  vena  portce  only  serving  to 
form  the  capillary  plexus  around  the  tubuli  uriniferi,  where  its 
branches  are  joined  by  the  efferent  vessels  of  the  glomeruli. 
From  this  it  is  obvious  that  if  the  renal  artery  be  tied,  the 
blood  is  shut  off  entirely  from  the  glomeruli,  and  the  kidney  by 
this  simple  operation  is  transformed  into  an  ordinary  secreting 
gland  devoid  of  any  special  filtering  mechanism  ;  and  actual 
observation  of  the  kidney  of  the  newt  has  shewn  that  under  these 
circumstances  there  is  no  reflux  from  the  capillary  network  sur- 
rounding the  tubuli  back  to  the  glomeruli.  Nussbaum '  has 
ingeniously  made  use  of  such  a  kidney  to  ascertain  what  sub- 
stances are  excreted  by  the  glomeruli,  and  what  by  the  tubuli 
'  Pfliiger's  Arckiv,  xvi.  (1877)  p.  139;  xvii.  (1S7S)  p.  5S0. 
F.  P.  27 


41 8  ACTIVITY   OF   THE   EPITHELIUM.         [BOOK    II. 

in  some  other  part  of  their  course.  He  finds  that  sugar,  peptones, 
and  albumin,  which  injected  into  the  blood  readily  pass  through 
the  untouched  kidney  and  appear  in  the  urine,  do  not  pass 
through  a  kidney  the  renal  arteries  of  which  have  been  tied. 
These  substances  therefore  are  excreted  by  the  glomeruli.  Urea 
on  the  other  hand,  injected  into  the  blood,  gives  rise  to  a  secretion 
of  urine,  when  the  renal  arteries  are  tied  ;  this  substance  there- 
fore is  secreted  by  the  epithelium  of  the  tubules,  and  in  being  so 
secreted  gives  rise  at  the  same  time  to  a  flow  of  water  through 
the  cells  into  the  interior  of  the  tubuli.  When  indigo-carmine  is 
injected  after  ligature  of  renal  arteries,  no  urine  is  found  in  the 
bladder,  but  the  pigment  can  be  traced,  as  in  Heidenhain's 
experiment,  through  the  epithelium  of  the  secreting  portions  of 
the  tubuli. 

Nussbaum'  also  made  an  interesting  experiment  on  the  artificial 
production  of  albuminuria  in  the  frog.  The  renal  arteries  being  tied, 
an  injection  of  urea  (i  cm.  of  a  lo  p.  c.  solution)  into  the  blood  gave 
rise  to  a  flow  of  urine  which  was  free  from  albumin.  Upon  loosing  the 
ligatures  so  as  to  reestablish  the  flow  of  blood  through  the  glomeruli, 
the  urine  at  once  became  albuminous.  The  arrest  of  the  circulation 
through  the  glomeruli  had  damaged  the  capillary  walls,  and  so  allowed 
the  passage  through  them  into  the  interior  of  the  Malpighian  capsules 
of  the  natural  proteids  of  the  blood,  which  in  a  normal  condition  of  the 
capillaries  cannot  effect  such  a  passage.  The  injury  however  was 
temporary  only  ;  in  a  short  time  the  capillary  walls  were  restored  to 
health  and  the  urine  ceased  to  be  albuminous. 

Experimental  evidence  then  justifies  the  conception  which  the 
structure  of  the  kidney  led  us  to  adopt.  The  secretion  of  urine 
by  the  kidney  is  a  double  process.  It  is  partly  a  process  of 
filtration,  whose  object  is  to  remove  as  rapidly  as  possible  a 
quantity  of  water  from  the  body,  and  this  part  of  the  work  of  the 
kidney  is  directly  dependent  on  blood-pressure.  It  is  also  how- 
ever a  process  of  active  secretion  by  the  epithelium  of  the  tubuli, 
and  this  part  of  the  work  of  the  kidney  is,  in  an  indirect  manner 
only,  dependent  on  blood-pressure.  Both  processes  may  give 
ri-se  to  a  discharge  of  water  from  the  blood,  and  both  may  give 
rise  to  the  presence  of  the  solid  constituents  of  the  urine,  in 
solution  in  that  water.  In  the  first  process  the  discharge  of 
water  is  the  primary  object,  and  the  solid  matters  which  escape 
at  the  same  time  are  of  secondary  importance ;  in  the  second 
process  the  excretion  of  the  solid  substance  is  the  primary  object, 
and  the  accompanying  water  of  secondary  importance,  and  indeed 
sometimes  absent.      The   first   process   is   governed    (mainly  at 

'  Op.  cit. 


CHAP.    IV.]  RKNAL   SECRETION.  4I9 

least)  by  the  vaso-motor  nervous  system  ;  the  second  process  is 
excited,  as  far  as  we  know  at  present,  by  substances  in  the  blood 
acting  directly  as  chemical  stimuli  to  the  epithelium  ;  but  future 
researches  may  disclose  the  existence  of  a  secretory  nervous 
mechanism  analogous  to  that  of  other  secretory  glands. 

Future  investigations  must  determine  what  constituents  of  the  urine 
besides  urea,  urates,  &c.  arc  thrown  into  the  urine  by  the  active 
secretory  process,  and  what  simply  pass  by  filtration  througli  the 
glomeruli.  The  whole  subjct  t  of  diuretics  requires  to  be  studied 
afresh  by  the  help  of  Nussbauni's  method. 

One  consiileration,  of  quite  secondary  importance  in  the 
glands  which  have  been  previously  studied,  acquires  great  pro- 
minence when  the  kidney  is  being  studied.  In  studying  the 
pancreas  and  gastric  glands,  we  concluded  without  much  discus- 
sion that  the  zymogen  and  pepsinogen  were  formed  in  the 
epithelium  cells  ;  for  no  great  manufacture  of  these  substances  is 
going  on  in  other  parts  of  the  body.  The  kidney  however  is 
emphatically  an  excreting  organ  :  its  great  function  is  to  get  rid 
of  substances  produced  by  the  activity  of  other  tissues  ;  its  work 
is  not  to  form  but  to  eject.  There  can  be  no  doubt,  to  i)Ut 
forward  a  strong  instance,  that  with  regard  to  urea  it  would  be 
absurd  to  suppose  that  the  whole  series  of  changes  from  the  pro- 
teid  condition  to  the  urea  stage  is  carried  on  by  the  kidney.  But 
there  still  remains  the  question.  Are  any  of  the  stages  carried  on 
in  the  kidney,  and  if  so,  what?  Is  the  secreting  activity  of  the 
renal  epithelium  contincd,  as  was  suggested  in  our  early  remarks 
on  secretion,  p.  266,  to  picking  out  the  already  formed  urea  from 
the  blood?  Or  does  the  secreting  cell  of  the  tubule  receive  from 
the  blood  some  antecedent  of  urea,  and  in  the  laboratory  of  its 
protoplasm  convert  that  antecedent  of  urea  into  urea  itself?  and 
if  so,  what  is  that  antecedent  wiiich  comes  to  the  kidney  in  the 
blood  of  the  renal  artery  ?  And  so  with  many  other  of  the 
urinary  constituents. 

In  order  to  complete  our  study  of  renal  activity,  this  question 
ought  to  be  considered  now  ;  but  for  many  reasons  it  will  be  more 
convenient  to  defer  the  matter  to  the  succeeding  chapter,  in 
which  we  deal  with  the  metabolic  events  of  the  body  in  general. 

Sec.  3.     Micturition. 

The  urine,  like  the  bile,  is  secreted  continuously  ;  the  flow 
may  rise  and  fall,  but,  in  health,  never  absolutely  ceases  for  any 
length  of  time.  The  cessation  of  renal  activity,  the  so-called 
suppression  of  urine,  entails  speedy  death.     The  minute  streams 

27 — 2 


420  MICTURITION.  [BOOK  II. 

passing  continuously,  now  more  rapidly  now  more  slowly,  along 
the  collecting  and  discharging  tubules,  are  gathered  into  the  renal 
pelvis,  whence  the  fluid  is  carried  along  the  ureters  by  the  peri- 
staltic contractions  of  the  muscular  walls  of  those  channels  (see 
p.  119)  into  the  urinary  bladder.  When  a  ureter  is  divided  in  an 
animal,  and  a  cannula  inserted,  the  urine  may  be  observed  to  flow 
from  the  cannula  drop  by  drop,  slowly  or  rapidly  according  to  the 
rate  of  secretion.  In  the  urinary  bladder,  the  urine  is  collected, 
its  return  into  the  ureters  being  prevented  by  the  oblique  valvular 
nature  of  the  orifices  of  those  tubes,  and  its  discharge  from 
thence  in  considerable  quantities  is  effected  from  time  to  time  by 
a  somewhat  complex  muscular  mechanism,  of  the  nature  and 
working  of  which  the  following  is  a  brief  account.  The  in- 
voluntary muscular  fibres  forming  the  greater  part  of  the  vesical 
walls  are  arranged  partly  in  a  more  or  less  longitudinal  direction 
forming  the  so-called  detrusor  urince,  and  partly  in  a  circular 
manner,  the  circular  fibres  being  most  developed  round  the  neck 
of  the  bladder  and  forming  there  the  so-called  sphincter  vesicce. 
After  it  has  been  emptied  the  bladder  is  contracted  and  thrown 
into  folds ;  as  the  urme  gradually  collects,  the  bladder  becomes 
more  and  more  distended.  The  escape  of  the  fluid  is  however 
prevented  by  the  resistance  offered  by  the  elastic  fibres  of  the 
urethra  which  keep  the  urethral  channel  closed.  Some  maintain 
that  a  tonic  contraction  of  the  sphincter  vesicae  aids  in  or  indeed 
is  the  chief  cause  of  this  retention.  When  the  bladder  has 
become  full,  we  feel  the  need  of  making  water,  the  sensation 
being  heightened  if  not  caused  by  the  trickling  of  a  few  drops 
of  urine  from  the  full  bladder  into  the  urethra.  We  are 
then  conscious  of  an  effort;  during  this  effort  the  bladder  is 
thrown  into  a  long  continued  contraction  of  an  obscurely  peri- 
staltic nature,  the  force  of  which  is  more  than  sufficient  to 
overcome  the  elastic  resistance  of  the  urethra,  and  the  urine 
issues  in  a  stream,  the  sphincter  vesicae,  if  it  act  as  a  sphincter, 
being  at  the  same  time  relaxed  after  the  fashion  of  the  sphincter 
ani.  In  its  passage  along  the  urethra,  the  exit  of  the  urine  is 
forwarded  by  irregularly  rhythmic  contractions  of*  the  bulbo- 
cavernosus  or  ejaculator  urinae  muscle,  and  the  whole  act  is 
further  assisted  by  pressure  on  the  bladder  exerted  by  means  of 
the  abdominal  muscles,  very  much  the  same  as  in  defaecation.^ 

The  continuity  of  the  sphincter  vesicee  with  the  rest  of  the  circular 
fibres  of  the  bladder  suggests  that  it  probably  is  not  a  sphincter,  but 
that  its  use  lies  in  its  contracting  after  the  rest  of  the  vesical  fibres, 
and  thus  finishing  the  evacuation  of  the  bladder.  On  the  other  hand, 
the  fact  that  the  neck  of  the  bladder  can  withstand  a  pressure  of  20 


CHAP.    IV. J  RENAL   SECRETION.  42I 

inches  of  water  so  long  as  the  bladder  is  governed  by  an  intact  spinal 
cord,  but  a  pressure  of  6  inches  only  when  tlie  hunbar  spinal  cord  is 
destroyed  or  tlie  vesical  nerves  are  severed,  affords  very  strong 
evidence  in  favour  of  the  view  that  the  o|;stru.:tion  at  the  neck  of  the 
bladder  to  the  exit  of  urine  depends  on  some  tonic  muscular  con- 
traction maintained  by  a  reflex  .or  automatic  action  of  the  lumbar 
spinal  cord". 

Micturition  therefore  seems  at  first  sight,  and  especially  when 
we  ajipeal  to  our  own  consciousness,  a  purely  voluntary  act.  A 
voluntary  efcitort  throws  the  bladder  into  contractions,  an  accom- 
panying voluntary  effort  throws  the  ejaculator  and  abdominal 
muscles  also  into  contractions,  and  the  resistance  of  the  urethra 
being  thereby  overcome  the  exit  of  the  urine  naturally  follows. 
If  we  adojjt  the  view  of  a  sphincter  vesicae,  we  have  to  add  to 
the  above  simple  statement  the  supposition  that  the  will,  while 
causing  the  detrusor  urince  to  contract,  at  the  same  time  lessens 
the  tone  of  the  sphincter,  probably  by  inhibiting  its  centre  in  the 
lumbar  cord. 

There  are  two  facts  however  which  prevent  the  acceptance  of 
so  simple  a  view.  In  the  first  place  Golt/,^  has  shewn  that  quite 
normal  micturition  may  take  place  in  a  dog  in  which  the  lumbar 
region  of  the  spinal  cord  has  been  completely  separated  by  section 
from  the  dorsal  region.  In  such  a  case  there  can  be  no  exercise 
of  volition,  and  the  whole  process  appears  as  a  reflex  action. 
When  the  bladder  is  full  (and  otherwise  apparently  under  the 
circumstances  the  act  fails)  any  slight  stimulus,  such  as  sponging 
the  anus  or  slight  pressure  on  the  abdominal  walls,  causes  a  com- 
plete act  of* micturition  ;  the  bladder  is  entirely  emptied,  and  the 
stream  of  urine  towards  the  end  of  the  act  undergoes  rhythmical 
augmentations  due  to  contractions  of  the  ejaculator  urinaj.  These 
facts  can  only  be  interpreted  on  the  view  that  there  exists  in  tiie 
lumbar  cord  (of  the  dog)  a  micturition  centre  capable  of  being 
thrown  into' action  by  appropriate  afferent  impulses,  the  action  of 
the  centre  being  such  as  to  cause  a  contraction  of  the  walls  of 
the  bladder  and  of  the  ejaculator  urinns,  and  possibly  at  the  same 
time  to  susi)end  the  tone  of  the  sphincter  vesicae.  Similar  in- 
stances of  rellex  micturition  have  been  observed  in  cases  of 
paralysis  from  disease  or  injury  of  the  spinal  cord;  and  involun- 
tary micturition  is  common  in  children,  as  the  result  of  irritation 
of  the  pelvis  and  genital  organs,  or  of  emotions.  In  the  atiult 
too,  emotions,  or  at  least  sensory  impressions,  may  in  a  rellex 
manner  be  the  cause  of  micturition.  In  such  cases  we  may  fairly 
suppose  that  the  centre  in  the  lumbar  cord  is  ati'ected  by  afferent 

'  Cf.  Ott,  Joum.  PItys.  II.  (1S79)  p.  59. 
"  Pfliigcr's  Archiv,  Vlll.  (1S74)  474. 


422  MICTURITION.  [BOOK  If. 

impulses  descending  from  the  brain.  And  this  leads  us  to  the 
conception  that  when  we  make  water  by  a  conscious  effort  of  the 
will,  what  occurs  is  not  a  direct  action  of  the  will  on  the  muscular 
walls  of  the  bladder,  but  tliat  impulses  started  by  the  will  descend 
from  the  brain  after  the  fashion  of  afferent  impulses  and  thus  in 
a  reflex  manner  throw  into  action  the  micturition  centre  in  the 
lumbar  spinal  cord.  Nor  is  this  view  negatived  by  the  fact  that 
paralysis  of  the  bladder,  or  rather  inability  to  make  water  either 
voluntarily  or  in  a  reflex  manner,  is  a  common  symptom  of  spinal 
disease  or  injury.  Putting  aside  the  cases  in  which  the  reflex  act 
is  not  called  forth  because  the  appropriate  stimulus  has  not  been 
applied,  the  failure  in  micturition  under  these  circumstances  may 
be  explained  by  supposing  that  the  shock  of  the  spinal  injury  or 
some  extension  of  the  disease  has  rendered  the  lumbar  centre 
unable  to  act. 

In  the  second  place,  in  cases  of  urethral  obstruction,  where 
the  bladder  cannot  be  emptied  when  it  reaches  its  accustomed 
fulness,  the  increasing  distension  sets  up  fruitless  but  powerful 
contractions  of  the  vesical  walls,  contractions  which  are  clearly 
involuntary  in  nature,  which  wane  or  disappear,  and  return  again 
and  again  in  a  completely  rhythmic  manner,  and  which  may  be 
so  strong  and  powerful  as  to  cause  great  suffering.  It  seems  that 
fibres  of  the  bladder,  like  all  other  muscular  fibres,  have  their 
contractions  augmented  in  proportion  as  they  are  subjected  to 
tension  (see  p.  90).  Just  as  a  previously  quiescent  ventricle  of 
a  frog's  heart  may  be  excited  to  a  rhythmic  beat  by  distending 
its  cavity  with  blood,  so  the  quiescent  bladder  is  excited,  by  the 
distention  of  its  cavity,  to  a  peristaltic  action  which  in  normal 
cases  is  never  carried  beyond  a  first  effort,  since  with  tha't  the 
bladder  is  emptied  and  the  stimulus  is  removed,  but  in  cases  of 
obstruction  is  enabled  clearly  to  manifest  its  rhythmic  nature. 

The  so-called  incontinence  of  urine  in  children  is  in  reality 
an  easily  excited  and  frequently  repeated  reflex  micturition. 
In  cases  of  spinal  disease  another  form  of  incontinence  is  com- 
mon. The  bladder  becoming  full,  but,  owing  to  a  failure  in  the 
mechanism  of  voluntary  or  reflex  micturition,  being  unable  to 
empty  itself  by  a  complete  contraction,  a  continual  dribbling  of 
urine  takes  place  through  the  urethra,  the  fulness  of  the  bladder 
being  sufficient  to  overcome  the  elastic  resistance,  or  the  tone  of 
the  sphincter  suffering  from  the  spinal  affection  and  becoming 
permanently  inhibited. 

The  latter  view  seems  improbable,  and  there  is  no  satisfactory 
evidence  that  intrinsic  contractions  of  the  bladder  do  not  occur  in 
these  cases. 


CHAr.    IV.]  RKNAL   SIX'KKTION.  423 

According  to  Sokowin",  contractions  of  the  bladder  may  be  brought 
about  in  cats  in  a  reflex  manner  by  two  mechanisms  :  by  one  in  which  the 
centre  hes  in  the  spinal  cord  at  about  the  region  of  the  fourth  lumbar 
vertebra  and  the  sacral  nerves  supply  both  the  afferent  and  efferent 
tracts,  and  anotlier  in  which  llic  inferior  mesentcri :  ganglion  serves  as 
a  centre,  the  afferent  and  efferent  fibres  passing  along  the  branches 
connecting  that  ganglion  with  the  hypogastric  plexus.  He  finds  in 
fact  that  the  inferior  mcsenteri:  ganglion  will  a:t  as  a  centre  for  reflex 
a.tion.  When  the  history  of  the  submaxillary  ganglion  (p.  267)  is 
borne  in  mind,  such  a  conclusion  will  naturally  be  received  with  great 
caution. 

'  Hofmann  u.  Schwalbe,  Jahresberichte,  vi.  (1877)  Abth.  ill.  p.  87. 


CHAPTER  V. 

THE  METABOLIC  PHENOMENA  OF  THE  BODY. 

We  have  followed  the  food  through  its  changes  in  the  alimentary 
canal,  and  seen  it  enter  into  the  blood,  either  directly  or  by  the 
intermediate  channel  of  the  chyle,  in  the  form  of  peptone  (or 
otherwise  modified  albumin),  sugar  (lactic  acid),  and  fats,  accom- 
panied by  various  salts.  We  have  further  seen  that  the  waste 
products  which  leave  the  body  are  urea,  carbonic  acid  and  salts. 
We  have  now  to  attempt  to  connect,  together  the  food  and  the 
waste  products ;  to  trace  out  as  far  as  we  are  able  the  various 
steps  by  which  the  one  is  transformed  into  the  other,  and  to 
inquire  into  the  manner  in  which  the  energy  set  free  in  this 
transformation  is  distributed  and  made  use  of 

The  master  tissues  of  the  body  are  the  muscular  and  nervous 
tissues ;  all  the  other  tissues  may  be  regarded  as  the  servants  of 
these.  And  we  may  fairly  presume  that  besides  the  digestive 
and  excretory  tissues  which  we  have  already  studied,  many  parts 
of  the  body  are  engaged  either  in  further  elaborating  the  com- 
paratively raw  food  which  enters  the  blood,  in  order  that  it  may 
be  assimilated  with  the  least  possible  labour  by  the  master 
tissues,  or  in  so  modifying  the  waste  products  which  arise  from 
the  activity  of  the  master  tissues  that  they  may  be  removed 
from  the  body  as  speedily  as  possible.  There  can  be  no  doubt 
that  manifold  intermediate  changes  of  this  kind  do  take  place 
in  the  body  ;  but  our  knowledge  of  the  matter  is  at  present  very 
imperfect.  In  one  or  two  instances  only  can  we  localize  these 
metabolic  actions  and  speak  of  distinct  metabolic  tissues.  In  the 
majority  of  cases  we  can  only  trace  out  or  infer  chemical  changes 
without  being  able  to  say  more  than  that  they  do  take  place  some- 
where ;  and  in  consequence,  perhaps  somewhat  loosely,  speak  of 
them  as  taking  place  in  the  blood. 


CHAP,    v.]  NUTRITION'.  425 

Sec.   I.     Met.abolic  Tissues. 
The  History  of  Glycogen. 

The  best-known  and  most  carefully  studied  example  of 
metabolic  activity  is  the  formation  at"  glycogen  in  the  hepatic 
cells. 

Claude  Bernard',  in  studying  the  history  of  sugar  in  the 
economy,  was  led  to  compare  the  relative  quantities  of  sugar  in 
the  portal  and  hepatic  veins,  expecting  to  find  that  the  sugar 
possibly  diminished  in  the  passage  uf  the  blood  through  the  liver; 
he  was  astonished  to  discover  that,  on  the  contrary,  the  quantity 
was  vastly  increased.  He  found,  and  any  one  can  make  the 
observation,  that  when  an  animal  living  under  ordinary  conditions 
is  killed,  the  hepatic  blood  after  death  contains  a  considerable 
amount  of  sugar  (grape-sugar),  even  when  there  is  little  or  none  in 
the  portal  blood  ;  moreover  a  simple  aqueous  infusion  of  the  liver 
is  rich  in  sugar.  Not  only  so,  but  the  sugar  continues  to  be  pre- 
sent in  the  liver  when  all  blood  has  been  washed  out  of  the  organ 
by  a  stream  of  water  driven  through  the  portal  vein,  and  goes  on 
increasing  in  amount  for  some  hours  after  death.  Only  one  inter- 
pretation of  these  facts  is  possible  ;  so  far  from  the  liver  destroying 
or  converting  the  sugar  brought  to  it  by  the  portal  vein,  it  is 
clearly  a  source  of  sugar ;  the  hepatic  tissue  e\ndently  contains 
some  substance  capable  of  giving  rise  to  the  presence  of  sugar. 
Bernard  further  found  that  when  the  liver  was  removed  from  the 
body  immediately  after  death,  and,  after  being  divided  into  small 
pieces,  was  thrown  into  boiling  water,  the  infusion  or  decoction 
contdned  \tr\  little  sugar,  and  that  the  small  quantity  which  was 
present  did  not  increase  even  when  the  decoction  was  allowed  to 
stand  for  some  time.  The  decoction,  however,  was  peculiarly 
opalescent,  indeed  milky  in  appearance ;  whereas  the  decoction 
of  a  liver  which  had  been  allowed  to  remain  exposed  to  warmth 
for  some  time  after  death,  before  being  boiled,  and  which  accord- 
ingly contained  a  large  amount  of  sugar,  was  quite  clear.  On 
adding  saliva,  or  other  amylolytic  ferment,  to  the  opalescent, 
sugarless,  or  nearly  sugarless,  decoction  and  exposing  it  to  a  gentle 
warmth  (35° — 40°),  the  opalescence  disappeared  ;  the  fluid  became 
clear,  and  was  then  found  to  contain  a  considerable  quantity  of 
sugar.  Here  again  the  explanation  was  obvious.  The  opalescence 
of  the  decoction  of  boiled  liver  is  due  to  the  presence  of  a  body 
which  is  capable  of  being  converted  by  the  action  of  a  ferment 
into  grape-sugar,  and  is  therefore  of  the  nature  of  starch.     At  the 

'  Notr<j.  Fond,  du  Foie,  1853. 


426  .      GLYCOGEN.  [BOOK   II. 

moment  of  death  the  liver  must  contain  a  considerable  quantity 
of  this  substance,  which  after  death  becomes  gradually  converted 
into  sugar,  either  through  the  action  of  some  amylolytic  ferment 
present  in  the  hepatic  cells  or  in  the  blood  of  the  hepatic  vessels 
or  possibly  by  some  special  agency.  Hence  the  post-mortem 
appearance  of  a  continually  increasing  quantity  of  sugar.  By  pre- 
cipitating the  opalescent  decoction  with  alcohol,  by  boiling  the 
precipitate  with  alcohol  containing  potash,  whereby  the  proteid 
impurities  clinging  to  it  were  destroyed,  and  by  removing  adherent 
fats  by  ether,  Bernard  was  able  to  obtain  this  sugar-producing  or 
glycogenic  substance  in  a  pure  state  as  a  white  amorphous  powder, 
with  a  composition  of  C^HjoOg,  and  therefore  evidently  a  kind 
of  starch.  Its  most  striking  differences  from  ordinary  starch  were 
that  it  gave  a  deep  red  and  not  a  blue  colour  with  iodine,  and  that 
when  dissolved  in  water  it  formed  a  milky  fluid.  He  gave  to  it 
the  name  oi  glycogen. 

Since  Bernard's  discovery  glycogen  has  been  recognised  as  a 
normal  constituent,  variable  in  quantity,  of  hepatic  tissue  both  in 
vertebrate  and  invertebrate  animals.  That  it  is  present  in  the 
hepatic  cells,  and  not  simply  contained  in  the  hepatic  blood,  is 
shewn  by  the  fact  that  it  remains  in  the  liver  after  all  blood  has 
been  washed  out  of  that  organ.  It  has  also  been  found  in  the 
placenta,  in  muscle,  white  corpuscles,  testes,  brain,  and  in  other 
situations  \  the  tissues  of  the  embryo  at  an  early  stage,  especially 
before  the  liver  has  become  functionally  active,  are  particularly 
rich  in  it. 

Formation  and  Uses  of  Glycogen.  The  amount  of 
glycogen  present  in  the  liver  of  an  animal  at  any  one  time  is 
largely  dependent  on  the  amount  and  nature  of  the  food  previously 
taken  '.  When  all  food  is  withheld  from  an  animal,  the  glycogen 
in  the  liver  diminishes,  rapidly  at  first,  but  more  slowly  after- 
wards. Even  after  some  days'  starvation  a  small  quantity  is  fre- 
quently still  found  ;  but  in  rabbits,  at  all  events,  the  whole  may 
eventually  disappear. 

If  an  animal,  after  having  been  starved  until  its  liver  may  be 
assumed  to  be  free  or  almost  free  from  glycogen,  be  fed  on  a  diet 
rich  in  carbohydrates  or  on  one  consisting  exclusively  of  carbo- 
hydrates, the  liver  will  in  a  short  time  (one  or  two  days)  be  found 
to  contain  a  very  large  quantity  of  glycogen.  Obviously  the  pre- 
sence  of  carbohydrates   in   food   leads   to   an   accumulation    of 

^  MacDonnel,  Xat.  Hist.  Rev,  1863,  p.  541.  Tscherinoff,  Moleschott's 
Unterstich.  X.  (1870)  226.  Dock,  Pfliiger's  Arckiv,'\'.  (1872)  571.  Menng, 
Pfliiger's  Archiv,  XIV.  (1877)  274.      Cf.  also  Pavy  on  Diabetes. 


CHAP,   v.]  NUTRITION.  427 

glycogen  in  the  liver;  and  this  is  true  both  of  starch  and  of 
dextrin  and  of  the  various  forms  of  sugar,  cane,  grape  and  milk 
sugar.  The  effect  may  be  quite  a  rapid  one,  for  glycogen  has 
been  found  in  the  liver  in  considerable  quantity  within  a  few  hours 
after  the  introduction  of  sugar  into  the  alimentary  canal  of  a 
starving  animal'. 

If  an  animal,  similarly  starved,  be  fed  on  an  exclusively  meat 
diet  a  certain  amount  of  glycogen  is  found  in  the  liver.  This 
appears  to  be  especially  the  case  with  dogs  (probably  with  other 
carnivorous  animals  also) ;  and  in  his  earlier  researches  Bernard 
was  led  to  regard  the  constant  jiresence  of  glycogen  in  the  livers 
of  dogs  fed  on  meat,  as  an  important  indication  of  the  conversion 
within  the  body  of  nitrogenous  into  non-nitrogenous  material. 
But  in  the  first  place,  the  quantity  of  glycogen  thus  stored  up  in 
the  liver  as  the  result  of  a  meat  diet,  is  much  less  than  that  which 
follows  upon  a  carbohydrate  diet ;  and  in  the  second  place,  ordi- 
nary meat,  especially  horse-flesh  on  which  dogs  are  ordinarily 
fed,  contains  in  itself  a  certain  amount  either  of  glycogen  or  some 
form  of  sugar.  Moreover  when  animals  are  fed  not  on  moat  but 
on  purified  protcid,  such  as  fibrin,  casein  or  albumin,  the  quantity 
of  glycogen  in  the  liver  becomes  still  smaller,  though  according  to 
most  observers  remaining  greater  than  during  starvation.  We 
may  infer  therefore  that  part  of  the  glycogen  which  appears  in  the 
liver  after  a  mjat  diet  is  really  due  to  carbohydrate  materials  pre- 
sent in  the  meat.  Part  however  would  appear  to  be  the  result  of 
the  simple  proteid  food  ;  but  in  this  respect  proteid  falls  very 
far  short  indeed  of  carbohydrate  material. 

With  regard  to  fats,  all  observers  are  agreed  that  these  lead 
to  no  accumulation  of  glycogeja  in  the  liver;  an  animal  fed  on 
an  exclusively  fatty. diet  has  no  more  glycogen  in  its  liver  than  a 
starving  animal. 

Hence  of  the  three  great  classes  of  food-stuffs,  the  carbo- 
hydrates stand  out  prominently  as  the  substances  which  taken  as 
food  lead  to  an  accumulation  of  glycogen  in  the  liver.  Confining 
our  attention  for  the  present  to  this  chief  source  of  glycogen,  the 
(.question  naturally  presents  itself,  What  is  the  exact  mode  in  which 
the  carbohydrates  of  food  thus  give  rise  to  an  excess  of  glycogen  in 
the  hepatic  cells  ?  Is  it  that  they  reaching  the  liver  as  sugar  in 
the  portal  blood  (we  may  accept  for  the  present  purpose  at  all 
events  the  view  that  the  carbohydrates  are  converted  into  sugar 
and  absorbed  by  the  portal  vein)  are  in  some  direct  manner 
reconverted  into  the  starch-like  glycogen  and  deposited  in  the 
hepatic  cells  ? 

'  Dock,  op.  cit. 


428  GLYCOGEN.  [BOOK  II. 

Or,  has  the  hepatic  glycogen  quite  a  dififerent  origin,  being 
formed  in  the  hepatic  cells  out  of  the  breaking  up  of  their 
protoplasm,  and  being  carried  thence  and  consumed  in  some 
way  or  other  as  the  needs  of  the  economy  for  carbohydrate 
material  demand,  so  that  the  excess  which  appears  in  the  liver 
after  an  amylaceous  diet  is  due  to  the  fact  that  the  carbohydrates 
taken  .'j  food  cover  the  necessary  expenditure  and  prevent  any 
demand  being  made  on  the  hepatic  store  ? 

Before  we  attempt  however  to  answer  these  questions  we  must 
turn  aside  to  consider  another  question,  What  becomes  of  the 
hepatic  glycogen  during  life?  Is  it  reconverted  little  by  litde 
into  sugar  which,  passing  into  the  blood  of  the  hepatic  veins,  is 
oxidized  or  otherwise  made  use  of,  or  is  it  in  the  hepatic  cells 
converted  into  some  more  complex  substance,  it  may  be  fat  or 
some  other  body  ? 

The  view  that  glycogen  is  converted  into  fat  is  based  chiefly 
on  the  fact  that,  as  we  shall  see  later  on,  the  carbohydrates  of  the 
food  are  undoubtedly,  in  some  way  or  other,  a  source  of  the  fat 
of  the  body,  that  a  large  quantity,  frequently  a  very  large  quantity, 
of  fat  is  found  in  the  hepatic  cells,  and  that  the  quantity  of  fat 
present  seems  to  be  increased  by  such  diets  as  naturally  increase 
the  glycogen  in  the  liver.  But  we  shall  have  occasion  to  point 
out  that  the  direct  conversion  of  carbohydrates  into  fat  is  at  least 
disputed  ;  and  no  one  has  yet  been  able  even  to  suggest  the  way  in 
which  glycogen  could  be  converted  into  fat.  In  the  absence  of 
more  direct  and  exact  information  the  discussion  as  to  the  fate 
of  the  hepatic  glycogen  has  been  made  to  turn  chiefly  on  the 
question,  whether  there  is  evidence  of  the  reconversi(.'n  normally, 
during  life,  of  the  glycogen  into  sugar,  whether  the  blood  of  the 
hepatic  vein  contains  in  life  more  sugar  than  that  of  the  portal 
vein.  Bernard  both  in  his  earlier  and  later  '  researches  maintained 
that  the  blood  of  the  hepatic  vein  under  normal  conditions  was 
richer  in  sugar  than  the  blood  of  the  portal  vein  or  indeed  of  any 
other  part  of  the  vascular  system  ;  and  this  he  regarded  as  an 
indication  that  the  liver  is  always  engaged  in  discharging  a  certain 
quantity  of  sugar  into  the  hepatic  veins.  Bernard's  views  have 
been  accepted  by  many  observers.  On  the  other  hand  Pavy  was 
the  first  to  maintain  that  the  blood  in  the  hepatic  vein,  if  care  be 
taken  to  keep  the  animal  in  a  perfectly  normal  condition,  contains 
no  more  sugar  than  does  the  blood  of  the  right  auricle  or  of  the 
portal  vein,  and  indeed  that  the  liver  itself,  if  examined  before 
atiy  post-mortem  changes  have  had  time  to  develope  themselves,  is 

'  Leijons  sur  le  Diabite,  iSy/- 


CHAP.    V.J  iNUTklTlON.  429 

absolutely  free  from  sugar;  in   this  he  has    been    supported  by 
'J'schcrinotT,  and  others. 

Now  the  ([uantitalive  determination  of  su^^'ar  in  blood  whichever 
procedure  be  adopted  is  open  to  many  sources  of  error".  And 
when  the  ([uantity  of  blooil  which  is  continually  flo\\ing  through 
the  liver  is  taken  under  consideration,  it  is  obvious  that  an  amount 
of  sugar,  which  in  the  specimen  of  blood  taken  for  examination 
fell  within  the  limits  of  errors  of  observation,  njigiu  when  multi- 
l)lied  by  the  whole  (piantity  of  blood,  and  by  the  number  of 
times  the  blood  passe(l  through  the  liver  in  a  certain  time,  reach 
dimensions  quite  surticient  to  account  for  the  conversion  into 
sugar  of  the  whole  of  the  glycogen  prjsent  in  the  liver  at  any 
given  time.  Hence  we  may  safely  conclude  that  the  comparative 
analyses  of  hepatic  and  portal  blootl,  if  they  do  not  of  themselves 
prove  that  the  liver  is  either  continually  or  at  intervals  converting 
some  of  its  glycogen  into  sugar  and  ilischarging  this  sugar  into  the 
general  system,  are  at  least  not  sufficiently  trustworthy  to  disprove 
the  possibility  of  such  a  discharge  of  sugar  being  one  of  the  normal 
functions  of  the  liver. 

Normal  hepatic  blood  was  obtained  by  Pavy,  by  means  of  an 
ingenious  cathcteris:ition.  He  introduced  through  the  jugular  vein, 
into  the  superior,  and  so  into  the  inferior  vena  cava,  a  long  catheter, 
constru.ted  in  such  a  manner  that  he  could  at  pleasure  plug  up  the 
vena  cava  below  the  cmbouchcment  of  the  hepatic  veins,  and  draw 
blood  exclusively  from  the  latter  ;  or  vice  versa. 

In  the  absence  of  positive  evidence  we  are  thrown  back  upon 
theoretical  considerations ;  and  undoubtedly  there  are  many  a 
priori  arguments  which  iTiay  be  urged  in  support  of  the  view 
that  the  glycogen  is  deposited  in  the  liver  simply  as  a  store  of 
carbohydrate  material,  being  accumulated  whenever  amylaceous 
material  is  abundant  in  the  alimentary  canal,  and  being  converted 
into  sugar  and  so  drawn  upon  by  the  body  at  large  to  meet  the 
general  demands  for  carbohydrate  material  during  the  intervals 
when  food  is  not  being  taken.  And  we  can  accept  this  view 
without  being  able  to  say  definitely  what  becomes  of  the  sugar 
thus  thrown  into  the  hepatic  blood.  Bernard  believed  that  this 
sugar  underwent  an  immediate  and  direct  oxidation,  but  we  have 
already  dwelt  (p.  366)  on  the  objections  to  such  a  view.  It  is 
sufficient  for  us  at  the  present  to  admit  that  the  sugar  is  made  use 
of  in  some  way  or  other. 

Now,  many  considerations  lead  us  to  believe  that  a  certain 
average  composition  is  necessary  for  that  great   internal  medium 

1  Cf.  Flugge,  Zt.f,  Biol,  Xlll.  p.  133. 


430  GLYCOGEN.  [BOOK   IL 

the  blood,  in  order  that  the  several  tissues  may  thrive  upon  it  to 
the  best  advantage,  one  element  of  that  composition  being  a 
certain  percentage  of  sugar.  It  would  appear  that  all  or  some 
at  least  of  the  tissues  are  continually  drawing  upon  the  blood  for 
sugar,  and  that  hence  a  certain'  supply  must  be  kept  up  to  meet 
this  demand  :  on  the  other  hand  an  excess  of  sugar  in  the  blood 
itself  would  be  injurious  to  the  tissues.  And  as  a  matter  of  fact 
we  find  the  quantity  of  sugar  in  blood-  is  small  but  constant ;  it 
remains  about  the  same  when  food  is  being  taken  as  in  the  interval 
between  meals.  If  sugar  be  in  too  large  quantities  or  too  rapidly 
injected  into  the  jugular  vein  a  certain  quantity  appears  in  the 
urine,  indicating  an  effort  of  the  system  to  throw  off  the  excess 
and  bring  back  the  blood  to  its  average  condition.  Such  a  con- 
stant percentage  of  sugar  would  obviously  be  provided  for  or  at 
least  largely  assisted  by  the  liver  acting  as  a  structure  where  the 
sugar  might  at  once  and  without  much  labour  be  packed  away  in 
the  form  of  the  less  soluble  glycogen,  when,  as  during  an  amy- 
laceous meal,  sugar  is  rapidly  passing  into  the  blood,  and  there  is 
a  danger  of  the  blood  becoming  loaded  with  far  more  sugar  than 
is  needed  for  the  time  being;  and  it  maybe  incidentally  noted 
that  a  larger  quantity  of  sugar  may  be  injected  into  the  portal 
than  into  the  jugular  vein  without  any  reappearing  in  the  urine, 
apparently  because  a  large  portion  of  it  in  such  a  case  is  retained 
in  the  liver  as  glycogen.  When  on  the  other  hand  sugar  ceases 
to  pass  into  the  blood  from  the  alimentary  canal,  the  average 
percentage  in  the  blood  is  maintained  by  a  reconversion  into 
sugar,  and  its  passage  into  the  hepatic  blood,  of  the  glycogen 
previously  stored  up. 

Moreover,  this  view,  that  the  glycogen  of  the  liver  is  a  reserve 
fund  of  carbohydrate  material,  is  strongly  supported  by  the  analogy 
of  the  migration  of  starch  in  the  vegetable  kingdom.  We  know 
that  the  starch  of  the  leaves  of  a  plant,  whether  itself  having 
previously  passed  through  a  glucose  stage  or  not,  is  normally  con- 
verted into  sugar,  and  carried  down  to  the  roots  or  other  parts, 
where  it  frequently  becomes  once  more  changed  back  again  into 
starch. 

A  similar  ai-gument  maybe  drawn  from  the  relations  of  glycogen  to 
muscle.  So  frequently  is  glycogen  found  in  muscle  that  it  may  be 
regarded  as  an  ordinary  though  not  an  invariable  constituent  of  that 
tissue  ;  indeed  it  may  almost  be  considered  as  a  constituent  of  all  con- 
tractile tissues.  According  to  Chandelon^  it  is  increased  in  quantity 
when  the  nerve  of  the  muscle  is  divided,  and  the  muscle  thus  brought 
into  a  state  of  quiescence.     On  the  other  hand  it  diminishes  or  even 

'  Pfluger's  Archiv,  XIII.  (1876)  p.  626. 


CHAP,  v.]  NUTKiriON.  43' 

disippcars  when  the  muscle  has  been  tctanizcd  or  has  entered  into 
Seo  mortis'.  IJut  mnscles  may  be  fully  alive  and  contracfle  from 
Sh  -lyco-en  is  wholly  ab,ent^  From  this  we  may  mfer,  not  that 
elvc^^n  Ts'^a  nccess.rv  chemical  factor  of  muscular  metabolism, 
but  °hSt  it  can  furni.h  materials  for  that  mctabo hsm,  and  hence  is 
store  up  n  the  n.uscle  so  as  to  be  ready  at  hand  for  use.  1  he  fact 
observed  bv  \Veiss3  that  in  starving'  ''cns  -lycouen  is  stdl  found  m  he 
pectoal  n,uscles  after  it  has  disappeared  from  the  hyer,  ^u^.^S^^ted  tha 
this  secondary  and  special  store  in  the  muscle  was  from  us  funct.ona 
n  no'lnnce  more  constant  than  what  maybe  considered  as  the  general 
arprnmr  store  in  the  liver  ;  but  Luchsinger*  states  that  this  .s  a 
toecia  feature  of  the  fow-l's  pectoral  muscles;  from  other  musrles 
.  gWn  may  disappear  long  before  the  store  m  the  l.ver  has  been 
exhausted. 

But  if  we  answer  the  question,  what  becomes  of  the  hepatic 
glvco-en  by  accepting  the  view  that  the  hepatic  glycogen  is  smiply 
store  glycogen,  waiting  to  be  converted  into  sugar  little  by  httle  as 
the  needs  of  the  economy  demand,  and  not  glycogen  on  its  way 
to  take  part,  through  the  agency  of  the  hepatic  protoplasm,  in  the 
formation  of  some\iiore  complex  compound,  such  as  fat,  we  have 
prepared  the  way  for  an  answer  to  tlie  question  with  which  we 
started,  in  what  is  the  exact  origin  of  the  hepatic  glycogen  ?     tor 
if  such  be  the  purpose  of  glycogen,  it  is  only  reasonable  to  suppose 
that  the  glycogen  which  makes  its  appearance  in  the  liver  alter 
an  amylaceous  meal  arises  from  a  direct  conversion  of  the  grape- 
su-ar  carried  to  the  liver  by  the  portal  vein,  the  sugar  becoming 
throu"h  some  action  of  the  hepatic  protoplasm  dehydrated  into 
starcir  by  a  process  the  reverse  of  that  by  which  in  the  alimentary 
canal    starch    is    hydrated    into  sugar  through  the  action  of  the 
salivary  and  pancreatic  ferments.     Vegetable  protoplasm  can  un- 
doubtedK' convert  both  starch  into  sugar  and  , sugar  into  starch  ; 
and  there  are  no  a  priori  arguments  or  positive  facts  which  would 
lead  us  to  suppose  that  the  activity  of  animal  protop  asm  cannot 
accomplish  the  latter  as  well  as  the  former  of  these  changes.     At 
the  same  time  it  must  be  remembered  that  this  view  does   not 
preclude  the  possibility  of  glycogen,  in  the  absence  of  a  supply  ot 
sn-ar   from  tlie   port  .1  blood,  as  for  instance  when  glycogen  is 
stored  up  in  the  liver  as  the  result  of  purely  proteid  food,  being 
formed  in  other  ways. 

It  has  been  stated  s  that  glycerine  introduced  into  the  alimentary 

»  Na-^'^e    rnii^'er's   Archiv,  ll.  (1869)  p.  97;  xiv.  (1877)  p.  484. 
»  Luchsinger.'Pfluijer's  ^;r/;/-j,  xviii.  (1S78)  p.  472. 

1   Wiener  Sitzungsbcncht,m.i)i,^\'6l\).  \.^^-       '^n-     j. 

s  Weiss,    Wiener  ^itzungsbericht,   lid.   67    (1873).      Luchsinger,     Pfluger's 
Arehiv,  vill.  (1874)  2S9. 


432  GLYCOGEN.  [BOOK   II. 

canal  gives  rise  to  an  increase  of  glycogen  in  the  liver  ;  and  Luchsinger  ' 
finds  that  in  an  animal,  the  liver  of  which  has  been  proved  to  be  free 
from  glycogen  by  the  examination  of  an  excised  lobule,  glycogen 
appears  in  the  liver  within  an  hour  of  the  glycerine  being  given  :  this 
seems  undoubtedly  to  shew  that  hepatic  glycogen  may  be  formed  in 
other  ways  than  by  the  direct  dehydration  of  sugar.  It  is  difficult  to 
suppose  that  glycerine  can  be  directly  converted  into  glycogen  ;  and  it 
has  been  urged  that  in  this  case  the  glycerine,  by  becoming  oxidized, 
causes  a  saving  in  the  expenditure  of  carbohydrate  material,  and  thus 
indirectly  leads  to  an  accumulation  of  glycogen.  But  this  view  is 
opposed  by  the  fact  that  lactic  acid,  to  which  we  should  readily  turn  as 
being  eminently  oxidizable,  and  therefore  eminently  calculated  to  save 
carbohydrate  expenditure,  does  not  lead  to  any  similar  storing  up  of 
glycogen.  And  Luchsinger^  states  that  glycerine  injected  in  consider- 
able quantities  under  the  skin,  and  absorbed  from  the  subcutaneous 
tissue,  leads  to  no  increase  of  glycogen  ;  so  that  the  glycogen  which 
appears  in  the  liver  when  glycerine  is  introduced  into  the. alimentary 
canal  would  seem  to  come  from  some  conversion  of  the  glycerine  either 
in  the  alimentary  canal  or  when  it  reaches  the  hepatic  cells  by  the 
portal  blood ;  difficult  as  any  chemical  conception  of  that  conversion 
may  be. 

The  statements  with  regard  to  the  glycogenic  infliTence  of  gelatine 
are  conflicting  3.  The  balance  of  evidence  is  perhaps  in  favour  of  gly- 
cogen being  stored  up  in  the  liver  as  the  result  of  a  diet  of  pure 
gelatine.  This  would  indicate  a  transformation  into  glycogen  of  the 
non-nitrogenous  moiety  resulting  from  that  splitting  up  of  gelatine  of 
which  we  shall  have  to  speak  later  on. 

In  general,  glycogen,  having  as  far  as  we  know  in  all  cases  the  same 
characters,  appears  to  be  formed  in  varying  quantity  when  any  of  the 
following  substances  are  given  as  food  :  5,tarch,  dextrin,  sugar  (cane, 
grape,  fruit,  milk),  inulin,  lichenin,  arbutin,  glycerine,  albumin,  fibrin, 
casein,  gelatine.  It  appears  not  to  be  formed  by  fat,  inosit,  quercite, 
mannite,  erythrite. 

The  question  may  be  asked.  How  is  it  possible  for  the  glyco- 
gen, which  at  the  temperature  of  the  body  is  so  readily  converted 
into  sugar  by  the  action  of  ferments,  to  remain  as  glycogen  in  the 
presence  of  the  ferment  which,  as  we  know  from  post-mortens 
changes,  exists  in  the  hepatic  tissue  ?  We  can  only  answer  that 
the  solution  of  this  problem  is  of  the  same  kind  as  that  of  the 
problems,  why  blood  does  not  clot  in  the  living  blood-vessels,  why 
the  living  muscle  does  not  become  rigid,  and  why  the  living 
stomach  or  pancreas  does  not  digest  itself.  It  might  be  added, 
bearing  in  mind  the  history  of  the  fibrin  ferment,  that  we  have 
no   proof   that   such   an   amylolytic   ferment   does   exist   in   the 

^  Pfliiger's  Archiv,  xviii.  (1878)  p.  472. 
=  Pfliiger's  Archiv,  VIII.  (1874)  289. 

3  Bernard,  MacDonnel,  Luchsinger,  Mering,  i7/.  «V.    V^olShtrg,  Zt.  f,  Biol., 
XII.  p.  266. 


CHAP,   v.]  NUTRITION.  433 

living  hepatic  cells.  It  is  possible  that  the  ferment  which  can  be 
extracted  after  death  only  makes  its  appearance  as  the  result  of 
clianges  which  have  taken  place  in  the  protoplasm  of  the  hepatic 
cells. 

If  as  Seegen  states  (see  p.  437)  the  sugar  formed  by  the  liver  isiruc 
grape-sugar  while  that  produced  by  the  action  of  ordinary  amylolytic 
ferments  is  another  though  allied  kind  of  sugar,  the  formation  of 
sugar  in  the  first  case  must  be  regarded  as  a  peculiar  and  complex 
process. 

It  is  clear  that  the  glycogen  is  contained  in  the  hepatic  cells  ;  but  it 
is  by  no  means  certain  that  it  exists  there  in  what  may  be  called  a  free 
state.  The  fact  that  under  llie  mi  ;roscopc  the  hepatic  cells  give  with 
iodine  the  colour  reaction  of  glycogen,  is  no  proof  of  the  glycogen 
being  free.  It  has  been  described  as  sometimes  occurring  in  granules  ; 
but  this,  if  ever,  is  certainly  not  always  its  condition.  It  is  worthy  of 
notice  th:U  all  the  means  adopted  to  extract  glycogen  from  a  tissue  are 
such  as  would  readily  decompose  unstable  complex  compounds.  If  we 
advance  the  view  that  the  glycogen  of  the  hepatic  protoplasm  does 
not  exist  as  an  independent  budy,  simply  mixed  with  the  other  proto- 
plasmic constituents,  but  is  loosely  connected  with  other  (possibly 
proteid)  substances  as  part  of  a  very  complex  tompound,  few  facts 
would  be  found  opposing,  and  many  supporting,  such  a  view. 

Diabetes.  Natural  diabetes  is  a  disease  characterized  by  the 
appearance  of  a  large  quantity  of  sugar  in  the  urine.  Into  the 
pathology  of  the  various  forms  of  this  disease  it  is  impossible  to 
enter  here  ;  but  a  temporary  diabetes,  the  appearance  for  a  while 
of  a  large  quantity  of  sugar  in  the  urine,  may  be  artificially  pro- 
duced in  animals  in  several  ways.  If  the  medulla  oblongata  of  a 
well-fed  rabbit  be  punctured  in  the  region  which  we  have  previously 
described  (p.  21S)  as  that  of  the  vaso-motor  centre  (the  area 
marked  out  by  Eckhard  as  the  diabetic  area  agreeing  very  closely 
with  that  defined  by  Owsjannikow  as  the  vaso-motor  area),  though 
the  animal  need  not  necessarily  be  in  any  other  way  obviously 
affected  by  the  operation,  its  urine  will  be  found,  in  an  hour  or 
two,  or  even  less,  to  contain  a  considerable  quantity  of  sugar,  and 
to  be  increased  in  amount.  A  little  later  the  quantity  of  sugar 
will  have  reached  a  maximum,  after  which  it  declines,  and  in  a 
day  or  two,  or  even  less,  the  urine  will  be  again  perfectly  normal. 
'I'lie  better  fed  the  animal,  or,  more  exactly,  tiie  richer  in  glycogen 
the  liver  at  the  time  of  the  operation,  the  greater  the  amount  of 
sugar.  If  the  animal  be  previously  starved  so  tliat  the  liver 
contains  little  or  no  glycogen,  the  urine  will  after  the  operation 
contain  little  or  no  sugar.  It  is  clear  that  the  urinary  sugar  of 
tliis  form  of  artificial  diabetes  comes  from  the  glycogen  of  the 
liver.  The  puncture  of  the  medulla  causes  such  a  change  in  the 
F.  V.  28 


434  DIABETES.  [book   II. 

liver  that  the  previously  stored-up  glycogen  disappears,  and  the 
blood  becomes  loaded  with  sugar,  much  if  not  all  of  which  passes 
away  by  the  urine.  In  the  absence  of  any  proof  to  the  contrary, 
we  may  assume  that  in  this  form  of  artificial  diabetes  the  glycogen 
previously  present  in  the  liver  becomes  converted  into  sugar,  just 
as  we  know  that  it  does  become  so  converted  by  post-mortem 
changes.  The  glycogenic  function  of  the  liver  is  therefore  subject 
to  the  influence  of  the  nervous  system,  and  in  particular  to  the 
influence  of  a  region  of  the  cerebro-spinal  centre  which  we  already 
know  as  the  vaso-motor  centre,  or  at  least  of  a  part  of  that  region. 
The  path  of  the  influence  may  be  traced  along  the  cervical  spinal 
cord  (and  not  along  the  vagi,  though  the  roots  of  these  nerves  lie 
so  close  to  the  diabetic  spot),  as  far  down  as  (in  rabbits)  the  level 
of  the  third  or  fourth  dorsal  vertebra',  or  even  a  little  lower,  from 
the  spinal  cord  to  the  first  thoracic  ganglion,  and  from  thence  to 
the  liver  by  some  channel  or  channels  at  present  undetermined. 
We  cannot  at  present  define  clearly  the  nature  of  that  influence. 
We  cannot  say  whether  the  temporary  diabetes  is  a  simple  effect 
of  dilation  of  the  hepatic  arteries  which  accompanies  the  diabetic 
puncture  or  of  some  direct  action  of  the  nerves  on  the  metabolic 
activity  of  the  hepatic  protoplasm. 

According  to  Eckhard^  the  phenomena  are  those  of  irritation,  and 
not  of  the  siinple  withdrawal  of  any  accustomed  nervous  influence. 
He  states  that  while  mechanical  injury  of  the  first  thoracic  ganglion 
(see  Fig.  37)  will  produce  diabetes,  no  such  effect  is  produced  if  the 
ganglion  be  carefully  removed,  or  if  its  connections  with  the  spinal 
cord  or  with  the  remainder  of  the  thoracic  chain  be  completely 
divided. 

Cyon  and  Aladoff^,  on  the  contrary,  regard  the  whole  matter- as 
one  of  simple  loss  of  vascular  tone.  They  state  that  the  diabetic 
puncture  produces  dilation  of  the  small  branches  of  the  hepatic 
artery,  from  injury  to  the  corresponding  portion  of  the  general  vaso- 
motor centre,  and  accordingly  find,  in  opposition  to  Eckhard,  that 
simple  division  of  the  nervous  path,  removal  of  the  first  thoracic 
ganglion,  or  division  of  certain  (variable)  nerves  proceeding  from  it, 
produces  diabetes  equally  well  as  irritation  of  the  ganglion.  Eckhard 
found  that  simple  section  of  the  splanchnic  nerves  not  only  did  not 
produce  diabetes  but  even  prevented  its  occurrence  when  performed 
previously  to  the  diabetic  puncture.  On  the  hypothesis  that  the 
phenomena  in  question  are  those  of  irritation  and  not  of  paralysis, 
this  fact  would  seem  to  shew  that  the  splanchnics  serve  as  the 
channels  by  which  the  impulses  set  up  in  the  medulla,  thoracic  gan- 
glion, &c.,  reach  the  liver.     Cyon  and  Aladoff  however  regard  the 

'  Eckhard,  Beitrdge,  VIII.  (1877)  p.  79. 

'^  Beitrdge,  IV.  (1869)  I  ;  vil.  i, 

3  Bull.  Acad..  Imp.  Set.  St.  Peter sb.,  xvi,  (1871)  p.  308. 


CHAP,    v.]  NUTRITION.  435 

absence  of  diabetes  after  simple  section  of  the  splanchnics  as  a  proof 
that  the  vasomotor  fibres  conGcrned  in  the  matter  pass  to  the  hver  by 
some  other  cli.mnel  than  the  splanchnics  ;  and  they  explain  the 
preventive  influence  of  previous  section  of  the  splanchnics,  by  sup- 
posinj^  that  this  operation,  l)y  withdrawing'  a  lar>;c  ciuantity  of  blood 
into  the  abdominal  org.ms,  prevents  the  effects  of  the  dilation  of  the 
comparatively  small  hepatic  artery  from  manifesting,'  tiiemselves.  For 
accordini^  to  them,  it  is  not  the  total  quantity  of  blood,  but  the  rela- 
tive proportion  of  arterial  blood  reaching  the  liver,  which  determines 
the  appe.lrance  of  the  sugar. 

Simple  section  of  the  spinal  cord  (in  rabbits)  sometimes  does  and 
sometimes  does  not  produce  diabetes,  and  in  all  cases  the  effect 
appears  rapidly  and  soon  disappears.  Complete  section  of  the  spinal 
cord  at  any  height  down  to  the  level  of  the  third  or  fourth  dorsal 
vertebra  renders  the  diabetic  puncture  ineffe-ctual',  and  prevents  the 
diabetes  of  morphia  poisoning  from  being  developed.  Section  of  the 
vagi  may  produce  a  very  slight  and  passing  diabetes,  but  stimulation 
of  t!ie  central  end  of  either  vagus  may  give  rise,  apparently  by  reflex 
excitation  of  the  medullary  centre,  to  a  marked  quantity  of  sugar  in 
the  urme.  The  diabetic  puncture  is  in  no  way  interfered  with  by 
previous  section  of  both  vagi. 

Artificial  diabetes  is  also  a  prominent  symptom  of  urari  posion- 
ing.  This  is  not  due  to  the  artificial  respiration,  which  is  had 
recourse  to  in  order  to  keep  the  urarized  animals  alive  ;  because, 
thou.i^h  disturbance  of  the  respiratory  functions  sufficient  to 
interfere  with  the  hepatic  circulation  may  produce  sugar  in  the 
urine,  artificial  respiration  may  be  carried  on  without  any 'sugar 
making  its  appearance.  Moreover,  it  is  seen  in  frogs,  in  which 
respiration  can  be  satisfactorily  carried  on  without  any  pulmonary 
respiratory  movements. 

A  very  similar  diabetes  is  seen  in  carbonic  oxide  poisoning ; 
and  is  one  of  the  results  of  a  sufficient  dose  of  morphia  or  of 
amyl  nitrite. 

According  to  Duck%  sugar  appears  in  the  urine  of  urarized  mammals, 
even  when  they  are  starving  and  presumably  contain  no  glycogen  in 
their  livers.  If  this  be  so,  urari  diabetes  must  have  quite  a  different 
causation  from  puncture  diabetes  ;  but  Winogradoff^  found  no  sugar 
in  the  urine  of  curarizcd  frogs  from  which  the  livers  had  been  removed, 
and  S;iikows'<y*  found  that  in  mammals  after  arsenic  poisoning  urari 
did  not  pro'luce  diabetes,  shewing  that  if  in  urari  poisoning  the  sugar 
does  not  come  from  the  liver  but  from  the  muscles,  arsenic  has  a  like 
effect  in  preventing  the  accumulation  of  glycogen  in  the  latter  as  in  the 
former. 

»  Eckliard,  Britrii^c-,  Vill.  p.  79. 

»  I'fluger's  Archiv,  V.  (1S72)  p    71. 

3  Virchow's /f /-fZ/jz/,  XXVII.  (1863)  p.  533. 

*  Cenlrbt.  med.  IVrx.  1865,  p.  769. 

28—2 


43^  DIABETES.  [BOOK   II. 

Eckhard^  found  that  morphia  diabetes  was,  like  the  puncture 
diabetes,  prevented  by  section  of  the  splanchnics  or  by  section  of  the 
spinal  cord  above  the  level  of  the  third  or  fourth  dorsal  vertebra. 
The  drug  appears  therefore  to  act  through  the  medullary  diabetic 
centre. 

The  subcutaneous  injection  of  glycerine  prevents  (but  not  in  all 
cases,  and  not  always  effectually)  the  appearance  of  diabetes  after  the 
puncture^  or  after  morphia  poisoning.  The  reason  of  this  is  not  at 
present  clear.     The  urine  at  the  same  time  becomes  bloody. 

The  injection  of  glycogen  in  sufficient  quantity  into  the  blood 
gives  rise  in  the  urine  not  only  to  sugar  but  to  a  much  larger  quantity 
of  a  substance  identical  apparently  with  Briicke's  achroodextrin  3. 

There  can  be  no  doubt  that  in  diabetes,  arising  from  whatever 
cause,  the  sugar  appears  in  the  urine  because  the  blood  contains 
more  sugar  than  usual.  The  system  can  only  dispose  (either  by 
oxidation,  or  as  seems  more  probable  in  other  ways)  of  a  certain 
quantity  of  sugar  in  a  certain  time.  Sugar  injected  into  the  jugular 
vein  reappears  in  the  urine,  whenever  the  injection  becomes  so 
rapid  that  the  percentage  of  sugar  in  the  blood  reaches  a  certain 
(low)  limit.  Sugar  in  the  urine  means  an  excess  of  sugar  in  the 
blood.  How  in  natural  diabetes  that  excess  arises,  we  have  at 
present  no  facts  to  shew  ;  but  it  is  extremely  probable  that  the 
sources  of  the  excess  may  be  various,  and  hence  that  several 
distinct  varieties  of  diabetes  may  exist.  In  one  among  many 
points,  the  clinical  history  of  diabetes  throws  light  on  the 
possible  sources  of  glycogen.  While  in  many,  especially  of  the 
less  severe  cases  of  diabetes,  withdrawal  of  all  amylaceous  food  is 
followed  by  a  disappearance  of  sugar  from  the  urine,  in  many 
instances  the  sugar  continues  to  be  discharged  even  though  the 
diet  be  perfectly  free  from  carbohydrates  ;  and  in  many  other  cases 
the  sugar  in  the  urine  is  far  in  excess  of  that  taken  as  food.  In 
these  cases  the  sugar  must  have  some  non-amylaceous  source;  from 
this  we  infer  that  glycogen  also  may  have  a  similar  origin  ;  and  the 
fact  that  the  urea  is  increased  (and  that  too  in  some  cases  in  ratia 
with  the  sugar4)  in  diabetes,  suggests  that  the  sugar  may  arise  from 
proteids  which  have  been  split  up  into  a  nitrogenous  (urea)  and  a 
non-nitrogenous  moiety. 

It  has  been  shewn  by  Wickham  Legg,  and  confirmed  by  Von 
Wittich,  that  ligature  of  the  bile-ducts  causes  a  disappearance  of 
glycogen  from  the  liver,  and  tTiat  (four  or  six  days)  after  the  ligature 
the  diabetic  puncture  produces  no  diabetes.  This  cannot  be  explained 
by  supposing,  as  Von  Wittich  does,  that  the  glycogen  formed  previous 

'   Op.  cit.  "  Luchsinger,Pfluger'.s  Archiv,  XI.  (1875)  p.  502. 

3  Boehm  and  Hoffmann,  Archiv  Exp.  Path.,  VII,  (1877)  P-  4^9- 
*  Ringer,  Med.   Chir.   Trans.,  XLlir. 


CHAP,   v.]  NUTRITION.  437 

to  the  operation  is  rapidly  converted  into  sugar  by  a  ferment  developed 
in  tlic  stagnmt  bile,  for  no  sugar  appears  in  the  urine'.  VV'c  are 
rather  led  to  infer  tiiat  the  formation  of  the  glycogen  is  prevented  by 
interference  with  the  nutritive  functions  of  the  hepatic  cells. 

y\ccording  to  Secgen-"  the  sugar  wiiich  is  formed  naturally  in  the 
Hvcr  post  mcjrtem  is  true  grape-sugar,  but  that  which  is  artificially 
formed  out  of  glycogen  by  the  action  o*"  ferments  (salivary,  pancreatic, 
&c.),  like  the  sugar  similarly  formed  out  of  starch,  is  not  true  grape- 
sugar  but  some  allied  form  (sec  p.  241).  It  is  possible  that  the 
phenomena  of  some  kinds  of  diabetes  may  depend  on  the  liver 
foniiing  an  abnormal  kind  of  j-ugar,  which  cannot  undergo  the  changes 
which  are  untiergone  by  the  normal  kind  or  kinds  usually  present  in 
tiic  body.  Such  an  explanation  of  diabetes  was  suggested  long  ago, 
but  has  not  hitherto  been  supported  by  suflicicnt  evidence,  and  further 
investigation  is  still  necessary  before  any  opinion  can  be  passed  as  to 
its  value. 

Various  suggestions  have  been  made  with  reference  to  the  chemical 
ways  in  which  cirbohydrate  material  might  make  its  appearance 
during  hepatic  metabolism  It  has  been  pointed  out,  for  instance, 
that  proteid  material  might  be  split  up  into  glycogen  and  the  bile- 
acids,  or  that  ghcin  might  be  split  up  into  urea  and  glucose 
(4C2HSNO2  =  2CH4N.,0  +  CcH,„Oo).  But  these  views  must  at 
present  be  considered  as  suggestions  only. 

The  History  of  Fat.     Adipose  Tissue. 

Of  all  the  tissues  of  the  body  adipose  tissue  is  the  most  fluctu- 
ating in  bulk ;  within  a  very  short  space  of  time  a  large  amount  of 
adipose  tissue  may  disappear,  and  within  an  almost  equally  short 
time  the  quantity  present  in  a  body  may  be  several  times  multiplied. 
Histological  inquiries  teach  us  that  when  an  animal  is  fattening  the 
minute  drops  or  specks  of  fat  normally  present  in  certain  con- 
nective-tissue corpuscles  are  seen  to  increase  in  number,  the  pror 
toplasm  enlarging  at  the  same  time.  As  these  specks  increase  they 
coalesce  into  drops,  w  hich  by  similar  coalescence  form  larger  drops, 
until,  the  protoplasm  first  ceasing  to  increase  and  then  diminishing, 
the  original  connective-tissue  corpuscle  is  transformed  into  a  fat- 
cell,  with  a  remnant  only  of  protoplasm  gathered  round  the  nucleus 
and  forming  an  imperfect  envelope  round  the  enlarged  contents. 
When,  on  the  contrary,  an  animal  is  fasting,  the  fat  seems  in  some 
way  to  escape  from  tlie  cell,  which  it  may  leave  as  an  empty  bag 
collapsed  around  the  nucleus.  These  facts  point  to  the  conclusion 
that  the  fat  of  adipose  tissue  is  not  simply  and  mechanically 
collected  in  the  cell,  but  is  formed  by  the  active  agency  of  the 

'  KU!z  .ind  K.  Frcriclis,   Tfliigcr's  Archiv,  XIII.  (1S76)  \i.  460. 
,     "  I'fliiger's  .<4r<-/;/'z',  xix.  (1S79)  p.  106. 


438  FAT.  [book   II. 

cell,  being  apparently  the  result  of  a  breaking  up  of  the  protoplasm  ; 
when  formed,  however,  it  appears  to  be  discharged  from  the  cell 
in  a  more  or  less  mechanical  manner,  as  the  needs  of  the  economy 
demand.  And  this  view  is  supported  by  the  fact  that  protoplasm, 
wherever  occurring,  both  during  life  and  after  death  (when  it 
could  not  possibly  be  supplied  with  fat  from  without),  is  subject 
to  fatty  degeneration,  in  which  the  fat  evidently  arises,  in  large 
part  at  least,  from  the  breaking  up  of  proteid  compounds. 

On  the  other  hand,  we  have  traced  the  fats  taken  as  food,  and 
found  that  they  pass  with  comparatively  little  change  from  the 
alimentary  canal  into  the  blood,  either  directly,  or  through  the 
intermediate  passage  of  the  chyle.  We  might  infer  from  this  that 
an  excess  of  fat  thus  entering  the  blood  would  naturally  be  simply 
stored  up  in  the  available  adipose  tissue,  without  any  further 
change,  the  connective-tissue  corpuscles  after  the  fashion  of  an 
amoeba  eating  the  fat  brought  to  them  but  not  digesting  it,  simply 
keeping  it  in  store  till  it  was  wanted  elsewhere. 

Which  of  these  views  is  the  true  one,  or  hovi^  far  are  both  these 
operations  carried  on  in  the  animal  body  ?  In  the  first  place,  it  is 
evident  that  in  an  animal  fattened  on  ordinary  fattening  food,  only 
a  small  fraction  of  the  fat  stored  up  in  the  body  can  possibly  come 
direct  from  the  fat  of  the  food.  Long  ago,  in  opposition  to  the 
views  of  Dumas  and  his  school,  who  taught  that  all  construction 
of  organic  material,  that  all  actual  manufacture  of  protoplasm  or 
even  of  its  organic  constituents,  was  confined  to  vegetables  and 
unknown  in  animals,  Liebig  shewed  that  the  butter  present  in  the 
milk  of  a  cow  was  much  greater  than  could  be  accounted  for 
by  the  scanty  fat  present  in  the  grass  or  other  fodder  she  con- 
sumed. He  also  urged,  as  an  argument  in  the  same  direction, 
that  the  wax  produced  by  bees  is  out  of  all  proportion  to  the 
fat  contained  in  their  food,  consisting  as  this  does  chiefly  of 
sugar.  And  Lawes  and  Gilbert '  have  shewn  by  direct  analysis 
that  for  every  loc^arts  of  fat  in  the  food  of  a  fattening  pig,  472 
parts  were  stored  up  as  fat,  during  the  fattening  period.  It  is 
clear  that  fat  is  formed  in  the  body  out  of  something  which  is 
not  fat. 

There  are  two  possible  sources  of  this  manufactured  fat.  In 
treating  of  digestion  (p.  313),  we  referred  to  the  possibility  of 
digested  carbohydrates  becoming  converted  into  fats  by  the  butyric 
acid  fermentation.  Analogous  ferment-actions  may  similarly 
elaborate  other  fats.  And  there  can  be  no  doubt  that  a  carbo- 
hydrate diet  is  most  efficacious  in  producing  an  accumulation  of 

'  Phil.  Trans.,  i860. 


CFJAr.   v.]  NUTRITION.  439 

fat  in  the  body  Sugar  or  starch,  in  some  form  or  other,  is  always 
a  large  constituent  of  ordinary  fattening  foods. 

Another  source  of  fat  is  to  be  found  in  the  proteids.  We  have 
seen  that  the  urea  of  the  urine  practically  rci^resents  the  whole  of 
the  nitrogen  which  passes  through  the  body.  Now  in  any  given 
quantity  of  urea  the  amount  of  carbon  is  far  less  than  that  found 
in  the  quantity  of  proteid  containing  the  same  amount  of 
nitrogen.  Thus  the  percentage  composition  of  the  two  being 
respectively, 

Carb.n.         Hydrogen.         Oxygen.  Nitrogen.         Sulphur. 

Urea        2000         6"66         2667         4667 

Proteid     53  7-30  2304  15-53  113 

100  grms.  of  urea  contain  about  as  much  nitrogen  as  300  grms  of 
proteid;  but  the  300  grms.  of  proteid  contain  139  grms.  (150  -  20) 
more  carbon  than  do  the  100  grms.  urea.  Hence  the  300  grms,  of 
proteid  in  passing  through  the  body  and  giving  rise  to  100  grms. 
of  urea,  would  leave  behind  139  grms.  of  carbon,  in  some  combi- 
nation or  other ;  and  this  surplus  of  carbon,  if  the  needs  of  the 
economy  did  not  demand  tliat  it  should  be  immediately  converted 
into  carbonic  acid  and  thrown  off  from  the  body,  might  be  deposited 
somewhere  in  the  form  of  fat.  We  have  already  seen,  in  treating 
of  the  action  of  the  pancreatic  juice  (p.  260),  that  there  is  evidence 
of  a  flitty  element  being  thrown  off  from  the  complex  proteid 
compound  in  the  very  process  of  digestion. 

It  is  clear  that  a  construction  of  fat  does  occur  in  the  body 
somewhere.  What  limits  can  we  place  on  the  degree  to  which 
this  construction  is  carried  ?  In  reference  to  this  point  it  is  worthy 
of  notice  that  the  composition  of  fat  varies  in  different  animals. 
The  fat  of  a  man  differs  from  the  fat  of  a  dog,  even  if  both  feed 
on  exactly  the  same  food,  fatty  or  otherwise.  Were  the  fat  which 
is  taken  as  food  stored  up  as  adipose  tissue  direct'ly  and  without 
change,  recourse  being  had  to  other  sources  of  food  for  the  con- 
struction of  fat  only  in  cases  where  the  fat  in  the  food  was  deficient, 
we  should  expect  to  find  that  the  constitution  of  the  fat  of  the 
body  would  vary  greatly  with  the  food.  So  far  from  this  being 
the  case,  Subbotin  '  finds  that  the  fat  of  the  dog  is,  as  far  as  compo- 
sition is  concerned,  almost  entirely  independent  of  the  food,  that 
the  normal  constituents  of  fat  make  their  appearance  as  usual, 
though  some  of  them  may  wliolly  be  absent  in  the  food,  and  that 
abnormal  fats  presented  as  food  are  not  to  be  found  in  the  fat  which 
is  stored  up  in  the  body  as  a  consequence  of  a  large  supply  of  that 
food. 

•  Zt.f.  Biol.,  VI.  (1870)  p.  73. 


440  FAT.  [book  II. 

Subbotin,  after  starving  a  dog  till  he  had  reason  to  think  all  fat  had 
disappeared  from  the  body,  fed  it  largely  on  palm-oil  (containing 
palmitin  and  olein  but  no  stearin)  and  the  very  leanest  meat.  The 
composition  of  the  fat  which  was  stored  up  during  this  diet  is.  shewn 
in  column  2,  the  normal  constitution  of  the  fat  of  a  dog  being  shewn 
in  column  i.  Another  dog,  after  a  similar  removal  of  the  natural  fat 
by  starvation,  was  fed  on  meat  and  a  soap  composed  of  palmitic  and 
stearic  acids.  The  animal  in  this  case  received  no  olein.  Yet  the 
composition  of  his  fat  was  that  given  in  column  3. 


I. 

2. 

3- 

A.              B. 

A. 

B. 

c. 

A.             B. 

Palmitin 

44-87      3972 

50-80 

53'3o 

55-36 

52-80     53"6o 

Stearin 

19-23      32-48 

900 

13-20 

13-24 

13-20     13-40 

Olein 

35-90      27-80 

40-20 

33-50 

30-80 

3400    33-00 

A  signifies  the  subcutaneous,  B  the  mesenteric,  and  C  the  suprarenal 
adipose  tissue. 

Moreover,  when  a  dog  was  fed,  after  a  preliminary  starvation 
period,  with  i  kgm.  of  spermaceti,  of  which  he  was  found  to  absorb  at 
least  800  grms.,  nothing  more  than  a  trace  of  the  spermaceti  was  to 
be  found  in  his  fat. 

Of  course  it  is  quite  possible  that  in  such  cases  as  these, 
though  the  stearin,  or  the  olein,  when  absent  from  the  food,  was  in 
some  way  or  other  constructed  anew,  yet  at  the  same  time  those 
constituents  which  were  present  were  simply  stored  up ;  but  it  is 
also  open  for  us  to  suppose  that  all  the  fat  taken  as  food  was  in 
some  way  or  other  disposed  of,  and  that  all  the  new  fat  which  made 
its  appearance  was  constructed  anew.  And  the  latter  view  is 
supported  by  the  histological  facts  mentioned  above  (p.' 437),  as 
well  as  by  other  considerations,  which  we  shall  presently  have  to 
urge.  At  the  present,  however,  we  may  be  content  with  the 
following  conclusions,  i.  Fat  is  formed  anew  in  the  animal  body. 
2.  The  carbon  elements  of  the  newly-formed  fat  may  be  supplied 
either  from  amylaceous  food,  or  from  the  carbon  surplus  of  proteid 
food,  or  from  fats  taken  as  food  which  are  not  the  natural  con- 
stituents of  the  body  fat.  3.  The  fat  stored  up  appears  as  fat- 
granules  or  drops  deposited  in  the  protoplasm  of  certain  cells,  and 
the  increase  of  the  fat  in  the  cells  is  accompanied  first  by  a  growth, 
and  subsequently  by  a  decay  of  the  protoplasm ;  but  there  is  no 
complete  evidence  to  shew  whether  the  fat-granules  which  appear 
are  simply  deposited  by  the  protoplasm  in  a  more  or  less  me- 
chanical manner,  without  their  forming  an  integral  portion  of  it, 
the  chief  stages  of  the  manufacture  of  the  fat  having  been  gone 
through  elsewhere,  or  whether  they  arise  from  a  breaking  up,  a 
functional  metabolism  of  the  protoplasm  of  the  fat-eell  itself. 


CHAP,   v.]    *  NUTRITION.  4^1 

The  question  touched  on  here  is  one  the  solution  of  which  is 
probibly  still  far  distant.  \Vc  know  that  protoplasm  such  as  that  of 
I'enicilliuni'  can  build  itself  up  out  of  ammonium  tartrate  and 
inor.Li.inio  salts,  and  can  by  a  decomposition  of  itself  give  rise  to  fats 
and  other  bodies ;  and  we  have  every  reason  to  suppose  that  this 
constructive  power  belongs  naturally  to  all  native  protoplasm  wherever 
found.  At  the  same  time,  we  see  that  even  in  Pcnicillium  it  is  of 
advantage  to  offer  to  the  protoplasm  as  food,  substances  such  as  sugar 
and  proteids  (peptone),  which  are,  so  to  speak,  already  on  the  way  to 
become  protoplasm  ;  the  organism  is  thus  saved  much  constructive 
labour.  And  wc  may  imagine  that  a  ceil  would  always  take  and 
assimilate  into  itself  alrcidy  constructed  fats,  sugar,  pmteids,  &c., 
rather  than  have  the  preliminary  troulilc  of  building  up  tlicse  sub- 
stances out  of  simpler  compounds.  But  when  wc  consider  how  in 
every  being,  every  cell  and  every  part  of  a  cell  has  its  own  individual 
characters,  stamped  on  it  by  long  hereditary  action,  we  see  a  reason 
why  every  bit  of  protoplasm,  especially  in  the  higher  more  differen- 
tiated organisms,  should  be  made  anew.  And  the  energy  required 
for  the  construction  is  always  at  hand.  The  food,  which,  instead  of 
being  directly  assimilated  without  loss  of  energy,  is  reduced  to  simple 
compounds,  sets  free  an  energy  which  remains  available  for  recon- 
struction. Of  course  in  every  such  decomposition  and  recomposition 
there  will  be  an  irrecoverable  lo^s  in  the  form  of  heat  which  escapes  ; 
but,  as  wc  know,  the  whole  of  animal  life  is  arranged  with  a  view  to 
this  continual  loss.  It  is  not  therefore  unreasonable  though  opposed 
to  established  ideas  to  suppose  that  the  animal  protoplasm  is  as  con- 
structive as  the  vegetable  protoplasm,  the  difference  between  the  two 
being  that  the  former,  unlike  the  latter,  is  as  destructive  as  it  is 
constructive,  and  therefore  requires  to  be  continually  fed  with  ready 
constructed  material. 


T/ic  Mammary   Gland. 

Since  milk  is  a  secretion,  and  indeed  an  excretion,  the  mam- 
mary gland  ought  not  to  be  classed  as  a  metabolic  tissue,  in  the 
limited  meaning  we  are  now  attaching  to  those  words.  Yet  the 
metabolic  phenomena  giving  rise  to  the  secretion  of  milk  are 
so  marked  and  distinct,  and  have  so  many  analogies  with  the 
purely  metabolic  events  in  adipose  tissue,  that  it  will  be  more 
convenient  to  consider  the  matter  here,  rather  than  in  any  other 
connection. 

Human  milk  has  a  specific  gravity  of  from  ro2S  to  i"034,  and 
when  quite  fresh  possesses  a  slightly  alkaline  reaction.  It  speedily 
becomes  acid,  and  cow's  milk,  even  when  quite  fresh,  is  some- 
times slightly  acid,  the  change  of  reaction  taking  place  during  the 
stagnation  of  the  milk  in  the  mammary  ducts. 

"   Huxley  and  Martin,  Elementary  Biology,  Lesson  V. 


442  MILK.  [book   1 1. 

The  constituents  of  milk  are : 

1.  Proteids,  viz.  casein,  and  an  albumin,  agreeing  in  its 
general  features  with  ordinary  serum-albumin.  The  casein  may  be 
thrown  down  by  the  careful  addition  of  acetic  acid  ;  but  the  most 
complete  precipitation  is  etfected  by  first  adding  to  the  milk  a 
slight  quantity  of  acetic  acid,  and  then  passing  through  it  a  stream 
of  carbonic  acid.  From  the  filtrate  the  serum-albumin,  which  is 
present  in  small  and  variable  quantities,  may  be  obtained  by 
coagulation  with  heat,  or  by  precipitation  with  potassium  fer- 
rocyanide,  &c. 

2.  Fats.     These  are  palmitin,  stearin,  and  olein. 

There  are  present  also,  to  the  extent  of  about  2  per  cent,  of  the 
total  fat,  the  glycerides  of  butyric,  capronic,  caprylic,  and  myristinic 
acids. 

3.  Milk-sugar,  the  conversion  of  which  into  lactic  acid  gives 
rise  to  many  of  the  features  of  milk. 

4.  Extractives,  including,  according  to  some  observers,  urea, 
and  salts.  The  last  consists  chiefly  of  potassium  phosphate,  with 
calcium  phosphate,  potassium  chloride,  small  quantities  of  mag- 
nesium phosphate,  and  traces  of  iron. 

The  following  is  the  composition  of  1000  parts  of 


Human  Milk. 

Cow's  Milk. 

Casein 

39-24 

48-28 

Albumin 

— 

576 

Fat 

26-66 

43 '05 

Sugar 

43 '64 

4o'37 

Salts 

1-38 

5-48 

Total  Solids 

IIO"92 

142-94 

Water 

889-08 

857-06 

Milk  is  an  emulsion,  the  fats  existing  in  the  form  of  globules 
of  various  but  minute  size,  each  protected  by  a  thin  envelope  of 
casein  or  albumin.  It  is  this  condition  of  the  fat  which  gives  to 
milk  its  peculiar  white  colour.  The  colosti'um,  or  secretion  of 
the  mammary  gland  at  the  beginning  of  lactation,  differs  from 
milk  in  being  very  deficient  in  casein  and  proportionately  rich  in 
albumin.  It  is  said  that  the  milk  at  the  end  of  a  long  lactation 
again  becomes  poor  in  casein  and  rich  in  albumin.  Milk  on 
standing  turns  sour  and  curdles.  This  is  due  to  the  milk-sugar 
becoming  converted  by  a  fermentative  process  into  lactic  acid, 
which  in  turn  precipitates  the  cas  jin.     The  change  may  be  rapidly 


CHAP.    V.J  NUTRITION.  443 

brought  about  by  means  of  a  ferment  contained   in    the  gastric 
mcml)ranc.     (Soe  p.  253) 

Milk,  hke  tlie  other  secretions  whirli  we  have  studicfl,  is  the 
result  of  the  activity  of  certain  protoplasmic  secreting  cells  forming 
the  e|)ilheliuni  of  the  mammary  gland.  As  far  as  the  fat  of  milk 
is  concerncfi,  the  processes  taking  place  in  the  gland  are  very  in- 
structive, since  the  fat  can  hese^n  to  be  gathered  in  the  epitlielium- 
rcll,  in  the  same  way  as  in  a  fat-cell  of  the  adipose  tissue,  and  to 
be  di-^charged  into  the  channels  of  the  gland,  either  by  a  breaking 
up  of  the  cells,  or  by  a  contractile  extrusion  very  similar  to  that 
which  takes  place  when  an  amoeba  ejecis  its  digested  food.  All  the 
evidence  we  possess  goes  to  prove  that  the  fat  is  formed  in  the 
rell  through  a  metabolism  of  the  protoplasm.  The  microscopic 
history  is  thoroughly  supported  by  other  facts.  Thus  the  quantity 
of  fat  present  in  milk  is  largely  and  directly  increased  by  proteid, 
but  not  increased,  on  the  contrary  diminsihed,  by  fatty  food'.  Tnis 
is  quite  intelligible  when  we  know,  as  will  be  shewn  in  a  succeeding 
section,  that  proteid  food  increases,  and  fatty  food  diminishes,  the 
metabolism  of  the  body ;  and  we  have  already  discussed  the 
manner  in  which  proteid  n-aterial  may  give  rise  to  fat.  A  bitch 
fed  on  meat  for  a  given  period  gave  off  more  fat  in  her  milk  than 
she  could  possibly  have  taken  in  her  food,  and  that  too  while  she 
was  gainmg  in  weight,  so  that  she  could  not  have  su])plied  the 
mammary  gland  with  fat  at  the  expense  of  fat  previously  existing 
in  her  body.  In  the  'ripening'  of  cheese  we  have  a  similar 
conversioa  of  proteids  into  fat.  We  have  also  evidence  that 
the  casein  is,  like  the  fat,  formed  in  the  gland  itself.  When 
milk  is  kept  at  35"  C.  out  of  the  body  the  casein  is  increased  at  the 
expense  of  the  albumin.  When  the  action  of  the  cell  is  imperfect, 
as  at  the  beginning  or  end  of  lactation,  the  albumin  is  in  excess  of 
the  casein  ;  but  as  long  as  the  cell  possesses  its  proper  activity  the 
formation  of  casein  becomes  prominent.  It  has  been  suggested 
thit  the  casein  may  be  formed  by  a  splitting  up  of  albumin  by  some 
fermentative  process,  but  no  such  ferment  has  yet  been  isolated. 
That  the  milk-sugar  also  is  formed  in  and  by  the  protoplasm  of 
the  cell,  is  indicated  by  the  fact  that  the  sugar  is  not  dependent  on 
( arbohydrate  food,  and  is  maintained  in  abundance  in  the  milk  of 
carnivora  when  these  are  fed  exclusively  on  meat,  as  free  as 
possible  from  any  kind  of  sugar  or  glycogen.  We  thus  have 
evidence  in  the  mammary  gland  of  the  formation,  by  the  direct 
metabolic  activity  of  the  secreting  cell,  of  the  representatives 
of  the  three  great  classes  of  food  stuffs,  ]iroteids,  fats  and  carbo- 
hydrates, out  of  the  compretiensive  substance  protoplasm.  And 
^  bubbotin  and  Kemmerich,  Ci/.  Med.  Wiss,,  l866,  p.  337. 


444  THE   SPLEEN.  [BOOK   II. 

what  we  see  taking  place  in  the  mammary  cell  is  probably  a 
picture  of  what  is  going  on  in  all  protoplasmic  bodies.  If  the  fat 
of  the  milk  were  not  ejected  from  the  mammary  cell,  the  mammary 
gland  would,  become  a  mass  of  adipose  tissue,  especially  if,  by  a 
slight  change  in  the  metabolism,  the  production  of  fat  were 
exalted  at  the  expense  of  the  production  of  casein  or  milk-sugar.  If, 
again,  by  a  similar  slight  change  the  milk-sugar  were  accumulated 
rather  than  the  fat  or  proteid,  we  should  have  a  result  which,  by 
an  easy  step,  would  bring  us  to  glycogenic  tissue.  And,  lastly, 
if  the  proteid  accumulation  were  greater  than  the  fatty,  or  the  sac- 
charine, these  being  carried  off  in  some  way  or  other,  we  should 
have  an  image  of  the  nutrition  of  an  ordinary  nitrogenous  tissue. 

That  both  the  secretion  and  ejection  of  milk  are  under  the  control 
of  the  nervous  system  is  shewn  by  common  experience,  but  the  exact 
nervous  mechanism  has  not  yet  been  fully  worked  out.  While  erection 
of  the  nipple  ceases  when  the  spinal  nerves  which  supply  the  breast 
are  divided,  the  secretion  continues,  and  is  not  arrested  even  when  the 
sympathetic  as  well  as  the  spinal  nerves  are  cut '. 

The  Spleen, 

The  Spleen  may  be  wholly  removed  from  an  animal  without 
any  obvious  changes  in  the  economy  taking  place ;  the  functions 
of  the  rest  of  the  body  appear  to  go  on  unimpaired.  We  are 
obliged  to  assume  that  some  compensating  actions  take  place : 
but  what  those  actions  are  we  do  not  know,  and  we  are  left  at 
present  by  these  experiments  almost  completely  in  the  dark  as  to 
the  functions  of  the  spleen.  The  most  that  has  been  observed  is 
a  slight  increase  in  the  lymphatic  glands,  and  in  the  activity  of 
the  medulla  of  bones. 

Schiff  ^  maintains  that  after  extirpation  of  the  spleen,  pancreatic 
juice  is  no  longer  able  to  digest  proteids.  He  believes  that  the  spleen 
during  its  turgescence  manufactures  a  substance,  which  being  carried 
to  the  pancreas,  gives  rise  by  a  kind  of  ferment  action  of  its  own  to 
the  pancreatic  proteolytic  ferment.  In  the  language  of  Heidenhain's 
results,  the  presence  of  the  splenic  product  is  necessary  for  the  con- 
version of  the  zymogen  into  the  pancreatic  proteolytic  ferment. 
Herzen  3  further  states  that  in  the  exceptional  cases  where  the  spleen 
does  not  become  turgid  during  digestion,  the  pancreatic  juice  is  inert 
towards  proteids.  The  evidence  in  favour  of  this  action  of  the  spleen 
is,  at  present,  not  cogent,  and  Mosler'*  denies  that  extirpation  of  the 

^  Eckhard,  Bdtrdge,  I.  and  Viii.  (1877)  p.  117.     Rohrig,  Virchow's  ^rr,^iV, 
IXVii.  {1876)  p.  119. 

^  Schweiz.  Zt.f.  Heilk.  \.  (1862)  p.  209.     See  also  Lemons  stir  la  Digestion. 
3  Cbt.f.  Med.  W.ss.,  1877,  p.  435.         ■»  Cbt.  f.  Med.  Wiss.,  1871,  p.  290. 


CHAP.    V.j  NUTRITION.  445 

spleen  has  any  influence  whatever  over  either  gastric  or  pancreatic 
digestion. 

After  a  meal  the  spleen  increases  in  size,  reaching  its  maximum 
about  five  hours  after  the  taking  of  food ;  it  rcmams  swollen  for 
.some  time,  and  then  returns  to  its  normal  bulk.  In  certain 
diseases,  such  as  in  the  pyrexia  attendant  on  fevers  or  inflam- 
mations, and  more  especially  in  ague,  a  similar  temporary 
enlargement  takes  place.  In  prolonged  ague  a  permanent 
hypertrophy  of  the  spleen,  the  so-called  ague-cake,  occurs. 

The  turgescence  of  the  spleen  seems  to  be  due  to  a  relaxation 
both  of  the  small  arteries  and  of  the  muscular  bands  of  the  tra- 
beculae;  to  be,  in  fact,  a  vaso-motor  dilation  accompanied  by 
a  local  inhibition  of  the  tonic  contraction  of  the  other  plain 
muscular  fibres  entering  into  the  structure  of  the  organ.  And 
the  condition  of  the  spleen,  like  that  of  other  vascular  ,reas, 
appears  to  be  regulated  by  the  central  nervous  .system  the 
digestive  turgescence  being  altogether  comparable  to  the  flushed 
condition  of  the  pancreas  and  the  gastric  membrane  during  their 
phases  of  activity. 

According  to  Tarchanoff'  section  of  the  splenic  nerves  causes  a 
turgescence  lastinj^  for  some  time,  but  disappearing  in  the  couric  of  a 
few  days.  Stimulation  of  the  spinal  cord  causes  a  shrinking,  which, 
howevet,  fails  to  make  its  appearance  if  the  splanchnic  nerves  be 
previously  divided.  The  shrinking  or  constriction  may  be  brought 
about  in  a  reflex  manner  by  stimulation  of  the  central  stump  of  the 
sciatic  nerve.  The  effect,  however,  is  in  the  case  of  this  nerve  slight, 
whereas  if  the  central  stump  of  the  vagus  be  stimulated,  a  very  marked 
shrin;ing  is  observed.  Local  stimulation  causes  local  shrinking  ;  if 
the  electrodes  of  an  interrupted  current  be  drawn  across  a  turgid 
spleen,  their  course  is  marked  by  a  white  line  of  constriction  lastmg 
for  some  little  time.  Contraction  of  the  spleen  is  also  caused  by 
quinine  and  strychnia. 

This  functional  intermittent  turgescence,  so  clearly  related  to 
the  ingestion  of  food,  may  be  connected  with  that  manufacture  of 
white  corpuscles  and  destruction  of  red  corpuscles  of  the  blood, 
of  which  we  spoke  in  an  early  chapter  (p.  38) ;  but  when  the 
peculiar  arrangements  of  the  blood-\essels  of  the  s])leen,  with 
their  large  open  venous  networks,  are  borne  in  mind,  it  seems 
in  the  highest  degree  probable  that  metabolic  events  of  great 
importance  (possibly  associated  in  some  way  with  the  metamor- 
phosis of  the  blood-corpuscles)  take  place  in  the  spleen,  though 
at   present   we   are   unable  to  follow  them.      And  this  view  is 

'  V Wuger' s  ^/r/iiv,  viii.  (1S74)  p.  97. 


44^  THE   SPLEEN.  [BOOK   II. 

supported  by  the  somewhat  peculiar  chemical  characters  of  the 
spleen-pulp,  which,  in  spite  of  its  containing  a  very  large  number 
of  blood-corpuscles,  differs  markedly  in  its  chemical  composition 
from  either  blood  or  serum.  Thus  a  special  proteid  of  the  nature 
of  alkali-albumin  seems  to  be  present,  holding  iron  in  some  way 
peculiarly  associated  with  it.  The  occurrence  of  this  ferruginous 
proteid,  accompanied  as  it  is  by  several  peculiar  but  at  present 
little  understood  pigments,  rich  in  carbon,  bears  out  the  histological 
conclusions  concerning  the  disappearance  of  the  red  corpuscles. 
The  inorganic  salts  of  the  spleen,  or  at  least  those  of  its  ash,  are 
remarkable  for  the  large  amount  of  both  soda  and  phosphates,  and 
the  scantiness  of  the  potash  and  chlorides  which  they  contain,  thus 
ditfering  from  blood-corpuscles  on  the  one  hand,  and  from  blood- 
serum  on  the  other.  But  perhaps  the  most  striking  feature  of 
the  spleen-pulp  is  its  richness  in  the  so-called  extractives.  Of 
these  the  most  common  and  plentiful  are  succinic,  formic,  acetic, 
butyric  and  lactic  acids  (these  may  arise  in  part  from  the  decom- 
position of  hsemoglobin),  inosit,  leucin,  xanthin,  hypoxanthin  and 
uric  acid.  Tyrosm  apparently  is  not  present  in  the  perfecdy  fresh 
spleen,  though  leucin  is :  both  are  found  when  decomposidon  has 
set  m.  The  constant  presence  of  uric  acid  is  remarkable,  especially 
smce  it  has  been  found  even  in  the  spleen  of  animals,  such  as  the 
herbivora,  whose  urine  contains  none.  No  less  suggestive  is  the 
fact  that  the  increase  of  uric  acid  in  the  urine  dunng  ague,  and 
during  ordinary  pyrexia,  seems  to  run  parallel  to  the  turgescence, 
and  therefore  presumably  to  the  activity,  of  the  spleen.  But 
these  facts  are  at  present  suggestive  only  j  they  point  to  an  active 
metabolism  associated  with  digestion  taking  place  in  the  spleen ; 
exact  information  as  to  the  nature  of  the  metabolism  is  however 
wanting.  The  thyroid  and  thymus  bodies,  often  in  descriptions 
associated  with  the  spleen,  though  different  m  structure,  the 
former  absolutely  so,  resemble  the  spleen  somewhat,  as  far  as 
their  extractives  are  concerned.  The  thymus  contains  leucin, 
xanthin  and  hypoxanthin,  with  lactic  and  succinic  acids;  uric 
acid  seems  to  be  absent.  The  extractives  of  the  thyroid  are 
scanty,  but  apparently  of  the  same  nature. 

Sec.  2.      The  History  cf  Urea  and  its  Allies. 

We  may  now  return  to  the  questions  which  we  left  unanswered 
at  p.  419.  Where  is  urea  formed  ?  what  are  its  immediate  ante- 
cedents ?'  what  are  the  various  chemical  links  between  it  and  the 
proteid  material  of  which  it  is  the  excretory  representative  ? 

We  have  seen,  p.  74,  that  the  muscular  tissues  contain  kreatin. 


CHAP,  v.]  NUTRITION.  447 

together  with  smaller  quantities  of  allied  nitroj^enous  crystalline 
bodies,  such  as  xanthin,  hypoxanthin,  &c  ;  and  we  cannot  go  far 
wrong  in  supposing  that  these  bo<.lie3  are  in  some  way  or  other  the 
products  ot"  muscular  metabolism.  We  do  not  know  in  what 
''■'amities  they  arj  formed  ;  but  since  they  are  such  bodies  as 
■  uld  readily  be  carried  away  from  the  muscle  by  the  blood- 
sifeam,  and  yet  are  always  to  be  found  in  the  muscle,  we  infer 
that  they  are  continually  being  formed,  and  as  continually  being 
converted  into  some  other  bodies  and  carried  away.  And  we 
may  further  say,  that  since  kreatin  exists  in  muscle  to  the  extent 
of  '2  or  '4  p.c,  and  since  muscle  forms  so  large  a  portion  of  the 
whole  body,  it  is  at  least  possible,  if  not  probable,  that  a  con- 
siderable amount  of  kreatin  passes  within  twenty-four  hours  into 
the  blood,  on  its  way'  to  become  transformed  by  other  tissues 
into  urea,  or  into  some  stage  nearer  to  urea  than  itselfc 

The  urine  contains  a  certain  amount  i"9  grm.  in  24  hours)  of 
kreatin,  or  kreatinin,  into  which  kreatin  is  easily  converted  ;  but  neither 
of  these  can  be  considered  as  the  normal  form  in  which  the  kreatin  of 
the  muscies  passes  out  of  the  body.  For  the  urinary  kreatin  is 
exceedingly  \-ariable  in  quantity,  vanishes  during  starvation,  and, 
though  not  at  all  increased  by  e.xercise,  is  largely  augmented  by 
a  flesh-diet ' ;  and  kreatin  injected  into  the  Wood,  even  in  small 
quantities,  reappears  unchanged  in  the  urine.  Without  laying  too 
much  stress  on  the  last  fact,  we  are  led  to  conclude  that  the  kreatin  or 
kreatinin  in  urine  has  an  origin  quite  independent  of  that  which  is 
present  in  the  muscles,  being  probably  derived  directly  from  the  food. 

With  regard  to  the  substances,  such  as  xanthin,  which  appear  in 
muscle  in  small  quantities  only,  our  information  is  too  imperfect  to 
allow  us  to  make  any  statement  whatever  about  them. 

While  then  we  have  some  reason  for  thinking  that  the  kreatin 
found,  and  presumably  formed,  in  muscle  is  a  more  or  less  distant 
antecedent  of  urea,  it  must  be  remembered  that  this  is  simply  a 
more  or  less  probable  view,  not  an  ascertained  or  clearly  proven 
fact. 

Of  the  metabolism  of  the  nervous  tissues  we  know  little ;  but 

kreatin  is  found  in  the  brain,  in  some  cases  in  not  inconsiderable 

quantit)-.      Now  the  bodies  of  the  nerve-cells  are  undoubtedly 

inposed  of  protoplasm ;    the  axis-cylinders  of  the  nerve-fibres 

-■  also  protoplasmic  in  nature,  and  it  is  at  least  possible  that 

ich  of  tho  peculiar  matrix  of  the  cerebral  and  cerebellar  con- 

lutions,    and   of   the   grey  matter  generally,  is  also  in  reality 

jtoplasmic.     Hence  we  may,  with  a  certam  amount  of  reason, 

.;[)pose  that  the  ner.'ous,  like  the  muscular  tissues,  are  continually, 

'  Voit,  Z.'.  A  ^*^-.  IV.  p.  77. 


44^  UREA.  [book   II. 

.but  to  a  much  less  extent,  supplying  an  antecedent  to  urea  in  the 
form  of  kreatin. 

Lastly,  the  spleen  contains  a  considerable  quantity  of  kreatin, 
as  well  as  of  xanthin,  &c. ;  and  these  are  present  also  in  various 
glandular  organs. 

We  thus  have  evidence  of  a  continual  formation  of  kreatin, 
possibly  in  large  quantities,  in  various  parts  of  the  body.  On  the 
other  hand,  urea  is  certainly  not  present  in  muscle  (save  in  certain 
exceptional  cases)  and  its  presence  in  nervous  tissue  is  extremely 
doubtful.  It  is  absent  from  the  spleen  (of  the  occurrence  of  urea 
in  the  liver  we  shall  speak  presently),  the  thymus,  and  thyroid 
bodies,  and  from  the  lymphatic  glands,  though  uric  acid,  as  we 
have  seen,  appears  to  be  a  normal  constituent  of  the  spleen.  It 
seems  very  tempting  to  jump  at  once  from  these  facts  to  the 
conclusion  that  kreatin  is  the  natural  antecedent  of  urea,  and  that 
as  far  as  nitrogenous  excretion  is  concerned  the  labour  of  the 
kidney  is  confined  to  the  simple  transformation  of  kreatin  into 
urea.  We  have  only  to  suppose  that  the  kreatin  passes  from  these 
several  tissues  into  the  blood,  in  which  it  may  be  found,  and  while 
circulating  in  the  blood  is  seized  upon  by  the  renal  epithelium  and 
converted  into  urea.  And  there  are  some  facts  which  support  this 
view.  But  there  are  others  which  oppose  it ;  and  while  it  cannot 
be  said  to  be  wholly  disproved,  it  cannot  at  present  be  accepted 
as  sufficiently  satisfactory  to  serve  as  a  foundation  fur  other 
arguments. 

In  the  first  place,  urea,  in  spite  of  its  absence  from  the  muscles 
and  other  tissues,  is  always  present  m  the  blood,  and  has  also  been 
found  in  the  chyle,  in  the  serous  fluids,  and  in  saliva.  It  might  be 
urged  of  course  that  this  urea  is,  so  to  speak,  an  overflow  from  the 
kidney,  that  owing  to  its  great  difTusibihty  it  has  passed  back  from 
■the  renal  epithelium  where  it  was  manufactured  into  the  blood  stream. 
When,  however,  we  reflect  how  all  diffusion  is  overborne  by  the 
natural  physiological  currents,  as  shewn  indeed  by  the  absence  of  urea 
from  muscle,  in  spite  of  its  presence  in  the  blood,  this  argument  loses 
all  the  little  force  it  had. 

In  certain  diseases  of  the  kidney,  the  excretion  of  urine  ceases. 
This  suppression  of  urine,  as  it  is  called,  i?  followed  by  an  accumulation 
of  urea  in  the  blood  and  all  parts  of  the  body,  and  is  accompanied  by 
symptoms  known  as  those  of  ursemic  poisoning,  though  the  toxic 
consequences  are  clue  not  to  the  presence  in  the  system  of  the  large 
quantity  of  urea,  but  of  other,  at  pi'esent  undefined,  substances  which 
have  at  the  same  time  ceased  to  be  excreted.  Oppler '  and  Zalesky 
stated  that  when  the  kidneys  of  an  animal  were  extirpated,  or  <ihe 
renal  arteries  ligatured,  though  urasmic  symptoms   set  in  as  usual, 

'  Virchow's  Archiv,  xxi,  p.  260. 


CHAr.    V.J  NUTRITION.  449 

there  was  no  accumulation  of  urea  in  the  blood  or  tissues,  and  no 
excess  of  carbonic  aciil  or  ammonium  carbonate,  such  as  might  have 
arisen  from  a  rapid  decomposition  of  urea.  Ther.-  was  however  a 
marked  accumulation  of  krcatin  or  of  kreatinin.  On  the  other  liand 
these  observers  found  th;it  when  the  ureters  were  ligatured,  so  that  the 
blood  was  still  brouj,'ht  under  the  influence  of  the  renal  epithelium, 
and  yet  the  products  of  the  activity  of  that  epithelium  not  allowed  to 
escape,  an  accumulation  of  urea  (in  birds  of  uric  acid)  and  not  of 
kreatin  was  observed.  These  result-;,  if  indi^putable,  would  indeed 
afi'ord  strong  evidence  of  the  conversion  of  kreatin  into  urea  by  the 
agency  of  the  renal  epithelium.  They  have  however  been  much 
disputed.  Thus  Grdhant ',  using  what  was  probably  a  better  method 
for  the  estimation  of  urea  (and  the  detection  of  urea  in  complex 
organic  fluids  is  subject  to  very  considerable  errors),  came  to  the  con- 
clusion that  the  urea  in  the  blood,  after  extirpation  of  both  kidneys, 
rose  from  "026  and  from  '088  to  "206  and  '276  per  cent,  in  24  and  27 
hours  respectively.  And  Gscheidlen '  has  come  to  a  similar  conclusion. 
The  results  according  to  both  these  latter  observers  are  the  same 
whether  the  kidneys  arc  extirpated  or  the  ureters  tied  ;  in  the  latter 
case  the  distension  of  tlie  tubules  soon  renders  the  epithelium  cells 
incapable  of  performing  their  functions,  and  thus  an  animal,  in  which 
the  ureters  have  been  ligatured,  is  practically  in  the  same  condition  as 
one  from  which  the  kidneys  have  been  removed.  Neither  Grehant 
nor  Gscheidlen  makes  any  statement  about  an  increase  of  kreatin. 
And  it  may  be  worth  while  to  notice  that  though  the  experiments  of 
these  observers  prove  that  all  the  urea  of  the  urine  is  certainly  not 
formed  in  the  kidney,  they  do  not  necessarily  oppose  the  view  that 
sfltiw  of  it  may  be  so  formed  out  of  kreatin  or  some  similar  ante- 
cedent. Nor  is  there  anxthinga  priori  to  contradict  the  supposition 
that  the  origin  of  urea  may  be  double,  part  being  formed  in  one  way 
and  jiart  in  another.  Lastly,  the  fact  that  the  urea  injected  into  the 
blood  causes  a  rapid  secretion  of  urine,  may  be  used  as  an  argument 
that  the  habit  of  the  renal  epithelium  is  to  pick  out,  so  to  speak,  the 
urea  from  the  blood  and  to  carry  it  into  the  channels  of  the  renal 
tubules. 

There  is  moreover  another  possible  source  of  urea  besides  the 
kreatin  formed  in  muscle  and  elsewhere.  We  have  seen  tliat  one 
result  of  the  action  of  the  pancreatic  juice  is  the  formation  of 
considerable  quantities  of  leucin  and  tyrosin.  In  dealing  with  the 
statistics  of  nutrition,  our  attention  will  be  drawn  to  the  fact  that 
the  introduction  of  i)roteic!  matter  into  the  alimentary  canal  is 
followed  by  a  large  and  rapid  excretion  of  urea,  suggesting  the  idea 
that  a  Certain  part  of  the  total  quantity  of  the  urea  normally 
secreted  comes  from  a  direct  metabolism  of  the  proteids  of  the 
food,  without  these  really  forming  a  part  of  tiie  tissues  of  the  body. 

'  Cbi.  Med.  Hiss.,  1870,  p.  249. 

'  iituJicn  ii.  d.  Unprung  d.  Harnstoffs.     Leipzig,  187 1. 
F.  P.  29 


450  UREA.  [BOOK   II. 

We  do  not  know  to  what  extent  normal  pancreatic  digestion  has 
for  its  product  leucin,  and  its  companion  tyrosin;  but  if,  especially 
when  a  meal  rich  in  proteids  has  been  taken,  a  considerable 
quantity  of  leucin  is  formed,  we  can  perceive  an  easy  and  direct 
source  of  urea,  provided  that  the  metabolism  of  the  bod}^  is 
capable  of  converting  leucin  into  urea.  That  the  body  can  effect 
this  change  is  shewn  by  the  fact  that  leutin,  Avhen  introduced  into 
the  alimentary  canal  in  even  large  quantuies,  do^^s  reappear  m  the 
urine  as  urea  ;  that  is,  the  urine  contains  no  leucin,  but  its  urea  is 
proportionately  increased ;  and  the  same  is  probably  the  case  with 
tyrosin,  though  this  is  disputed.  Now  the  leucin  formed  in  the 
alimentary  canal  is  probably  caiTied  by  the  portal  blood  straight  to 
the  liver ;  and  the  liver,  unlike  other  glandular  organs,  does,  even 
in  a  perfectly  normal  state  of  things,  contain  urea.  We  are  thus 
led  to  the  view  that  among  the  numerous  metabolic  events  which 
occur  in  the  hepatic  cells,  the  formation  of  urea  out  of  leucin  or 
out  of  other  antecedents  may  be  ranked  as  one.  Probable,  how- 
ever, as  this  view  may  seem,  it  has  not  as  yet  been  established  as 
a  fact. 

Meissner  '  found  a  large  quantity  of  urea  in  the  liver  of  mammals, 
ind  of  urates  in  the  liver  of  birds.  Cyon^  attempted  to  demonstrate 
che  formation  of  urea  in  the  liver  by  passings  a  stream  of  fresh  blood 
dirough  the  liver  of  an  animal  recently  killed,  and  estimating  the  per- 
centage of  urea  in  the  blood  used  before  and  after.  He  found  it  to  be 
increased  from  'oS  to  •176.  This  however  is  not  conclusive,  for,  as 
Gscheidlen  has  urged  ^,  the  increased  quantity  in  the  blood  which  had 
been  circulated  might  have  been  simply  urea  which  had  been  washed 
out  from  the  liver,  where  it  had  previously  been  staying.  A  strong 
presumption  in  favour  of  urea  arising  through  the  hepatic  metabolism, 
from  leucin  as  an  antecedent,  is  afforded  by  the  fact  that  in  cases  of 
acute  atrophy  of  the  liver,  where  the  hepatic  cells  lose  their  functional 
activity,  the  urea  of  the  urine  is  replaced  by  leucin  and  tyrosin.  And 
lastly,  it  may  be  remarked  that  not  only  are  leucin  and  tyrosin  found 
in  nearly  all  the  tissues  after  death,  especially  in  the  glandular  tissues, 
but  they  also  appear  with  striking  readiness  in  almost  all  decompo- 
sitions of  proteid,  and,  in  the  case  of  the  former,  of  gelatiniferous 
substances. 

The  view  that  leucin  is  transformed  into  urea  lands  us  however  in 
very  considerable  difficulties.  Leucin,  as  we  know,  is  amido-caproic 
acid  ;  and,  with  our  present  chemical  knowledge,  we  can  conceive  of 
no  other  way  in  which  leucin  can  be  converted  into  urea  than  by  the 
complete  reduction  of  the  former  to  the  ammonia  condition  (the 
capruic  acid  residue  being  either  elaborated  into  a  fat  or  oxidized  into 
carbonic  acid)  and  by  a  reconstruction  of  the  latter  out  of  the  am- 
monia so  formed.    We  have  a  somewhat  parallel  case  in  glycin.    This, 

'  Zt.f.  rat.  Med.,  (3)  XXXI.  144.  =  Cbt.f.  Med.  Wiss.,  1870,  p,  580, 

3  Cf.  also  Munk,  I'fliiger's  ArcJiiv,  XI.  (1875)  p.  100. 


CHAP.    V.J  NUTRITION.  45 1 

which  is  amiuo-acctic  acid,  when  introduced  i'.ito  the  alimentary  canal, 
also  reappears  as  urea  ;  here  too,  a  reconstruction  of  urea  out  of  an 
ammonia  pliase  mu^t  take  place'.  .And  there  arc  other  facts  which 
point  in  exactly  the  simc  direction,  viz.  in  a  derivation  of  tiic  normal 
urea  of  the  urine  from  a  simple  ammonia  antecedent.  O.  .Schultzcn '■' 
finds  that  when  an  ap])ropriate  quantity  of  sarcosin  is  given  by  the 
mouth,  urea  disappears  froui  the  urine,  being  replaced  by  a  compound 
of  sarcosin  and  carbonic  acid  (in  company  with  a  compound  of  sar- 
cosin with  sulphamic  acid).  The  interpretation  of  this  result  is  that 
in  normal  metabolism  the  prolcids  are  ultimately  broken  down  to 
carbamic  acid  and  ammonia,  whicli  uniting  and  be.oming  subsequently 
dehydrated,  form  urea  ;  thus  CO.jN^H,;  anmionium  carbamate-  H.^0  = 
C0N._,H4  urea  ;  but  that  carbamic  acid,  having  a  greater  affinity  for 
sarcosin  than  ammonia,  seizes  the  former  in  preference  when  it  is  at 
hand,  and  consequently  gives  rise  to  Schultzcn's  compound. 

There  are  however  many  objections  to  Schultzen's  view  in  respect 
to  both  the  nature  and  the  mode  of  origin  of  the  compound  described 
by  him  \  More  valid  is  the  argument  which  may  be  drawn  from  the  fact 
that  \shcn  ammonium  chloride  is  given  to  a  dog  a  very  large  portion 
reappears  as  urea,  t.t:  there  is  an  increase  in  the  urea  of  the  urine 
corresponding  to  a  large  portion  of  the  nitrogen  contained  in  the  am- 
monium chloride-'.  Ikit  even  granted  that  the  urea  of  the  urine  may 
h^  formed  out  of  ammonia,  there  still  remains  the  question,  Is  the 
urea  formed  by  the  union  of  ammonia  with  carbonic  acid  and  subse- 
quent dehydration,  the  whole  of  the  nitrogen  of  the  urea  coming  into 
it  as  ammonia,  or  by  the  union  of  ammonia  w  ith  carbamic  acid  with 
dehydration,  as  advocated  by  Schultzen,  or  lastly  by  the  union  of 
ammonia  with  some  cyanogen  body.-*  Cur  information  will  not  at 
present  allow  us  to  decide  this  point,  though  arguments  have  been 
adduced  in  favour  of  the  latter  view  5. 

To  sum  up  our  imperfect  knowledge  concerning  the  history  of 
urea.  Wc  have  evidence,  not  exactly  complete  but  fairly  satis- 
factory that  a  part  at  least  of  the  urea  is  sim[)ly  withdrawn  from 
the  blood  by  the  renal  epithelium.  The  activity  of  the  protoplasm 
of  the  secreting  cells  must  therefore,  as  far  as  this  part  of  the  urea 
is  concerned,  be  confined  to  absorbing  the  urea  from  the  renal 
blood,  and  to  passing  it  on  into  the  cavities  of  the  renal  tubules. 
I'lie  mechanism  by  which  this  is  efTected  we  cannot  at  present 
fathom,  but  it  seems  more  comparable  to  a  selection  of  food  than 

'  Cf.  Salkow.ski,  Z(.  f.  Pliysiolog.  Chciii.,  I.  (1877)  I-  Schiniedeberg, 
Anhivf.  lixp.  Pit/i.,  vill.  (1877)  p"".  I. 

'  Utr.  Deut.  Clum.  GeselL,  1872,  p.  578. 

3  Cf,  Hoppe-Seylcr  and  Biiuuiann,  Bi:r.  d.  Deuls<h,  Chan.  GesclL,  vii. 
P-  34- 

♦  Van  Knieriem,  Zl.  f.  /u'ol.,  x.  (1874)  p.  263.  Salkowski,  Zt. /.  Physiol. 
<^':i-m.,  I.  (1S77)  p.  I.  Muiik,  ibid.  II.  (1878)  p.  29.  Ilallervorden,  Arch.  f. 
/  .r/>.  J'alh.,  X.  (1S7S)  i\  125. 

5  Cf.  Salkowski,  oj>.  cit.,  and  sec  Appendix  sub  voce  Urea. 

29 — 2 


452  URIC   ACID.  [book   II. 

to  anything  else ;  the  cells  appear  to  treat  urea  much  in  the  same 
way  as  they  treat  indigo-carmine  (p.  416).  The  antecedents  of 
the  urea  in  the  blood  are,  we  may  at  present  suppose,  partly  the 
kreatin  formed  in  muscle  and  elsewhere,  partly  the  leucin  and 
other  like  bodies  formed  in  the  alimentary  canal  as  well  as  in 
various  tissues.  The  transformation  of  these  bodies '  into  urea 
may  take  place  in  the  liver  and  possibly  in  the  spleen,  but  we 
have  no  exact  proof  of  this,  nor  can  we  say  exactly  in  what  way 
the  transformation  is  effected.  There  is  no  proof  of  any  body 
existing  in  the  blood  capable  of  effecting  this  transformation  ;  and 
we  may  probably  rest  assured  that  in  this,  as  in  other  metabolic 
events,  the  activity  exercised  in  the  change  comes  from  some 
tissue,  and  cannot  be  manifested  by  simple  blood  plasma. 

Lastly,  it  is  possible  that  the  kidney  may,  besides  the  simpler 
duty  of  withdrawing  ready  formed  urea  from  the  blood,  be  exercised 
in  transforming  various  nitrogenous  crystalline  bodies  to  serve  as 
part  of  the  supply  of  urea  which  passes  from  it. 

Uric  Acid.  This,  like  urea,  is  a  normal  constituent  of  urine, 
and.  like  urea,  has  been  found  in  the  blood,  and  in  the  liver  and 
spleen  ;  we  have  already,  p.  446,  referred  to  its  relations  with  this 
latter  organ.  In  some  animals,  such  as  birds  and  most  reptiles,  it 
takes  the  place  of  urea.  In  various  diseases  the  quantity^  in  the 
urine  is  increased ;  and  at  times,  as  in  gout,  uric  acid  accumulates 
in  the  blood,  and  is  deposited  in  the  tissues.  By  oxidation  a 
molecule  of  uric  acid  can  be  split  up  into  two  molecules  of  urea, 
and  a  molecule  of  mesoxalic  acid.  It  may  therefore  be  spoken  of 
as  a  less  oxidized  product  of  proteid  metabolism  than  urea;  but 
there  is  no  evidence  whatever  to  shew  that  the  former  is  a  necessary 
antecedent  of  the  latter ;  on  the  contrary,  all  the  facts  known  go 
to  shew  that  the  appearance  of  uric  acid  is  the  result  of  a  metabol- 
ism slightly  diverging  from  that  leading  to  urea.  And  we  have  no 
evidence  to  prove  that  the  cause  of  the  divergence  lies  in  an 
insufficient  supply  of  oxygen  to  the  organism  at  Urge;  on  the 
contrary,  uric  acid  occurs  in  the  rapidly  breathing  birds,  as  well 
as  in  the  more  torpid  reptiles.  It  has  been  urged^  that  birds, 
though  breathing  with  great  energy,  yet  consume  oxygen  to  such 
an  extent  that  in  spite  of  their  income  they  are  always  in  lack  of 
it ;  but  of  this  there  is  no  proof,  while  the  richness  of  their  blood 
in  red  corpuscles  points  in  the  opposite  direction.  Nor  can  the 
fact  that  in  the  frog  urea  again  replaces  uric  acid  be  explained  by 

'  It  need  hardly  be  pointed  out  that  an  increase  in  the  quantity  of  uric  acid 
in  the  urine  must  be  distinguished  from  an  increase  in  'Ca.^ prominence  of  uric 
acid  due  to  the  precipitation  of  its  alkaline  salts 

-  Odling,  Lectures  on  Aniinal  Chemistry,  p.  144. 


CHAP,    v.]  NUTRITION.  453 

reference  to  that  .Tiiimal  h.ivinc;  so  large  a  cutaneous  in  addition  to 
its  pulmonary  nspiration.  The  final  causes  of  the  divergence  are 
to  be  sought  rather  in  the  fact  that  urea  is  the  form  adaptjd  to  a 
fluid,  and  uric  acid  to  a  more  solid  excrement. 

Hippuric  Acid.  In  the  urine  of  herbivora  uric  acid  is  for 
the  most  j)art  absent,  being  replaced  by  hippuric  acid.  In  the 
urine  of  omnivorous  man,  both  acids  may  be  present  together. 
The  history  of  the  hijjpuric  acid  of  urine  is  very  instructive ;  for 
though  at  first  sight  its  presence  might  appear  to  indicate  that  the 
metabolism  of  the  herbivora  is  in  some  points  fundamentally 
different  from  that  of  carnivora,  there  can  be  little  doubt  that  the 
hippuric  acid  which  appears  in  the  urine  of  herbivora  comes 
directly  from  the  ingested  food.  Hip[)uric  acid  is  a  compound 
of,  or  rather  a  result  of  the  union  or  conjugation  of,  benzoic  acid 
and  glycin  ;  and  when  benzoic  acid  is  introduced  into  the  stomach 
of  an  animal,  whether  herbivorous  or  not,  it  reappears  not  as 
benzoic  but  as  hippuric  acid.  It  evidently  meets,  somewhere  in 
the  body,  with  glycin  ;  and  uniting  with  this  becomes  hippuric 
acid,  in  which  form  it  passes  out  by  the  urine,  Nitrobenzoic  acid 
in  a  similar  way  bectmies  nitrohippuric  acid  ;  and  many  other 
bodies  of  the  aromatic  class,  by  a  like  assumption  of  glycin, 
become  conjugated  in  their  passage  through  the  body. 

The  knowledge  of  the  fact  that  benzoic  acid  is  thus  converted 
into  hippuric  acid  naturally  suggested  the  idea  that  the  food  of 
herbivora  might  contain  either  benzoic  acid,  or  some  allied  body, 
and  that  the  i)resence  of  hippuric  acid  as  a  normal  constituent  of 
urine  might  be  thus  accounted  for.  And  Meissner  and  Shepard'. 
have  shewn  that  all  the  hippuric  acid  of  herbivorous  urine  is  in 
reality  due  to  the  presence  in  ordinary  fodder  (hay)  of  a  particular 
constituent  containing  a  benzoic  residue ;  when  this  constituent  is 
withdrawn,  the  hippuric  acid  disappears  from  the  urine.  They 
regarded  this  substance  as  a  particular  form  of  cellulose  ;  but  this 
does  not  seenii  certain^ 

As  far  as  we  know,  glycin  docs  not  exist  performed  or  in  a  free 
state  in  any  tissue  of  the  body,  but  it  makes  its  appearance  during  the 
decomposition  ol'  proteids  and  of  gclatmc,  and  may  be  tornied  bv 
various  reactions  from  those  bodies  :  and  the  presence  in  the  bile  of 
plycocholic  acid,  which  results  from  the  union  or  conjugation  of 
glycin  and  cholalic  acil  (see  p.  256),  shews  that,  in  the  liver  at  all 
events,  compounds  of  glycin  may  be  formed.     Kiihuc  and  Hallwachs^ 

'  Di<:  Hippursiitire,  Hannover,  1S66. 

'  Cf.  Wciske,  Zt.  f  Biol.,  .Kli.  (1S76)  p.  241, 

3  Virchow's  Archtv,  xil.  (1S57)  3S6. 


454  THE   STATISTICAL   METHOD.  [BOOK   II. 

observed  that  benzoic  acid  when  injected  into  the  portal  vein  suffi- 
ciently slowly  issued  by  the  urine  as  hippuric  acid,  but  when  injected 
into  the  jugular  vein,  especially  with  any  rapidity,  passed  out  in  the 
urine  as  unchanged  benzoic  acid  ;  they  also  found  that  benzoic  acid 
introduced  into  the  stomach,  passed  out  as  benzoic  acid  when  the  liver 
had  been  excised.  Hence  they  concluded  that  the  transformation  of 
benzoic  into  hippuric  acid  took  place  in  the  liver,  the  former  acid 
finding  in  that  organ  the  glycin  necessary  for  the  transformation. 
Meissner  and  Shepard' however  maintained  that  the  transformation 
of  benzoic  into  hippuric  acid  took  place  not  so  much  in  the  liver  as  in 
the  kidney;  and  Bunge  and  Schmiedeberg^  have  brought  forward 
experimental  evidence  to  the  same  effect. 

Of  the  meaning  of  the  appearance  in  the  tissues  of  such  bodies 
as  xanthin,  &c.,  and  of  the  exact  nature  of  the  metabolism  which 
they  undergo,  we  know  nothing.  We  cannot  say  whether  they 
are  simply  the  accidental  bye-products  of  nitrogenous  metabol- 
ism, the  result  of  imperfect  chemical  machinery ;  or  whether 
they,  though  small  in  quantity,  serve  some  special  ends  in  the 
economy. 

Sec.  3,     The  Statistics  of  Nutrition. 

The  preceding  sections  have  shewn  us  how  wholly  impossible 
it  is  at  present  to  master  the  metabolic  phenomena  of  the  body  by 
attempting  to  trace  out  forwards  or  backwards  the  several  changes 
undergone  by  the  individual  constituents  of  the  food,  the  body  or 
the  waste  products.  Another  method  is  however  open  to  us,  the 
statistical  method.  We  may  ascertain  the  total  income  and  the 
total  expenditure  of  the  body  during  a  given  period,  and  by  com- 
paring the  two  may  be  able  to  draw  conclusions  concerning  the 
changes  which  must  have  taken  place  in  the  body  while  the 
income  was  being  converted  into  the  outcome.  Many  researches 
have  of  late  years  been  carried  out  by  this  method ;  but  valuable 
as  are  the  results  which  have  been  thereby  gained,  they  must  be 
received  with  caution,  since  in  this  method  of  inquiry  a  small 
error  in  the  data  may,  in  the  process  of  calculation  and  inference, 
lead  to  most  wrong  conclusions.  The  great  use  of  such  inquiries, 
is  to  suggest  ideas,  but  the  views  to  which  they  give  rise  need 
to  be  verifi-id  in  other  ways  before  they  can  acquire  real  worth. 

Composition  of  the  Animal  Body.  The  first  datum 
we  require  is  a  knowledge  of  the  composition  of  the  body,  as  far 
as  the  relative  proportion  of  the  various  tissues  is  concerned.     In 

'  Op.  cit. 

=  Archiv  f.  Exp.  Pathol.,   Vi.    (1876)   p.   233.     Cf.  also    Koch^,    Pfluger's 
Archiv,  XX.  {1879)  p.  64. 


CIIAP.    v.]  NUTRITION.  455 

tlic  liuman  body,  according  to  E.  Bischoft"',  the  cliicf  tissues  are 
rouiul  in  the  following  proportions  by  weight : 

Adult  man  New-born  baby 

(aged  33).  (boy). 

177  p.c. 

22-9     „ 
30     „ 

1 1 '5    .. 


Skeleton 

15-9 

Muscles 

41-8 

Thoracic  viscera 

17 

Abdominal  viscera 

7-2 

Fat 

i8-2 

Skin 

6-9 

15rain 

i-y 

i5'8    „ 

An  analysis  of  a  cat  gave  Bidder  and  Schmidt^  the  following : 
Muscles  and  tendons  .   45*0  p.c. 

Bones  147    ,, 

Skin  i2'o   ,, 

Mesentery  and  adi]Jose  tissue      3 "8    „ 
Liver  4-8   „ 

Blood  (escajiing  at  death)  6'o    „ 

Other  organs  and  tissues  137    „ 

One  point  of  importance  to  be  noticed  in  these  analyses  is 
that  the  skeletal  muscles  form  nearly  half  the  body ;  and  we  have 
already  seen  (p.  40)  that  about  a  quarter  of  the  total  blood  in  the 
body  is  contained  in  them.  Wc  infer  from  this  that  a  large  part  of 
the  metabolism  of  the  body  is  carried  on  in  the  muscles.  Next 
to  the  muscles  we  must  place  the  livei',  for  though  far  less  in  bulk 
than  them,  it  is  subject  to  a  very  active  metabolism,  as  shewn  by 
the  fact  that  it  alone  holds  about  a  quarter  of  fhe  whole  blood. 

The  Starving  Body.  Before  attempting  to  study  the 
influence  of  food,  it  will  be  useful  to  ascertain  what  changes  occur 
in  a  body  when  ail  food  is  withheld.  Voit  ^  found  that  a  cat  lost 
in  a  hunger  period  of  13  days  734  grammes  of  solid  material,  of 
which  248-8  were  fat  and  118-2  muscle,  the  remainder  being 
derived  from  the  other  tissues.  The  percentage  of  dry  solid 
matter  lost  by  the  more  important  tissues  during  the  period  was  as 
follows  : 

Adipose  tissue  97-0 

Spleen  63-1 

Liver  56-6 

Muscles  30-2 

Blood  17-6 

Brain  and  spinal  cord  o-o 

'  Quolci!  \<y  Rankc,  Gruitdziig,;  p.  14^  =  Die  VcrJauungssalte,  p.  329. 

3  Zt.f.  Biol.,  II.  (i«66)  307. 


456  THE   STATISTICAL   METHOD.  [BOOK   II 

Thus  the  loss  during  starvation  fell  most  heavily  on  the  fat, 
indeed  nearly  the  whole  of  this  disappeared.  Next  to  the  fat,  the 
glandular  organs,  the  tissues  which  we  have  seen  to  be  eminently 
metaboHc,  suffered  most.  Then  come  the  muscles,  that  is  to  say, 
the  skeletal  muscles,  for  the  loss  in  the  heart  was  very  trifling; 
obviously  this  organ,  on  account  of  its  importance  in  carrying  on 
the  work  of  the  economy,  was  spared  as  much  as  possible ;  it  was 
in  fact  fed  on  the  rest  of  the  body.  The  same  remark  applies  to 
the  brain  and  spinal  cord ;  in  order  that  life  might  be  prolonged 
as  much  as  possible,  these  important  organs  were  nourished 
by  material  drawn  from  less  noble  organs  and  tissues.  The 
blood  suffered  proportionately  to  the  general  body-waste,  becoming 
gradually  less  in  bulk  but  retaining  the  same  specific  gravity ;  of 
the  total  dry  proteid  constituents  of  the  body  17  "3  p.c,  was  lost, 
which  agrees  very  closely  with  the  17 '6  p.c.  lost  by  the  blood.  It 
is  worthy  of  remark  that  the  tissues  in  general  became  more 
watery  than  in  health. 

We  might  infer  from  these  data  the  conclusions  that  metabolism 
is  most  active  first  in  the  adipose  tissue,  next  in  such  metabolic  tissues 
as  the  hepatic  cells  and  spleen-pulp,  then  in  the  muscles,  and  so  on  ; 
but  these  conclusions  must  be  guarded  by  the  reflection  that  because 
the  loss  of  cardiac  and  nervous  tissue  was  so  small,  we  must  not 
therefore  infer  that  their  metabolism  was  feeble  ;  they  may  have  under- 
gone rapid  metabolism,  and  yet  have  been  preserved  from  loss  of 
substance  by  their  drawing  upon  other  tissues  for  their  material. 

During  this  starvation-period,  the  urine  contained  in  the  form 
of  urea  (for,  as  we  shall  see,  the  other  nitrogenous  constituents  of 
urine  may  for  the  most  part  be  disregarded)  27  7  grammes  oi 
nitrogen.  Now  the  amount  of  muscle  which  was  lost  during  the 
period  contained  about  15 "2  of  nitrogen.  Thus,  more  than  half 
the  nitrogen  of  the  outcome  during  the  starvation-period  must 
have  come  ultimately  from  the  metabolism  of  muscular  tissue. 
This  is  an  important  fact  of  which  we  shall  be  able  to  make  use 
hereafter.  Bidder  and  Schmidt'  came  to  the  conclusion,  from 
their  observations  on  a  starving  cat,  that  the  quantity  of  urea 
excreted  per  diem,  in  all  but  the  earlier  days  of  the  inanition 
period,  bore  a  fixed  ratio  to  the  body  weight.  In  the  first  two  or 
three  days  of  the  period,  the  daily  quantity  of  urea  was  much 
greater  than  this.  They  were  thus  led  to  distinguish  two  sources 
of  urea:  a  quantity  arising  from  the  functional  activity  of  the 
whole  body,  and  therefore  bearing  a  fixed  ratio  to  the  body-weight, 
and  continuing  until  near  the  close  of  life ;  and  a  quantity  arising 

'  Die  Verdinmngssdfte,  1852. 


CHAP,    v.]  NUTRITION.  457 

from  the  amount  of  surplus  nitrogenous  or  proteid  materinl  which 
happcnc'i  to  be  stored  up  in  the  body  at  the  commencement  of 
the  period,  and  which  was  rai)idly  got  rid  of.  The  latter  they 
regarded  as  not  entering  distinctly  into  the  comi:)Ositinn  of  the 
tissues,  but  as,  so  to  speak,  floating  capital,  upon  which  each  or 
any  of  the  tissues  could  draw.  They  spoke  of  its  direct  meta- 
bolism as  a  luxi/s  consinnption.  Bischofif  and  Voit',  however,  by 
means  of  more  extended  observations,  concluded  that  though  the 
urea  of  the  first  two  or  three  days  much  e.xceeds  that  of  the 
subseciuent  days  of  a  starvation-i)eriod,  no  such  fixed  relation  of 
urea  to  body-w.-ight  as  that  suggested  by  Bidder  and  Schmidt 
obtains  ;  but  that  the  quantity  which  is  passed  is  directly  de- 
pendent on  the  amount  of  proteid  material  present  in  the  food 
during  the  days  antecedent  to  the  commencement  of  the  starvation- 
periotl.  This  question  of  a  luxus  consumption  is  one  to  wiiich 
we  shall  frequontly  have  to  refer. 

The  Normal  Diet.  What  is  the  proper  diet  for  a  given 
animal  under  given  circumstances  can  only  iDe  determined  when 
the  laws  of  nutrition  are  known.  Meanwhile  it  is  necessary  to 
gain  an  approximate  idea  of  what  may  be  considered  as  the  normal 
diet  for  a  body  such  as  that  of  man  under  ordinary  circumstances. 
This  may  be  settled  either  by  taking  a  very  large  average,  or  by 
determining  exactly  the  conditions  of  a  particular  case.  In  the  table 
below  is  given  both  the  average  result  obtained  by  Moleschott  * 
from  a  large  number  of  public  diets,  and  the  diet  on  which 
Ranke  3  found  himself  in  good  health,  neither  losing  nor  gaining 
weight. 


Moleschott. 

Ranke  (weight  74  kilos). 

Proteids 

30 

ICO 

Fat 

.  H 

100 

Amyloido 

404 

240 

Salts 

30 

25 

Water 

2800 

2600 

Of  these  two  diets,  which  agree  in  many  respects,  that  of 
Ranke  is  probably  the  better  one,  since  in  public  diets,  from  which 
Molescliott's  table  is  drawn,  the  cheaper  carbohydrates  are  used 
to  the  exclusion  of  the  dearer  fats. 

'  Die  Gcsdz<  d .  F.rniihrung  desFUischfresxos,  i860. 

'  Die  Xakrum^sinitlt-I,  p.  216. 

3   Tel  nuts,  p.  249;   Grundziige,  p.  158. 


458  THE   STATISTICAL   METHOD.  [BOOK   II. 

Comparison  of  Income  and  Outcome. 

Method.  We  have  now  to  inquire  how  the  elements  of  such 
a  diet  are  distributed  in  the  excreta,  in  order  that,  from  the  manner 
of  the  distribution,  we  may  infer  the  nature  of  the  intermediate 
stages  which  take  place  within  the  body.  By  comparing  the  ingesta 
with  the  excreta,  we  shall  learn  what  elements  have  been  retamed 
in  the  body,  and  what  elements  appear  in  the  excreta  which  were 
not  present  in  the  food  ;  from  these  we  may  infer  the  changes 
which  the  body  has  undergone  through  the  influence  of  the  food. 

In  the  first  place,  the  real  income  must  be  distinguished  from 
the  apparent  one  by  the  subtraction  of  the  faeces.  We  have  seen 
that  by  far  the  greater  part  of  the  faeces  is  undigested  matter,  i.e. 
food  which,  though  placed  in  the  alimentary  canal,  has  not  really 
entered  into  the  body.  The  share  in  the  fasces  taken  up  by  matter 
which  has  been  excreted  from  the  blood  by  the  alimentary  canal, 
is  so  small  that  it  may  be  neglected ;  certainly  with  regard  to 
nitrogen,  the  vrhole  quantity  of  this  element,  which  is  present  in 
the  fsces,  may  be  regarded  as  indicating  simply  undigested 
nitrogenous  matter. 

In  comparing  the  income  and  outcome  of  a  given  period  great 
difficulty  is  often  found  in  determining  whether  the  faeces  passed  in  the 
early  days  of  the  period  belong  to  the  income  of  the  period,  or  are  the 
remains  of  food  taken  before.  The  difficulty,  however,  is  frequently 
lightened  when  the  'diet  of  the  experimental  period  differs  from  the 
foregoing  diet.  Thus  in  the  dog,  the  fiEces  of  a  bread  diet  may  easily 
be  distinguished  from  those  of  a  meat  diet. 

The  income,  thus  corrected,  will  consist  of  so  much  nitrogen, 
carbon,  hydrogen,  oxygen,  sulphur,  phosphorus,  saline  matters, 
and  water,  contained  in  the  proteids,  fats,  carbohydrates,  salts, 
and  water  of  the  food,  together, with  the  oxygen  absorbed  by  the 
lungs,  skin,  and  alimentary  canal.  The  outcome  may  be  regarded 
as  consisting  of  (i)  the  respiratory  products  of  the  lungs,  skin, 
and  alimentary  canal,  consisting  chiefly  of  carbonic  acid  and 
water,  with  small  quantities  of  hydrogen  and  carburetted  hydro- 
gen, these  two  latter  coming  exclusively  from  the  alimentary  canal  ; 
(2)  of  perspiration,  consistmg  chiefly  of  water  and  salts,  for  the 
dubious  excretion  (see  p.  400)  of  urea  by  the  skin  may  be  neg- 
lected and  the  other  organic  constituents  of  sweat  amount  to 
very  little ;  and  (3)  of  the  urine,  which  is  assumed  to  contain  all 
the  nitrogen  really  excreted  by  the  body,  besides  a  large  quantity 
of  saline  matters,  and  of  water.  Where  greater  accuracy  is  re- 
quired the  total  nitrogen  of  the  urine  ought  to  be  determined;  it 


CHAP,    v.]  NUTRITION.  459 

is  maintained,  however,  that  no  errors  of  serious  importance  arise 
when  the  urea  alone,  as  determined  by  Liebig's  method,  is  taken 
as  the  measure  of  the  total  quantity  of  nitro^^en  in  the  urine. 

It  has  been  ani  indeed  still  is  debated  whether  the  body  may  not 
suffer  lo'^s  of  nitrogen  by  other  channels  than  by  the  urine,  whether 
nitrogen  may  not  leave  the  body  by  the  skin  or  indeed  in  a  gaseous  sfite 
by  the  lungs.  While  Boiissingiult,  Regnault,  Reiset,  and  Harral 
believed  that  su^h  was  the  case.  Bidder  and  Schmidt,  Bischoff  and 
Voit,  Rankc,  Henneberg  and  others  have  come  to  the  contrary  con- 
cius  on  that  all  the  nitrogen  of  the  ingesta  passes  out  as  the  nitrogen 
of  the  urine  and  faeces,  a  view  \vhi:h  derives  its  strongest  support  from 
the  observations  of  \'oit  on  a  pigeon '.  That  indefatigable  observer 
fed  for  a  considerable  time  a  pigeon  on  a  known  diet  (peis),  the 
nitrogen  of  samples  of  which  was  carefully  determined,  and  during 
the  whole  period  collected  and  determined  the  nitrogen  of  the  faeces 
and  urine.  At  the  end  of  the  period,  the  nitrogen  of  the  latter  was 
found  to  correspond  almost  exactly  to  the  nitrogen  of  the  fool,  allow- 
ance being  made  for  a  retention  of  a  small  quantity  of  nitrogen  in  the 
body  to  supply  a  slight  gain  in  weight  which  was  assumed  to  be 
'flesh.'  Quite  recently  Seegen  and  Nowak-have  revived  the  older 
views  of  the  French  physiologists,  since  they  find  an  actual  increase 
of  nitrogen  (4  to  9  m.  grm.  per  hour  per  kilo  of  body-weight  of 
animal)  in  the  air  of  a  confined  chamber  in  which  an  animal  has  been 
kept  for  several  hours,  the  air  being  continually  supplied  with  oxygen, 
and  the  carbonic  acid  and  other  products  removed.  They  urge  against 
Voit's  experiment  that  peas  and  other  articles  of  food  vary  so  much  in 
their  nitrogen  that  in  calculating  the  whole  nitrogen  of  the  ingesta 
during  a  long  time  from  the  determined  nitrogen  of  samples,  errors 
are  introduced  of  such  a  magnitude  as  to  render  the  data  almost 
valueless. 

Of  these  elements  of  the  income  and  outcome,  the  nitrogen, 
the  carbon,  and  the  free  oxygen  of  respiration  are  by  far  the  most 
important.  Since  water  is  of  use  to  the  body  for  merely 
mechanical  purposes,  and  not  solely  as  food  in  the  strict  sense  of 
the  word,  the  hydrogen  element  becomes  a  dubious  one ;  the 
sulphur  of  the  proteids,  and  the  phosphorus  of  the  fats,  are  in- 
significant in  amount;  while  the  saline  matters  stand  on  a  wholly 
different  footing  from  the  other  parts  of  food,  inasmuch  as  they 
are  not  sources  of  energy,  and  pass  through  the  body  with  com- 
paratively little  change.  The  body-weight  must  of  course  be 
carefully  ascertained  at  the  beginning  and  at  the  end  of  the 
period,  correction  being  made  where  possible  for  the  freces. 

It  will  be  seen  that  the  labour  of  such  inquiries  is  consider- 
able,     i'he  urine,  which  must  be  carefully  kept  separate  from  the 

'  /Inn.  Chem.  Pharm.  Suppl.  II.  1S63. 
'  Pfliiger's  Archiv,  XIX.  U879)  p.  34. 


460  THE   STATISTICAL   METHOD.  [BOOK  II. 

faeces,  requires  daily  measurement  and  analysis.  Any  loss  by  the 
skin,  either  in  the  form  of  sweat,  or,  in  the  case  of  woolly 
animals,  of  hair,  must  be  estimated  or  accounted  for.  The  food 
of  the  period  must  be  as  far  as  possible  uniform  in  character,  in 
order  that  the  analyses  of  specimens  may  serve  faithfully  for 
calculations  involving  the  whole  quantity  of  food  taken ;  and  this 
is  especially  the  case  when  the  diet  is  a  meat  one,  since  portions 
of  meat  differ  so  much  from  each  other.  But  the  greatest 
difficulty  of  all  lies  in  the  estimation  of  the  carbonic  acid  pro- 
duced and  the  oxygen  consumed.  In  the  earlier  researches,  such 
as  those  of  Bischoff  and  Voit,  this  element  was  neglected  and 
the  variations  occurring  were  simply  guessed  at,  through  which 
very  serious  errors  were  introduced.  No  comparison  of  income 
and  outcome  can  be  considered  satisfactory  unless  the  carbonic 
acid  produced  be  directly  measured  by  means  of  a  respiration 
chamber.  And  in  order  that  the  comparison  should  be  really 
complete,  the  water  given  off  by  skin  and  lungs  must  be  directly 
measured  also ;  but  this  seems  to  be  more  difficult  than  the 
determination  of  the  carbonic  acid. 

Pettenkofer  and  Voit '  were  the  first  to  make  use  on  a  large  scale  of 
this  means  of  inquiry.  Their  apparatus  consists  essentially  of  a  large 
air-tight  chamber,  capable  of  holding  a  man  comfortably.  By  means 
of  a  steam-engine  a  current  of  pure  air,  measured  by  a  gasometer,  is 
drawn  through  the  chamber.  Measured  portions  of  the  outgoing  air 
are  from  time  to  time  withdrawn  and  analysed  ;  and  from  the  data 
afforded  by  these  analyses,  the  amount  of  carbonic  acid  (and  other 
gases)  and  water  given  off  by  the  occupant  of  the  chamber  during  a 
given  time  is  determined.  The  apparatus  works  so  well  that  Petten- 
kofer and  Voit  were  able  almost  exactly  to  recover  the  carbonic  acid 
produced  by  the  burning  of  a  stearin  candle  in  the  chamber,  the  error 
not  amounting  to  more  than  3  per  cent.  ;  the  recovery  of  the  water 
was  less  satisfactory,  the  discrepancies  being  very  considerable. 

If  the  total  amount  of  carbonic  acid  and  water  given  out  by 
the  lungs  and  skin  be  known,  as  well  as  the  amount  of  urine  and 
fseces,  then  the  quantity  of  oxygen  can  be  determined  by  a  simple 
calculation.  For  evidently  the  difference  between  the  terminal 
weight  plus  all  the  egesta  and  the  initial  weight  plus  all  the  ingesta 
can  be  nothing  else  than  the  weight  of  the  oxygen  absorbed 
during  the  period. 

Let  us  imagine,  then,  an  experiment  of  this  kind  to  have  been 
completely  carried  out,  that  the  animal's  initial  and  terminal 
weights  have  been  accurately  determined,  the  composition  of  the 
food   satisfactorily   known    to    consist  of  so  much   proteid,    lat, 

'  Ann.  Chem.  Pharm.  Suppl.  II.  1S63.  ^  ;  : 


CIIAF.    v.]  NUTRITION.  4^1 

carbohydrates,  salts,  and  water,  and  to  contain  so  nnirh  nitrogen 
and  carbon,  the  weiglit  of  the  faeces  and  the  nitrogen  they  contain 
ascertained,  the  nitrogen  of  the  urine  determined,  tlie  carbonic 
acid  and  water  given  off  by  tlie  wliole  body  carefully  nieasureii, 
and  the  amount  of  oxygen  absorbed  calculated — wiuit  interpreta- 
tion can  be  placed  on  the  results  ? 

Let  us  suppose  that  the  animal  has  gained  lo  in  weight  during 
the  period.      Of   what  does  w  consist?      Is   it   fat   or  protciil 
material  which  has  been  laid  on,  or  simply  water  which  has  been 
retained,    or  some   of  one  and  of  the   other?      Let  us  further 
suppose  that  the  nitrogen  of  the  urine  passed  during  the  period 
is  less,  say  by  x  grammes,  than  the  nitrogen  in  the  food  taken,  of 
course  after  deduction  of  the  nitrogen  in  the  faeces.     This  means 
that  X  grammes  of  nitrogen  have  been  retained  in  the  body  ;  and 
we  may  with  reason  infer  that  they  have  been  retained  in  the  form 
of  proteid  material.     We  may  even  go  farther  and  say  that  they 
are  retained  in  the  form  of  tlesh,  i.e.  of  muscle.     In  this  inference 
\ve  are  going  somewhat  beyond  our  tether,  for  the  nitrogen  might 
be  stored  up  as  hepatic,  or  s[)lenic,  or  any  other  form  of  proto- 
plasm.     Indeed  it  might  be  for  the  while  retained  in  the  form  of 
some  nitrogenous  crystalline  body  ;  but  this  last  event  is  unlikely  ; 
and  if  we  use  the  word  '  ilesh '  to  mean  protoplasm  of  any  kind, 
contractile  or  metabolic,  or  of  any  other  kind,  we  may  without 
fear  of   any  great  error  reckon    the   deficiency   of   x   grammes 
nitrogen  as  indicating  the  storing  up  of  a  grammes  flesh.     There 
still  remain    iv -a  grammes  of   increase  to   be   accounted   for. 
Let  us  "suppose  that  the  total  carbon  of  the  egesta  has  been  found 
to  be  J' grammes  less  than  that  of  the  ingesta ;  in  other  words, 
that  y  grammes  of  carbon  have  been  stored  up.      Some  carbon  has 
been  stored  up  in  the  flesh  with  the  nitrogen  just  considered  ; 
this  we  must  deduct  from  _>-,  and  we  shall  then  have  y    grammes 
of   carbon   to  account    for.      Now   there  are   only  two   principal 
forms  in  which  carbon  can  be  stored  up  in  the  body :  as  glycogen 
or  as  fat.     The  former  is  even   in  most  favourable  cases  incon- 
siderable, and  we  therefore  cannot  err  greatly  if  wc  consider  the 
retention  of  y  grammes  carbon  as  indicating  the  laying  on   ot  b 
grammes  fat.       If  a-f-^  are  found   equal   to  w,  then   the  whole 
change  in  the  economy  is  known  ;  if  70  -  (a  +  b)  leaves  a  residue 
c,  we  inter  that  in  addition  to  the  laying  on  of  flesh  and  fat  some 
water   has  been  retained   in  the   system.     If  7C>  —  {a  +  b)   gives  a 
negative  quantity,  then  water  must   have  been   given   oft"  at   the 
same  time  that  flesh  and  fat  were  laid  on.      In  a  similar  way  the 
nature  of  a  loss  of  weight  can   be  ascertained,  whether   of  flesh, 
or  fat,  or  of  water,  and  to  what  e.xtent  of  each.     The  careful 


462  NITROGENOUS   METABOLISM.  [BOOK  II. 

comparison,  the  debtor  and  creditor  account  of  income  and  out- 
come, enables  us,  with  the  cautions  rendered  necessary  b)'  the 
assumptions  just  now  mentioned,  to  infer  the  nature  and  extent 
of  the  bodily  changes.  The  results  thus  gained  ought  of  course, 
if  an  account  is  kept  of  the  water,  to  agree  with  the  amount  of 
oxygen  consumed,  and  also  to  tally  with  the  conclusions  arrived 
at  concerning  the  retention  or  the  reverse  of  water. 

Pettenkofer  and  Volt  did  succeed  in  drawing  up  a  completely 
accurate  balance  sheet,  the  discrepancy  being  exceedingly  small ;  but  it 
has  been  justly  urged  that,  in  face  of  the  possible  sources  of  error,  so 
complete  an  accuracy  is  in  itself  suspicious. 

Having  thus  studied  the  method  and  seen  its  weakness  as  well 
as  its  strength,  we  may  briefly  review  the  results  which  have  been 
obtained  by  its  means. 

Nitrogenous  Metabolism.  When  a  diet  of  lean  meat,  as 
free  as  possible  from  fat,  is  given  to  a  dog,  which  has  previously 
been  deprived  of  food  for  some  time,  and  whose  body  diereforejs 
greatly  deficient  m  flesh,  it  might  be  expected  that  the  great  mass 
of  food  would  be  at  once  stored  up,  and  only  a  small  quantity  be 
immediately  worked  off  as  an  additional  quantity  of  urea, 
occasioned  by  the  increased  labour  thrown  on  tlie  economy  by  the 
very  presence  of  the  food.  This  however  is  not  the  case  ;  the 
larger  portion  passes  off  as  urea  at  once,  and  only  a  comparatively 
small  quantity  is  retained.  If  the  diet  be  continued,  and  we  are 
supposing  the  meals  given  to  be  ample  ones,  the  proportion  of 
the  nitrogen  which  is.  given  off  in  the  form  of  urea  goes  on 
increasing  until  at  last  a  condition  is  established  in  which  the 
nitrogen  of  the  egesta  exactly  equals  that  of  the  ingesta.  This 
condition,  which  is  spoken  of  as  nitrogenous  equilibrium,  is 
attained  in  dogs  with  an  exclusively  meat  diet  only  when  largd 
quantities  of  food  are  given,  and  is  not  easily  maintained  for  any 
length  of  time.  The  exact  quantity  of  meat  required  to  attain 
nitrogenous  equilibrium  \aries  with  the  previous  condition  of  the 
dog;  it  is  frequently  seen  when  1500  or  1800  grms.  of  meat  are 
given  daily.  Thus  the  most  strikmg  effect  of  a  purely  nitrogenous 
diet  is  largely  to  increase  the  nitrogenous  metabolism  of  the  body. 
This  result  has  been  explained  by  supposing  that  with  the  meat 
diet  the  consumption  of  oxygen  is  largely  increased  ;  in  other 
words,  that  the  oxidizing  activity  of  the  body  is  directly  aug- 
mented by  a  meat  diet.  This  in  turn  may  be  due  in  part  to  the 
fact  that  proteid  food  largely  increases  the  number  of  the  red 
corpuscles,  and  so  augments  the  amount  of  oxygen  with  which 
the  tissues  are  supplied ;  but  as  we  ha.ve  already  urged  more  than 


CHAP,   v.]  NUTRITION.  463 

once  the  oxidative  activity  of  tlie  tissues  is  deterrmned  by  tlic 
tissues  themselves  rather  than  by  the  mere  abundance  of  oxygen 
at  their  disposal  ;  and  probably  other  agencies  are  at  work. 

When  nitrogenous  eciuilibriuin  is  establishetl,  it  does  not  mean 
that  a  body  eciuilibrium  is  established,  that  the  body  weight 
neither  increases  nor  diminishes.  On  the  contrary,  when  the 
meal  necessary  to  balance  the  nitrogen  is  a  large  one,  the  body 
may  gain  in  weight,  and  the  increase  is  proved,  both  by  calculation 
liom  the  income  and  outcome,  and  by  actual  examination  of  the 
liody,  to  be  due  to  the  laying  on  of  fiat.  The  amount  so  stored 
up  may  be  far  greater  than  can  possibly  be  accounted  for  by  any 
fat  still  adhering  to  the  meat  given  as  food.  We  are  therefore 
driven  to  the  conclusion  that  the  proteid  food  is  split  into 
a  urea  moiety  and  a  fatty  n)oiety,  that  the  urea  moiety  is 
at  once  discharged,  and  that  such  of  the  fat  as  is  not  made  use  of 
direcdy  by  the  body  is  stored  up  as  adipose  tissue.  And  this  dis- 
ruption of  the  i)roteid  food  at  the  same  time  explains  why  the 
meat  diet  so  largely  and  immediately  increases  the  urea  of  the 
egesta.  We  have  already  pointed  out  that  possibly  this  disruptive 
metabolism  of  proteids  is  largely  carried  on  in  the  alimentary 
canal  itself  by  the  aid  of  the  pancreatic  juice  ;  whether  or  to  what 
extent  other  organs  share  in  the  action  we  do  not  at  present 
know. 

V'oit  and  others  with  him  speak  in  the  most  decided  way  of  the 
proteids  of  the  body  as  exist! nL,^  in  two  forms  :  organ  or  tissue  proteid 
and  circulating  or  blood  proteid.  They  regard  the  former  as  entering 
into  the  formation  of  tlic  tissues  and  undergoing  functional  meta- 
bolism, the  latter  as  simply  tarrying  in  the  blood  and  undergoing  a 
diroct  oxidative  metabolism.  It  is  of  course  the  latter  alone  which 
suffers  the  kixus  consumption.  To  these  two  Voit  has  been  led  to  add 
a  tliird,  or  intermediate  proteid,  viz.  store  or  surplus  proteid,  which  is 
more  labile  than  tissue  proteid  and  )et  more  stable  than  the  circulating 
proteid.  We  have  again  and  again  insisted  in  the  course  of-  this  work 
that  the  oxidations  of  the  body  take  place  not  in  the  blood  but  in  the 
tissues  ;  and  are  consequently  prepared  to  reject  Voit's  conclusions 
unless  evidence  of  a  strictly /Ji^j-zV/zv  character  can  be  offered  in  their 
favour.  No  such  evidence  however  is  forthcoming  '  ;  the  inost  that 
can  be  said  in  favour  of  them  is  that  they  aflord  an  easy  explanation 
of  the  phenomena  of  proteid  metabolism  ;  on  the  other  hand,  if  we 
admit  a  large  luxus  consumption  in  the  alimentary  canal,  the  remaining 
phenomena  can  be  explained  without  throwing  on  the  tissues  what 
may  appear  too  heavy  a  metabolic  tas.^  And  in  speaking  of  the 
metabolism  of  any  tis-.ue  it  must  be  remembered  that  the  metabolic 
changes  need  not  necessarily  involve  the  so-called  structural  ele- 
ments.    A  fat-cell  may  probably  accumulate  in  and  discharge  from  its 

'  Cf.  lloppe-Scyler,  Plluger's  Archiv,  vii.  (1873)  399- 


464  FATTY   AND   CARBOHYDRATE   FOOD.      [BOOK   II. 

protoplasm  a»  considerable  quantity  of  fat  without  the  morphological 
relations  of  the  cell  undergoing  any  marked  change  ;  and  we  can 
readily  imagine  that  a  tissue  may  suffer  partial  disintegration  and  re- 
integration without  any  interference  with  its  morphological  framework. 
Our  knowledge  however  of  this  matter  is  very  imperfect ;  we  know 
that  when  a  muscle  contracts  it  loses  some  of  its  substance,  but  we 
do  not  at  all  know  which  parts  of  the  fibre  bear  the  loss.  Bearing 
tbis  in  mind,  there  is  nothing  absolutely  to  forbid  the  idea  that  certain 
tissues  (possibly  the  liver)  may  serve,  within  limits,  as  storehouses  ol 
proteid  material  in  the  same  way  that  adipose  tissue  serves  as  a  store- 
house of  fatty  and  the  liver  of  starchy  material.  In  this  sense  Voit's 
surplus  proteid  might  be  accepted  even  when  his  circulating  proteid  is 
rejected. 

The  characteristic  metabolic  effects  of  proteid  food  are  shewn 
not  only  by  these  calculations  of  what  is  supposed  to  take  place 
in  the  body,  but  also  by  direct  analysis.  Lawes  and  Gilbert' 
laboriously  analysing  the  body  of  a  pig,  which  had  been  fed  on  a 
known  diet,  ana  comparing  the  analysis  with  that  of  another  pig 
of  the  same  litter,  killed  at  the  time  when  the  first  was  put  on  the 
fixed  diet,  found  that  of  the  dry  nitrogenous  material  of  the  food 
'only  7 '34  p.  c.  was  laid  up  as  dry  proteid  material  during  the 
fattening  period,  though  the  amount  of  proteid  food  was  low;  in^ 
the  sheep  the  increase  was  only  4'i4  p.c. 

The  Effects  of  Fatty  and   of  Carbohydrate   Food. 

Unlike  those  of  proteid  food,  the  effects  of  fats  and  carbohydrates 
cannot  be  studied  alone.  When  an  animal  is  fed  simply  on  non- 
nitrogenous  food,  death  soon  takes  place  ;  the  food  rapidly  ceases 
to  be  digested,  and  starvation  ensues.  We  can  therefore  only 
study  the  dietetic  effects  of  these  substances  when  taken  in 
connection  with  proteid  material. 

When  a  small  quantity  of  fat  is  taken,  in  company  with  a  fixed 
moderate  quantity  of  proteid  material,  the  whole  of  the  carbon 
of  the  food  reappears  in  the  egesta.  No  fat  is  stored  up,  some 
even  of  the  previously  existing  fat  of  the  body  may  be  consumed. 
As  the  fat  of  the  meal  is  increased,  a  point  is  soon  reached  at 
which  carbon  is  retained  in  the  body  as  fat.  So  also  with  starch 
or  sugar.  When  the  quantity  of  this  is  small,  there  is  no  retention 
of  carbon  ;  as  soon  however  as  it  is  increased  beyond  a  certain 
limit,  carbon  is  stored  up  in  the  form  of  fat,  or,  to  a  smaller 
extent,  as  glycogen.  Fats  and  carbohydrates  therefore  differ 
essentially  from  proteid  food  in  that  they  are  not  distinctly  provo- 
cative of  metabolism.  This  is  exceedingly  well  shewn  in  the 
results  of  Lawes  and  Gilbert,  for  in  the  pig  previously  mentioned 

'  Phil.  Trans.,  1859,  Part  2. 


ClIAr.   v.]  NUTRITION.  4O5 

472  parts  of  fat  were  stored  up  for  every  100  |)arts  of  fat  in  the 
food,  and  of  the  total  dry  non-nitrogenous  food  21 '2  p.  c.  was 
retained  in  the  body  as  fat.  No  clearer  proof  than  this  could  be 
atTorded  that  fat  is  formed  in  the  body  out  of  something  which  is 
not  fat. 

Pettenkofer  and  Voit'  came  to  the  conclusion  that,  marked  as  was 
the  difference  between  proteid  and  non-nitrogenous  food  as  regards 
the  increase  of  metabolism,  fat  did  nevertheless  to  a  certain  extent 
behave  like  proteids  ;  when  an  excess  of  fat  was  given  the  consumption 
of  c.irbon  in  the  body  was  increased,  so  that  only  a  portion  (though  a 
large  portion)  of  the  excess  of  fat  in  the  food  was  stored  up. 

As  one  might  imagine,  the  presence  of  fat  or  carbohydrates  in 
the  food  was  found  to  check  proteid  metabolism ;  nitrogenous 
equilibrium  was  established  with  a  much  less  expenditure  of  pro- 
teid food.  For  instance,  with  a  diet  of  800  grms.  meat  and  150 
grms.  fat,  the  nitrogen  in  the  egesta  became  equal  to  that  in  the 
ingesta  in  a  dog,  in  whose  case  1800  grms.  meat  would  have  to  be 
given  to  produce  the  same  result  in  the  absence  of  fats  or 
carbohydrates. 

On  the  other  hand,  it  was  found,  that  with  a  fixed  quantity  of 
fatty  or  carbohydrate  food,  an  increase  of  the  accompanying  pro- 
teid led  not  to  a  storing  up  of  the  surplus  carbon  contained  in  the 
extra  quantity  of  proteid,  but  to  an  increase  in  the  consumption 
of  carbon.  Proteid  food  increases  not  only  proteid  but  also  non- 
nitrogenous  metabolism.  This  explains  how  an  excess  of  proteid 
food  may,  by  the  increase  of  metabolism,  actually  reduce  the  fat  of 
the  body,  as  is  exemplified  in  the  dietetic  system  known  as  that  of 
Mr.  Banting. 

There  can  be  no  doubt  then  that  both  a  proteid  diet  and  a 
carbohydrate  diet  may  give  rise  to  the  formation  of  fat  within  the 
body.  And  the  question  which  we  have  already  (p.  440)  partly 
discussed  comes  again  before  us.  In  what  way  is  this  fat  so 
"  formed  ?  Is  the  sugar,  arising  during  digestion  from  the  carbohy- 
drate, converted  by  a  series  of  fermentative  changes  into  fat  ?  or 
is  the  sugar  directly  consumed  by  the  tissues  in  oxidative  changes, 
by  which  means  the  fatty  derivatives  of  the  metabolized  proteids 
are  sheltered  from  oxidation  and  stored  up  as  (at  ?  What  light 
does  the  statistical  method  throw  on  this  vexed  question?  Weiske 
and  Wildt*  have  attempted  to  settle  it.  They  took  two  young 
pigs  of  the  same  litter  ;  one  they  killed  and  analysed  as  a  standard 
of  comparison.  The  other  tiiey  fed  for  six  months  on  known  food 
(chiefly  potatoes)  and   then  killed  and  analysed   it.     Supposing 

•  Z<:/.  Biol.  IX.  »  Zt.f.  Biol.  X. 

F.  r.  30 


466  FATTY   AND   CARBO-HYDRATE   FOOD.     [BOOK   II. 

that  the  fattened  pig  had  to  start  with  the  same  composition  as 
the  other,  they  calculated  that  it  had  stored  up  5*5  kilos  of  fat. 
During  the  six  months  it  had  consumed  i4'3  kilos  of  proteid 
material,  of  which  it  had  stored  up  i'3  kilos  and  metabolized 
13  kilos.  On  the  supposition  that  the  metabolism  of  this  13  kilos 
consisted  in  its  being  split  up  into  a  urea  and  a  fatty  moiety,  about 
6  kilos  of  fat  would  thus  have  been  produced.  In  other  words, 
more  than  the  fat  actually  stored  up  might  have  come  from  the 
proteid  of  the  food.  This  of  course  does  not  prove  that  this  was 
its  actual  source;  and  on  the  other  hand  Lawes  and  Gilbert^ 
found  that  in  the  case  of  two  pigs  fed  ad  libitum  on  Indian  corn 
and  barley-meal  respectively,  as  much  as  40  per  cent,  of  the  fat 
produced  and  stored  up  in  the  body  could  not  have  come  from 
the  metabolized  proteids  of  the  food.  In  spite  of  the  analogy  of 
mammar.y  metabolism  (see  p.  444),  we  may  conclude  that  some 
fat  may  come  direct  from  carbohydrate  food. 

Lawes  and  Gilbert  urge  very  justly  that  Weiske  and  Wildt,  in  the 
experiment  just  quoted,  did  not  use  a  sufficiently  fattening  diet,  and  in 
another  experiment  used  too  much  nitrogen.  They  state  that  if  a  pig 
were  fed  on  a  rich  barley-meal  diet  so  that  it  doubled  its  weight  in 
about  eight  or  ten  weeks,  the  amount  of  proteid  metabolized,  in  spite 
of  the  diet  being  richer  in  proteid  material  than  are  potatoes,  would 
probably  be  insufficient  to  account  for  the  fat  stored  up.  This  question 
is  from  a  dietetic  point  of  view  one  of  extreme  importance  ;  for  if  all 
stored  fat  does  oome  from  proteid  food,  then  all  fattening  food  must 
contain  a  due  proportion  of  it. 

We  have  at  present  no  exact  information  concerning  the  nutri- 
tive differences  between  fats  and  carbohydrates,  beyond  the  fact 
that  in  the  final  combustion  of  the  two,  while  carbohydrates  re- 
quire sufficient  oxygen  only  to  combine  with  their  carbon,  there 
being  already  sufficient  oxygen  in  the  carbohydrate  itself  to  form 
water  with  the  hydrogen  present,  fats  require  in  addition  oxygen 
to  burn  off  some  of  their  hydrogen.  Hence  in  herbivora  a 
larger  portion  of  the  oxygen  consumed  reappears  in  the  carbonic 
acid  of  the  egesta,  than  in  carmvora,  where  more  of  it  leaves  the 
body  as  formed  water ;  the  proportions  of  the  oxygen  in  the  car- 
bonic acid  expired  to  the  oxygen  consumed  being  on  an  average 
90  p.  c.  in  the  former  and  60  p.  c.  in  the  latter.  When  a  herbi- 
vorous animal  starves,  it  feeds  on  its  own  fat,  and  under  these 
circumstances  the  oxygen  proportion  in  the  expired  carbonic  acid 
falls  to  the  carnivorous  standard.  The  carbohydrates  are  notabl)i 
more  digestible  than  the  fats,  but  on  the  other  hand  the   fats 

'  "Sources  of  Fat  of  Animal  Body."  Phil.  Mag.  Dec  1866,  See  alsd 
Journ.  Anat.  and  Phys.  xr.  {1877)  p.  577. 


CHAI".    v.]  NUTRITION.  467 

contain  more  jiotential  energy  in  a  given  weight.  As  to  the  die- 
tetic or  rather  nietabol'c  ditlerence  between  starcli  and  sugar,  we 
know  nothing  very  definite.  Lawe.s  and  (iilberl  •  lound  that  cane- 
sugar  was  rather  more  fattening  than  starch. 

The  Effects  of  Gelatine  Feed.  It  is  a  matter  of  common 
experience  that  gelatine  will  not  sujipiy  the  place  of  proteids  as  a 
constituent  of  food.  Animals  fed  on  gelatine  with  fat  or  carbo- 
hydrates die  very  mucii  in  the  same  way  as  when  they  are  fed  on 
non-nitrogenous  material  alone.  Nevertheless  the  researches  of 
Voit'  shew,  as  might  be  expected,  that  the  presence  of  gelatine  in 
food  is  not  without  effect.  According  to  him  nitrogenous  equili- 
brium is  establishetl  at  a  lower  level  of  proteid  food  when  gelatine 
is  added.  Tims  tiie  nitrogen  of  the  ingesta  and  egesta  became 
equal  in  a  dog  on  a  ration  of  400  grms.  proteid  and  200  grms. 
gelatine.  A  dog  moreover  uses  up  less  of  the  nitrogen  of  the 
body  on  a  diet  of  gelatine  and  fat,  than  on  a  diet  of  fat  alone  ; 
and  the  consumption  of  fat  also  seems  to  be  lessened  by  the 
presence  of  gelatine.  All  these  facts  become  intelligible  if  we 
suppose  that  gelatine  is  rapidly  split  up  into  a  urea  and  a  fat 
moiety,  in  the  same  way  that  we  have  seen  a  certain  quantity  of 
proteid  material  to  be.  It  is  this  direct  metabolism  of  proteid 
matter  which  gelatine  can  take  up ;  it  seems  however  unable  to 
imitate. the  other  function  of  proteid  matter,  and  to  take  part  in 
the  formation  of  living  protoplasm.  What  is  the  cause  of  this 
difference,  we  cannot  at  present  say. 

The  Effects  of  Salts  as  Food.  All  food  contains, besides 
the  potential  substances  which  we  have  just  studied,  certain  saline 
matters  organic  and  inorganic,  having  in  themselves  little  or  no 
latent  energy,  but  yet  either  absolutely  necessary  or  highly  bene- 
ficial to  the  body.  These  must  ha\e  important  functions  in 
directing  the  metabolism  of  the  body  :  the  striking  distribution  of 
them  in  the  tissues,  the  preponderance  of  sodium  and  chlorides  in 
blood-serum  and  of  potassium  and  pliosphates  in  the  red  corpuscles 
for  instance,  must  have  some  meaning  ;  but  at  present  we  are  in 
the  dark  concerning  it.  The  element  phosphorus  seems  no  less 
important  from  a  biological  point  of  view  than  carbon  or  nitrogen. 
It  is  as  absolutely  essential  for  the  growth  of  a  lowly  being  like 
Penicillium  as  for  man  himself  We  find  it  probably  playing  an 
important  part  as  the  conspicuous  constituent  of  lecithin,  we  fmd 
it  peculiarly  associated  witli  the  proteids,  apparently  in  the  form  of 

•  Brit.  Assoc.  Reports,   1S54.  '  Zt.  f.  Biol.  viii.  297. 

30—2 


468  THE   ENERGY   OF   THE   BODY.  [BOOK   II. 

phosphates  ;  but  we  cannot  explain  its  role.  The  element  sulphur, 
again,  is  only  second  to  phosphorus,  and  we  find  it  as  a  constituent 
of  nearly  all  proteids ;  but  we  cannot  tell  what  exactly  would 
happen  to  the  economy  if  all  the  sulphur  of  the  food  were  with- 
drawn. We  know  that  the  various  saline  matters  are  essential  to 
health,  that  when  they  are  not  present  in  proper  proportions, 
nutrition  is  affected  as  is  shewn  by  certain  forms  of  scurvy ;  we 
are  aware  of  the  peculiar  dependence  of  proteid  qualities  on  the 
presence  of  salts ;  but  beyond  ihis  we  know  very  little. 


Sec,  4.     The  Energy  of  the  Body. 

Broadly  speaking,  the  animal  body  is  a  machine  for  converting 
potential  into  actual  energy.  The  potential  energy  is  supplied  by 
food ;  this  the  metabolism  of  the  body  converts  into  the  actual 
energy  of  heat  and  mechanical  labour.  We  have  in  the  present 
section  to  study  what  is  known  of  the  laws  of  this  conversion,  and 
of  the  distribution  of  the  energy  set  free. 

The  Income  of  Energy. 

Neglecting  all  subsidiary  and  unimportant  sources  of  energy, 
we  may  say  that  the  income  of  animal  energy  consists  in  the  oxida- 
tion of  food  into  its  waste  products,  viz.  the  oxidation  of  proteids 
into  urea  and  carbonic  acid,  of  fats  into  carbonic  acid  and  water, 
and  of  carbohydrates  into  carbonic  acid.  Taking  as  our  guide 
the  principle  laid  down  by  the  chemist,  that  the  potential  energy 
of  any  body,  considered  in  relation  to  any  chemical  change  in  it, 
is  the  same  when  the  final  result  is  the  same,  whether  that  result 
be  gained  at  one  leap  or  by  a  series  of  steps — that,  for  instance, 
the  energy  set  free  by  the  oxidation  of  i  grm.  of  fat  into  carbonic 
acid  and  water  is  the  same,  whatever  the  changes  forwards  or  back- 
wards which  the  fat  undergoes  before  it  finally  reaches  the  stage  of 
carbonic  acid  and  water ;  and  similarly,  that  the  energy  available 
for  tlie  body  in  i  grm.  of  dry  proteid  is  the  energy  given  out  by 
the  complete  combustion  of  that  i  grm.,  less  the  energy  given  out 
by  the  complete  combustion  of  that  quantity  of  urea  to  which  the 
I  grm.  of  proteid  gives  rise  in  the  body — we  may  easily  calculate 
the  total  energy  of  any  diet.  Frankland'  has  supplied  the  follow- 
ing data,  given  both  in  gram,  -degree  C  units  of  heat,  and  metre- 
kilogramme  units  of  force. 

'  Phih  Mag,  XXXII.  p.  182. 


CHAl'.   V.J  NUTRITION.  469 

The  direct  oxidatiun  of  the  give*  rise  to 

following,  dried  at  100*.  C.  gram.-deg.     mct.-k.lo. 

I  grm.  Ikcf  fat                                          9069  ^841 

I  grm.  Butter                                               7264  3077 

I  grm.  Arrowroot                                        3912  1657 

I  grm.  Bccf-muscle  purified  with  ether  5103  2 161 

I  grm.  Urea                                                 2206  934 

Supposing  that  all  the  nitrogen  of  proteid  food  goes  out  as 
urea,  I  grm.  of  dry  i)roteid,  such  as  dried  beef-muscle,  would  give 
rise  to  al)out  ^  grm.  of  urea ;  hence 

gram.-dcg.         met. -kilo. 

I  grm.  Proteid  5103         2161 

less 
J  grm.  Urea  735  311 

would  give  as 

Available  energy  of  Proteid  4368  1850 

In  a  normal  diet,  such  as  Ranke's,  p.  457,  w^ould  be  found : 

gram.-des.  met. -kilo. 

100  grm.  Proteid  436800  185000 

100  grm.  Fat  906900  384100 

240  grm.  Starch  938880  397680 


Total  Income  2  28 1580  966780 

or  in  round  numbers,  one  million  metre- kilogrammes. 

The  Expenditure. 

There  are  only  two  ways  in  which  energy  is  set  free  from 
the  body — mechanical  labour  and  heat.  The  body  loses  energy 
in  proilucing  muscular  work,  as  in  locomotion,  in  all  kinds  of 
labour,  in  the  movements  of  the  air  in  respiration  and  speech, 
and,  though  to  a  hardly  recognizable  extent,  in  the  movements 
of  the  air  or  contiguous  bodies  by  the  pulsations  of  the 
vascular  system.  The  body  loses  energy  in  the  form  of  heat  by 
conduction  and  radiation,  by  respiration  and  perspiration — in  fact, 
by  the  warming  of  all  the  egesta.  .\11  the  internal  work  of  the 
body,  all  the  mechanical  labour  of  the  internal  muscular  mechan- 
isms with  their  accompanying  friction,  all  the  molecular  labour 
of  the  nervous  and  other  tissues,  is  converted  into  heat  before  it 
leaves  the  body.  The  most  int-nse  mental  action,  unaccompanied 
by  any  muscular  manifestations,  the  most  energetic  action  of  the 
luart  or  of   the   bowels,  with  the   slight   exceptions   mentioned 


470  THE   EXPENDITURE   OF   ENERGY.         [BOOK   II. 

above,  the  busiest  activity  of  the  secreting  or  inetabolic  tissues, 
all  these  end  simply  in  augmentating  the  expenditure  of  income 
in  the  forn^  of  heat. 

A  normal  daily  expenditure  in  the  way  of  mechanical  labour 
can  be  easily  determined  by  observation.  Whether  the  work  take 
on  the  form  of  walking,  or  of  driving  a  machine,  or  of  any  kind 
of  muscular  toil,  a  good  day's  work  may  be  put  down  at  about 
150,000  metre-kilogrammes.  The  normal  daily  expenditure  in  the 
way  of  heat  cannot  be  so  readily  determined.  Direct  calori- 
metric  observations  are  attended  with  this  difficulty,  that  the  body 
while  within  the  calorimeter  is  placed  in  abnormal  conditions, 
which  produce  an  abnormal  metabolism.  Hence  results  arrived 
at  by  this  method  are  of  little  value  unless  they  be  accompanied 
by  a  comparison  of  the  egesta  and  ingesta,  so  that  the  rate  and 
nature  of  the  metabolism  going  on  may  be  known.  Many 
attempts  have  been  made  to  calculate  the  amount  in  an  indirect 
manner.  As  trustworthy  as  any  is  the  plan  of  simply  subtracting 
the  normal  daily  mechanical  expenditure  from  the  normal  daily 
income.  Thus,  150,000  m.-k.  subtracted  from  one  million  m.-k. 
gives  850,000  m.-k.  as  the  daily  expenditure  in  the  form  of  heat; 
i.e.  between  one-fifth  and  one-sixth  of  the  total  income  is  expended 
as  mechanical  labour,  the  remaining  four-fifths  or  five-sixths 
leaving  the  body  in  the  form  of  heat. 

The  Sources  of  Muscular  Energy.  Liebig,  satisfied 
with  having  proved  that  the  animal  body  was  constructive  as  far  as 
the  formation  of  fat  was  concerned,  held  to  the  distinction 
between  nitrogenous  or  plastic  and  non-nitrogenous  or  respiratory 
food.  Put  broadly,  his  view  was  that  all  the  nitrogenous  food 
went  to  build  up  the  proteid  tissues,  the  muscular  flesh,  and  other 
forms  of  protoplasm,  and  that  the  nitrogenous  egesta  arose  solely 
from  the  functional  metabolism  of  these  tissues,  while  the  non- 
nitrogenous  food  was  used  with  equal  exclusiveness  for  respiratory 
or  calorific  purposes,  being  either  directly  oxidized  in  the  blood, 
or  if  present  in  excess,  stored  up  as  fatty  tissue.  According  to 
him  the  two  classes  of  income  corresponded  exactly  to  the  two 
forms  of  expenditure.  We  have  already  urged  several  objections 
against  this  view.  We  have  seen '  that  in  the  blood  itself  very 
little  oxidation  takes  place,  that  it  is  the  active  tissue,  and  not  the 
passive  blood-plasma,  which  is  the  seat  of  oxidation.  We  have 
further  seen  that  proteid  food  may  undoubtedly  be  in  Liebig's 
sense  respiratory,  and  incidentally  give  rise  to  the  storing  up  of 
fat.  One  division  of  Liebig's  view  is  thereby  overthrown.  We 
have  now  to    inquire  whether   the    other   division   holds  good, 


CHAP,    v.]  NUTRITION.  4/1 

whether  muscle  or  other  protoplasm  is  fed  exclusively  on  the 
protcid  material  of  food,  and  whether  muscular  energy  comes 
exclusively  from  the  metabolism  of  the  proteid  constituents  of 
muscle.  We  have  already  seen  (p.  75)  that  when  the  muscle 
itself  is  examined,  we  find  no  proof  of  nitrogenous  waste,  but,  on 
the  other  hand,  clear  evidence  of  the  production  of  non -nitrogenous 
bodies,  such  as  carbonic  and  lactic  acid.  We  have  now  to  ask 
the  question.  Does  muscular  exercise  increase  the  urea  given  off 
by  the  body  as  a  whole  ?  For  this,  according  to  Liebig's  theory, 
it  certainly  ought  to  do.  Conllicting  evidence  has  been  offered 
on  this  point ;  but  by  far  the  strongest  and  clearest  is  that  which 
gives  a  negative  answer. 

In  addition  to  the  careful  observations  of  Lawes  and  Gilbert, 
Edw.ird  Smith,  Ranke,  Voit  and  others,  the  long-continued  and 
admirable  inquiries  of  Parkcs'  arc  especially  deserving  of  attention. 
This  observer  determined  both  the  total  nitrogen  of  the  urine  and  of 
the  faices,  so  that  no  possible  source  of  error  could  lie  in  this  direction  ; 
and  examined  the  effect  of  exercise,  slight  and  severe,  on  both  a  non- 
nitrogcnous  and  on  a  mixed  nitrogenous  diet.  He  found  no  marked 
increase  in  the  urea,  but  often  a  diminution,  during  the  exercise, 
though  subsequently  a  slight  increase  took  place.  This  after-increase 
possibly  had  nothing  to  do  with  the  muscles  in  particular,  but  was  the 
result  of  the  exercise  on  the  body  at  large. 

The  results  of  Flint*,  gained  by  observations  on  a  celebrated 
.pedestrian,  rather  illustrate  the  effects  of  protracted  exercise  on  general 
proteid  metabolism  under  a  rich  diet  than  contradict  the  more  exact 
inquiries  of  Parkes. 

More  than  this,  the  experience  of  Fick  and  Wislicenus^  lands 
us  in  an  absurdity  if  we  suppose  the  whole  energy  of  muscular 
work  to  arise  from  proteid  metabolism.  They  performed  a  certain 
amount  of  work  (an  ascent  of  the  Faulhorn)  on  a  non-nitrogenous 
diet,  and  estimated  the  amount  of  urea  passed  during  the  period. 
Assuming  the  urea  to  represent  the  oxidation  of  so  much  proteid 
matter,  which  oxidation  represented  iji  turn  so  much  energy  set 
free,  they  foimd  that  whereas  the  actual  work  done  amounted  to 
129*026  and  148-656  metre-kilos,  for  each  respectively,  the  total 
energy  available  from  ])roteid  metabolism  during  the  period  was  in 
the  case  of  the  first  68  69,  and  of  the  second  68-376  metre-kilos. 
That  is  to  say,  the  energy  set  free  by  the  proteid  metabolism  of 
the  muscles  engaged  in  the  work  was  at  the  most  far  less  than  that 
necessary  to  accomplish  the  work  actually  done.     Their  muscular 

'  Proc.  A'oy,  Soc.  XV.  (1867)  p.  339;   XVI.  p.  44  ;  XIX.  p.  349  ;  XX.  p.  402. 
'  Jount.  Aitat.  Phys.  Vol.  XI.  (1S76)  ;  XII.  (1877).      Cf.   North.  Journ.  of 
Phys.  I.  {1S7S)  p.  171, 

3  Phil.  Mag.  XXX f.  (1866)  p.  4S5. 


472  THE   EXPENDITURE   OF   ENERGY.        [BOOK   II. 

energy    therefore    must   have    had    other   sources   than   proteid 
metabohsm. 

The  total  nitrogen  excreted  v/as  estimated  (A)  for  12  hours  previous 
to  the  commencement  of  the  labour,  (B)  for  the  period  of  the  labour 
and  (C)  for  six  hours  succeeding  the  labour  ;  the  latter  in  order  that 
there  might  be  no  possible  retention  within  the  body  of  the  urea 
formed  during  the  labour  period. 

The  total  nitrogen  execreted.  Fick.  Wislicenus. 

A.  In  12  hours  before  the  labour 6'9rgrm.         6"68grm. 

B.  In  3  hours  labour 3-31  ^'l^ 

C.  In  6  hours  rest  after  labour 2*43  2*42 

B.  Corresponds  in  dry  proteid  sub- 1 «-       ^   .  o 

stance  consumed  into  urea  ...  j    °     20  95  20  89 

C.  „  „  y  „  16-19 i6-ii 

The  total  proteid    consumed    therefore!        ^.  ; 

during  and  after  labour  was /  3/7  3/ 00 

The  oxidation  of  these  within  the  body  1  ^/-.^  ,„.     - 

to  urea,  would  produce  in  metre-kilos  /             "°  3/0 

Whereas  the  actual  work  done  was,  also  1               ^  o  ^  ^ 

in  metre-kilos |  ^^9-096  148-656 

The  argument  may  be  made  still  stronger  by  the  following  con- 
siderations. A  large  internal  amount  of  muscular  energy,  that  of  the 
vascular  and  respiratory  mechanisms,  did  not  appear  in  the  work 
done,  being  transformed  into  heat  before  it  left  the  body.  On  the 
supposition  that  this  muscular  energy  also  arose  from  proteid  mefi- 
bolism,  we  must  add  to  the  above  estimate  of  work  done,  quantities 
calculated  to  have  been  in  the  case  of  Fick  30'54i,  of  Wislicenus 
35'63i  metre-kilos,  bringing  up  the  totals  to  i59'637  and  i84"287 
respectively.  But  even  this  is  not  all.  Supposing  that  the  whole 
energy  set  free  by  a  muscular  contraction  arises  from  proteid  meta- 
bolism, since  some  of  this  energy  goes  out  directly  as  heat,  we  must 
add  to  the  above  estimate  of  mechanical  work,  the  work  which  might 
have  been  done  by  the  heat  given  out  at  the  same  time.  Heidenhain 
calculates  that  while  ^ths  of  the  total  energy  of  the  body  takes  on  the 
form  of  heat,  the  share  of  the  energy  set  free  in  the  contraction  of 
any  individual  muscle  which  must  be  reckoned  as  heat  amounts  to 
about  half  Hence  the  sums  given  above  must  be  doubled  ;  so  that 
the  real  contrast  is  between  3i9'274  and  368 '574  metre-kilos  of 
actual  energy  expended  on  the  one  hand  and  66690  and  68376 
metre-kilos  of  energy  available  through  proteid  metabolism  on  the 
other. 

That  on  the  contrary  the  production  of  carbonic  acid  is  at 
once  and  largely  increased  by  muscular  exercise  is  beyond  all 
doubt.  One  hour's  hard  labour  will  increase  fivefold  the  quantity 
of  carbonic  acid  given  off  within  the  hour.  And  Pettenkofer  and 
Voit  found  that  a  man  in  24  hours  consumed  954  grms.  oxygen 
and  produced   1284  grms.   carbonic  acid  when  doing  work,   as 


CHAI'.    v.]  NUTRITION.  473 

against  708  grnis.  oxygen  consumed  and  911  grms.  carbonic  acid 
produced  when  remaining  at  rest,  the  quantity  of  urea  secreted 
being  in  the  first  case  37  grms.,  in  the  second  37*2  grms. 

These  observers  found  that  the  production  of  carbonic  acid  was 
very  distinctly  diminished,  and  the  consumption  of  oxygen  increased, 
during  the  night  as  compared  with  the  diy.  Thui  the  12842  grms. 
of  carbonic  acid  of  tlie  whole  period  of  24  hours  was  furnished  by 
884 "6  grms.  given  out  between  6  A.iM.  and  6  P.M.,  and  399  6  grms. 
between  6  P..M.  and  6  a.m.  Similarly,  of  the  954'5  grms.  oxygen 
294"8  grms.  were  taken  in  between  6  a.m.  and  6  P.M.,  and  6597  grms. 
between  6  p.m.  and  6  a.m.  These  figures  very  strikingly  indicate 
the  independence  of  muscular  contraction  and  iiiDncdiate  oxidation. 
During  the  day  when  the  body  is  at  work,  or  at  least  manifesting 
activity  in  one  direction  or  another,  while  the  production  of  carbonic 
acid  is  much  greater,  the  consumption  of  oxygen  is  much  less  than 
during  the  night  when  the  body  is  at  rest  and  asleep. 

It  is  evident  that  the  conchisions  arrived  at  by  the  statistical 
method  entirely  corroborate  those  gained  by  an  examination  of 
muscle  itself,  viz.  that  during  muscular  contraction  an  explosive 
decomposition  takes  place,  the  non-nitrogenous  products  of  which 
alone  escape  from  the  muscle  and  from  the  body,  any  nitrogenous 
products  which  result  being  retained  within  the  muscle.  We 
must  therefore  reject  the  second  as  well  as  the  first  division  of 
Liebig's  view,  that  the  muscle  is  fed  exclusively  on  protcid 
material,  and  that  its  energy  arises  from  proteid  metabolism. 

We  must,  however,  guard  ourselves  against  rushing  into  the 
extreme  opinion  that  a  muscle  is  simply  a  machine  for  getting  work 
out  of  the  oxidation  of  non-nitrogenous  food.  The  hypothesis  ad- 
vanced at  p.  117  concerning  the  re  entrance  of  the  nitrogenous  pro- 
ducts of  metabolism  into  the  com['osition  of  the  nascent  contractile 
substance,  is  undoubtedly  a  very  rough  and  provisional  idea.  But  if 
it  means  anything  it  means  this,  that  the  de:omposition  which  gives 
rise  to  the  carbonic  and  lactic  acid,  is  a  decomposition  of  the  ifhole 
contractile  siibstan:e  and  not  of  any  non-nitrogenous  portion  of  it,  and 
that  before  a  fresh  decomposition  can  take  place  the  whole  complex 
explosive  contractile  material  has  to  be  made  anew,  and  not  simply  a 
non-nitrogenous  gap  filled  up.  And  this  is  probably  true,  not  of 
musculir  tissue  only,  but  of  ail  forms  of  active  protoplasm  however 
otherwise  modified.  It  is,  as  we  have  seen,  not  in  the  case  of  mus-le 
alone  that  the  oxygen  disappears  into  the  molecular  recesses  of  the 
tissue  to  reappear  again  in  oxidized  products  whose  oxidation  does 
not  take  place  at  the  moment  of  their  production.  We  have  more  than 
once  insisted  that  the  oxidations  of  the  body,  in  general  at  least,  are 
oxidations  by  the  tissues,  and  are  oxidations  in  which  the  oxygen  is 
first  absorbed  and  made  latent  by  the  physiological  actions  of  the 
protoplasm.  In  the  at  present  unknown  molecular  actions,  by  which 
the  raw  material  of  Jthe  protoplasm  is  united  with  the  absorbed  oxygen 


474  ANIMAL    HEAT.  [BOOK    II. 

in  the  manufacture  of  the  explosive  material,  nitrogenous  compounds 
evidently  play  a  peculiar  part.  This  is  clearly  shewn  by  the  metabolic 
activity  of  proteid  matters  illustrated  in  the  previous  section.  Indeed 
the  whole  secret  of  life  may  almost  be  said  to  be  wrapped  up  in  the 
(jccult  properties  of  certain  nitrogen  compounds  ;  and  Pfliiger'  has 
drawn  some  very  suggestive  comparisons  between  the  so-cahed 
chemical  properties  of  the  cyanogen  compounds,  and  the  so-called 
vital  properties  of  protoplasm.  If  we  admit  that  the  energy  of 
muscular  contraction  (and  with  that  the  energy  of  all  other  vital 
manifestations)  arises  from  an  e\plosive  decomposition  of  a  complex 
substance,  which  we  may  call  real  protoplasm,  and  that  this  complex 
protoplasm  is  capable  of  reconstruction  withm  Umits  which,  as 
we  urged  at  p.  441,  may  be  very  wide,  we  acquire  a  conception  of 
physiological  processes  which,  if  not  precise  and  definite,  is  at  least 
simple  and  consistent,  and  moreover  a  first  step  towards  a  future 
molecular  physiology. 

The  Sources  and  Distribution  of  Heat.  We  have 
already,  seen  that  the  conception  of  the  non  nitrogenous  portions 
of  food  being  solely  calorifacient  or  respiratory,  proves  to  be 
unfounded  when  we  attempt  to  trace  the  history  of  the  food  on  its 
way  through  the  body.  The  same  view  is  still  more  strikingly 
shewn  to  be  inadequate  when  we  study  the  manner  in  which  the 
heat  of  the  body  is  produced.  We  may  indeed  at  once  affirm 
that  the  heat  of  the  body  is  generated  by  the  oxidation,  not  of 
any  particular  substances,  but  of  the  tissues  at  large.  Wherever 
metabolism  of  protoplasm  is  going  on,  heat  is  being  set  free.  In 
growth  and  in  repair,  in  the  deposition  of  new  material,  in  the 
transformation  of  lifeless  pabulum  into  living  tissue,  in  the  con- 
structive metabolism  of  the  body,  heat  may  be  undoubtedly  to  a 
certain  extent  absorbed  and  rendered  latent :  the  energy  of  the 
construction  may  be,  in  part  at  least,  supplied  by  the  heat  present. 
But  all  this,  and  more  than  this,  viz.  the  heat  present  in  a  potential 
form  in  the  substances  so  built  up  into  the  tissue,  is  lost  to  the 
tissue  during  its  destructive  metabolism ;  so  that  the  whole 
metabolism,  the  whole  cycle  of  changes  from  the  lifeless  pabulum 
through  the  living  tissue  back  to  the  lifeless  products  of  vital 
action  is  eminently  a  source  of  heat. 

Of  all  the  tissues  of  the  body  the  muscles  not  only  from  their 
bulk,  forming  as  they  do  so  large  a  portion  of  the  whole  frame, 
but  also  from  the  characters  of  their  metabolism,  must  be  regarded 
as  the  chief  sources  of  heat.  Whenever  a  muscle  contracts,  heat 
is  given  out.  When  a  mercury  thermometer  is  plunged  into  a 
mass  of  muscles,  such  as  those  of  the  thigh  of  the  dog,  a  rise  of 
the  mercury  is  observed  upon  the  muscles  being  thrown  into  a 

*  Pfliiger's  Archiv,  x.  (1875)  P-  ^Si- 


CIIAr.    v.]  NUTRITION.  475 

prolonged  contraction.  More  exact  results  however  are  obtained 
by  means  of  a  thermopile,  by  the  hel[)  of  which  the  heat  given 
out  by  a  few  repeated  single  contractions,  or  iadeed  by  a  single 
contraction,  may  be  observed  and  measured.  Kick'  found  that 
the  greatest  heat  given  out  by  the  muscles  of  the  thigh  of  a  frog 
in  a  single  contraction  was  yi  micro-units  of  heat^  for  a  gramme 
of  muscle,  the  result  being  obtained  by  dividing  by  five  the  total 
amount  of  heat  given  out  in  five  successive  single  contractions. 
We  have  no  satisfactory  quantitative  determinations  of  the  heat 
given  out  by  the  muscles  of  warm-blooded  animals,  but  there  can 
bo  no  doubt  that  it  is  much  greater  than  that  given  out  by  the 
muscles  of  the  frog. 

The  thermopile  mny  consist  either  of  a  single  junction  in  the  form 
of  a  needle  plunged  into  the  substance  of  the  muscle  or  of  several 
junctions  either  in  the  shape  of  a  flat  surface  carefully  opposed  to  the 
surface  of  muscle  (Hcidenhain-^)  the  pile  being  balanced  so  as  to 
move  with  the  contni'^tinrr  nni-;cle,  and  thus  to  keep  the  contact  exact 
or  m  the  shape  of  a  thin  wedge  (Fick-')  the  edge  of  which  comprising 
the  actual  junctions  is  thrust  into  a  mass  of  muscles  and  held  in 
position  by  them.  In  all  cases  the  fellow  junction  or  junctions  must 
be  kept  at  a  constant  temperature. 

The  amount  of  heat  given  out  by  a  muscle  when  thrown  into 
contraction  by  the  application  of  a  stimulus  will  of  course  depend 
on  the  amount  of  energy  set  free  by  the  decomposition  of  the 
explosive  contractile  substance,  part  of  this  energy  going  to 
produce  movement,  and  part  being  transformed  into  heat.  We 
have  seen  in  treating  of  muscle  itself  that  the  total  amount  of 
energy  set  free  by  the  action  of  a  stimulus  will  depend  not  only 
on  the  strength  of  the  stimulus,  but  also  on  a  variety  of  circum- 
stances, notably  on  the  amount  of  resistance  against  which  the 
muscle  has  to  contract ;  mere  extension  of  the  muscular  fibre 
increases  the  metabolism  uf  the  muscular  substance,  and  leads  to 
a  freer  expenditure  of  energy,  see  p.  90.  The  ratio  of  the  ex- 
pended energy  going  out  as  heat  to  that  producing  movement 
appears  to  vary  with  circumstances,  and  according  to  Fick5 
increases  with  an  increase  of  the  resistance.  Hence  muscles 
contracting  against  a  great  resistance,  economise  so  to  speak  the 
expenditure  of  their  substance,  inasmuch  as  more  and  more  of  the 
energy  set   free  is  devoted   to  the   specific   muscular  movement 

'  Pflu/er's  ^rcitT,  XVI.  (1877)  p.  58. 

'  The  m  cro-unit  being  a  milligramme  of  water  rai-ecl  one  degree  centigrade. 

5  Mechanische  Leislung,  &'c.,  T864.  •♦  Op.  cit.  s  Qp  cit. 


476  ANIMAL   HEAT.  [BOOK   11. 

instead  of  the  more  general  development  of  heat,  which  latter 
task  might  be  more  cheaply  undertaken  by  less  specialized  tissues. 
It  is  impossible  to  say  at  present  what  are  the  exact  limits  of  the 
ratio  of  heat  to  movement.  Fick  calculates  that  in  the  bloodless 
muscles  of  the  frog,  the  amount  of  work  ma}"^  vary  from  one-fourth 
to  one  twenty-fifth  of  the  heat  given  out.  If  we  may  venture  to 
argue  from  the  muscles  of  a  frog  to  those  of  the  mammal,  and  to 
take  somewhat  below  the  mean  of  the  above  two  limits,  say  one- 
tenth,  then,  upon  the  calculation  that  the  total  external  work  of 
the  body  is  about  one-fifth  of  the  total  energy  set  free  in  the  body, 
it  is  clear  that  the  heat  given  out  by  the  muscles,  at  those  times 
only  when  they  are  contracting,  must  form  a  very  large  part  of  the 
total  heat  given  out  by  the  body.  But  the  skeletal  muscles, 
though  frequendy,  are  not  continually  contracting;  they  have 
periods,  at  times  long  periods,  of  rest ;  and  during  these  periods 
of  rest,  metabolism,  of  a  subdued  kind  it  is  true,  but  still  a 
metabolism,  involving  an  expenditure  of  energy,  is  going  on. 
This  quiescent  metabolism  must  also  give  rise  to  a  certain  amount 
of  heat ;  and  if  we  add  this  amount,  which  in  the  present  state  of 
our  knowledge  we  cannot  exactly  gauge,  to  that  given  out  during 
the  movements  of  the  body,  it  is  very  clear,  even  in  the  absence 
of  exact  data,  that  the  metabolism  of  the  muscles  must  supply  a 
very  large  proportion  of  the  total  heat  of  the  body.  They  are 
par  excellence  the  thermogenic  tissues. 

Next  to  the  muscles  in  importance  come  the  various  secreting 
glands.  In  these  the  protoplasm,  at  the  periods  of  secretion  at 
all  events,  is  in  a  state  of  metabolic  activity,  which  activity  as 
elsewhere  must  give  rise  to  heat.  In  the  case  of  the  salivary 
gland  of  the  dog  Ludwig  and  Spiess^  found  that  the  temperature 
of  the  saliva  secreted  during  stimulation  of  the  chorda,  might  be 
as  much  as  i°  or  15°  higher  than  that  of  the  blood  in  the  carotid 
artery  at  the  same  time,  and  in  all  probability  the  investigation  of 
other  secreting  glands  would  lead  to  similar  results.  Of  all  these 
various  glands,  the  liver  deserves  special  attention  on  account  of 
its  size  and  large  supply  of  blood  and  because  it  appears  to  be 
continually  at  work.  We  find  indeed  that  the  blood  in  the  hepatic 
veins  is  the  warmest  in  the  body.  Heidenhain^  observed  in  the 
dog  a  temperature  of  4073°  C.  in  the  hepatic  vein,  while  that  of 
the  vena  cava  inferior  was  38'35°  to  39*58°,  and  that  of  the  right 
heart  377°.  Bernard  previously  had  found  the  blood  of  the 
hepatic  vein  warmer  than  that  of  either  the  portal  vein  or  the 

'   Wien.  Sitzungsbei-ichte,  Bd.  25  (1857). 
"  Pfliiger's  Archiv,  III.  (1870)  p.  504. 


CUM',    v.]  NUTRITION.  477 

aorta,  shewing  that  tlic  increased  temperature  is  not  due  simply  to 
the  liver  being  tar  removed  from  the  surface  of  the  body. 

The  brain  too  may  be  regarded  as  a  source  of  heat,  since  its 
temperature  is  higlier  than  that  of  the  arterial  blood  with  which  it 
is  sup|)hed  ;  though  from  the  smaller  quantity  of  blood  passing 
through  its  vessels  it  cannot  in  this  respect  compare  with  cillier 
the  liver  or  the  muscles  as  a  source  of  heat  to  the  body. 

The  blood  itself  cannot  be  regarded  as  a  source  of  any  con- 
siderable amount  of  heat,  since,  as  we  have  so  frequently  urged, 
the  oxidations  or  otiier  metabolic  changes  taking  place  in  it  are 
comparatively  slight.  The  heat  evolved  by  the  indifferent  tissues 
such  as  bone,  cartilage  and  connective  tissue  may  be  passed  over 
as  insignificant;  and  we  cannot  even  regard  the  adipose  tissue  as 
a  seat  of  the  production  of  heat  since  the  fat  of  the  fat-cells  is  in 
all  probability  not  oxidized  in  situ  but  simply  carried  away  from 
its  place  of  storage  to  the  tissue  which  stands  in  need  of  it,  and  it 
is  in  the  tissue  that  it  undergoes  the  metabolism  by  which  its 
latent  energy  is  set  free.  Some  amount  of  heat  is  also  produced 
by  the  changes  which  the  food  undergoes  in  the  alimentary  canal 
before  it  really  enters  the  body. 

Hence  taking  a  survey  of  the  whole  body  we  may  conclude 
that  since  metabolism  is  going  on  to  a  greater  or  less  extent  every- 
where, heat  is  everywhere  being  generated ;  but  that,  looked  at 
from,  a  quantitative  point  of  view,  the  muscles  and  the  glandular 
organs  must  be  regarded  as  the  main  sources  of  the  heat  of  the 
body,  the  muscles  being  in  all  probability  the  more  important  of 
the  two. 

But  heat,  while  being  thus  conlinually  produced,  is  as  con- 
tinually being  lost,  by  the  skin,  the  lungs,  the  urine  and  the  fasces. 
The  blood  passing  from  one  part  of  the  body  to  the  other,  and 
carrying  warmth  from  the  tissues  where  heat  is  being  rapidly 
generated,  to  the  tissues  or  organs  where  heat  is  being  lost  by 
radiation,  conduction  or  evaporation,  tends  to  equalize  the 
temperature  of  the  various  parts,  and  thus  maintains  a  'constant 
bodily  temperature.* 

When  the  production  of  heat  is  not  great  as  compared  with 
the  loss  there  ij  no  great  accumulation  of  heat  within  the  body, 
the  temperature  of  which  consequently  is  but  slightly  raised  above 
that  of  surrounding  objects.  Tims  the  temperature  of  the  frog, 
for  instance,  is  rareiy  more  than  '04°  to  '05°  C.  above  that  of  the 
atmosphere,  though  in  the  breeding  season  the  difference  may 
amount  to  i"".  Such  animals,  and  they  comprise  all  classes  e.xcept 
birds  and  mammals,  are  spoken  of  as  cold-blooded.  Exceptions 
among  them  are  not  uncommon.     Some  fish,  such  as  the  tunny, 


4/8  ANIMAL   HEAT.  [BOOK   II. 

are  warmer  than  the  water  in"  which  they  Hve,  and  in  a  species  of 
Python  {F.  bivittatus)  a  difference  of  as  much  as  12°  C.  has  been 
observed,  Hiiber  found  that  in  a  beehive  the  temperature  rose 
at  times  as  much  as  to  40°  C.  In  the  so-called  warm-blooded 
animals,  birds  and  mammals,  the  loss  and  production  of  heat  are 
so  balanced  that  the  temperature  of  the  body  remains  constant  at, 
in  round  numbers,  35  or  40°  C,  whatever  be  the  temperature  of 
the  air.  The  temperature  of  man  is  about  37 '6°  C.  ;  in  some 
birds  it  is  as  high  as  44°  C.  (Hirundo),  and  in  the  wolf  it  is  said 
to  be  as  low  as  35  24°  C. 

This  temperature  is  with  slight  variations  maintained  through- 
out life.  After  death  the  generation  of  heat  rapidly  diminishes, 
and  the  body  speedily  becomes  cold ;  but  for  some  short  time 
immediately  following  upon  systemic  death,  a  rise  of  temperature 
may  be  observed,  due  to  the  fact  that,  while  the  metaboHsm  of 
the  tissues  is  still  going  on,  the  loss  of  heat  is  somewhat  checked 
by  the  cessation  of  the  circulation.  The  onset  of  pronounced 
rigor  mortis  causes  a  marked  accession  of  heat,  and  when  occur- 
ring after  certain  diseases,  may  give  rise  to  a  very  considerable 
elevation  of  temperature.  This  mean  bodily  temperature  of 
warm-blooded  animals  is,  during  health,  maintained,  with  slight 
variations  of  which  we  shall  presently  speak,  within  a  very  narrow 
margin,  a  rise  or  indeed  a  fall  of  much  more  than  a  degree  above 
or  below  the  limit  given  above  being  indicative  of  some  failure  in 
the  organism,  or  of  some  unusual  influence,  being  at  work.  It  is 
evident,  therefore,  that  the  mechanisms  which  co-ordinate  the 
loss  with  the  production  of  heat  must  be  exceedingly  sensitive. 
It  is  obvious,  moreover,  that  these  mechanisms  may  act  when  the 
bodily  temperature  is  tending  to  rise,  by  either  checking  the 
production  or  by  augmenting  the  loss  of  heat ;  and  when  the 
bodily  temperature  is  tending  to  fall,  by  either  increasing  the 
production  or  by  diminishing  the  loss  of  heat.  As  the  regulation 
of  temperature  by  variations  in  the  loss  of  heat  is  far  better 
known  than  regulation  by  variations  in  production,  it  will  be  best 
to  consider  this  first. 

Regulation  by  variations  in  loss.  Heat  is  lost  to  the 
body  by  the  warming  of  the  faeces  and  of  the  urine,  by  the 
warming  of  the  expired  air,  by  the  evaporation  of  the  water  of 
respiration,  by  conduction  and  radiation  from  the  skin,  and  by 
the  evaporation  of  the  water  of  perspiration.  Helmholtz  has 
calculated  that  the  relative  amounts  of  the  loss  by  these  several 
channels  are  as  follows  :  In  warming  the  fseces  and  urine  2 '6  per 
cent.     In  warming  the  expired  air  5*2  per  cent      In  evaporating 


ClIAI'.     v.]  NUTRITION.  479 

the  water  of  respiration  147  per  cent.  In  conduction  and 
radiation  and  evaporation  by  the  skin  77*5  per  cent. 

'The  two  chief  means  of  loss  then,  which  are  at  all  susceptible 
of  any  great  amount  of  variation,  and  which  can  be  used  to 
»:gulate  the  temperature  of  the  botly,  are  the  skin  and  the  lungs. 

The  more  air  passes  in  and  out  of  the  lungs  in  a  given  time, 
the  greater  will  be  the  loss  in  warming  the  expired  air,  and  in 
eva|)orating  the  water  of  respiration.  And  in  such  animals  as 
the  dog,  which  do  not  perspire  freely  by  the  skin,  res[)iration  is 
a  most  important  means  of  regulating  the  temperature.' 

While  Bernard  %  G.  Liebig^,  Ilcidcnhain  and  oHcr  observers, 
found  the  blood  of  the  right  heart  warmer  (from  "i  to  ■3")  than  that  of 
the  left.  Colin-'  and  Jacobson  and  Bernhardt 5  state  that  the  left  heart 
is  warmer  or  at  last  as  warm  as  the  right.  From  the  latter  observa- 
tions it  might  be  inferred  that  the  loss  of  heat  by  respiration  is 
neiitralizcdbychemic.il  changes  going  on  in  the  lungs.  Heidenhain 
and  Korner",  however  make  the  important  observation  that  the 
higher  temperature  of  the  right  ventricle  is  independent  of  the  re- 
spiration, and  tlicy  attribute  the  difference  between  the  two  ventricles 
solely  to  the  fact  that  the  right  ventricle  lies  nearer  to  tlu  abdominal 
viscera,  the  hit^h  temper  iture  of  which  has  already  been  mentione'l. 
And  they  argue  that  the  loss  of  heat  from  the  bo  ly  to  the  air  has  been 
already  achieved  before  the  inspired  air  reaches  the  pulmonary  alveoli, 
the  evaporation  of  water  taking  place  chielly  in  the  nasal  and  bronchial 
passages. 

The  great  regulator  however  is  undoubtedly  the  skin.  The 
more  blood  passes  through  the  skin  the  greater  will  be  the  loss 
of  heat  by  conduction,  radiation,  and  evaporation.  Hence,  any 
action  of  the  vasomotor  mechanism  which,  by  causing  dilation 
of  the  cutaneous  vascular  areas,  leads  to  a  larger  flow  of  blood 
through  the  skin,  will  tend  to  cool  the  body  ;  and  conversely,  any 
vaso-motor  action  which,  by  constricting  the  cutaneous  vascular 
areas,  or  by  dilating  the  splanchnic  vascular  areas,  causes  a 
smaller  How  througii  the  skin,  and  a  larger  flow  of  blood  through 
the  abdominal  viscera,  will  tend  to  heat  the  body.  Besides  this 
the  special  nerves  of  perspiration  will  act  directly  as  regulators  of 
temperature,  increasing  the  loss  of  heat  when  they  promote,  and 
lessening  the  loss  when  they  cease  to  promote,  the  secretion  of 

'  .See  Riegel,  Pfluger's  Archiv,  V.  (1872)  651. 

*  Zt-fT.  Je  J'/ivs.  Exp.,  1^55. 

3  Uihcr    die    Tempaaturiinli.TSchicde    des   vciioscn    uiid    arUridUii    Blitta. 
Gies  en,  1S53. 

*  Compt.  Rend.,  LXII.  (1865)  p.  6S0. 
s  Cbt.  f.  Med.  IViss.,  1S68,  p.  643. 

'  Pfliiger's  Archiv,  iv.  (1871)  yj6. 


480  ANIMAL   HEAT.  [liOOK    II. 

the  skin.  The  working  of  tliis  heat-regulating  mechanism  is  well 
seen  in  the  case  of  exercise.  Since  every  muscular  contraction 
gives  rise  to  heat,  exercise  Tnast  increase  for  the  time  being  the 
production  of  heat ;  yet  the  bodily  temperature  rarely  rises  so 
much  as  a  degree  C.,  if  at  all.  By  the  exercise  the  respiration  is 
quickened,  and  the  loss  of  heat  by  the  lungs  increased.  The 
circulation  of  blood  is  also  quickened,  and  the  cutaneous  vascular 
areas  becoming  dilated,  a  larger  amount  of  blood  passes  through 
the  skin.  Added  to  this,  the  skin  perspires  freely.  Thus  a  large 
amount  of  heat  is  lost  to  the  body,  sufficient  to  neutralise  the 
increase  caused  by  the  muscular  contraction,  the  increase  which 
the  more  rapid  flow  of  blood  through  the  abdominal  organs  might 
tend  to  bring  about  being  more  than  sufficiently  counteracted  by 
their  smaller  supply  for  the  time.  The  sense  of  warmth  which  is 
felt  during  exercise  in  consequence  of  the  flushing  of  the  skin, 
is  in  itself  a  token  that  a  regulative  cooling  is  being  carried  on. 
In  a  similar  way  the  application  of  external  cold  or  heat,  either 
partially  or  completely,  defeats  its  own  ends.  Under  the  influence 
of  external  cold  the  cutaneous  vessels  are  constricted,  and  the 
splanchnic  vascular  areas  dilated,  so  that  the  blood  is  withdrawn 
from  the  colder  and  coohng  regions  to  the  hotter  and  heat-pro- 
ducing organs.  This  vascular  change  may  be  used  to  explain  the 
fact  that  stripping  naked  in  a  cold  atmosphere  often  gives  rise  to 
an  actual  increase  in  the  mean  temperature  of  the  blood,  as 
indicated  by  a  thermometer  placed  in  the  mouth,  though  possibly 
the  effect  may  be  partly  due  to  an  actual  increase  of  the  produc- 
tion of  heat.  Under  the  influence  of  external  warmth,  on  the 
other  hand,  the  cutaneous  vessels  are  dilated,  a  rapid  discharge  of 
heat  takes  place ;  and  if  the  circumstances  be  such  that  the  body 
can  perspire  freely,  and  the  perspiration  be  readily  evaporated,  the 
temperature  of  the  body  may  remain  very  near  to  the  normal, 
even  in  an  excessively  hot  atmosphere.  Thus,  more  than  a 
century  ago,  Drs.  Fordyce  and  Blagden  ^  were  able  to  remain 
with  impunity  in  a  chamber  heated  even  to  127°  (260°  Fahr.), 
and  with  ease  in  one  so  hot,  that  it  became  painful  for  them  to 
touch  the  metal  buttons  of  their  clothing.  It  is  unnecessary  to 
give  any  more  examples  of  this  regulation  of  temperature  by 
variations  in  the  loss  of  heat ;  they  all  readily  explain  themselves. 

Regulation  by  variations  in  production.  It  is  not 
however  solely  by  variations  in  the  loss  of  heat  that  tlie  constant 
temperature  of  the  warm-blooded  animal  is  maintained.  Varia- 
tions in   the   amount  of   heat   actually  generated   in    the   body 

'  Phil.  Trans.,  1775,  pp.  Ill,  484. 


en  AT.   v.]  NUTRITION.  48 1 

constitute  an  important  factor  not  only  in  the  maintenance  of 
the  normal  temperature,  but  also  probably  in  the  production  of 
the  abnormally  high  or  low  temperatures  of  various  diseases. 
Many  considerations  have  long  led  physiologists  to  suspect  the 
existence  of  a  nervous  mechanism  by  which  afferent  impulses 
arising  in  the  skin  or  elsewhere  might  through  the  central 
nervous  system  originate  efferent  impulses  whose  effect  would  be 
to  increase  or  diminish  the  metabolism  of  the  muscles  or  other 
organs  and  thus  to  increase  or  diminish  the  amount  of  heat 
generated  for  the  time  being  in  the  body.  The  existence  in  fact 
of  a  metabolic  or  thermogenic  nervous  mechanism  comparable 
in  many  resjjects  to  the  vaso-motor  mechanism  or  to  the  various 
secreting  nervous  mechanisms  seems  in  itself  probable.  And  we 
have  now  a  certain  amount  of  experimental  evidence  that  such 
a  mechanism  does  really  exist.  The  warm-blooded  animal  is 
distinguished  from  the  cold-blooded  animal  by  the  fact  that  when 
it  is  exposed  to  cold  or  heat,  it  does  not  like  the  latter  become 
colder  or  hotter,  as  the  case  may  be,  but,  within  certain  limits, 
maintains  its  normal  temperature.  If  the  temperature  of  the 
warm-blooded  animal  during  exposure  to  cold  is  maintained  by 
means  of  an  increased  production  of  heat  and  not  simply  by  a 
diminished  loss,  we  ought  to  find  evidence  of  an  increased  meta- 
bolism during  that  exposure.  We  ought  to  find  under  these 
circumstances  an  increased  production  of  carbonic  acid,  and  an 
increased  consumption  of  oxygen,  since  it  is  to  these  products, 
rather  than  to  the  nitrogenous  factors,  on  the  peculiarities  of 
which  as  uncertain  signs  of  metabolism  we  have  already  insisted, 
we  must  look  for  indications  of  the  rise  or  fall  of  metabolic 
activity.  Now  Pflijger  and  his  pupils  have  shewn  that  exposure 
to  cold  does  most  markedly  increase  the  production  of  carbonic 
acid  and  consumption  of  oxygen  in  a  warm-blooded  animal 
(rabbit,  guinea-pig),  whereas  in  a  cold-blooded  animal  (frog)  the 
metabolism,  as  measured  by  the  amounts  of  the  same  products 
is  diminished  by  cold  and  increased  by  heat.  The  body  of  the 
latter  behaves  in  this  respect  like  a  mixture  of  dead  substances 
in  a  chemist's  retort ;  heat  promotes  and  cold  retards  chemical 
action  in  both  cases.  In  the  body  of  the  warm-blooded  animal, 
on  the  other  hand,  there  is  a  mechanism  by  which  such  a  reaction 
is  brought  about  that  chemical  action  is  actually  increased  by  the 
application  of  cold.  And  Plliiger  has  further  shewn  that  this 
mechanism  is  of  a  nervous  nature,  since  warm-blooded  animals, 
in  which  the  action  of  the  nervous  system  is  suspended  by  urari 
poisoning,  section  of  tiie  medulla  oblongata,  or  otherwise,  be- 
have like  cold-blooded  animals  towards  heat  and  cold  ;  their 
F.  P.  31 


482  ANIMAL   HEAT.  [BOOK   II. 

metabolism   is   increased    by   the    former    and    diminished   by 
the  latter. 

We  may  regard  it  then  as  established  that  such  a  thermotaxic 
nervous  mechanism  does  exist,  and  the  importance  of  such  a 
mechanism  in  explaining  not  only  the  maintenance  of  the  normal 
temperature  but  the  abnormal  variations  of  temperature  in  disease 
can  hardly  be  exaggerated.  Much  however  still  requires  to  be 
learnt  before  we  can  speak  with  confidence  as  to  its  exact  nature 
or  expound  the  details  of  its  work. 

The  view  that  the  generation  of  heat  in  the  animal  body  is  regulated 
by  a  special  mechanism,  and  that  of  a  nervous  nature,  has  long  seemed 
probable,  though  much  of  the  evidence  brought  forward  in  its  favour 
was  imperfect  and  indecisive.  The  results  of  injuries  to  and  diseases 
of  the  nervous  system  seemed  to  point  in  this  direction.  Thus  Brodie' 
long  ago  called  attention  to  a  rise  of  temperature  after  injury  to  the 
spinal  cord  ;  in  a  previous  memoir''  he  had  contended,  on  insufficient 
grounds  it  is  true,  for  a  direct  generation  of  heat  by  means  of  the 
nervous  system.  Since  that  time  many  clinical  cases  have  been 
observed  on  the  one  hand  of  a  lowering  and  on  the  other  hand  oi 
a  rise  of  temperature  as  the  result  of  injury  to,  or  disease  of,  the  spinal 
cord,  or  other  parts  of  the  central  nervous  system.  A  certain  amount 
of  experimental  evidence  is  also  forthcoming.  Tscheschichin^  ob- 
served in  rabbits  a  fall  of  temperature  after  section  of  the  spinal  cord, 
but  a  marked  rise  of  temperature  after  a  section  carried  through  the 
juncture  of  the  medulla  oblongata  and  pons  Varolii.  Naunyn  and 
Quincke "*,  on  the  contrary,  found  that,  in  dogs,  section  of  the  spinal 
cord  was  followed  at  first  by  a  fall,  but  subsequently  by  a  rise  of 
temperature,  the  latter  being  the  more  marked  the  higher  up  the 
division  of  the  cord,  and  reaching  to  as  much  as  3°  or  4°.  They 
explained  the  initial  fall  as  due  to  an  increased  escape  of  heat,  due  to 
the  vaso-motor  paralysis,  which  the  section  caused,  allowing  a  large 
portion  of  the  blood  to  pass  through  the  cutaneous  vessels  ;  and  they 
remarked  that  the  fall  was  less  the  more  rapidly  after  the  operation 
the  animal  was  surrounded  by  cotton  wool  or  like  bad  conductors  of 
heat.  The  subsequent  rise  of  temperature  they  attributed  to  an  actual 
increased  production  which  in  time  overcame  the  increased  escape 
due  to  vaso-motor  paralysis.  They  thought  that  they  had  satisfied 
themselves  that  the  rise  was  not  due  to  fever  occasioned  by  the  mere 
wound,  as  Schroffs  has  since  concluded.  Parinaud"  finds  that  in 
rabbits  section  of  the  spinal  cord  invariably  produces  a  continued  fall 
of   temperature,   especially  of  the   deeper   parts  of  the  body,  more 

^  Med.  Chir.  Trans.  Vol.  XX.  (1837)  p.  1 19. 

=  Phil.  Trans.  1811,  1812. 

3  Du  Bois-Reymond's  yi;r^?z',  1866,  p.  151. 

*  Du  bois-Reymond's  ^r^/zzw,  1869,  pp.  174,  521. 
5  Wien.  Sitzungsberichte,  LXXIII.  (1876). 

*  Archives  de  Physiologie  {\x.)  iv.  (1877),  PP-  63,  310. 


CHAl'.    v.]  NUTRITION.  483 

marked  in  the  paralysed  than  in  the  non-paralysed  parts.  Tscheschi- 
chin  attributed  the  rise  which  he  observed  after  the  section  of  the 
medulla  to  the  removal  of  some  inhibitory  action  exerted  by  the 
hij^hcr  parts  of  the  i>rain  on  thermogenic  centres  lower  down. 

Hul  in  ail  such  ex|jcrinients  and  observations  it  is  obvious  that 
clirficuliies  ari  .c  on  account  of  the  complications  introduced  by  the 
mechanisms  of  the  vaso-motor  system.  We  have  already  seen,  in 
tre  itin'4  of  th  it  system,  how  intricate  is  its  working  ;  and  the  study  of 
an  elaborate  inquiry  of  Heidenhain',  in  which  that  acute  and  careful 
observer  discusses  in  a  particular  case  the  possibility  of  a  direct 
nervous  regulation  of  the  generation  of  heat  and  finally  rejects  it  iji 
favour  of  a  simple  vaso-motor  explanation  of  the  phenomena  observed, 
will  illustrate  very  clearly  the  dangers  of  inferring  the  existence  of  a 
distinct  thermogenic  nervous  action,  in  the  absence  of  a  criterion  more 
satisfactory  than  a  mere  rise  or  fall  of  temperature  in  this  or  that  part. 
The  only  really  satisfactory  criterion  short  of  direct  calorimetric 
observations  (which  as  we  have  seen  arc  attended  with  the  greatest 
difficulties)  is  the  measurement  of  the  actual  metabolism  going  on  by 
a  quantitative  determination  of  the  carbonic  acid  produced  and  o.\ygen 
consumed. 

The  phenomena  of  the  rise  of  temperature  (pyrexia)  in  certain 
diseases  almost  irresistibly  suggest  the  idea  of  an  actual  increase  in 
the  production  of  heat.  And  while  m  iny  incidental  features,  such  for 
instance  as  the  fa  -t  that  even  profuse  sweating  by  jaborandi  has  com- 
paratively little  effect  on  the  high  temperature  of  the  cold  stage  of 
ague',  concur  in  indicating  that  the  rise  of  temperature  cannot  be  due 
to  a  mere  diminution  of  loss,  .and  none  speak  distinctly  in  favour  of 
such  an  explanation,  here  also  as  in  the  experiments  quoted  above  the 
desideratum  is  a  direct  measurement  either  of  the  amount  of  heat 
given  out,  or  of  the  actual  metabolism,  as  shewn  by  the  quantities  of 
carbonic  acid  produced  and  oxygen  consumed.  Lcyden  and  Fraenkel  ^ 
find  the  excretion  of  carbonic  acid  increased  in  the  dog  during  pyrexia  ; 
and  in  all  probability  future  investigations  will  very  speedily  enlarge 
our  knowledge  in  this  direction. 

That  the  maintenance  of  the  temperature  of  the  warm-blooded 
mammal  during  exposure  to  cold  is  due  to  an  increased  metabolism  is 
shewn  by  the  experiments  of  Colasanti  •*  who  under  Pfliiger's  guidance 
found  that  in  guinea-pigs  cold  increases,  in  a  very  remarkable  and 
regular  manner,  both  the  production  of  carbonic  acid  and  the  con- 
sumption of  oxygen,  the  ratio  of  the  oxygen  consumed  to  the -oxygen 
contained  in  the  carbonic  acid  expired  renTaining  constant  during  the 
experiments.  Sandcrs-Ezn  s  had  previously  found  that  in  rabbits  the 
production  of  carbonic  acid  was  increased  by  sudden  exposure  of  the 

'  Pfliiger's  .-f/Y/z/f,  ill,  (1S70)  504;  Ibid.  v.  (1872)  77. 

'  Ringer,  Lancet,  Oct.  5,  1S7S. 

3  Virclijw's  Archiv,  J!d.  76  (1S79)  P-  '36.  See  also  the  references  given 
there. 

*■  Pfliiger's  Archiv,  xiv.  (1877)  p.  92.  See  also  the  subsequent  controversy 
carried  on  in  that  and  the  following  volume. 

5  Ludwig's  Arbdteu,  1867. 

3T— 2 


484  ANIMAL   HEAT.  [BOOK  II. 

bodily  surface  to  cold  and  diminished  by  sudden  exposure  to  warmth, 
and  Rohrig  and  Zuntz '  had  observed  in  rabbits  an  increase  in  both 
the  carbonic  acid  produced  and  in  the  oxygen  consumed  to  result  from 
cold  baths,  and  also  though  to  a  less  extent  from  saline  baths.  A  strong 
contrast  to  the  behaviour  of  the  warm-blooded  guinea-pig,  in  which  a 
fall  of  30°  C.  in  the  surrounding  medium  actually  doubled  the  amount 
of  the  metabolism,  is  afforded  by  the  cold-blooded  frog,  in  which, 
according  to  Pfliiger  and  Schulz%  repeating  the  earlier  experiments  of 
Marchand  and  Moleschott,  cold  depresses  and  heat  exalts  the  metabolic 
activity  of  the  tissues. 

The  exact  nature  of  this  metabolic  mechanism  was  indicated  by 
the  experiments  of  Zuntz  and  Rohrig  3,  who  found  that  in  urari 
poisoning  there  was  a  marked  diminution  of  the  bodily  metabolism 
as  shewn  by  the  quantities  of  oxygen  consumed  and  carbonic  acid 
produced  ;  these  indeed  might  fall  to  half  the  normal.  At  the  same 
time  the  bodily  temperature  fell  considerably  ;  and  that  this  fall  was 
the  effect  and  not  the  cause  of  the  diminution  of  the  metabolism  was 
shewn  by  the  fact  that  the  metabolism  continued  to  diminish,  when 
loss  of  heat  from  the  body  was  prevented  by  wrappings  of  cotton 
wool.  While  under  urari  too,  the  metabolic  activity  was  far  less 
influenced  by  cold  and  other  baths. 

Pfliiger  has  since  in  an  elaborate  research '*  shewn  (i)  that  in  rabbits 
poisoned  with  urari  there  is  a  large  decrease  of  metabolism,  the 
carbonic  acid  produced  diminishing  37*4  p.  c.  and  the  oxygen  con- 
sumed 3  5  "2  p.  c.  ;  the  normal  being  of  the  former  570  c.  c.  of  the 
latter  673  c.  c.  per  kilo  per  hour,  while  the  urarized  animal  gave 
357  c.c.  carbonic  acid  and  436  c.c.  o  :ygen,  all  measured  at  0°  C.  and 
760  mm.  mercury  ;  (2)  that  in  the  urarized  animal  increased  tempera- 
lure  produces  an  increase  of  metabolism  (an  increase  of  44  c.c.  oxygen 
consumed  per  1°  C.  per  kilo  per  hour,  and  of  8r6  c.c.  carbonic  acid 
produced  per  1°  C.  per  kilo  per  hour)  and  diminished  temperature  a 
diminution  of  metabolism  ;  (3)  that  elimination  of  nervous  action  by 
section  of  the  medulla  oblongata  gives  rise  to  similar  but  less  striking 
results,  whereas  (4)  in  the  normal  animal  cold  produces,  as  has  been 
previously  observed,  a  marked  rise  of  metabolism.  If  in  spite  of  the 
increased  metabolism  the  external  cold  succeeds  in  reducing  the  tem- 
perature of  the  animal,  then,  as  the  temperature  falls  a  point  is  reached 
at  which  the  reaction  of  the  nervous  system  is  powerless  against  the 
direct  depressing  action  of  the  low  temperature  and  metabolism  is 
diminished.  Pfliiger  further  observed  that  in  the  urarized  animal,  the 
metabolism  is  not  directly  proportional  to  the  temperature  but  increases 
with  enormous  rapidity  when  the  temperature  rises  above  the  normal. 
The  production  of  carbonic  acid  and  consumption  of  oxygen  ap- 
parently do  not  run  exactly  parallel ;  with  a  rise  of  temperature  above 
the  normal  the  production  of  carbonic  acid  is  much  more  rapid  than 
the  consumption  of  o-<ygen,  and  conversely  when  the  temperature 
sinks  below  the  normal  the  production  of  carbonic  acid  diminishes 

*  Pfliiger's  Archiv,  IV.  (1S71)  p    57. 
="  Pfliiger's  ^;r/iiz^,  XIV.  (1877)  73. 

3  Op.  at.  and  Zuntz,  Pfliiger's  Archiv,  XII.  (1876)  p.  522. 

*  Pfliiger's  Archiv,  xviil,  (1^78)  p.  247. 


CIIAI'.   v.]  NUTRITION.  485 

more  slowly  than  tlie  consumption  of  oxygen  ;  but  on  the  latter  point 
furtlier  and  more  extcncleil  observations  are  needed. 

I'he  interpretation  which  may  naturally  be  put  on  the  results  of  the 
forc^oinj^  experiments,  especially  of  those  with  urarized  animals,  is 
that  external  cold  acts  as  a  stimulus  to  the  skin,  giving  rise  to  afferent 
impulses  whicli,  reaching  some  central  nervous  mechanism,  give  rise 
to  efferent  impulses,  and  tiiese  in  turn  passing  to  the  muscles,  increase 
the  metabolic  activity  of  these  organs,  and  thus  give  rise  to  an  increased 
production  of  heat.  When  the  muscular  nerves  are  paralyzed  by 
urari,  the  efierent  impulses  can  no  longer  reach  the  muscles,  and  hence 
no  increase  of  metabolism  takes  place  in  them.  Pointing  in  the  same 
direction  are  the  experiments  of  Samuel  *,  who  found  tlvit  while  rabbits 
in  a  normal  condition  will  bear  exposure  to  even  severe  cold  without 
any  great  change  in  their  bodily  temperature,  this  sinks  rapidly,  and 
death  ensues,  when  the  chief  muscular  parts  of  the  body  arc  eliminated 
from  the  total  action  of  the  organism  by  ligature  of  all  four  arteries  of 
the  limbs  or  by  section  of  their  main  nerve-trunks  ;  the  wounds  neces- 
sary for  the  operation  producing  of  themselves  only  a  slight  effect. 
■  And  we  have  been  prepared  by  previous  considerations  to  look  to  the 
muscles  as  the  chief  source  of  heat  (p.  475). 

Although  in  the  above  experiments  the  diminution  of  metabolism 
and  of  the  production  of  heat  was  coincident  with  the  absence  of 
muscular  contractions,  it  is  not  absolutely  necessary  to  suppose  that 
the  occurrence  of  contractions  is  essential  to  an  increase  in  the  pro- 
duction of  heat.  In  the  cases  where  the  metabolism  was  even  largely 
increased,  muscular  contractions  (at  least  visible  muscular  contractions), 
though  sometimes  observed,  were  not  invariably  present  And  indeed 
there  is  no  d  priori  reason  positively  contradicting  the  hypothesis  that 
the  metabolism  of  even  muscular  tissue  might  be  intluenced  by  nervous 
or  by  other  agency  in  such  a  way  that  a  large  decomposition  of  the 
muscular  substance,  productive  of  much  heat,  might  take  place  without 
any  contraction  being  necessarily  caused.  If  we  were  to  permit  our- 
selves to  suppose  that  the  contractile  material,  whose  metabolism  when 
resulting  in  a  contraction  gives  rise  to  so  much  heat,  could  undergo 
the  same  amount  of  metabolism,  in  so  far  a  diflerent  fashion,  that  all 
the  energy  thereby  set  free  took  on  the  form  of  heat,  variations  in 
the  temperature  of  the  body,  at  present  difficult  to  understand,  would 
become  readily  intelligible. 

Although  the  experiments  of  Pfliiger  have  been  chiefly  directed 
towards  the  thermotaxic  nervous  mechanism  by  which  external  cold 
is  made  to  increase  metabolism,  we  may  fairly  suppose  that  a  com- 
plementary mechanism  by  which  metabolism  may  be  diminished  also 
exists,  a  sort  of  inhibitory  thermotaxic  mechanism.  And  this  suggests 
that  pyrexia  or  fever  is  the  result  of  a  paralysis  or  suspension  of 
this  mechanism,  the  metabolism  of  the  body  running  riot  so  to  speak, 
in  the  absence  of  directive  and  restraining  nervous  influences.  Cola- 
santi "  makes  the  interesting  observation  that  in  a  guinea-pig  suflering 
from  pyrexia  the  usual  reaction  towards  external  cold  was  absent. 

'  Ueber  die  EntstehiDig  der  Eii^euwcirne,  &-'c.,  Leipzig,  1876. 
•  0/>.  dr. 


486 


ANIMAL    HEAT. 


[BOOK   II, 


Bernard  '  felt  justified  in  speaking  most  distinctly  of  '  thermogenic  ' 
or  'calorific'  and  of  'frigorific'  nerves,  in  complete  analogy  with  vaso- 
dilator and  vaso-constrictor  nerves.  He  states^  that  after  division  of 
one  cervical  sympathetic  the  temperature  of  the  ear  of  the  side  operated 
on  remains  considerably  higher  than  that  of  the  other  side,  at  a  time 
when  the  increased  vascularity  has  nearly  disappeared,  thus  indicating 
that  the  former  is  not  wholly  dependent  on  the  latter ;  and  Knock  ^ 
confirms  this.  Bernard'*  also  observed,  after  division  of  the  cervical 
sympathetic  on  one  side,  that  a  stimulation  of  the  central  end  of  the 
divided  auricular  nerve  sufficiently  intense  to  give  rise  to  pain,  occa- 
sioned on  the  side  in  which  the  sympathetic  was  intact,  a  fall  (of  as 
much  as  2°  C.)  of  temperature  in  the  ear,  unaccompanied  by  any  pallor^ 
while  on  the  side  on  which  the  sympathetic  had  been  divided,  a  rise 
of  temperature  was  at  the  same  time  observed.  That  is  to  say,  the 
sensation  of  pam  gave  rise,  by  rtflex  action  through  the  intact  cervical 
sympathetic,  to  a  refrigeration  of  the  ear,  without  any  vascular  change 
in  the  ear  and  in  spite  of  an  increased  temperature  of  other  parts  of 
the  body.  In  the  submaxillary  gland  he  found,  as  Lud-wig  and 
Spiess  had  previously  shewn  (see  p.  476),  that  stimulation  of  the 
chorda  tympani  produces  a  rise  of  temperature,  and  he  states  that 
the  rise  manifested  itself,  though  to  a  less  degree  than  in  normal  cir- 
cumstances, even  when  all  the  vessels  were  cut  or  when  the  veins  were 
ligatured.  On  the  other  hand  he  obtained  a  fall  of  temperature  when 
the  sympathetic  was  stimulated,  a  fall  moreover  which  he  asserted  to 
be  still  recognizable  after  division  of  the  blood-vessels  or  ligature  of  the 
veins  of  the  gland.  If  it  could  be  shewn  that  under  stimulation  of 
the  sympathetic  a  fall  of  temperature  at  all  corresponding  to  the  rise 
obtained  by  Ludwig  and  Spiess,  manifested  itself,  Bernard's  view  that 
the  sympathetic  \'i  par  excellence  a  frigorific  nerve,  while  the  cerebro-, 
spinal  nerves  contain  all  the  calorifaciant  fibres,  would  receive  a  striking 
confirmation.  But  these  experiments  of  Bernard's  need  repetition, 
and  Heidenhain's^  observations,  as  far  as  they  go,  point  to  a  slight 
rise  rather  than  a  fall  of  temperature  as  the  result  of  sympathetic 
stimulation. 

By  regulative  mechanisms  of  this  kind  the  temperature  of  the 
warm-blooded  animal  is  maintained  within  very  narrow  limits.  In 
ordinary  health  the  temperature  of  man  varies  between  36°  and 
38°,  the  narrower  limits  being  36*25°  and  37*5°,  when  the  ther- 
mometer is  placed  in  the  axilla.  In  the  mouth  the  reading  of  the 
thermometer  is  somewhat  ("25°  to  i'5°)  higher;  in  the  rectum  it 
is  still  higher  (about  "9°  C.)  than  in  the  mouth.  The  temperature 
of  infants  and  children  is  slightly  higher  and  much  more  suscep- 
tible of  variation  than  that  of  adults,  and  after  40  years  of  age  the 

'  Chaltur  Animale  {i?i'j6),  passijn.  '  Op.  cit.  p.  283. 

3  Quoted  by  Eemard  loc.  cit.  The  observations  of  Goltz,  see  p.  184,  on  the 
foot  of  the  dog  would  seem  to  shew  that  this  at  least  does  not  hold  good  for 
the  sciatic  nerve. 

*  Op.  cit.  p.  295.  s  Breslau.  Sttidin,  iv.  (1868). 


CIIAl'.    \-.]  NUTRITION.  4S7 

avcrnge  maxinuim  temperature  (of  heallh)  is  somewhat  lower  than 
before  that  epoch.  A  diurnal  variation,  independent  of  food  or 
other  circumstances,  has  been  observed',  the  maximum  ranging 
from  9  A.M.  to  6  p.m.  and  the  minimum  from  11  p.m.  to  3  a.m. 
Meals  cause  sometimes  a  slight  elevation,  sometimes  a  slight 
depression,  the  direction  of  the  influence  depending  on  the  nature 
of  the  food  :  alcohol  seems  always  to  produce  a  fall.  Exercise 
and  variations  of  external  temperature,  within  ordinary  limits, 
cause  very  slight  change,  on  account  of  the  compensating  in- 
fluences which  have  been  discussed  above.  The  rise  from  even 
active  exercise  does  not  amount  to  1°  C.  ;  when  labour  is  carried 
to  exhaustion  a  de])ression  of  temperature  may  be  observed.  In 
travelling  from  very  cold  to  very  hot  regions  a  variation  of  less 
than  a  degree  occurs,  and  the  temperature  of  tropical  inhabitants 
is  practically  the  same  as  those  dwelling  in  arctic  regions. 

When  external  cold  or  warmth  passes  certain  limits,  or  when 
during  the  application  of  these  agents  the  regulative  mechanisms 
are  interfered  with,  the  temperature  of  the  body  may  be  lowered 
or  raised  until  death  ensues.  When  the  cold  or  warmth  applied 
is  not  very  great,  as  in  cold  and  warm  baths,  it  has  been  noticed 
that  the  temperature  is  more  easily  raised  by  warmth  than  de- 
pressed by  cold.  Death  ensues  from  extreme  cold  by  a  depression 
of  the  activities  of  all  the  tissues,  more  especially  of  the  nervous  ; 
asphyxia  is  produced  in  animals  when  the  fall  of  temperature  is 
rapid.  Puppies  can  be  recovered  after  the  temperature  in  the 
rectum  has  fallen  to  about  4°  or  5°  C,  and  hybernating  mnmmals 
may  be  cooled  with  impunity  down  to  nearly  freezing-point. 
Horvaih^  observed  when  external  warmth  is  brought  to  bear  on 
a  mammal  in  such  a  way  as  to  cause  a  rise  of  temperature  in  the 
body,  death  ensues  when  an  elevation  of  about  6°  or  7°  C.  above 
the  normal  is  reached  ;  and  Dernards  places  the  lethal  bodily 
temperature  of  a  mammal  at  about  46°.  The  exact  cause  of  the 
death  has  not  been  as  yet  sufficiently  explained.  It  cannot  be 
due,  as  Bernard  suggests,  to  the  muscles  entering  into  rigor  caloris, 
for  the  animals  frequently  succumb  betbre  this  takes  place.  A 
high  temperature  makes  the  heart  irregular,  and  finally  stops  its 
beat,  but  probably  other  tissues  are  also  injuriously  affected,  so 
tliat  death  cannot  be  attributed  to  the  stoppage  of  the  heart 
alone. 

One  of  the  most  marked  phenomena  of  starvation  is  the  fall  of 
temperature,  which  becomes  very  rapid  during  the  last  days  of 

'  Ringer,  Proc.  Roy.  Sec,  xvii.  p.  287  ;  idu/.  xxvi.  (1877)  p.  186. 
"  Cdt/.  Med.   IViss.,  1 871,  p.  513. 
3  Lef.  sur  la  Chakur  Auimalc,  1876. 


488  TROPHIC   NERVES.  [BOOK  II. 

life.  Indeed  the  low  temperature  of  the  body  is  a  powerful  factor 
in  bringing  about  death,  for  life  may  be  much  prolonged  by 
wrapping  a  starving  animal  in  some  bad  conductor  so  as  to 
economise  the  bodily  heat^.  . 


Sec.    5.      The    Influence     of    the     Nervous     System    on 
Nutrition, 

In  the  preceding  sections  we  had  more  than  once  to  refer  to 
the  possibility  of  the  nervous  system  having  the  power  of  directly 
affecting  the  metabolic  actions  of  the  body,  apart  from  any 
irritable,  contractile,  or  secretory  manifestations.  Thus  the 
phenomena  of  diabetes  cannot,  at  present  at  all  events,  be  satis- 
factorily explained  as  a  purely  vasomotor  effect,  and  the  production 
of  heat  is,  as  we  have  seen,  under  the  special  guidance  of  the 
nervous  system.  In  treating  of  the  salivary  glands  we  met  with 
the  striking  fact  that  when  all  the  nerves  of  the  gland  have  been 
divided,  and  a  '  paralytic  '  secretion  set  up,  the  tissue  of  the  gland 
may  ultimately  degenerate.  This  result  differs  from  the  wasting 
of  a  muscle  which  follows  upon  severance  of  its  motor  nerve,  since 
this  may  be,  partly  at  all  events,  explained  by  the  fact  that  the 
muscle  is  no  longer  functional ;  and  indeed,  if  the  muscle 
is  rendered  functional,  if  it  is  directly  stimulated  for  instance 
from  time  to  time  with  a  galvanic  current,  the  atrophy  may  be 
postponed  or  even  altogether  prevented.  But  the  salivary  gland 
in  the  case  in  question  is  functional,  it  does  go  on  secreting  j 
nevertheless  in  the  absence  of  its  usual  nervous  guidance  its  nutri- 
tion becomes  profoundly  affected,  We  are  not  justified  in  saying 
that  in  this  case  the  nutrition  of  the  salivary  cell  is  directly  depen- 
dent on  the  nervous  system,  because  all  biological  studies  teach 
us  that  the  growth,  repair,  and  reproduction  of  protoplasm  may  go 
on  quite  independently  of  any  nervous  system,  and  the  nutrition 
of  the  nervous  system  itself  cannot  be  dependent  on  the  action  of 
that  system  on  itself;  but  we  may  go  so  far  as  to  infer  that  the 
nutrition  of  the  salivary  cell  is  in  the  complex  animal  body  so 
arranged  to  meet  the  constantly  recurring  influences  brought  to 
bear  on  it  by  the  nervous  system,  that,  when  those  influences  are 
permanently  withdrawn,  it  is  throv/n  out  of  equilibrium ;  its 
molecular  processes,  so  to  speak,  run  loose,  since  the  bit  has  been 
removed  from  their  mouths.  And  we  might  expect  that  similar 
instances  would  be  met  with  where  nutrition  became  abnormal  after 
the  removal  of  wonted  nervous  influences.     Such  instances  indeed 

*  Chossat,  Rech.  Exp.  sur  T Inanition,  Paris,  1843. 


CHAP.   V.J     ■  NUTRITION.  489 

are  not  uncommon  ;  the  most  familiar  being  perhaps  the  rapid 
occurrence  of  bed-sores,  in  consequence  of  injuries  to  or  of  dis- 
ease of  the  spinal  cord  or  brain.  And  there  are  many  pathological 
phenomena,  iiiHammation  itself  to  begin  with,  which  seem  inex- 
plicable, except  when  regarded  as  the  result  of  nervous  action.  In 
all  these  cases,  however,  there  are  many  attendant  circumstances 
to  be  considered  before  we  can  feel  justified  in  speaking  of  any 
direct  influence  of  the  nervous  system  on  nutrition,  of  any  specific 
action  of  what  have  been  called  'trophic'  nerves.  Perhaps  the 
instance  which  has  been  best  worked  out  is  the  connection  of  the 
nutrition  of  the  eye  and  face  with  the  fifth  or  trigeminal  nerve. 
When  in  a  rabbit  the  trigeminus  is  divided  in  the  skull  there  is  loss 
of  sensation  in  those  parts  of  the  face  of  which  it  is  the  sensory 
nerve.  Very  soon,  within  twenty-four  hours,  the  cornea  becomes 
cloudy  ;  and  this  is  the  precursor  of  an  inflammation  which  may 
involve  the  whole  eye  and  end  in  its  total  disorganisation.  At  the 
same  time  the  nasal  chambers  of  the  same  side  are  inflamed,  and 
very  frequently  ulcers  make  their  appearance  on  the  lips  and  gums. 
Seeing  how  delicate  a  structure  the  eye  is,  and  how  carefully  it  is 
protected  by  the  mechanisms  of  the  eyelids  and  tears,  it  seems 
reasonable  to  suppose  that  the  inflammation  in  question  might 
simply  be  the  result  of  the  irritation  caused  by  dust  and  contact 
with  foreign  bodies,  to  which  the  eye,  no  longer  guided  and  pro- 
tected by  sensations,  these  being  destroyed  by  the  section  of  the 
nerve,  became  subject.  In  the  same  way  the  ulcers  on  the  lips 
and  gums  might  be  explained  as  injuries  inflicted  by  the  teeth 
on  those  structures  in  their  insensitive  condition.  And  Snellen 
found  that  the  inflammation  of  the  eye  might  be  greatly  lessened 
or  altogether  prevented  if  the  organ  were  carefully  covered  up 
and  in  all  possible  ways  protected  from  the  irritating  influences 
of  foreign  bodies.  Other  observers  however  have  failed  to  pre- 
vent the  inflammation  in  spite  of  every  care.  This  negative 
result  is  in  itself  no  strong  argument,  but  the  question  cannot 
yet  be  considered  as  entirely  cleared  up. 

Sinitzen  found  that  after  removal  of  the  superior  cervical  sympathetic 
ganglion,  the  inflammatory  effects  of  section  of  the  trigeminus  were 
very  much  lessened.  Sinitzen' s  explanation,  that  the  tissues  of  the 
face  become  less  irritable  after  removal  of  the  ganglion,  seems,  how- 
ever, hardly  satisfactory.  According  to  Merkel '  the  inflammatory 
phenomena  depend  on  a  particular  portion  of  the  nerve  being  divided. 
He  states  tliat  if  a  certain  tract  along  tiic  inner  border  of  the  nerve 
be  alone  cut,  there  is  no  loss  of  sensation  either  in  the  cornea  or  other 
parts  of  the  face,  but  yet  inflammation  comes  on  as  usual  ;  if,  on  the 

'  Untersuch.  Anat.  Inst.  Rostock,  p.  i. 


490  TROPHIC   NERVES.  '      [BOOK   II. 

other  hand,  the  whole  nerve  with  the  exception  of  this  tract  be 
carefully  divided,  no  inflammation  ensues  though  sensation  is  lost. 
Merkel  traces  the  fibres  forming  the  inner  border  to  a  deep  origin, 
different  from  that  of  the  rest  of  the  nerve.  If  these  results  be 
corroborated,  the  trigeminus  must  be  held  to  contain  '  trophic ' 
fibres. 

In  a  mammal  division  of  both  vagi  is  followed  by  pneumonia 
(inflammation  of  the  lungs)  ending  in  death.  This  has  been  adduced 
as  an  instance  of  the  trophic  action  on  the  pulmonary  tissues  of  certain 
fibres  of  the  vagi  ;  but  the  real  explanation  seems  to  be  that,  owing  to 
a  paralysis  of  the  oesophagus  and  larynx  caused  by  section  of  the 
vagi,  food  accumulating  in  the  pharynx  passes  into  the  air-passages 
and  so  sets  up  the  pneumonia.'  In  birds  death  follows  sometimes 
from  pneumonia  of  a  similar  causation,  but  more  frequently  from 
inanition  on  account  of  the  food  not  being  able  to  enter  the  stomach. 
The  immediate  cause  of  death  however  is  in  many  cases  at  all  events 
a  paralysis  of  the  heart,  and  according  to  Eichhorsf",  the  histological 
changes  (acute  fatty  degeneration)  in  the  cardiac  muscle  are  of  such 
a  character  as  to  suggest  a  trophic  action  of  the  vagus  fibres  on  that 
tissue  ;  he  also  finds  similar  changes  in  the  hearts  of  rabbits.  The 
matter  however  requires  further  elucidation. 

Such  instances  of  nerves  manifesting  even  a  doubtful  trophic 
action  are  rare ;  yet  there  seems  to  be  no  reason  why  the  fifth 
nerve  or  the  vagus  should  be  conspicuous  in  possessmg  trophic 
fibres.  When  the  sciatic  nerve  of  the  frog  is  divided,  no  nutri- 
tive alterations  beyond  those  explicable  as  the  result  of  loss  of 
function  are  observed ;.  and  indeed  the  majority  of  the  effects 
on  growth  and  nutrition  resulting  from  the  section  of  nerves,  or 
from  paralysis,  can  be  referred  to  the  absence  of  the  usual  func- 
tional activity,  accompanied  in  son:ie  cases  with  an  altered 
vascular  supply.  Nevertheless  the  numerous  phenomena  of  dis- 
ease, joined  to  the  facts  mentioned  above,  turn  the  balance  of 
evidence  in  favour  of  the  view  that  some  more  or  less  direct 
influence  of  the  nervous  system  on  metabolic  actions,  and  so  on 
nutrition,  wiil  be  established  by  future  inquiries. 

The  influence  which  light  acting  on  the  retina  appears  to  exercise 
on  the  metabolism  of  the  body  may  be  quoted  as  an  illustration  of  the 
statement  just  made.^ 

Among  the  pathological  facts  which  may  be  quoted  as  suggestive 
of  trophic  action  are  the  occurrence  of  certain  eruptions,  such  as 
lichen,   zona,   ecthyma,  &c.,  in   various    spinal   or   cerebral  diseases, 

'  Cf.  Steiner,  Arch.  f.  Anaf.  u.  Phys.,  1S78  (Phys."  Abth.),  p.  218,  and 
references  there  given. 

^  Die  trophischen  Beziehimgender  Ne^-iivagi  zicm  Herzmuskel  (Berlin,  1879). 
Cf.  also  Zander,  Pfliiger's  ^rc/^/z/,  XIX.  (1879)  p.  263. 

3  Cf.  Pfliiger  and  Von  Platen,  Pfliiger's  Archhi,  xi.  (1875)  pp.  263,  272. 
Fubini,  Moleschott's  Unter stick,  xi.  (1876)  p.  48S. 


CHAP,    v.]  NUTRITION.  49I 

frequently  accompanied,  as  in  maladies  affecting  the  posterior  cornua, 
M'ith  intermittent  pains  ;  the  npid  and  peculiar  degeneration  of  and 
loss  ot  contniLtiliiy  in  the  yktlctal  n-.u  clcs  in  certain  afiections  ot 
the  spinal  cord,  the  changes  in  the  muscles  being  more  rapid  and  pro- 
fuuncl  than  in  the  nerves  ;  the  so-callcl  acute  bed-sores  of  cerebral 
apoplexy  ;  some  :;t  least  of  the  cases  of  vesical  alTections  attendant 
on  Sj)inal  or  ccrcbr  il  tliseases  or  injuries  ;  the  more  rapid  atrophy  and 
loss  of  contractility  whijh  is  seen  in  muscles  after  contusions  than 
alter  sections  of  nerves  ;  and  indeed  the  general  phenomena  and 
especially  the  topography  of  the  emption  of  a  large  number  of  cuta- 
neous diseases.  The  pathological  evidence  of  '  trophic '  action, 
though  indirect,  affords,  by  its  abundance  and  prominence,  a  striking 
contrast  to  the  scanty  and  uncertain  indications  of  experimental 
inquiry. 

Sec.  6.     Dietetics. 

We  may  sum  up  the  main  results  of  the  previous  sections 
somewhat  in  the  following  way.  Althougli  the  body  consists, 
like  the  food,  of  proteids,  fats  and  carbohydrates,  yet  the  con- 
version of  the  one  into  the  other  is  not  direct.  Assimilation  does 
not  proceed  in  such  a  way^hat  the  proteids  of  the  food  all  become 
the  proteids  of  the  body,  the  fats  of  the  food  the  fats  of  the  body, 
and  the  starch  and  sugar  of  the  food  the  glycogen,  dextrin,  and 
sugar  of  tiie  body.  We  cannot  even  say  that  the  non-nitrogenous 
food  supplies  alone  the  non-nitrogenous  parts  of  the  body,  while 
the  nitrogenous  food  remains  as  the  sole  source  of  the  nitrogenous 
tissues.  We  have  seen  that  under  all  circumstances  a  certain 
quantity  of  proteid  food  is  immediately  metabolized,  probably 
while  still  within  the  alimentary  canal,  and  that  when  an  excess 
of  proteid  food  is  taken  a  luxus  consumption  leads  to  the 
accumulation  of  bodily  fat.  On  the  other  hand,  we  find  that 
a  large  proportion  of  the  carbonic  acid  of  the  egesta  comes  from 
the  metabolism  of  nitrogenous  tissues,  such  as  muscle ;  and  we 
have  had  proof  that  the  energy  set  free  by  muscular  contraction 
may  be  far  greater  than  could  be  supplied  by  the  proteid  food 
taken,  and  that  therefore  the  non-nitrogenous  factors  of  the 
metabolism  which  set  free  the  energy  must  have  ultimately  come 
from  non-nitrogenous  food.  We  have  abundant  evidence  that 
the  various  food-stuffs  become  more  or  less  metabolised,  and  their 
elements  more  or  less  rearranged  and  mixed  before  they  appear 
as  constituents  of  the  bodily  tissues. 

We  have  seen  that  the  oxidations  of  the  body  are,  as  in  the 
case  of  muscle,  of  a  peculiar  character,  and  carried  on  by  the 
tissues  themselves.  While  at  present  we  should  be  hardly  justified 
in   denying  that   any   oxidations   at  all  take  place  in  the  blood 


492  DIETETICS.  [BOOK  II. 

plasma,  such  as  do  occur  must  be  slight  in  amount  as  compared 
with  those  going  on  in  the  tissues.  We  might  also  say  that  one 
body  only,  viz.  lactic  acid,  presents  itself  as  a  substance  likely  to 
be  directly  oxidized  in  the  blood  itself ;  and  even  with  regard  to 
this  the  evidence  is  as  much  against  as  for  any  such  direct  oxidation 
taking  place.  The  great  mass  of  the  oxidation  of  the  body  is  of 
an  indirect  kind,  determined  by  the  activity  of  the  several  tissues. 
The  blood  serves  as  an  oxygen  carrier  for  the  tissues ;  and  it  is 
not  itself  the  large  combustion  agent  it  was  once  thought  to  be. 
The  tendency  of  all  recent  inquiries  is  to  shew  that  the  body 
cannot  be  compared,  either  as  a  whole,  or  in  its  parts,  to  a 
furnace  for  the  direct  combustion  of  combustible  food.  On  the 
contrary,  we  are  driven  nearer  and  nearer  to  the  conclusion  that 
all  food  which  has  become  absorbed  into  the  blood  must  become 
tissue  before  it  becomes  waste  product,  and  only  becomes  waste 
product  through  a  metabolism  of  the  tissue.  When  we  say 
'  become  tissue  '  we  must  leave  it  at  present  wholly  undecided 
how  far  the  constant  metabolism  which  this  view  demands  affects 
the  so-called  structural  elements  of  the  more  highly  organised 
tissues ;  it  is  quite  open  however  for  u^  to  imagine  that  in  muscle, 
for  instance,  there  is  a  framework  of  more  stable  material,  giving 
to  the  muscular  fibre  its  histological  features,  and  undergoing  a 
comparatively  slight  and  slow  metabolism,  while  the  energy  given 
out  by  muscle  is  supplied  at  the  expense  of  more  fluctuating 
molecules  which  fill  up  so  to  speak  the  interstices  of  the  more 
durable  frame-work,  and  metabolism  of  which  alone  is  large  and 
rapid. 

The  characteristic  feature  of  proteid  food  is  that  it  increases 
the  oxidative,  metabolic  activity  of  the  tissues,  leading  to  a  rapid 
consumption,  not  only  of  itself,  but  of  non-nitrogenous  food  as 
well.  Where  therefore  a  rapid  renewal  of  the  tissues  is  sought  for, 
an  excess  of  proteid  food  may  be  desirable.  But  it  must  be  borne 
in  mind  that  by  the  very  nature  of  its  rapid  metabolism,  proteid 
food  must  tend  to  load  the  body  with  the  so-called  extractives, 
Le.  with  nitrogenous  crystalline  bodies.  How  far  these  are  of 
use  to  the  body,  and  what  part  they  play,  is  at  present  unknown 
to  us.  That  they  are  of  some  use  is  suggested  by  the  beneficial 
effects  of  the  extractum  carnis  when  taken  as  food  in  conjunction 
with  non-nitrogenous  material,  though  it  is  possible  that  the 
dietetic  value  of  this  preparation  may  be  due  to  the  small  amount 
of  non-crystalline  extractives  which  it  contains.  That  when  in 
excess  these  nitrogenous  products  may  be  highly  injurious  is 
indicated  by  the  little  we  know  of  the  connection  between  the 
symptoms  of  gout  and  the  presence  of  uric  acid.     A  large  meal 


CHAP.   V.J  NUTRITION.  493 

of  protoiil  material  must  tax  the  system  to  the  utmost  in  arisin;^ 
rid  of  or  stowinL?  away  the  nitro^^enous  crystaUine  bodies  getting 
throuL^h  the  ki.xus  consumption  eitlier  in  the  alimentary  canal  or 
in  the  liver. 

One  value  of  fats  and  carbohydrates  lies  in  their  being  sources 
of  energy,  more  than  three-fourths  of  the  normal  income  of  potential 
energy  coming  from  them  (p.  469)  ;  and,  as  we  have  seen,  they 
are  ultimate  sources  of  muscular  energy  as  well  as  of  heat.  But 
their  great  characteristic  is  that  they  do  not,  like  proteid  food, 
excite  the  metabolic  activity  of  the  body.  Hence,  to  a  far  greater 
extent  than  is  the  case  with  proteid  food,  they  can  be  retained 
and  stored  up  in  the  body  with  comparative  ease.  The  digested 
elements  of  fatty  or  carbohydrate  food  which  go  to  form  the 
protoplasm  of  adipose  tissue,  become  part  and  parcel  of  a  sub- 
stance which  can  perform  its  metabolism  without  any  explosive 
expenditure  of  energy,  and  which  therefore,  instead  of  giving  rise 
to  bodies  demanding  immediate  excretion  from  the  system,  can 
deposit  its  metabolic  products  as  apparently  little,  but  as  we  have 
seen  in  reality  greatly,  changed  fat.  In  this  way  the  non-nitro- 
genous food  of  to-day  is  rendered  available  for  future  and  even 
far  distant  wants. 

In  comparing  fats  with  carbohydrates,  we  can  only  point  to 
the  much  greater  potential  energy  of  the  former  than  of  the  latter, 
weight  for  weight  (see  p.  469). 

A  diet  may  be  chosen  either  for  the  simple  maintenance 
of  health,  or  for  the  sake  of  muscular  energy,  or  for  fattening 
purposes.  For  the  first  purpose  there  is,  we  may  suppose,  a 
normal  diet ;  and  in  the  case  of  man,  instinct  and  experience  have 
probably  not  erred  far  in  choosing  some  such  proportions  as  those 
given  on  p.  457.  If,  as  we  have  urged,  all  food  becomes  tissue 
before  it  leaves  the  body  as  waste  product,  the  dominant  principle 
of  all  nutrition,  and  the  ultimate  tribunal  of  all  questions  of  diet, 
must  be  the  individual  character  of  the  tissue,  the  idiosyncrasy  of 
the  body.  The  same  mysterious  qualities  which  cause  the  same 
blood-plasma  to  become  here  a  muscle,  and  there  a  secreting  cell, 
convert  the  same  food  into  the  body  of  a  man  or  of  a  sheep.  All 
the  simpler  and  more  general  laws  of  metabolism  are  made  sub- 
servient to  more  intricate  and  special  laws  of  protoplasmic  con- 
struction. We  can  only  speak  of  a  normal  diet  in  the  same  way 
that  we  speak  of  the  average  intelligence  of  man. 

In  seeking  to  supply  such  a  normal  diet  out  of  ordinary 
articles  of  food,  we  must  bear  in  mind  that  the  nutritive  value 
of  any  substance,  estimated  in  terms  of  the  potential  energy  of 
tlie  proteids,  fats,  or  carbohydrates  it  contains,  must  of  course  be 


494  DIETETICS.  [book   II. 

corrected  by  its  digestibility.  One  gramme  of  cheese  has,  as  far 
as  potential  energy  is  concerned,  an  exceedingly  high  value  ;  but 
the  indigestibility  of  cheese  brings  its  nutritive  value  to  a  very 
low  level.  Here  too  the  factor  of  idiosyncrasy  makes  itself 
exceedingly  felt. 

In  feeding  for  fattening  purposes  the  comparatively  cheap 
carbohydrates  are  of  course  chiefly  depended  on.  If  the  view- 
mentioned  on  p.  465  be  correct,  that  the  fat  really  stored  up  all 
comes  from  proteid  metabolism,  an  equivalent  of  this  food-stuff 
must  always  be  given.  If,  as  seems  probable,  this  view  is  a 
too  hurried  generalisation,  there  still  remains  the  possibility  that 
for  economical  fattening,  with  the  least  waste,  a  certain  proportion 
between  the  nitrogenous  and  non-nitrogenous  foods  must  always 
be  maintained. 

From  what  has  been  previously  said  it  is  evident  that  proteid 
food  is  not  the  only  food-stuff  to  be  regarded  in  selecting  a  diet 
for  muscular  labour.  We  should  however  equally  err  in  the 
opposite  direction  if  we  selected  exclusively  non-nitrogenous  food 
on  which  to  do  work,  since,  as  we  have  seen,  there  is  no  evidence 
that  the  fats  or  carbohydrates  are  the  direct,  though  they  may  be 
in  part  the  ultimate  source,  of  muscular  energy.  Considering  how 
complex  a  thing  strength  is,  how  much  it  depends  on  the  vigour 
of  parts  of  the  body  other  than  the  muscles,  a  normal  diet, 
calculated  to  develope  equally  all  parts  of  the  body,  is  probably 
the  best -diet  for  active  labour.  It  is  possible  however  that  an 
excess  of  proteid  food,  by  reason  of  the  renewal  of  tissue  caused 
by  its  metabolic  activity,  may  be,  in  such  cases,  of  service. 

Lastly,  the  several  saline  matters,  including  the  extractives  of 
animal  and  vegetable  food,  are  no  less  essential  elements  of  a 
diet  than  proteids,  fats,  or  carbohydrates.  Of  use,  not  for  the 
energy  they  themselves  possess,  but  by  reason  of  their  regulating 
the  energy  of  the  food-stuffs  more  strictly  so  called,  they  are 
necessary  to  life :  the  body  in  their  absence  fails  to  carry  out  its 
usual  metabolism,  and  disease  if  not  death  follows. 

The  dietetic  superiority  of  fresh  meat  and  vegetables  depends  in 
part  on  their  still  I'etaining  these  various  saline  and  extractive  matters. 
A  diet  from  which  phosphorus  (or  even  possibly  phosphates),  or 
chlorides,  or  potash,  or  soda  salts  are  absent,  is,  as  soon  as  the  store 
of  the  substance  in  the  body  is  exhausted,  useless  for  nutritive  pur- 
poses. Calcium  and  magnesium  may,  to  a  certain  extent,  be  replaced 
by  bases  closely  allied  to  them  ;  but  the  metabolic  i-ole  of  phosphorus 
or  of  sulphur  cannot  be  taken  up  by  an  analogous  body;  and,  as  is 
illustrated  by  their  distribution  in»the  body,  the  physiological  functions 
of  potash  and  soda  are  widely  different  if  not  antagonistic,  closely 


CHAP,   v.]  -  NUTRITION.  495 

allied  as  are  these  two  alkalis  when  regardcrl  troin  a  cliemical  point  of 
view.  Like  medicines  and  poisons — and  indeed  they  are  in  a  manner 
nitiiral  mtdicines — the  action  of  these  bodies  depends  in  part  on  their 
dose.  Indispensable  as  are  potash  salts  to  the  economy,  a  large  dose 
of  tliem  is  injurious ;  and  a  dog  fed  on  nothing  but  Liebig's  extract 
dies  sooner  than  a  dog  not  fed  at  all,  on  account  of  the  potash  salts 
of  the  extract  exerting  their  deleterious  intluencc  in  the  absence  of  the 
food  whose  metabolism  their  function  is  to  direct. 

The  physiology  of  nutrition  may  be  said  to  have  been  founded  by 
Liebig,  when  he  proved  the  formation  of  fat  in  the  animal  body,  aud 
published  his  views  on  the  nature  and  use  of  food.  The  labours  of 
Regnaiiit  and  Reiset '  added  much  to  our  knowledge  of  the  Statistics 
of  Respiration.  The  fir^t  elaborate  mquiry  into  the  Statistics  of 
Metabolism  in  general  was  that  of  Bidder  and  Schmidt^  ;  this  was 
followed  by  the  investigations  of  the  Munich  school,  viz.,  Bischoff, 
Bisjhoff  and  Voit^,  Voit,  and  Pettenkofer  and  Voit'.  Although  we 
have  h;id  occasion  to  combat  some  of  the  views  of  this  school,  it 
must  be  admitted  that  their  extended  and  laborious  researches  have 
been  the  means  of  an  immense  advance  in  our  knowledge.  Their 
method  has  been  largely  adopted,  with  excellent  results,  by  the  various 
agricultural  stations  in  Germiny  ;  and  in  this  country  the  inquiries  of 
Lawes  and  Gilbert  ^  have  given  us  information  of  peculiarly  valuable 
character,  inasmuch  as  it  is  chiefly  based  on  direct  analysis  and 
observation,  and  therefore  free  from  the  possibilities  of  error  attaching 
to  mere  calculations.  If,  however,  one  discovery  can  be  pointed  to  as 
influencing  our  views  of  the  nature  and  laws  of  animal  metabolism 
more  than  any  other,  it  is  that  by  Bernard^,  of  the  formation  of 
glycogen  by  the  liver. 

'  Ann.  Ch.  Phys.  (1S49)  (3)  XXVI.  32. 

»  Op.  cit.  3  Op,  cit. 

*  Op.  cit.  and  many  subsequent  memoirs  in  the  Zt.  fiir  Biol. 

5  Op.  .it.  ^  Op.  cii. 


BOOK    III. 


THE  CENTRAL  NERVOUS   SYSTEM   AND   ITS 
INSTRUMENTS. 


F.  P.  32 


CHAPTER    I. 

SENSORY   NERVES. 

In  studying  the  plienomeiia  of  motor  nerves  we  are  greatly  assisted 
by  two  facts  : — First,  that  the  muscular  contraction  by  which  we 
judge  of  what  is  going  on  in  the  muscle,  is  a  comparatively  simple 
thing,  one  contraction  differing  from  another  only  by  such  features 
as  amount,  rapidity,  and  frequency  of  repetition,  and  all  such 
differences  being  capable  of  exact  measurement.  Secondly,  that 
when  we  apply  a  stimulus  directly  to  the  nerve  itself,  the  effects 
differ  in  degree  only  from  those  which  result  when  the  nerve  is  set 
in  action  by  natural  stimuli,  such  as  the  will.  When  we  come,  on 
the  other  hand,  to  investigate  the  phenomena  of  afferent  nerves, 
our  labours  are  for  the  time  rendered  heavier,  but  in  the  end  more 
fruitful,  by  the  facts  : — First,  that  we  can  only  judge  of  what  is 
going  on  in  an  afferent  nerve  by  the  effects  it  produces  in  some 
central  nervous  organ,  in  the  way  of  exciting  or  modifying  reflex 
action,  or  modifying  automatic  action,  or  affecting  consciousness  ; 
and  we  are  consequently  met  on  tlie  very  threshold  of  every  inquiry 
by  the  difficulty  of  clearly  distinguishing  the  events  whicii  belong 
exclusively  to  the  afferent  nerve  from  those  which  belong  to  the 
central  organ.  Secondly,  that  the  effects  of  applying  a  stimulus  to 
the  peripheral  end-organ  of  an  afferent  nerve  are  very  different 
from  those  of  applying  the  same  stimulus  directly  to  the  nerve- 
trunk.  This  may  be  shewn  by  the  simple  experience  of  comparing 
the  sensation  caused  by  the  contact  with  any  sharp  body  of  a  nerve 
laid  bare  by  a  wound  with  that  caused  by  contact  of  an  intact  skin 
with  the  same  body.  These  differences  reveal  to  us  a  complexity 
of  impulses,  of  which  the  phenomena  of  motor  nerves  gave  us  not 
so  much  as  a  hint ;  but  for  the  time  being  they  increase  the 
difficulties  of  our  study. 

An  afferent  impulse  passing  along  an  afferent  nerve  may  in 
certain  cases  simj)ly  produce  a  change  in  our  consciousness 
unaccompanied  by  any  visible  bodily  movements  ;  in  other  cases 
it  may  give  rise  to  rellex  movements,  or  modify  existing  reflex  or 

32-2 


500  SENSORY  NERVES.  [BOOK   III. 

automatic  actions  without  causing  any  change  in  consciousness ; 
in  still  other  cases  it  may  bring  about  both  results  at  the  same  time. 
An  afferent  nerve  the  stimulation  of  which  gives  rise  to  a  sensation, 
and  so  leads  to  a  modification  of  consciousness,  may  be  more 
closely  defined  as  a  '  sensory '  nerve.  There  is  however  no  distinct 
proof,  having  regard  to  the  difficulties  just  mentioned,  that  the 
afferent  fibres  which  in  the  body  are  commonly  used  to  cause 
or  affect  reflex  action  differ  at  all  in  kind  from  those  whose  function 
it  is  to  modify  consciousness.  On  the  contrary,  such  evidence  as 
we  have  goes  to  shew  that  an  appropriate  stimulus  of  the  same 
fibre  may  give  rise  to  one  or  other  or  both  events  ;  and  that  whether 
the  one  or  the  other,  or  both,  events  occur  depends  on  the  condi- 
tion of  the  central  organ,  and  on  the  relation  of  its  several  parts  to 
the  afferent  nerve.  The  stimulation  of  the  same  nerve  (and  there 
are  no  positive  facts  which  would  preclude  us  from  saying  '  of  the 
same  fibre ')  rnay  under  certain  circumstances,  as  for  instance 
when  the  brain  has  been  removed,  simply  cause  a  reflex  action  and 
under  other  circumstances  give  rise  merely  to  a  sensation.  Hence 
an  afferent  nerve  is  frequently  spoken  of  as  a  sensory  nerve  even 
under  circumstances  where  there  is  no  evidence  of  consciousness 
being  actually  affected,  because  by  a  slight  change  of  circumstances 
the  same  stimulation  of  the  same  nerve  might  give  rise  to  a  distinct 
sensation  ;  the  substitution  of  the  specific  for  the  general  term  being 
justified  by  the  convenience  of  the  former. 

AH  the  spinal  nerves  are  mixed  nerves,  composed  of  efferent 
and  afferent,  of  motor  and  sensory  fibres.  When  a  spinal  nerve  is 
divided,  stimulation  of  the  peripheral  portion  causes  muscular  con- 
traction, of  the  central  portion,  a  sensation  (or  a  reflex  action). 
At  the  junction  of  the  nerve  with  the  spinal  cord  the  sensory  fibres 
are  gathered  into  the  posterior  and  the  motor  fibres  into  the 
anterior  root.  The  proof  of  this,  which  was  first  made  known  by 
Charles  Bell  and  Majendie,  their  discoveries  forming  the  foundation 
of  modern  nervous  physiology,  is  simply  as  follows. 

When  the  anterior  root  is  divided,  the  muscles  supphed  by  the 
nerve  cease  to  be  thrown  into  contractions  either  by  the  will,  or  by 
reflex  action,  while  the  structures  to  which  the  nerve  is  distributed 
retain  their  sensibility.  During  the  section  of  the  root,  or  when 
the  proximal  stump,  that  connected  with  the  spinal  cord,  is 
stimulated,  no  sensory  effects  are  produced.  When  the  distal 
stump  is  stimulated,  the  muscles  supplied  by  the  nerve  are  thrown 
into  contractions.  When  the  posterior  root  is  divided,  the  muscles 
supplied  by  the  nerve  continue  to  be  thrown  into  action  by  an 
exercise  of  the  will  or  as  part  of  a  reflex  action,  but  the  structures 
to  which  the  nerve  is  distributed  lose  the  sensibility  which  they 


CHAI".    I.J  SliNSORY   NERVES.  5oI 

previously  possessed.  During  the  section  of  the  root,  and  when 
the  proximal  stump  is  stimulated  sensory  eflects  arc  produced  When 
the  distal  stump  is  stimulated  no  movements  arc  called  forth.  These 
facts  demonstrate  that  sensory  impulses  pass  exclusively  by  the 
posterior  root  from  the  peripheral  to  the  central  organs,  and  that 
motor  impulses  pass  exclusively  by  the  anterior  root  from  the 
central  to  the  peripheral  organs. 

An  exception  must  be  made  to  the  abov  egeneral  statement,  on 
account  of  the  so-called  recurrent  sensibility  which  is  witnessed  in 
conscious  mammals,  under  favourable  circumstances.  It  often  happens 
that  when  \.\\^  pcrif>licral  stump  of  the  divided  anterior  root  is  stimulated 
signs  of  pain  are  witnessed.  These  are  not  caused  by  the  concurrent 
muscular  contractions  or  cramp  which  the  stinuilation  occasions,  for 
they  remain  if  the  whole  trunk  of  the  nerve  be  divided  some  little  way 
below  the  union  of  the  roots  above  the  origins  of  the  muscular  branches, 
so  that  no  contractions  take  place.  They  disappear  if  the  posterior 
root  be  also  cut,  and  they  are  not  seen  if  the  mixed-nerve  trunk  be 
divided  close  to  the  union  of  the  roots.  The  phenomena  arc  probably 
due  to  the  f  ict,  that  bundles  of  sensory  fibres  of  the  posterior  root  after 
running  a  short  distance  down  the  mixed  trunk  turn  back  and  run 
upwards  in  the  anterior  root,  and  by  this  recurrent  course  give  rise  to 
the  re:;urrent  sensibility.  When  the  anterior  root  is  divided  some  few 
fibres  in  it  do  not,  like  the  rest,  degenerate,  and  when  the  posterior  root 
is  divided,  a  few  fibres  in  the  anterior  root  are  seen  to  degenerate  like 
those  of  the  posterior  root. 

Concerning  the  ganglion  on  the  posterior  root,  we  may  say 
definitely  that  it  is  neither  a  centre  of  reflex  nor  of  automatic 
action.  Our  knowledge  concerning  its  function  is  almost  limited 
to  the  fact  that  it  is  in  some  way  intimately  connected  with  the 
nutrition  of  the  nerve.  When  a  mixed  nerve-trunk  is  divided,  the 
peripheral  portion  degenerates  from  the  point  of  section  down- 
wards towards  the  periphery.  The  central  portion  does  not  so 
degenerate,  and  if  the  length  of  nerve  removed  be  not  too  great, 
the  central  portion  uniting  with  the  degenerating  peripheral  portion 
may  grow  downwards,  and  thus  regenerate  the  nerve.  This  de- 
generation is  ob.served  when  the  mi.xed  trunk  is  divided  in  any 
part  of  its  course  from  the  periphery  to  close  up  to  the  ganglion. 
\Vhen  the  posterior  root  is  divided  between  the  ganglion  and  the 
spinal  cord,  the  portion  attached  to  the  spinal  cord  degenerates, 
but  that  attached  to  the  ganglion  remains  intact.  When  the 
anterior  root  is  divided,  the  proximal  portion  in  connection  with 
the  spinal  cord  remains  intact,  but  the  distal  portion  between  the 
section  and  the  junction  with  the  other  root  degenerates;  and  in 
the  mixed  nerve-trunk  many  degenerated  fibres  are  seen,  which,  of 
they  be  carefully  traced  out,  are  found  to  be  motor  fibres.     If  the 


502  ROOTS   OF   SPINAL   NERVES.  [BOOK   III. 

posterior  root  be  divided  carefully  between  the  ganglion  and  the 
junction  with  the  anterior  root,  the  posterior  root  above  the 
section  remains  intact,  but  in  the  mixed  nerve-trunk  are  seen 
numerous  degenerated  fibres,  which  when  examined  are  found  to 
have  the  distribution  of  sensory  fibres.  Lastly,  if  the  posterior 
ganglion  be  excised,  the  whole  posterior  root  degenerates,  as  do 
also  the  sensory  fibres  of  the  mixed  nerve-trunk.  Putting  all 
these  facts  together,  it  would  seem  that  the  growth  of  the  motor 
and  sensory  fibres  takes  place  in  opposite  directions,  and  starts 
from  different  nutritive  or  '  trophic '  centres.  The  sensory  fibres 
grow  away  from  the  ganglion  either  towards  the  periphery,  or 
towards  the  spinal  cord.  The  motor  fibres  grow  outwards  from 
the  spinal  cord  towards  the  periphery.  This  difference  in  their 
mode  of  nutrition  is  frequently  of  great  help  in  investigating  the 
relative  distribution  of  motor  and  sensory  fibres.  When  a  pos- 
terior root  is  cut  beyond  the  ganglion,  or  the  ganglion  excised,  all 
the  sensory  nerves  degenerate,  and  the  sensory  fibres,  by  their 
altered  condition,  can  readily  be  traced  in  the  mixed  nerve- 
branches.  Conversely,  when  the  anterior  roots  are  cut,  the  motor 
fibres  alone  degenerate,  and  can  be  similarly  diagnosed  in  a  mixed 
nerve-tract.  Thus  also  in  a  mixed  nerve  like  the  vagus,  the  fibres 
which  spring  from  the  real  vagus  root  may  be  distinguished  from 
those  proceeding  from  the  spinal  accessory,  by  section  of  the 
vagus  and  spinal  accessory  roots  respectively ;  and  in  the  mixed 
vago-sympathetic  trunk,  met  with  in  many  animals,  the  vagus 
fibres  may  be  disdnguished  from  the  sympathetic,  since,  after  a 
section  of  the  mixed  trunk,  the  former  degenerate  from  above 
downwards,  whereas  the  latter  degenerate  in  an  upward  direction 
from  the  inferior  cervical  ganglion  below  to  the  superior  cervical 
ganglion  above ;  for  the  ganglia  of  the  sympathetic  behave  in 
this  respect  like  the  spinal  ganglia  of  the  posterior  roots.  This 
method  of  diagnosis  is  often  spoken  of  as  the  Wallerian  method, 
after  A.  Waller',  to  whom  we  are  indebted  for  the  discovery  of 
most  of  these 'facts. 

According  to  Wundt^  afferent  impulses  suffer  a  delay  in  passing 
through  the  spinal  ganglia,  reflex  acts  having  a  markedly  shorter  latent 
period  when  they  are  initiated  by  a  stimulus  applied  to  the  posterior 
root  than  when  the  stimulus  is  appUed  to  the  mixed  nerve-trunk  just 
below  the  ganglion.  Exner^  however  finds  that  the  negative  variation 
travels  at  the  same  rate  through  a  spinal  ganglion  as  along  an  ordinary 
nerve-trunk. 

'  Miiller's  Archiv,  1852,  p.  392. 

=  Mechanik  der  Nerven,  (1876),  2te  Abth.  p.  45. 

3  Arck  f.  Anat.  unci  Phys.,  iS'j'j,  Phys.  Abth.  p.  567. 


CHAP.   I.]  SENSORY   NERVES.  503 

In  the  cranial  nerves  ihc  motor  and  sensory  tracts  are  far 
less  mixed  than  in  the  spinal  nerves.  The  olfactory,  optic  and 
acoustic  nerves  are  purely  sensory  nerves.  The  fifth  glosso- 
pliaryngeal  and  vagus  are  mixed  nerves;  and  Steiner'  finds  that 
in  the  dog  the  afferent  and  efferent  fibres  are  gathered  into  two 
bundles  so  distinct  that  they  may  be  separated  by  the  knife,  the 
afferent  bundle  lying  to  the  outside  of  the  efferent  bundle. 

The  facial  and  hypoglossal  are  for  the  most  part  motor 
(efferent)  nerves,  but  contain  sensory  (afferent)  fibres.  The  third, 
fourth,  sixth  and  spinal  accessory  are  exclusively  motor  (efferent) 
nerves.  These  statements  refer  to  what  are  commonly  looked  upon 
as  the  trunks  of  the  respective  nerves.  More  exactly  speaking,  the 
sensory  fibres  of  the  facial  come  from  the  fifth,  pneumogastric  and 
glosso-pharyngeal  nerves,  so  that  the  facial  proper  is  in  reality  a 
purely  motor  nerve.  So  likewise  is  the  hypoglossal,  its  sensory 
fibres:  coming  from  the  fiftii,  pneumogastric,  and  three  upper  cer- 
vical nerves.  The  fifth  is  a  mixed  nerve  entirely  on  the  plan  of  a 
spinal  nerve,  having  distinct  motor  and  sensory  roots.  The  glosso- 
pharyngeal seems  also  to  be  essenticdly  a  sensory  nerve,  its  motor 
filaments  springing  from  the  fifth  and  facial  nerves.  Concerning 
the  vagus  some  have  maintained  that  the  pneumogastric  root 
proper  is  entirely  sensory  (afferent),  and  that  all  the  efferent  func- 
tions of  the  vagus  are  dependent  on  the  fibres  of  the  spinal  ac- 
cessor)'^ which  join  it.  To  this  point  we  shall  return  when  we  come 
to  consider  briefly  the  special  fiyiction  of  these  several  nerves. 

We  have  already  stated  (p.  125)  that  isolated  pieces  of  motor 
and  of  sensory  nerves  behave  exactly  alike  as  far  as  all  the  physical 
manifestations  attendant  on  the  passage  of  a  nervous  impulse  are 
concerned ;  the  negative  variation  makes  its  appearance  in  the 
same  way  and  seems  to  have  the  same  characters  in  both  kinds  of 
nerves.  The  same  is  also  true,  as  far  as  we  know,  of  nerves 
within  the  body. 

iMoreover,  the  rate  at  which  nervous  impulses  travel  appears 
to  be  about  the  same  in  motor  and  sensory  nerves;  at  least  we 
have  no  evidence  of  any  fundamental  difference  in  this  respect 
between  the  two.  We  have  seen  that  the  velocity  of  a  nervous 
impulse  in  the  motor  nerve  of  a  frog  is  about  28  metres  per  sec. 
The  velocity  of  a  motor  impulse  in  man,  as  judged  by  the  diflference 
of  the  latent  period  ot  the  contraction  of  the  thumb-muscles  when 
stimulation  is  brought  to  bear  on  the  motor  nerve  at  the  wrist,  or 
high  up  in  the  arm,  is  about  t,^  metres  per  sec.  In  warm-blooded 
animals,'  however,  the  rate  of  transmission  of  motor  impulses  is 
very  variable,  being  in  particular  closely  dependent  on  temperature, 

'  Arch./.  Anai.  uud  Phys.,  1878,  I'liys.  Abth.  p.  21S. 


S04  AFFERENT  AND  EFFERENT  NERVE  FIBRES.   [BOOK   III. 

and  probably  also  on  other  circumstances.  Thus  Helmholtz  and 
Baxt'  obtained  a  range  from  as  low  as  30  m.  when  the  arm  was 
cooled  to  as  high  as  89*4  m.  when  the  arm  was  heated.  The 
velocity  of  a  sensory  impulse  is  estimated  by  measuring  the  time 
taken  between  a  stimulus  bemg  brought  to  bear  on  some  sentient 
surface,  as  the  skin,  and  the  making  of  a  signal  by  the  individual 
experimented  on  at  the  instant  that  he  feels  the  stimulus.  The 
time  taken  up  in  the  sensory  impulse  becoming  converted  into  a 
sensation  after  reaching  the  nervous  central  organs,  in  the  mental 
operation  of  determining  to  make  the  signal,  and  in  the  beginning 
to  make  the  signal,  corresponds  in  a  way  to  the  purely  muscular 
portion  of  the  latent  period  in  the  experiment  for  determining  the 
velocity  of  a  motor  impulse.  The  application  of  the  stimulus  and 
the  making  of  the  signal  {ex.  gr.  closing  a  galvanic  circuit)  being 
both  recorded  on  a  rapidly  travehing  surface,  the  time  taken  up  in 
the  whole  operation  can  be  easily  measured ;  and-  the  difference 
between  the  time  taken  when  the  stimulus  is  applied  to  some  spot 
separated  from  the  central  nervous  system  by  a  short  piece  of 
nerve,  ex.  gr.  the  top  of  the  thigh,  and  that  taken  when  a  long 
piece  of  nerve  intervenes,  ex.  gr.  when  the  stimulus  is  applied  to 
the  toe,  will  give  the  time  required  for  the  sensory  impulse  to  pass 
along  a  piece  of  sensory  nerve  as  long  as  the  ditference  of  length 
between  the  above  two  nerves ;  from  which  the  velocity  can  be 
calculated.  Observations  carried  on  in  this  way  led  to  most  dis- 
cordant results,  varying  from  26  metres  to  94  metres,  or  even  more 
per  sec.  The  difference  here  is  far  too  great  to  allow  any  value  to 
be  attached  to  an  average.  When  it  is  remembered  how  complex 
are  all  the  central  nervous  operations  in  these  instances,  as  com- 
pared with  the  changes  going  on  in  a  muscle  during  the  latent 
period  of  its  contraction,  and  how  these  central  operations  might 
vary  according  as  one  or  other  spot  of  skin  was  stimulated,  quite 
independently  of  the  length  of  nerve  between  the  centre  and  the 
spot  stimulated,  these  discrepancies  will  not  be  wondered  at;  and 
it  may  fairly  be  concluded  that  the  velocity  of  a  sensory  impulse 
does  not  materially  differ  from  that  of  a  motor  impulse. 

There  are,  however,  certain  phenomena  which  might  at  first 
sight  be  interpreted  as  indicating  that  afferent  and  efferent  nerve 
fibres  behave  differently  towards  stimuli.  We  have  already  (p.  95) 
stated  that  according  to  most  observers  when  an  ordinary  motor 
nerve,  such  as  a  nerve  supplying  a  muscle,  is  heated,  no  indica- 
tions of  the  generation  of  nervous  impulses,  no  contractions  of  the 
muscle  for  instance,  are  observed.  The  heat  does  not  act  as  a 
stimulus ;  it  may  increase  the  irritability  of  the  nerve  for  the  time 
'  Berlin.  Monatsbericht,  1870. 


CHAP.   I.]  SENSORY   NERVES.  505 

being,  but  apparently  cannot  originate  the  explosive  discharge 
which  we  call  an  impulse.  We  have  also  seen  that  during  the 
passage  of  a  constant  current  along  the  nerve  of  a  niuscle-ncrve 
preparation  no  contractions  are  visible,  no  impulses,  save  in  certain 
particular  cases,  are  generated,  so  long  as  the  current  is  not 
suddenly  varied  in  strength.  But  Griilzner'  finds  that  when 
afferent  nerve-fibres,  such  as  those  in  the  central  stump  of  the 
divided  sciatic  or  in  the  central  stump  of  the  vagus,  are  heated  to 
45°  or  50°  events  occur,  clearly  proving  that  impulses  are  generated 
in  the  afferent  fibres  by  the  elevation  of  temperature.  In  the  case 
of  the  sciatic  the  animal  shews  sign  of  pain,  the  blood-pressure  is 
affected,  &c. ;  and  in  the  case  of  the  vagus  the  heart  is  slowed  by 
reflex  inhibitory  impulses  passing  down  the  other,  intact,  vagus, 
though  heating  the  peripheral  instead  of  the  central  stump  of  the 
divided  vagus,  has  no  effect  whatever  on  the  heart.  Similarly 
when  the  same  nerves  or  other  nerves  containing  afferent  fibres 
are  submitted  to  the  action  of  the  constant  current,  there  are  like 
evidences  of  the  continued  generation  of  nervous  impulses  during 
the  whole  time  of  the  passage  of  the  current,  e\cn  though  it  be 
kept  as  uniform  in  strength  as  possible.  On  the  other  hand  many 
chemical  substances  which  act  as  powerful  stimuli  to  motor  nerves 
are  ineffectual  towards  afferent  fibres.  These  results,  however, 
until  the  contrary  is  proved  by  further  inquiries  into  the  phe- 
nomena attending  the  generation  and  transmission  of  nervous 
impulses,  may  be  taken  as  indicating  not  so  much  that  the 
afferent  and  efferent  fibres  are  themselves  acted  upon  in  a 
different  way  by  heat  or  by  the  constant  current  as  that  the 
molecular  disturbances  generated  in  both  cases  have  different 
effects  according  as  they  impinge  upon  a  central  or  a  peripheral 
mechanism.  We  can  readily  imagine  that  molecular  disturbances 
which  would  be  impotent  to  stir  the  sluggish  muscular  substance 
to  a  contraction,  and  thus  so  to  speak  be  lost  upon  the  muscle,  might 
produce  a  very  great  effect  on  the  more  sensitive  and  mobile 
material  of  the  central  nervous  system.  We  may  for  the  present 
therefore  conclude  that  there  is  no  distinct  proof  of  an  absolute 
difference  between  afferent  and  efferent  fibres,  but  we  must  at  the 
same  time  be  cautious  not  to  consider  the  grosser  phenomena, 
presented  by  a  muscle-nerve  preparation,  as  a  satisfactory  test  of 
all  the  changes  which  may  take  place  in  a  nerve-fibre.  The 
necessity  of  this  caution  will  be  almost  immediately  illustrated 
from  another  point  of  view. 

The  apparent  identity  in  function  between  afferent  and  efferent 
fibres,  taken  into  consideration   with    the   facts  just   mentioned 
'  Pfliiger's  Archiv,  xvii.  (1878)  p.  215. 


506      "  MOTOR   AND    SENSORY   NERVES.         [BOOK  III. 

concerning  the  regeneration  of  nerves,  suggests  the  inquiry  whether 
by  a  change  of  the  peripheral  or  central  organs  a  motor  nerve  can  be 
converted  into  a  sensory  nerve,  or  vice  versa.  Experiments  made 
with  a  view  of  obtaining  a  functional  union  between  purely  motor 
and  sensory  nerves  have,  in  the  hands  of  most  observers  (Fiourens, 
Bidder,  Schifif,  &c.),  failed;  and  though  Phihpeaux  and  Vulpian^ 
were  so  far  more  successful,  that  they  obtained  an  apparent  union 
betv/een  a  sensory  and  a  motor  nerve-trunk,  their  results  do  not 
prove  that  a  fibre,  which  is  ordinarily  a  purely  sensory,  may  act  as 
a  motor  fibre,  and  vice  versa. 

These  observers,  having  in  young  dogs  divided  the  hypoglossal 
nerve  and  removed  its  central  portion  as  completely  as  possible,  united 
by  fine  sutures  its  peripheral  end  with  the  central  portion  of  the  lingual 
of  the  same  side,  having  similarly  removed  from  this  the  peripheral 
portion.  Thus  the  central  lingual  was  united  with  the  peripheral 
hypoglossal.  Complete  union  took  place,  and  it  was  found  that,  after 
some  weeks,  the  portion  of  nerve  between  the  tongue  and  the  point  of 
union,  i.e.  the  part  which  had  previously  been  the  peripheral  hypo- 
glossal, was  in  a  sound  and  healthy  condition.  Stimulation  of  the 
lingual  nerve  above  the  point  of  union  produced  contractions  in  the 
tongue  of  that  side,  whether  the  stimulus  were  electrical  or  mechanical ; 
and  the  contractions  were  still  visible  when  the  lingual,  in  order  to  pre- 
clude any  reflex  action,  was  divided  high  up  previous  to  stimulation. 
Here  the  sensory  lingual  was  apparently  the  means  of  causing  motor 
effects.  It  must  be  remembered,  however,  that  this  is  not  a  case  of 
the  union  of  motor  and  sensory  fibres.  The  peripheral  portion  of  the 
hypoglossal  in  reality  became  wholly  degenerated,  and  the  portion  of 
nerve  which  apparently  was  hypoglossal  nerve,  was  in  truth  new  nerve 
produced  by  a  downward  growth  of  the  lingual.  If  any  real  union  took 
place  it  must  have  been  between  the  lingual  fibres  and  the  end- plates  of 
the  glossal  muscular  fibres.  The  force  of  this  experiment  is  moreover 
lessened  by  the  fact  observed  by  Vulpian^  himself,  that  when  the  hypo- 
glossal is  simply  removed,  or  a  large  piece  of  the  nerve  cut  out,  so  that 
the  peripheral  portions  degenerate,  stimulation  of  the  lingual  nerve  of 
the  same  side  causes  movements  of  the  tongue,  though  when  the  hypo- 
glossal is  intact,  stimulation  of  the  lingual  produces  no  such  effect. 
The  motor  effects  thus  seen  are  due  to  the  chorda  fibres  present  in  the 
lingual,  and  Vulpian  finds  that  the  movements  obtained  on  stimulating 
the  lingual  nerve  after  the  apparent  vmion  of  the  lingual  and  hypo- 
glossal, do  not  occur  if  the  chorda  fibres  in  the  lingual  be  brought  into 
a  state  of  degeneration  by  previous  section  of  the  chorda  nerve.  Schiff  3 
has  observed  after  section  of  the  hypoglossal,  spontaneous  contractions 
of  the  glossal  muscular  fibres,  contractions  which  are  at  first  inhibited, 
but  at  a  later  period  increased,  by  stimulation  of  the  (chorda  fibres  in 

'  Vulpian,  Le^.  Systhne  Nei-v.,  274. 

^  Ct.  Rd.,  T.  76,  p.  146  (1873). 

■^  K.  Accad.  del  Lined,  (3)  I.  (1877). 


CHAP.    1.]  SENSOKY   NERVES.  507 

the)  lingual  and  that  to  such  an  extent  as  to  move  the  tongue  up  and 
down  ;  this  curious  fact  helps  to  explain  why  the  section  of  the  hypo- 
glossal seems  necessary  lo  developc  the  UKHor  etfccts  of  stimulatin;^  the 
lingual.  Vulpian  and  i'hilipcaux  also  made  experiments  on  the  union 
of  liic  vaj^us  and  hypoglossal,  but  the  results  were  even  less  satisfactory 
tlian  those  with  ihc  lingual  and  hypoglossal,  and  Vulpian  himself 
admits  that  the  functional  union  of  motor  and  sensory  fibres  is  as  yet 
unproved. 

We  have  already  seen  (p.  123)  that  a  sensory  nerve  in  its 
simplest  form  may  be  regarded  as  a  strand  of  eminently  irritable 
protoplasm,  forming  a  link  between  a  superficial  cell  which  alone 
IS  subject  to  extrinsic  stimuli,  and  a  ceniral  (reflex  or  automatic) 
cell  which  receives  stimuli,  chiefly  in  the  form  of  nervous  impulses 
proceeding  from  the  former  along  the  connecting  strand.  In  the 
earliest  stages  of  the  development  of  a  sensory  nervous  system, 
the  superficial  sensory  cell  is  susceptible  of  stimuli  of  all  kinds, 
provided  thoy  are  sufticiently  strong;  and  probably  all  the  impulses 
which  it  transmits  to  the  central  cell  resemble  each  other  very 
closely,  ditifering  only  in  degree.  It  is  obvious  however  that  the 
economy  would  gain  by  a  further  division  of  labour,  by  a  differenti- 
ation of  the  simple  uniform  superficial  cell  into  a  number  of  cells, 
each  of  which  was  more  susceptible  to  particular  stimuli  than  its 
fellows.  Thus  one  cell,  or  rather  one  group  of  cells,  would  become 
eminently  susceptible  to  the  influence  of  light:  in  them  the  impact 
of  rays  of  light  would  give  rise  to  nervous  impulses  more  readily 
than  in  the  other  groups  ;  another  group  would  develope  a  sensitive- 
ness to  waves  of  sound,  and  so  on.  In  this  way  the  primary 
homogeneous  bodily  surface  would  be  differentiated  into  a  series 
of  sense-organs,  disposed  and  arranged  among  ectodermic  cells, 
the  purpose  of  the  latter  being  simply  protective,  and  therefore 
not  demanding  the  existence  of  any  direct  connection  with  the 
central  nervous  system.  Similar  but  less  highly  marked  differenti- 
ations would  be  established  in  the  endings  of  the  afferent  nerves 
connecting  the  central  nervous  system  with  the  internal  surfaces 
and  ])arts  of  the  body. 

-Moreover  it  is  obvious  that  the  sensory  impulses  transmitted  to 
the  central  nervous  system  by  these  difterenliated  sense-organs 
would  be  themselves  largely  differentiated.  Just  as  the  impulses 
whicli  pass  along  a  motor  nerve  differ  according  to  the  nature  of 
the  stimulus  which  is  applied  to  the  nerve  {whether,  for  instance, 
the  stimulus  be  a  single  induction-shock,  or  several  shocks  repeated 
slowly,  or  several  shocks  repeated  rapidly,  and  so  on,  the  effect  on 
the  muscle  being  in  each  case  a  difterent  one),  so  to  a  much  greater 
degree  the  impulses  generated  by  light  in  a  visual  sense-organ  must 


5o8  SPECIAL   SENSES.  [BOOK  III. 

naturally  differ  from  those  generated  by  simple  pressure  in  a  tactile 
sense-organ. 

And  since  these  various  sensory  impulses  have  much  work  to 
perform  on  arriving  at  the  central  nervous  system,  in  the  way  of 
influencing  the  multitudinous  molecular  operations  going  on  in 
the  central  cells,  and  of  affecting  consciousness,  this  differentiation 
of  sensory  organs  and  sensory  impulses,  will  naturally  be  accom- 
panied by  a  corresponding  differentiation  of  those  central  cells 
which  the  impulses  are  the  first  to  reach  on  arriving  at  the  central 
organ.  Those  cells,  for  instance,  of  the  central  nervous  system, 
which  first  receive  the  particular  nervous  impulses  coming  from 
the  visual  sense-organs,  will  be  set  apart  for  the  task  of  so 
modifying  and  preparing  those  impulses  as  to  adapt  them  in  the 
best  possible  way  for  the  work  which  they  have  to  do.  Hence 
^d^ckv  peripheral  sense-organ  will  be  united  by  means  of  its  nerve 
with  a  corresponding  ce7itral  sense-organ,  the  former  being  able  to 
affect  other  parts  of  the  central  nervous  system  only  through  the 
medium  of  the  latter.  This  at  least  we  know  to  be  the  case  as 
far  as  relates  to  all  the  central  nervous  operations  in  which  con- 
sciousness is  concerned ;  for  of  the  total  characters  which  belong 
to  an  affection  of  consciousness  by  means  of  any  of  the  sense- 
organs,  i.e.  which  belong  to  any  particular  sensations,  while  some 
are  gained  during  the  rise  of  the  sensory  impulses  in  the  peripheral 
sense-organ,  others  first  appear  in  the  central  sense-organ  in  the 
course  of  the  changes  through  which  the  impulses  give  rise  to  a 
sensation.  Thus  a  stimulus  of  any  kind  applied  to  the  optic 
nerve  along  any  part  of  its  course  gives  rise  to  a  sensation  of 
light,  and  precisely  the  same  stimulus  applied  to  the  acoustic 
nerve  along  any  part  of  its  course  gives  rise  to  a  sensation  of 
sound ;  and  so  on.  All  the  evidence  we  possess  goes  against  the 
view  that  an  isolated  piece  of  optic  nerve  differs  in  function  from 
a  similarly  isolated  jDiece  of  acoustic  nerve ;  such  facts  as  are 
within  our  knowledge  go  to  shew  that  the  disturbances  generated 
in  a  piece  of  optic  nerve  by  a  galvanic  current  are  the  same  as 
those  generated  in  a  piece  of  acoustic  nerve.  We  are  therefore 
driven  to  the  conclusion  that  the  difference  in  this  case  arises  in 
the  central  organs. 

In  all  these  differentiated  sensory  mechanisms,  or  special 
senses  as  they  are  called,  we  have  then  to  deal  with  two  elements  : 
the  peripheral  sense-organ,  in  which  we  have  to  study  how  the 
special  physical  agent  gives  rise  to  special  sensory  impulses  ;  and 
the  central  sense-organs,  in  which  our  study  is  confined  to  the 
manner  in  which  these  special  impulses  modify  the  operations  of 
the  central  nervous  system.     Inasmuch  as  in  a  normal  body  the 


CHAP.   I.]  SENSORY   NERVES.  509 

peripheral  organ  remains  in  connection  with  the  central  organ, 
and  our  study  of  the  special  senses  is  carried  on  ch icily  by 
subjective  observations  in  which  we  make  use  of  our  own  con- 
sciousness, it  frequently  becomes  very  diflicult  to  distinguish  in 
any  given  sensation  the  peripheral  from  the  central  element.  The 
two  become  more  distinct,  the  more  complex  the  sense  and  the 
more  highly  organised  the  sense-organs.  For  this  reason  it  will 
be  most  convenient  to  commence  our  study  of  the  special  senses 
witli  the  sense  of  vision. 


CHAPTER    II. 

SIGHT. 

A  RAY  of  ]ight  falling  on  the  retina  gives  rise  to  what  we  call  a 
sensation  of  light ;  but  in  order  that  distinct  vision  of  any  object 
may  be  gained,  an  image  of  the  object  must  be  formed  on  the 
retina,  and  the  better  defined  the  image  the  more  distinct  will  be 
the  vision.  Hence  in  studying  the  physiology  of  vision,  our  first 
duty  is  to  examine  into  the  arrangements  by  which  the  formation 
of  a  satisfactory  image  on  the  retina  is  effected  ;  these  we  may 
call  briefly  the  dioptric  mechanisms.  We  shall  then  have  to 
inquire  into  the  laws  according  to  which  rays  of  light  impinging 
on  the  retina  give  rise  to  sensory  impulses,  and  those  according  to 
which  the  impulses  thus  generated  give  rise  in  turn  to  sensations. 
Here  we  shall  come  upon  the  difficulty  of  distinguishing  between 
the  unconscious  or  physical  and  the  conscious  or  psychical  factors. 
And  we  shall  find  our  difilculties  increased  by  the  fact,  that  in 
appealing  to  our  own  consciousness  we  are  apt  to  fall  into  error 
by  confounding  primary  and  direct  sensations  with  states  of  con- 
sciousness which  are  produced  by  the  weaving  of  these  primary 
sensations  with  other  operations  of  the  central  nervous  system,  or, 
in  familiar  language,  by  confounding  what  we  see  with  what  we 
think  we  see.  These  two  things  we  will  briefly  distinguish  as  visual 
sensations  and  visual  judgments  ;  and  we  shall  find  that  both  in 
vision  with  one  eye,  but  more  especially  in  binocular  vision,  visual 
judgments  form  a  very  large  part  of  what  we  frequently  speak  of 
as  our  sight. 

Sec.  I.     Dioptric  Mechanisms. 
The  forjncJion  of  the  Image. 

The  eye  is  a  camera,  consisting  of  a  series  of  lenses  and  media 
arranged  in  a  dark  chamber,  the  iris  serving  as  a  diaphragm  ;  and 
the  object  of  the  apparatus  is  to  form  on  the  retina  a  distinct 
image  of  external  objects.     That  a  distinct  image  is  formed  on 


CHAP.   II. J  SIGHT.  51  I 

the  retina,  may  be  ascertained  by  removing  the  sclerotic  from  tlie 
back  of  an  eye,  and  looking  at  the  hinder  surface  of  the  trans- 
parent retina  while  rays  of  liglit  i)roceeding  from  any  external 
object  are  allowed  to  fall  on  the  cornea. 

A  diojitric  apparatus  in  its  simplest  form  consists  of  two  media 
separated  by  a  (spherical)  surface  ;  and  the  optical  properties  of 
such  an  apparatus  depend  upon  (i)  the  curvature  of  the  surface, 
(2)  the  relative  refractive  power  of  the  media.  The  eye  consists 
of  several  media,  bounded  by  surfaces  which  arc  approximately 
spherical  but  of  different  curvature.  The  surfaces  are  all  centred 
on  a  line  called  the  optic  axis,  which  meets  the  retina  at  a  point 
somewhat  above  and  to  the  inner  (nasal)  side  of  the  fovea 
centralis.  In  passing  from  the  outer  surface  of  the  cornea  to  the 
retina  the  rays  of  light  traverse  in  succession  the  cornea,  the 
aqueous  humour,  the  lens  and  the  vitreous  humour.  Refraction 
takes  place  at  all  the  surfaces  bounding  these  several  media,  but 
particularly  at  the  anterior  surface  of  the  cornea,  and  at  both  the 
anterior  and  posterior  surfaces  of  the  Lns,  Since  the  anterior 
and  posterior  surfaces  of  the  cornea  are  parallel,  or  very  nearly 
so,  the  rays  of  light  would  suffer  little  or  no  change  of  direction 
in  passing  through  the  cornea,  if  it  were  bounded  on  both  sides 
by  the  same  medium.  The  direction  of  the  rays  of  light  in  the 
aqueous  humour  would  therefore  remain  the  same  if  the  cornea 
were  made  exceedingly  thin,  if  in  foct  its  two  surfaces  were  made 
into  one,  forming  a  single  anterior  surface  to  the  aqueous  humour  ; 
or,  which  comes  to  the  same  thing  in  the  end,  since  the  refractive 
power  of  the  substance  of  the  cornea  is  almost  exactly  the  same 
as  that  of  the  aqueous  humour,  the  refraction  at  the  posterior 
surface  of  the  cornea  may  be  neglected  altogether.  Thus  the  two 
surfaces  of  the  cornea  are  practically  reduced  to  one.  The  lens 
varies  in  density  in  (iifierent  parts,  the  refractive  power  of  the 
central  portions  being  greater  than  that  of  the  external  layers  ; 
but  the  refractive  power  of  the  whole  may,  without  any  serious 
error,  be  assumed  to  be  uniform,  a  mean  being  taken  between  the 
refractive  powers  of  the  several  parts.  The  refractive  power  of 
the  vitreous  humour  is  almost  exactly  the  same  as  that  of  the 
aqueous  humour. 

Thus  the  apparently  complicated  natural  eye  may  be  simplified 
into  a  'diagrammatic  eye,'  in  which  the  refracting  surfaces  are 
reduced  to  three,  viz.  (i)  the  anterior  surface  of  the  cornea,  (2)  • 
the  anterior  surface  of  the  lens  sejjarating  the  lens  from  the 
aqueous  humour,  and  (3)  the  posterior  surface  of  the  lens  sej)arating 
the  lens  from  the  vitreous  humour.  The  media  will  similarly  be 
reduced  to  two ;  the  mean  substance  of  the  lens,  and  the'  aqueous 


512  ACCOMMODATION.  [BOOK   III. 

or  vitreous  humour.  This  '  diagrammatic  eye  '  is  of  great  use  in 
the  various  calculations  which  become  necessary  in  studying  physio- 
logical optics  ;  for  the  rpagnitudes  which  are  derived  by  calculation 
from  it  represent  the  corresponding  magnitudes  in  an  average 
natural  eye  with  sufficient  accuracy  to  serve  for  all  practical 
purposes.  The  values  adopted  by  Listing  for  the  constants  of 
this  '  diagrammatic  eye,'  and  to  him  we  are  indebted  for  the 
introduction  of  it,  are  as  follows  : 

Radius  of  curvature  of  cornea  8  mm. 

„  „  of  anterior  surface  of  lens    ...  lo     „ 

„  „  of  posterior      „         „  ...       6     „ 

Refractive  index  of  aqueous  or  vitreous  humour  ...  y^ 

Mean  refractive  index  of  lens jf 

Distance    from    anterior     surface     of    cornea    to 

anterior  surface  of  lens 4  mm. 

Thickness  of  lens 4     ,, 

The  calculated  position  of  the  principal  posterior  focus,  i.e.  the 
point  at  which  all  rays  falling  on  the  cornea  parallel  to  the  optic 
axis  are  brought  to  a  focus,  is  in  the  diagrammatic  eye  i4'647o 
mm.  behind  the  posterior  surface  of  the  lens,  or  22-6470  mm. 
behind  the  anterior  surface  of  the  cornea.  That  is  to  say,  the 
^fovea  centralis  must  occupy  this  position  in  order  that  a  distinct 
image  of  a  distant  object  may  be  formed  upon  it.  It  must  be 
understood  that  these  values  refer  to  the  eye  when  at  rest,  i.e. 
when  it  is  not  undergoing  any  strain  of  accommodation. 

Acco7ninodatio7t. 

When  an  object,  a  lens,  and  a  screen  to  receive  the  image,  are 
so  arranged  in  reference  to  each  other,  that  the  image  falls  upon 
the  screen  in  exact  focus,  the  rays  of  light  proceeding  from  each 
luminous  point  of  the  object  are  brought  into  focus  on  the  screen 
in  a  point  of  the  image  corresponding  to  the  point  of  the  object. 
If  the  object  be  then  removed  farther  away  from  the  lens  the 
rays  proceeding  in  a  pencil  from  each  luminous  point  will  be 
brought  to  a  focus  at  a  point  in  front  of  the  screen,  and  subse- 
quently diverging,  will  fall  upon  the  screen  as  a  circular  patch 
composed  of  a  series  of  circles,  the  so-called  diffusion  circles, 
arranged  concentrically  round  the  principal  ray  of  the  pencil.  If 
the  object  be  removed,  not  farther,  but  nearer  the  lens,  the  pencil 
of  rays  will  meet  the  screen  before  they  have  been  brought  to 
focus  in  a  point,  and  consequently  will  in  this  case  also  give  rise 


CHAP.    II.J  SIGHT.  513 

to  difi'usion  circles.  When  an  object  is  placed  before  the  eye,  so 
that  the  imago  falls  into  exact  focus  on  the  retina,  and  the  pencils 
of  rays  proceeding  from  each  luminous  point  of  the  object  are 
brought  into  focus  in  points  on  the  retina,  the  sensation  called 
forth  is  that  of  a  distinct  image.  When  on  the  contrary  die  object 
is  too  far  away,  so  that  the  focus  lies  in  front  of  the  retina,  or  too 
near,  so  that  die  focus  lies  behind  the  retina,  and  the  pencils  fall 
on  the  retina  not  as  points,  but  as  systems  of  diffusion  circles,  the 
image  produced  is  indistinct  and  blurred.  In  order  that  objects 
both  near  and  distant  may  be  seen  with  equal  distinctness  by  the 
same  dioptric  apparatus,  the  focal  arrangements  of  the  apparatus 
must  be  accommodated  to  the  distance  of  the  object,  either  by 
changing  the  refractive  power  of  the  lens,  or  Ijy  altering  the 
distance  between  the  lens  and  the  screen. 

That  the  eye  does  possess  such  a  power  of  accommodation  is 
shewn  by  every-day  experience.  If  two  needles  be  fixed  upright 
some  two  feet  or  so  apart,  into  a  long  piece  of  wood,  and  the  wood 
be  held  before  the  eye,  so  that  the  needles  are  nearly  in  a  line,  it 
will  be  found  that  if  attention  be  directed  to  the  far  needle,  the 
near  one  appears  blurred  and  indistinct,  and  that,  conversely,  when 
the  near  one  is  distinct,  the  far  one  appears  blurred.  By  an  effort 
of  the  will  we  can  at  pleasure  make  either  the  far  one  or  the  near 
one  distinct ;  but  not  both  at  the  same  time.  When  the  eye  is 
arranged  so  that  the  far  needle  appears  distinct,  the  image  of  that 
needle  falls  exactly  on  the  retina,  and  each  pencil  from  each 
luminous  point  of  the  needle  unites  in  a  point  upon  the  retina; 
but  when  this  is  the  case,  the  focus  of  the  near  needle  lies  behind 
the  retina,  and  each  pencil  from  each  luminous  point  of  this 
needle  falls  upon  the  retina  in  a  series  of  diffusion  circles.  Simi- 
larly, when  the  eye  is  arranged  so  that  the  near  needle  is  distinct, 
the  image  of  that  needle  falls  upon  the  retina  in  such  a  way,  that 
each  pencil  of  rays  from  each  luminous  point  of  the  needle  unites 
in  a  point  on  the  retina,  while  each  pencil  from  each  luminous 
point  of  the  far  needle  unites  at  a  point  in  front  of\\\t  retina,  and 
then  diverging  again  falls  on  the  retina,  in  a  series  of  diffusion 
circles.  If  the  ne^tr  needle  be  gfadually  brought  nearer  and 
nearer  to  the  eye,  it  will  be  found  that  greater  and  greater  effort  is 
required  to  see  it  distinctly,  and  at  last  a  point  is  reached  at  which 
no  effort  can  make  the  image  of  the  needle  appear  anything  but 
blurred.  The  distance  of  this  point  from  the  eye  marks  the  limit 
of  accommodation  for  near  objects.  Similarly,  if  the  person  be 
short-sighted,  the  far  needle  may  be  moved  away  from  the  eye, 
until  a  point  is  reached  at  which  it  ceases  to  be  seen  distinctly 
and  appears  blurred.  In  the  one  case,  the  eye,  with  all  its  power, 
F-  ^  33 


514  ACCOMMODATION.  ['BOOK   III. 

is  unable  to  bring  the  image  of  the  needle  sufficiently  forward  to 
fall  on  the  retina  ;  the  focus  lies  permanently  behind  the  retina:. 
In  the  other,  the  eye  cannot  bring  the  image  sufficiently  backward 
to  fall  on  the  retina  ;  the  focus  lies  permanently  in  front  of  the 
retina.  In  both  cases  the  pencils  of  rays  from  the  needles  strike 
the  retina  in  diffiision  circles. 

The  same  phenomena  may  be  shewn  with  greater  nicety  by 
what  is  called  Scheiner's  experiment^.  If  two  smooth  holes  be 
pricked  in  a  card,  at  a  distance  from  each  other  less  than  the 
diameter  of  the  pupil,  and  the  card  be  held  up  before  one  eye, 
with  the  holes  horizontal,  and  a  needle  placed  vertically  be  looked 
at  through  the  holes,  the  following  facts  may  be  observed.  When 
attention  is  directed  to  the  needle  itself,  the  image  of  the  needle  « 
appears  single.*  Whenever  the  gaze  is  directed  to  a  more  distant 
object,  so  that  the  eye  is  no  longer  accommodated  for  the  needle, 
the  image  appears  double  and  at  the  same  time  blurred.  It  also 
appears  double  and  blurred  when  the  eye  is  accommodated  for  a 
distance  nearer  than  that  of  the  needle.  When  only  one  needle 
is  seen,  and  the  eye  therefore  is  properly  accommodated  for  the 
distance  of  the  needle,  no  effect  is  produced  by  blocking  up  one 
hole  of  the  card,  except  that  the  whole  field  of  vision  seems 
dimmer.  When,  however,  the  image  is  double  on  account  of  the 
eye  being  accommodated  for  a  distance  greater  than  that  of  the 
needle,  blocking  the  left-hand  hole  causes  a  disappearance  of  the 
right-hand  or  opposite  image,  and  blocking  the  right-hand  hole 
causes  the  left-hand  image  to  disappear.  When  the  eye  is  accom- 
modated for  a  distance  nearer  than  that  of  the  needle,  blocking 
either  hole  causes  the  image  on  the  same  side  to  vanish.  The 
following  diagram  will  explain  how  these  results  are  brought 
about. 

Let  a  (Fig.  52)  be  a  luminous  point  in  the  needle,  and  ae,  af 
the  extreme  right-hand  and  left-hand  rays  of  the  pencil  of  rays 
proceeding  from  it,  and  passing  respectively  through  the  right-hand 
e,  and  left-hand  f,  holes  in  the  card.  (The  figure  is  supposed  to 
be  a  horizontal  section  of  the  eye.)  When  the  eye  is  accommo- 
dated for  <a!,  the  rays  e  and /meet  together  in  the  point  c,  the  retina 
occupying  the  position  of  the  plane  nn  ■  the  luminous  point 
appears  as  one  point,  and  the  needle  will  appear  as  one  needle. 
When  the  eye  is  accommodated  for  a  distance  beyond  a,  the  retina 
may  be  considered  to  lie^  no  longer  at  7i7i,  but  nearer  the  lens,  at 

*  Scheinei",  Oculus.     Innsbruck,  1619. 

^  Of  course,  in  the  actual  eye,  as  we  shall  see,  accommodation  is^effected  by 
a  change  in  the  lens,  and  not  by  an  alteration  in  the  position  of  the  retina;  but 
for  convenience'  sake,  we  may  here  suppose  the  retina  to  be  moved. 


CHAP.    II.] 


SIGHT. 


5'5 


;;;;;/  for  example ;  the  rays  ae  will  cut  this  plane  at  /,  and  the  rays 
af  at  q ;  hence  the  luminous  point  will  no  longer  appear  single, 
but  will  be  seen  as  two  points,  or  rather  as  two  systems  of  dift'usion 
circles,  and  the  single  needle  will  appear  as  two  blurred  needles. 
The  rays  passing  through  the  right-hand  hole  <r,  will  cut  the  retina 
at  /,  i.e.  on  the  right-hand  side  of  the  optic  axis  j  but,  as  we  shall 


Fig.  52.     Diagram  ok  Scheiner's  Experiment. 

see  in  speaking  of  the  judgments  pertaining  to  vision,  the  image 
on  the  right-hand  side  of  the  retina  is  referred  by  the  mind  to  an 
object  on  the  left-hand  side  of  the  person  ;  hence  the  affection 
of  the  retina  at  /,  produced  by  the  rays  ae  falling  on  it  there, 
gives  rise  to  an  image  of  the  spot  a  at  F,  and  similarly  the  left- 
hand  spot    q   corresponds  to   the  right-hand    Q.     Blocking    the 

33—2 


5l6  ACCOMMODATION.  [BOOK^   HI. 

left-hand  hole,  therefore,  causes  a  disappearance  of  the  right-hand 
image,  and  vice  versa.  Similarly  when  the  eye  is  accommodated 
for  a  distance  nearer  than  the  needle,  the  retina  may  be  supposed 
to  be  removed  to  //,  and  the  right-hand  ae  and  left-hand  af  rays, 
after  uniting  at  c,  will  diverge  again  and  strike  the  retina  at  p'  and 
q' .  The  blocking  of  the  hole  e  will  now  cause  the  disappearance 
of  the  image  q  on  the  left-hand  side  of  the  retina,  and  this  will 
be  referred  by  the  mind  to  the  right-hand  side,  so  that  Q,  will  seem 
to  vanish. 

If  the  needle  be  brought  gradually  nearer  and  nearer  to  the 
eye,  a  point  will  be  reached  within  which  the  image  is  always 
double.  This  point  marks  with  considerable  exactitude  the  near 
limit  of  accommodation.  With  short-sighted  persons,  if  the  needle 
be  removed  farther  and  farther  away,  a  point  is  reached  beyond 
which  the  image  is  always  double ;  this  marks  the  far  limit  of 
accommodation. 

The  experiment  may  also  be  performed  with  the  needle  placed  hori- 
zontally, in  which  case  the  holes  in  the  card  should  be  vertical.  The 
adjustment  for  the  eye  for  near  or  far  distances  may  be  assisted  by 
using  two  needles,  one  near  and  one  far.  In  this  case  one  needle 
should  be  vertical  and  the  odier  horizontal,  and  the  card  turned  round 
so  that  the  holes  lie  horizontally  or  vertically  according  to  whether  the 
vertical  or  horizontal  needle  is  being  made  to  appear  double. 

In  what  may  be  regarded  as  the  normal  eye,  the  so-called 
emmetropic  eye,  the  near  limit  of  accommodation  is  about  lo  or  12 
cm.  and  the  far  limit  may  be  put  for  practical  purposes  at  an 
infinite  distance.  The  '  range  of  distinct  vision  '  therefore  for  the 
emmetropic  eye  is  very  great.  In  the  myopic,  or  short-sighted  eye, 
the  near  limit  is  brought  much  closer  (5  or  6  cm.)  to  the  cornea; 
and  the  far  limit  is  at  a  variable  but  not  very  great  distance,  so  that 
the  rays  of  light  proceeding  from  an  object  not  many  feet  away  are 
brought  to  a  focus,  not  on  the  retina  but  in  the  vitreous  humour. 
The  range  of  distinct  vision  is  therefore  in  the  myopic  eye  very 
limited.  In  the  hypermetropic,  or  long-sighted  eye,  the  rays  of 
light  coming  from  even  an  infinite  distance  are,  in  the  passive  state 
of  the  eye,  brought  to  a  focus  beyond  the  retina.  The  near  limit 
of  accommodation  is  at  some  distance  off,  and  a  far  limit  of  ac- 
commodation does  not  exist.  The  presbyopic  eye,  or  the  long- 
sight  of  old  people,  resembles  the  hypermetropic  eye  in  the 
distance  of  the  near  point  of  accommodation,  but  difi^ers  from  it 
inasmuch  as  the  former  is  an  essentially  defective  condition  of  the 
accommodation  mechanism,  whereas  in  the  latter  the  power  of 
accommodation  may  be  good  and  yet,  from  the  internal  arrange- 
ments of  the  eye,  be  unable  to  bring  the  image  of  a  near  object 


CHAP.    II.]  SIGHT.  517 

on  to  the  retina.  When  a  normal  eye  becomes  presbyopic,  the 
far  limit  may  remain  the  same,  but  since  the  power  of  accommo- 
dating for  near  objects  is  weakened  or  lost,  the  change  is  distinctly 
a  reduction  of  the  range  of  distinct  vision.  In  the  normal  emme- 
tropic eye,  when  no  effort  of  accommodation  is  made,  the  principal 
focus  of  the  eye  lies  on  the  retina,  in  the  myopic  eye  in  front  of  it, 
and  in  the  hypermetropic  eye  behind  it. 

Mechanism  of  Accommodation.  In  directing  our  at- 
tention from  a  far  to  a  very  near  object  we  are  conscious  of  a 
distinct  effort,  and  feel  that  some  change  has  taken  place  in  the 
eye ;  when  we  turn  from  a  very  near  to  a  far  object,  if  we  are 
conscious  of  any  change  in  the  eye,  it  is  one  of  a  different  kind. 
The  former  is  the  sense  of  an  active  accommodation  for  near 
objects  ;  the  latter,  when  it  is  felt,  is  the  sense  of  relaxation  after 
exertion. 

Since  the  far  limit  of  an  emmetropic  eye  is  at  an  infinite  distance, 
no  such  thing  as  active  accommodation  for  far  distances  need  exist.  The 
only  change  that  will  take  plate  ii,  the  eye  in  turning  from  near  to  far 
objects  will  be  a  more  passive  undoing  of  the  accommodation  previously 
made  for  the  near  object.  And  that  no  such  active  accommodation 
for  far  distamcs  takes  place  is  shewn  by  the  facts— that  the  eye,  when 
opened  after  being  closed  for  some  time,  is  found  not  in  medium  state 
but  adjusted  for  distance  ;  that  when  the  accommodation  mechanism 
of  the  eye  is  paralysed  by  atropin  or  nervous  disease,  the  accommo- 
dation for  distant  objects  is  unaffected  ;  and  that  we  are  conscious  of 
no  effort  in  turning  from  moderately  distant  to  far  distant  objects.  The 
sense  of  effort  often  spoken  of  by  myopic  persons  as  being  felt  when 
they  attempt  to  see  things  at  or  beyond  the  far  limit  of  their  range  seems 
to  arise  from  a  movement  of  the  eyelids,  and  not  from  any  internal 
changes  taking  place  in  the  eye. 

What  then  are  the  changes  whicli  take  place  in  the  eye,  when 
we  accommodate  for  near  objects  ?  It  might  be  thought,  and 
indeed  once  was  thought,  that  the  curvature  of  the  cornea  was 
changed,  becoming  more  convex,  with  a  shorter  radius  of  curvature, 
for  near  objects.  Young,  however,  shewed  that  accommodation 
took  place  as  usual  wiien  tlic  eye  (and  head)  is  immersed  in  water. 
Since  the  refractive  powers  of  aqueous  humour  and  water  are  very 
nearly  alike,  the  cornea,  with  its  parallel  surfaces,  placed  between 
these  two  fluids,  can  have  little  or  no  effect  on  the  direction  of  the 
rays  passing  through  it  when  the  eye  is  immersed  in  water.  And 
accurate  measurements  of  the  dimensions  of  an  image  on  the 
cornea  have  shewn  that  these  undergo  no  change  during  accom- 
modation, and  that  therefore  the  curvature  of  the  cornea  is  not 
altered.     Nor  is  there  any  change  in  the  form  of  the  bulb  ;  for 


5l8  ACCOMMODATION.  [BOOK   III. 

any  variation  in  this  would  necessarily  produce  an  alteration  in 
the  curvature  of  the  cornea,  and  pressure  on  the  bulb  would  act 
injuriously  by  rendering  the  retina  ansemic  and  so  less  sensitive. 
In  fact,  there  are  only  two  changes  of  importance  which  can  be 
ascertained  to  take  place  in  the  eye  during  accommodation  for 
near  objects. 

One  is  that  the  pupil  contracts.  When  we  look  at  near  objects, 
the  pupil  becomes  small ;  when  we  turn  to  distant  objects,  it  dilates. 
This  however  cannot  have  more  than  an  indirect  influence  on  the 
formation  of  the  image;  the  chief  use  of  the  contraction  of  the 
pupil  in  accommodation  for  near  objects  is  to  cut  off  the  more 
divergent  circumferential  ravs  of  light. 

The  other  and  really  efficient  change  is  that  the  anterior  surface 
of  the  lens  becomes  more  convex.  If  a  light  be  held  before  the 
eye,  three  reflected  images  may  be  seen  by  a  bystander  :  one  a  very 
bright  one  caused  by  the  anterior  surface  of  the  cornea,  a  second 
less  bright,  by  the  anterior  surface  of  the  lens,  and  a  third  very 
dim,  by  the  posterior  surface  of  the  lens.  When  the  eye  is 
accommodated  for  near  objects,  no  change  is  observed  in  either 
the  first  or  the  third  of  these  images ;  but  the  second,  that  from 
the  anterior  surface  of  the  lens,  is  seen  to  become  distinctly 
smaller,  shewing  that  the  surface  has  become  more  convex. 
When,  on  the  contrary,  vision  is  directed  from  near  to  far  objects, 
the  image  from  the  anterior  surface  of  the  lens  grows  larger, 
indicating  that  the  convexity  of  the  surface  has  diminished,  while 
no  change  takes  place  in  the  curvature  either  of  the  cornea  or  of 
the  posterior  surface  of  the  lens.  And  accurate  measurements  of 
the  size  of  the  image  from  the  anterior  surface  of  the  lens  have 
shewn  that  the  variations  in  curvature  which  do  take  place,  are 
sufficient  to  account  for  the  power  of  accommodation  which  the 
eye  possesses. 

The  observation  of  these  reflected  images  is  facilitated  by  the 
simple  instrument  introduced  by  Helmholtz  and  called  a  Phakoscope. 
It  consists  of  a  small  dark  chamber,  with  apertures  for  the  observed 
and  observing  eyes  ;  a  needle  is  fixed  at  a  short  distance  in  front  of 
the  former,  to  serve  as  a  near  object,  for  which  accommodation  has 
to  be  made  ;  and  by  means  of  two  prisms  the  image  from  each  of  the 
three  surfaces  of  the  observed  eye  is  made  double  instead  of  single. 
When  the  anterior  surfu.ee  of  the  lens  becomes  more  convex  the 
two  images  reflected  fro.n  that  surface  approach  each  other,  when 
it  becomes  less  convex  they  retire  from  each  other.  The  approach 
and  retirement  are  more  readily  appreciated  than  is  a  simple  change 
of  size. 

These  observations  leave  no  doubt  that  the  essential  change  by 
which  accommodation  is  effected,  is  an  alteration  of  the  convexity 


CILVr   II.]  SIGHT.  519 

of  the  anterior  surface  of  the  lens.  And  that  the  lens  is  the 
agent  of  accommodation,  is  shewn  by  the  fact  that  after  removal 
of  the  lens,  as  in  the  operation  for  cataract,  the  power  of 
accommodation  is  lost. 

In  the  cases  which  have  been  recorded,  where  eyes  from  wliich  the 
lens  liad  been  removed  seemcl  still  to  possess  some  accommodation, 
wc  must  suppose  that  no  real  accommodation  took  place,  but  that  the 
pupil  contracted  when  a  near  object  was  looked  at,  and  so  assisted  in 
making  vision  more  distinct. 

Concerning  the  nature  of  the  mechanism  by  wliich  this  increase 
of  the  convexity  of  the  lens  is  effected,  the  view  most  generally 
adopted  is  as  follows.  In  the  passive  condition  of  the  eye, 
when  it  is  adjusted  for  far  objects,  the  suspensory  ligament  keeps 
the  lens  tense  witli  its  anterior  surface  somewhat  flattened. 
Accommodation  for  near  objects  consists  essentially  in  a  con- 
traction of  the  ciliary  muscle,  which,  by  pulling  forward  the 
choroid  coat  and  tlie  ciliary  processes,  slackens  the  suspensory 
ligament,  and  allows  the  lens  to  bulge  forward  by  virtue  of 
its  elasticity,  and  so  to  increase  the  convexity  of  its  anterior 
surface. 

Though  all  the  parts  surrounding  the  lens  are  highly  vascular,  the 
change  in  the  lens  cannot  hi  considered  as  the  result  of  any  vaso- 
motor action,  since  accommodation  may  be  effected  in  a  practically 
bloodless  eye  by  artificial  stimulation  with  an  interrupted  current,  or 
by  other  means.  Again,  the  fact  that  accommodation  may  take  place 
in  eyes  from  which  the  iris  is  congenitally  absent,  disproves  the  sug- 
gestion that  the  change  in  the  lens  is  caused  either  by  the  compression 
of  the  cirjumference  of  the  lens,  or  in  any  other  way  by  contraction 
of  the  iris.  On  the  other  hand,  the  observations  of  Hensen  and 
Volckers',  who  saw  the  choroid  drawn  forward  during  accommodation 
(brought  about  by  stimulation  of  the  ciliary  ganglion),  and  satisfied 
themselves  that  the  cornea  served  as  a  functional  fixed  attachment  for 
the  ciliary  muscle,  offer  a  strong  support  to  the  generally  accepted  ex- 
jjlanation.  To  which  it  may  be  added,  that  the  lens  is  certainly  elastic, 
and,  moreover,  that  its  natural  convexity  appears  to  be  diminished  by 
the  action  of  the  suspensory  ligament,  sin.e  after  removal  from  the 
body  its  anterior  surface  is  found  to  be  more  convex  than  when  in  the 
natural  position  in  the  body,  flock-  has  carefully  repeated  Hensen 
and  Volckers'  experiment  on  the  dog,  stimulating  the  radix  brevis  of 
the  ganglion  instead  of  the  ganglion  itself  He  fully  confirms  their 
results,  and  especially  insists  that  the  choroid  is  pulled  forward  by  the 
ciliary  muscles  (longitudinal  fibres)  and  not  by  muscular  fibres  present 
in  the  choroid  itself. 

'  Mec/iaiiisnius  d.   Accommod.,  Kiel,   1868.     Abst.  in  Cbt.  f.  Med.  VViss., 
1S68,  p.  455. 
"  Cbt.f.  Med.  IViss.,  1S78,  p.  769. 


520  MOVEMENTS   OF   THE   TUPIL.         [BOOK   III 

Accommodation  is  a  voluntary  act ;  since,  however,  the  change 
in  the  lens  is  always  accompanied  by  movements  in  the  iris,  it  will 
be  convenient  to  consider  the  latter,  before  we  discuss  the  nervous 
mechanism  of  the  whole  act. 

Movements  of  the  Pupil.  Though  by  making  the  efforts 
required  for  accommodation  we  can  at  pleasure  contract  or  dilate 
the  pupil,  it  is  not  in  our  power  to  bring  the  will  to  act  directly 
on  the  iris  by  itself.  This  fact  alone  indicates  that  the  nervous 
mechanism  of  the  pupil  is  of  a  peculiar  character,  and  such  indeed 
we  find  it  to  be.  The  pupil  is  co7iiracfed  (i)  when  the  retina  (or 
optic  nerve)  is  stimulated,  as  when  light  falls  on  the  retina,  the 
brighter  the  light  the  greater  being  the  contraction,  (2)  when  we 
accommodate  for  near  objects.  The  pupil  is  also  contracted  when 
the  eyeball  is  turned  inwards,  when  the  aqueous  humour  is 
deficient,  in  the  early  stages  of  poisoning  by  chloroform,  alcohol, 
&c.,  in  nearly  all  stages  of  poisoning  by  morphia,  physostigmin, 
and  some  other  drugs,  and  in  deep  slumber.  The  pupil  is  dilated 
(i)  when  stimulation  of  the  retina  (or  optic  nerve)  is  arrested  or 
diminished ;  hence  the  pupil  dilates  in  passing  into  a  dim  light, 
(2)  when  the  eye  is  adjusted  for  far  objects.  Dilation  also  occurs 
when  there  is  an  excess  of  aqueous  humour,  during  dyspnoea, 
during  violent  muscular  efforts,  as  the  result  of  a  strong  stimulation 
of  sensory  nerves,  as  an  effect  of  emotions,  in  the  later  stages 
of  poisoning  by  chloroform,  &c.,  and  in  all  stages  of  poisoning 
by  atropin  and  some  other  drugs.  Contraction  of  the  pupil 
is  caused  by  contraction  of  the  circular  fibres  or  sphincter  of 
the  iris.  Dilation  is  caused  by  contraction  of  the  radial  fibres  of 
the  iris. 

The  existence  of  radial  fibres  has  been  denied  by  many  observers, 
but  the  preponderance  of  evidence  is  clearly  in  favour  of  their  being 
really  present. 

Contraction  of  the  pupil,  brought  about  by  light  falling  on  the 
retina,  is  a  reflex  act,  of  which  the  optic  is  the  afferent  nerve,  the 
third  or  oculo-motor  the  efferent  nerve,  and  the  centre  some 
portion  of  the  brain  lying  below  the  corpora  quadrigemina  in  the 
floor  of  the  aqueduct  of  Sylvius.  This  is  proved  by  the  following 
facts.  When  the  optic  nerve  is  divided,  the  falling  of  light  on  the 
retina  no  longer  causes  a  contraction  of  the  pupil.  When  the 
third  nerve  is  divided,  stimulation  of  the  retina  or  of  the  optic 
nerve  no  longer  causes  contraction  ;  but  direct  stimulation  of  the 
peripheral  portion  of  the  divided  third  nerve  causes  extreme 
contraction  of  the  pupil.     After  removal  of  the  region  of  the  brain 


CHAT.    11.]  SIGHT.  521 

spoken  of  above,  stimulation  of  the  retina  is  similarly  inefiectual. 
But  if  the  same  region  of  the  brain  and  its  connections  with  the 
optic  nerve  and  thini  nerve  be  left  intact,  contraction  of  the  pupil 
will  occur  as  a  result  of  light  falling  on  the  retina,  though  all  other 
nervous  parts  be  removed. 

Certain  reservations  must  however  be  inndc  to  the  al)ovc  statements, 
since  in  the  excised  eye  of  the  eel  or  frog  the  pupil  will  still  contract 
on  exposure  to  light  tliough  the  nervous  centre  is  absent'.  Holmgren 
and  Kdgren''  find  that  in  the  frog  this  contraction  of  the  pupil  of  the 
excised  eye  on  exposure  to  light  disappears  when  the  retina  is  de- 
stroyed ;  there  seems  therefore  to  be  witliin  tlic  bulb  some  nervous 
connection  between  the  retina  and  iris. 

The  nervous  centre  is  not  a  double  centre  with  two  completely 
independent  halves,  one  for  each  eye;  there  is  a  certain  amount 
of  functional  communion  between  the  two  sides,  so  that  when  one 
retina  is  stimulated  both  pupils  contract.  It  might  be  imagined 
that  this  cerebral  centre  acted  as  a  tonic  centre,  whose  action  was 
simply  increased  not  originated  by  the  stimulation  of  the  retina  ; 
but  this  is  disproved  by  the  fact  that,  if  the  optic  nerve  be 
divided,  subsequent  section  of  the  third  nerve  produces  no  further 
dilation. 

In  considering  the  movements  of  the  pupil,  however,  we  have 
to  deal  not  only  with  contraction  but  with  active  dilation  ;  and 
this  renders  the  whole  matter  much  more  complex  than  might 
be  supposed  to  be  the  case  from  the  simple  statement  just 
made. 

The  iris  is  supplied,  in  common  with  the  ciliary  muscle  and 
choroid,  by  the  short  ciliary  nerves  coming  from  the  ophthalmic  or 
lenticular  (ciliary)  ganglion,  which  is  connected  by  its  roots  with 
the  third  nerve,  the  cervical  sympathetic  nerve,  and  with  the  nasal 
branch  of  the  ophthalmic  division  of  the  fifth  nerve.  The  short 
ciliary  nerves  are,  moreover,  accompanied  by  the  long  ciliary  nerves 
coming  from  the  same  nasal  branch  of  the  ophthalmic  division  of 
the  fifth  nerve.  What  are  the  uses  of  these  several  nerves  in 
relation  to  the  pupil  ? 

If  the  cervical  sympathetic  in  the  neck  be  divided,  all  other 
portions  of  the  nervous  mechanism  being  intact,  a  contraction  of 
the  jHipil  (not  always  very  well  marked)  takes  place,  and  if  the 
peripheral  portion  {i.e.  the  upper  portion  still  connected  with  the 
eye)  be  stimulated,  a  well-devjloped  dilation  is  the  result.  The 
sympathetic  has,  it  will  be  observed,  an  effect  on  the  iris  the 

'  Brown-Sequard,  Cotupl.  Rend.,   .\XV.    (1S47)  482,   50S ;  Free.   Roy.  Soc, 
VIII.  (1856)  p.  233. 

'  Hofmann  and  .Schwalbe's  Dcrich',  v.  (1876)  p.  103. 


-522  -  MOVEMENTS   OF   THE   PUPIL.  [BOOK   III. 

opposite  of  that  which  it  exercises  on  the  blood-vessels ;  when  it 
it  is  stimulated  the  pupils  are  dilated  while  the  blood-vessels  are 
constricted.  This  dilating  influence  of  the  sympathetic  may,  as  in 
the  case  of  the  vaso-motor  action  of  the  same  nerve,  he  traced 
back  down  the  neck,  along  the  rami  communicantes  and  roots  of 
the  last  cervical  and  first  dorsal  or  two  first  dorsal  spinal  nerves, 
to  a  region  in  the  lower  cervical  and  upper  dorsal  cord  (called  by 
Budge '  the  centrum  cilio-spinale  inferius),  and  from  thence  up 
through  the  medulla  oblongata  to  a  centre,  which,  according  to 
Hensen  and  Volckers%  lies  in  the  floor  of  the  front  part  of  the 
aqueduct  of  Sylvius. 

Considering  how  vascular  the  iris  is,  it  does  not  seem  unreasonable 
to  interpret  some  of  the  variations  in  the  condition  of  the  pupil  as  the 
results  of  simple  vascular  turgescence  or  depletion  brought  about  by 
vaso-mortor  action  or  otherwi-e,  the  small  or  contracted  pupil  corre- 
sponding to  the  dilated  and  filled,  and  the  large  or  dilated  pupil  to  con- 
stricted and  emptied  condition  of  the  blood-vessels 3.  Thus  slight 
oscillations  of  the  pupil  may  be  observed  synchronous  with  the  heart- 
beat and  others  synchronous  with  the  respiratory  movements.  But 
the  variations  in  the  pupil  seem  too  marked  to  be  merely  the  effects  of 
vascular  changes,  and  indeed  that  constriction  of  the  pupil  cannot  be 
wholly  the  result  of  turgescence,  nor  dilation  wholly  the  result  of  de- 
pletion of  the  vessels  of  the  iris,  is  shewn  by  the  fact  that  both  these 
events  may  be  witnessed  in  a  perfectly  bloodless  eye,  and  moreover 
when  the  cervical  sympathetic  is  stimulated  the  dilation  of  the  pupil 
begins  before  the  contraction  of  the  blood-vessels,  and  may  be  over 
before  this'  has  arrived  at  its  maximum.  Hence  we  are  driven  to 
conclude  that  the  dilating  sympathetic  fibres  do  not  end  in  blood- 
vessels, but  are  connected  either  directly  or  indirectly  with  the  muscular 
fibres  of  the  dilator. 

The  pupil  then  seems  to  be  under  the  dominion  of  two 
antagonistic  mechanisms  :  one  a  contracting  mechanism,  reflex  in 
nature,  the  third  nerve  serving  as  the  efferent,  and  the  optic  as 
the  afferent  tract ;  the  other  a  dilating  mechanism,  tonic  in 
nature,  of  which  the  cervical  sympathetic  Is  the  efferent  channel. 
Hence,  Avhen  the  third  or  optic  nerve  is  divided,  not  only  does 
contraction  of  the  pupil  cease  to  be  manifest,  but  active  dilation 
occurs,  on  account  of  the  tonic  dilating  influence  of  the  sympa- 
thetic being  left  free  to  work.  When,  on  the  other  hand,  the 
sympathetic  is  divided,  this  tonic  dilating  influence  falls  away, 
and  contraction  results.  WJien  the  optic  or  third  nerve  is 
stimulated,  the  dilating  effect  of  the  sympathetic  is  overcome,  and 

'   Ueber  die  Bewegung  dcr  Iris,  1855, 

^  Archivf.  Ophthaltiiol.,  xxiv.  (1878). 

3  Cf.  Mosso,  Sui  novimenti  idraulici  dell'  iride.     Turin,  1875, 


CHAP.   II.]  SIGHT.  523 

contraction  results  ;  and  when  the  sympathetic  is  stimulated,  the 
contracting  influence  of  the  third  nerve  is  overcome,  and  dilation 
ensues. 

But  there  are  considerations  which  shew  thiit  the  matter  is  still 
more  complex  than  this.  A  small  quantity  of  atropin  introduced  into 
the  eye  or  into  the  system  causes  a  dilaiion  of  the  pupil.  This  might 
be  attributed  to  a  paralysis  of  the  third  nerve,  and  indeed  it  is  found 
that  after  atropin  the  falling  ot"  light  on  the  retina  no  longer  causes 
contraction  of  the  pupil.  A  difficulty  however  is  introduced  by  the 
fact  that  when  the  third  nerve  is  divided,  and  w-hen  tiierefore  the  con- 
tracting eftects  of  stimulation  of  the  retina  are  placed  entirely  on  one 
side,  and  there  is  nothing  to  prevent  the  sympathetic  produ-ing  its 
dilating  effects  to  the  utmost,  dilation  is  still  further  increased  by 
atropin.  When  physostigmin  is  introduced  into  the  eye  or  system, 
contraction  of  the  pupil  is  caused,  whether  the  tliird  nerve  be  divided 
or  not  ;  and  when  the  dose  is  sufficiently  strong  the  contraction  is  so 
great  that  it  cannot  be  overcome  by  stimulation  of  the  sympathetic. 
The  dilation  which' is  caused  by  a  sufficient  dose  of  atropin  is  greater 
than  that  which  can  ordinarily  be  produced  by  stimulation  of  the  sym- 
pathetic, and  the  contraction  caused  by  a  sufficient  dose  of  physos- 
tigmin is  greater  than  that  which  is  ordinarily  produced  in  a  reflex 
manner  by  stimulation  of  the  optic  nerve,  or  e\en  than  that  produced 
by  direct  stimulation  of  the  third  nerve.  Evidently  these  drugs  act  on 
some  local  mechanism,  the  one  in  such  a  way  as  to  cause  dilation,  the 
other  in  such  a  way  as  to  cause  contraction.  Such  a  local  mechanism 
cannot  however  lie  in  the  ophthalmic  ganglion,  for  both  drugs  produce 
these  effects  in  a  most  marked  degree  after  the  ganglion  has  been 
excised.  We  must  suppose  therefore  that  the  mechanism  is  situated 
in  the  iris  itself  or  in  the  choroid,  where  indeed  ganglionic  nerve-cells 
ai'e  abundant.  But  if  we  admit  the  existence  of  such  a  local  mechanism, 
it  is  at  least  probable  that  both  the  sympathetic  and  the  third  nerve 
act  not  directly  on  either  the  sphincter  or  dilator  pupilliE,  but  indirectly 
through  means  of  the  local  nervous  mechanism. 

The  share  of  the  fifth  nerve  in  the  work  of  the  iris  seems  to  be  in 
part  a  sensory  one  ;  the  iris  is  sensitive,  and  the  sensory  impulses 
which  are  generated  in  it  pass  from  it  along  the  fibres  of  the  fifth 
nerve. 

Though  the  ophthalmic  ganglion  does  receive  fibres  directly  from 
the  cavernous  plexus  of  the  sympathetic,  the  dilating  action  of  the  sym- 
pathetic would  seem  to  be  carried  out  not  by  these  fibres  but  by  fibres 
joining  the  ophthalmic  branch  of  the  fifth  nerve  higher  up  in  its  course 
and  passing  to  the  iris  apparently  by  the  long  ciliary  nerves.  Accord- 
ing to  Oehl'  when  these  fiijres,  which  appear  to  run  alongside  the  oph- 
thalmic branch  rather  than  actually  to  become  part  of  the  nerve,  are 
destroyed,  stimulation  of  the  sympathetic  in  the  neck  produces  no 
dilation  of  the  pupil  whatever.  Section  of  the  ophthalmic  branch 
itself  causes  contraction,  and  stimulation  of  the  pcrij)heral  end  dilation 
of  the  pupil  ;  and  the  effects  are  still  seen  after  the  sympathetic  fibres 

'  Ilenle  and  Meissner's  Bcricht,  1862,  p.  506. 


524  MOVEMENTS  OF   THE   PUPIL.  [BOOK  III. 

have  become  degenerated  in  consequence  of  the  removal  of  the  superior 
cervical  ganglion.  From  these  facts  Oehl  infers  that  the  fifth  nerve 
itself  contains  dilating  fibres,  and  he  believes  that  these  take  their 
origin  from  the  Gasserian  ganglion.  Oehl's  results,  independently 
arrived  at  by  Rosenthal^,  were  conducted  on  dogs  and  rabbits.  Gutt- 
mann^  came  to  a  similar  conclusion  as  regards  frogs  ;  he  found  the 
dilator  fibres  of  the  cervical  sympathetic  passed  through  the  Gasserian 
ganglion  and  were  there  reinforced  by  fibres  taking  origin  in  the  gang- 
lion itself.  Hensen  and  Volckers^  also  found  in  the  dog  dilating  fibres 
in  the  fifth  nerve,  and  Vulpian  '^  has  observed  reflex  dilation  of  the  pupil 
after  section  of  both  cervical  and  thoracic  sympathetic,  and  removal 
of  both  the  upper  and  lower  cervical  ganglia.  These  dilating  fibres  of 
the  fifth  nerve  have  however  been  thought  by  some  to  be  vaso-motorial 
in  nature,  producing  changes  in  the  pupil  in  an  indirect  way  by 
affecting  its  blood-supply. 

When  atropin  is  applied  locally  so  as  to  affect  the  pupil  of  one  eye 
only,  the  large  amount  of  fight  entering  through  the  dilated  pupil  may 
cause  a  contraction  of  the  pupil  of  the  other  eye. 

The  movements  of  the  pupil  may  be  brought  about  through  reflex 
action  by  sensory  impulses  other  than  those  arising  in  the  retina  or 
optic  nerve.  Holmgren  s  finds  that  in  rabbits,  after  section  of  the  optic 
nerve,  dilation  of  the  pupil  follows  upon  the  hearing  a  noise,  and  indeed 
upon  any  sufficiently  acute  sensation. 

We  have  already  stated  that  when  we  accommodate  for  near 
objects  the  pupil  is  contracted  ;  the  one  movement  is  '  associated' 
with  the  other,  that  is  to  say,  the  special  central  nervous 
mechanism  employed  in  carrying  out  the  one  act  is  so  connected 
by  nervous  ties  of  some  kind  or  other  with  that  employed  in 
carrying  out  the  other,  that  when  we  set  the  one  mechanism  in 
action  we  unintentionally  set  the  other  in  action  also.  A  similar 
associated  contraction  of  the  pupil  occurs  when  the  eye  is  directed 
inward.  Conversely,  the  drugs  which  have  a  special  action  on  the 
pupil,  such  as  atropin  and  calabar  bean,  also  affect  the  mechanism 
of  accommodation.  Atropin  paralyses  it,  so  that  the  eye  remains 
adjusted  for  far  objects  ;  and  physostigmin  throws  the  eye  into  a 
condition  of  forced  accommodation  for  near  objects.  The  latter 
effect  may  be  explained,  on  the  view  stated  above,  by  supposing 
that  the  calabar  bean  throws  the  ciliary  muscle  into  a  state  oi 
tetanic  contraction  in  the  same  way  that  it  does  the  sphincter 
pupillae. 

According  to  Hensen  and  Volckers*  the  nervous  centre  of  accom- 
modation lies  in  dogs  in  the  hind  part  of  the  floor  of  the  third  ventride, 
and  is  connected  with  the  most  anterior  bundles  of  the  roots  of  the 

'  See  Guttmann,  Centralblatt  f.  med.  IViss.  1864,  p.  598. 

=^  Op.  cit.  3   Op.  cit. 

4  Ct.  Rd.,  T.  86  (1878)  p.  1436.  s  Loc.  cit. 

^  Archivf.  Ophthabnol.,  XXIV.  (1878). 


CHAP.   II.]  S|^IIT.  525 

third  nerve.  Immediately  beliind  tiiis  accommodation  centre,  in  the 
front  part  of  the  tloor  of  tlie  aqueduct  of  SyU  ius,  comes  tlie  centre  for 
the  contraction  of  tiic  pupils,  and  in  spite  of  the  association  of  the 
two  centres  in  their  ordinary  functional  activity,  Mensen  and  V'olckers 
find  that  accommodation  may  be  brou<jht  about  by  carefully  stimulat- 
ing the  axommodation  centre  by  means  of  the  interrupted  current 
without  any  accompanying  change  in  the  iris  except  a  passive  bulging 
forward  caused  by  the  increase  in  the  curvature  of  the  lens.  The  same 
observers  state  that  tiilation  of  the  pupil  results  when  the  tloor  of  the 
aqueduct  of  Sylvius  is  stimulated  not  in  the  median  line  but  more  to 
the  side  ;  ami  that  the  muscles  of  the  eyeball  supplied  by  the  third 
nerve  have  their  ner\ous  centres  placed  also  in  the  floor  of  the  aqueduct 
of  Sylvius,  but  behind  that  for  the  contraction  of  the  pupil. 

We  can  accommodate  at  will ;  but  few  persons  can  effect  the 
necessary  change  in  the  eye  unless  they  direct  their  attention  to 
some  near  or  far  object,  as  the  case  may  bj,  and  thus  assist  their 
will  by  visual  sensations.  By  practice,  however,  the  aid  of  ex- 
ternal objects  may  be  dispensed  with  ;  and  it  is  when  this  is 
achieved  that  the  pupil  may  seem  to  be  made  to  dilate  or  con- 
tract at  i)leasure,  accommodation  being  effected  without  the  eye 
being  turned  to  any  particular  object. 

Imperfections  in  the  Dioptric  Apparatus. 

The  emmetropic  eye  may  be  taken  as  the  normal  eye.  The 
myopic  and  hypermetropic  eyes  may  be  considered  as  imperfect 
eyes,  though  the  former  possesses  certain  advantages  over  the 
normal  eye.  An  eye  might  be  myopic  from  too  great  a  con- 
vexity of  the  cornea,  or  of  the  anterior  surface  of  the  lens,  or 
from  permanent  spasm  of  the  accommodation-mechanism,  or  from 
too  great  a  length  of  the  long  axis  of  the  eyeball.  According  to 
Donders  the  last  is  the  usual  cause.  Similarly,  most  hyperme- 
tropic eyes  possess  too  short  a  bulb.  The  presbyopic  eye  is,  as 
we  have  seen,  an  eye  normally  constituted  in  which  the  power  of 
accommodation  has  been  lost  or  is  failing. 

According  to  Iwanoff '  and  v.  Arlt^  in  the  strongly  marked  myopic 
eye  there  is  hypertrophy  of  the  longitudinal  (meridional)  fibres  of  the 
ciliary  muscle  and  atrophy  or  absence  of  the  circular  fibres  ;  in  the 
hypermetropic  eye  on  the  other  hand  the  circular  fibres  are  well 
developed  and  the  nieri'lional  fibres  scanty. 

Spherical  Aberration.  In  a  spherical  lens  the  rays  which 
impinge  on  the  circumference  are  brought  to  a  focus  sooner  than 
those  which  pass  nearer  the  centre,  and  the  focus  of  a  luminous 

*  Archivf.  Ophtltalni.,  xv.  p.  2S4. 

"   U.  d.  Ursac/iot,  &-c.  dcr  Kurzsichtigk,it,  1S76. 


526  -  DIOPTRIC   IMJpRFECTIONS.  [BOOK    III. 

point,  ceasing  to  be  a  p.oint,  is  spread  over  a  surface.  Hence 
when  rays  are  allowed  to  fall  on  the  whole  of  the  lens,  the  image 
formed  on  a  screen  placed  in  the  focus  of  the  more  central  rays 
is  blurred  by  the  diffusion-circles  caused  by  the  circumferential 
rays  which  have  been  brought  to  a  permature  focus.  In  an 
ordinary  optical  instrument  spherical  aberration  is  obviated  by  a 
diaphragm  which  shuts  off  the  more  circumferential  rays.  In  the 
eye  the  iris  is  an  adjustable  diaphragm ;  and  when  the  pupil  con- 
tracts in  near  vision  the  more  divergent  rays  proceeding  from  a 
near  object,  which  tend  to  fair  on  the  circumferential  parts  of  the 
lens,  are  cut  off.  As,  however,  the  refractive  power  of  the  lens 
does  not  increase  regularly  and  progressively  from  the  centre  to 
the  circumference,  but  varies  most  irregularly,  the  purpose  of  the 
narrowing  of  the  pupil  cannot  be  simply  to  obviate  spherical 
aberration  ;  and  indeed  the  other  optical  imperfections  of  the 
eye  are  so  great,  that  such  spherical  aberrations  as  are  caused  by 
the  lens  produce  no  obvious  effect  on  vision. 

Astigmatism.  We  have  hitherto  treated  the  eye  as  if  its 
dioptric  surfaces  were  all  parts  of  perfect  spherical  surfaces.  In 
reality  this  is  rarely  the  case,  either  with  the  lens  or  with  the 
cornea.  Slight  deviations  do  not  produce  any  marked  effect,  but 
there  is  one  deviation  which  is  present  to  a  certain  extent  in  most 
eyes,  and  is  very  largely  developed  in  some,  known  as  regular 
astigmatism.  This  exists  when  the  dioptric  surface  is  not  spherical 
but  more  convex  along  one  meridian  than  another,  more  convex, 
for  instance,  along  the  vertical  than  along  the  horizontal  meridian. 
When  this  is  the  case  the  rays  proceeding  from  a  luminous  point 
are  not  brought  to  a  single  focus  at  a  point,  but  possess  two  linear 
foci,  one  nearer  than  the  normal  focus  and  corresponding  to  the 
more  convex  surface,  the  other  farther  than  the  normal  and 
corresponding  to  the  less  convex  surface.  If  the  vertical 
meridians  of  the  surface  be  more  convex  than  the  hoj-izontal,  then 
the  nearer  linear  focus  will  be  horizontal  and  the  farther  linear 
focus  will  be  vertical,  and  vice  versa.  (This  can  be  shewn  much 
more  effectually  on  a  model,  than  in  a  diagram  in  which  we  are 
limited  to  two  dimensions.)  Now,  in  order  to  see  a  vertical  line 
distincdy,  it  is  much  more  important  that  the  rays  which  diverge 
from  the  line  in  the  series  of  horizontal  planes  should  be  brought 
to  a  focus  properly  than  those  which  diverge  in  the  vertical  plane 
of  the  line  itself;  and  similarly,  in  order  to  see  a  horizontal  line 
distinctly  it  is  much  more  important  that  the  rays  which  diverge 
from  the  line  in  the  series  of  vertical  planes  should  be  broujj,ht  to 
a  focus  properly  than  those  which  diverge  in  the  horizontal  plane 


CHAP.  U.]  SIGHT.  527 

of  the  line  itself.  Hence  a  horizontal  line  held  1  cfore  an  astig- 
matic dioi>tric  surface,  most  convex  in  the  vertical  meridians,  will 
give  rise  to  the  image  of  a  horizontal  line  at  the  nearer  focus,  tl  e 
vertical  rays  diverging  from  the  line  being  here  brought  to  a 
linear  horizontal  focus.  Similarly,  a  vertical  line  held  before  the 
same  surface  will  give  rise  to  an  image  of  a  vertical  line  at  the 
farther  focus,  the  horizontal  rays  diverging  from  tl.e  vertical  line 
being  here  brought  to  a  linear  vertical  focus.  In  other  words, 
with  a  dioptric  surface  most  convex  in  the  vertical  meridians, 
horizontal  lines  are  brought  to  a  focus  sooner  than  are  vertical 
lines. 

Most  eyes  are  thus  more  or  less  astigmatic,  and  generally  with 
a  greater  conve.xity  along  the  vertical  meridians.  If  a  set  of 
horizontal  or  vertical  lines  be  looked  at,  or  if  the  near  point  of 
accommodation  be  determined  by  Scheiner's  experiment  (p.  514), 
for  the  needle  placed  first  horizontally  and  then  vertically,  the 
horizontal  lines  or  needle  will  be  distinctly  visible  at  a  shorter 
distance  from  the  eye  than  the  vertical  lines  or  needle.  Similarly, 
the  vertical  line  must  be  farther  from  the  eye  than  a  horizontal  one, 
if  both  are  to  be  seen  distinctly  at  the  same  time.  The  cause  of 
astigmatism  is,  in  the  great  majority  of  cases,  the  unequal  curva- 
ture of  the  cornea  ;  but  sometimes  the  fault  lies  in  the  lens,  as  was 
the  case  with  Young. 

When  the  curvature  of  the  cornea  or  lens  ditiers  not  in  two  meri- 
dians only  but  ni  several,  irregular  astigmatism  is  the  result.  A  certain 
amount  of  irregular  astigmatism  exists  in  most  lenses,  thus  causing  the 
imaye  of  a  bright  point,  such  as  a  star,  to  be  not  a  circle  but  a  radiate 
figure. 

Chromatic  Aberration.  Thedifferent  raysof  the  spectrum 
are  of  different  refrangibility,  those  towards  the  violet  end  of  the 
spectrum  being  brought  to  a  focus  soorier  than  those  near  the  red 
end.  This  in  optical  instruments  is  obviated  by  using  compound 
lenses  made  uf)  of. various  kinds  of  glass.  In  the  eye  we  have  no 
evidence  that  the  lens  is  so  constituted  as  to  correct  this  fault ;  still 
the  total  dispersive  power  of  the  instrument  is  so  small,  that  such 
amount  of  chromatic  aberration  as  does  exist  attracts  little  notice. 
Nevertheless  sonie  slight  aberration  may  be  detected  by  careful 
observation.  When  the  spectrum  is  observed  at  some  distance 
the  violet  end  will  not  be  seen  in  focus  at  the  same  time  as  the  red. 
If  a  luminous  point  be  looked  at  tlirough  a  narrow  orifice  covered 
by  a  piece  of  violet  glass,  which  while  shutting  out  the  yellow  and 
green  allows  the  red  and  blue  rays  to  pass  through,  there  wi^l  be 
seen  alternately  an  image  having  a  blue  centre  with  a  red  fringe, 


528 


DIOPTRIC   IMPERFECTIONS. 


[BOOK  111. 


or  a  red  centre  with  a  blue  fringe,  according  as  the  image  of  the 
point  looked  at  is  thrown  on  one  side  or  other  of  the  true  focus. 
Thus  supposing/ (Fig.  53)  to  be  the  plane  of  the  mean  focus  of 
A,  the  violet  rays  will  be  brought  to  a  focus  in  the  plane  V,  and 
the  red  rays  in  the  plane  Ji  ;  if  the  rays  be  supposed  to  fall  on 
the  retina  between  Kand/,  the  diverging  or  blue  rays  will  form 
a  centre  surrounded  by  the  still  converging  red  rays  ;  whereas  if 
the  rays  fall  on  the  retina  between  f  and  R,  the  converging  red 
rays  will  form  a  centre  with  the  still  diverging  blue  rays  forming  a 
fringe  round  them;  when  the  object  is  in  focus  at/,  the  two  kinds 
of  rays  will  be  mixed  together. 


Fig.  53.    Diagram  illustrating  Chroaiatic  Aberration. 

Ilk  is  the  dioptric  surface,  hv  represents  the  hlue,  and  hr  the  red  rays  ;  f^is  the  focal  plane  of 
the  blue,  R  of  the  red  rays. 

Entoptic  Phenomena.  The  various  media  of  the  eye  are 
not  uniformly  transparent ;  the  rays  of  light  in  passing  through 
them  undergo  local  absoiption  and  refraction,  and  thus  various 
shadows  are  thrown  oti  the  retina,  of  which  we  become  conscious 
as  imperfections  in  the  field  of  vision,  especially  when  the  eye  is 
directed  to  a  uniformly  illuminated  surface.  These  are  spoken  of 
as  entoptic  phenomena,  and  are  very  varied,  many  forms  having 
been  described. 

The  most  common  are  those  caused  by  the  presence  of  float- 
ing bodies  in  the  vitreous  humour,  the  so-called  miisctz  volitantes. 
These  are  readily  seen  when  the  eye  is  turned  towards  a  uniform 
surface,  and  are  frequently  very  troublesome  in  looking  through  a 
microscope.  They  assume  the  form  of  rows  and  groups  of  beads, 
of  single  beads,  of  streaks,  patches  and  granules,  and  may  be  re- 
cognised by  their  almost  continual  movement,  especially  when  the 
head  or  eye  is  moved  up  and  down.  When  an  attempt  is  made 
to  fix  the  vision  upon  them,  they  immediately  float  away.  Tears 
on  the  cornea,  temporary  unevenness  on  the  anterior  surface  of 
the  cornea  after  the  eyelid  has  been  pressed  on  it,  and  imperfec- 
tions in  the  lens  or  its  capsule,  also  give  rise  to  visual  images. 
Not  unfrequently  a  radiate  figure  corresponding  to  the  arrange- 
ment of  the  fibres  of  the  lens  makes  its  appearance. 


CHAT.    II.]  SIGHT.  529 

Imperfections  in  the  margin  of  the  pupil  appear  in  the  shadow  of 
the  iris  which  bounds  the  field  of  vision  ;  and  the  movements  of  the 
iris  in  one  eye  may  be  rendered  visible  by  iilttrnalely  closing  and 
openmg  the  other  ;  the  field  of  the  first  may  be  ob->erved  to  contract 
when  light  enters,  and  to  expand  when,  the  light  is  shut  off  from  tiic 
second.  The  media  of  the  eye  arc  lluorescent  ;  a  condition  which 
favours  the  perception  of  the  ultra-violet  rays.  If  a  white  sheet  or 
white  cloud  be  looked  at  in  daylight  through  a  Nicol's  prism,  a  some- 
what bright  double  cone  or  double  tuft,  with  the  apices  touching,  of  a 
faint  blue  colour,  is  seen  in  the  centre  of  the  field  of  vision,  crossed  by 
a  similar  double  cone  of  a  somewhat  yellow  darker  colour.  These  are 
spoken  of  as  liaidinger's  brushes  ;  they  rotate  as  the  prism  is  rotated, 
and  are  supposed  to  be  due  to  the  unequal  absorption  of  the  polarized 
light  in  the  yellow  spot.  The  prism  must  be  frequently  rotated,  as 
when  the  prism  remains  at  rest  the  phenomena  fade.  Lastly,  accord- 
ing to  Helmholtz,  the  optical  arrangements  have  a  further  imperfection 
in  that  the  dioptric  surfaces  are  not  truly  centred  on  the  optic  axis. 

Sec.  2.     Visual  Sens.-\tions. 

Light  failing  on  the  retina  excites  sensory  impulses,  and  these 
passing  up  the  optic  nerve  to  certain  parts  of  the  brain,  produce 
changes  in  certain  cerebral  structures,  and  thus  give  rise  to  what  we 
call  a  sensation.  In  a  sensation  we  ought  to  be  able  to  distinguish 
between  the  events  through  which  the  impact  of  the  rays  of  light 
on  the  retina  is  enabled  to  generate  sensory  impulses,  and  the 
events,  or  rather  series  of  events,  through  which  these  sensory  im- 
pulses (for,  judging  by  the  analogy  of  motor  nerves,  we  have  no 
reason  to  think  that  they  undergo  any  fundamental  changes  in 
passing  along  the  optic  nerve),  by  the  agency  of  the  cerebral  ar- 
rangements, develope  into  a  sensation.  Such  an  analysis,  however, 
is,  at  present  at  least,  in  most  particulars,  quite  beyond  our  power ; 
and  we  must  therefore  treat  of  the  sensations  as  a  whole,  dis- 
tinguishing between  the  peripheral  and  central  phenomena,  on  the 
rare  occasions  when  we  are  able  to  do  so. 

The  Origin  of  Visual  Impulses. 

Of  primary  importance  to  the  understanding  of  the  way  in 
which  luminous  undulations  give  rise  to  those  nervous  changes 
which  pass  along  the  optic  nerve  as  visual  impulses,  is  the  lact 
that  the  rays  of  light  produce  their  effect  by  acting  not  on  the  optic 
nerve  itself  but  on  its  terminal  organs  (see  p.  507),  They  pass 
through  the  anterior  layers  of  the  retina  apparently  without  in- 
ducing any  effect ;  it  is  not  till  they  have  reached  the  region  of  the 
rods  and  cones  that  they  set  up  the  changes  concerned  in  the 
generation  of  visual  impulses  \  and  the  impulses  here  generated 
F.  P.  34 


530  VISUAL   SENSATIONS.  ■        [BOOK  II. 

travel  back  to  the  layer  of  fibres  in  the  anterior  surface  of  the 
retina  and  thence  pass  along  the  optic  nerve.  That  the  optic  fibres 
are  themselves  insensible  to  light  and  that  visual  impulses  begin 
in  the  region  of  rods  and  cones  is  shewn  by  the  phenomena  of 
the  blind  spot  and  of  Purkinje's  figures  respectively. 

Blind  Spot.  There  is  one  part  of  the  retina  on  which  rays 
of  light  falling  give  rise  to  no  sensations ;  this  is  the  entrance  of 
the  optic  nerve,  and  the  corresponding  area  in  the  field  of  vision 
is  called  the  blind  spot.  If  the  visual  axis  of  one  eye,  the  right 
for  instance,  the  other  being  closed,  be  fixed  on  a  black  spot  in  a 
white  sheet  of  paper,  and  a  small  black  object,  such  as  the  point 
of  a  quill  pen  dipped  in  ink,  be  moved  gradually  sideways  over 
the  paper  away  to  the  outside  of  the  field  of  vision,  at  a  certain 
distance  the  black  point  of  the  quill  will  disappear  from  view.  On 
continuing  the  movement  still  farther  outward  the  point  will  again 
come  into  view  and  continue  in  sight  until  it  is  lost  in  the 
periphery  of  the  field  of  vision.  If  the  pen  be  used  to  make  a 
mark  on  the  paper  at  the  moment  when  it  is  lost  to  view  and  at 
the  moment  when  it  comes  into  sight  again ;  and  if  similar 
marks  be  made  along  the  other  meridians  as  well  as  the 
horizontal,  an  irregular  outline  will  be  drawn  circumscribing  an 
area  of  the  field  of  vision  within  v.'hich  rays  of  light  produce  no 
visual  sensation.  This  is  the  blind  spot.  The  dimensions  of  the 
figure  drawn  vary  of  course  with  the  distance  of  the  paper  from 
the  eye.  If  this  distance  be  known,  the  size  as  well  as  the  position 
of  the  area  of  the  retina  corresponding  to  the  blind  spot  may  be 
calculated  from  the  diagrammatic  eye  (p.  512).  The  position 
exactly  coincides  with  the  entrance  of  the  optic  nerve,  and  the 
dimensions  (about  1*5  mm.  diameter)  also  correspond.  While 
drawing  the  outline  as  above  directed  the  indications  of  the  large 
branches  of  the  retinal  vessels  as  they  diverge  from  the  entrance 
of  the  nerve  can  frequently  he  recognised.  The  existence  of  the 
blind  spot  is  also  shewn  by  the  fact  that  an  image  of  light,  suf- 
ficiently small,  thrown  upon  the  optic  nerve  by  means  of  the 
ophthalmoscope,  gives  rise  to  no  sensations. 

The  existence  of  the  blind  spot  proves  that  the  optic  fibres  them- 
selves are  insensible  to  light ;  it  is  only  through  the  agency  of  the 
retinal  expansion  that  they  can  be  stimulated  by  luminous  vibrations. 

Purkinje's  Figures.  If  one  enters  a  dark  room  with  a 
candle,  and  while  looking  at  a  plain  (not  parti-coloured)  wall, 
moves  the  candle  up  and  down,  holding  it  on  a  level  with  the  eyes 
by  the  side  of  the  head,  there  will  appear  in  the  field  of  vision  of 


CHAP.  11.] 


SIGHT. 


531 


the  eye  of  the  same  side,  projected  on  the  wall,  an  image  of  the 
retinal  vessels,  quite  similar  to  that  seen  on  looking  into  an  eye 
with  tlie  opiithalmoscope.  The  field  of  vision  is  illuminated 
with  a  glare,  and  on  this  the  branched  retinal  vessels  appear  as 
shadows.  In  this  mode  of  experimenting  the  light  enters  the  eye 
through  the  cornea,  and  an  image  of  the  candle  is  formed  on  the 
nasal  side  of  the  retina;  and  it  is  the  light  emanating  from  this 
image  which  throws  shadows  of  the  retinal  vessels  on  to  the  rest 
of  the  retina.  A  far  better  method  is  for  a  second  person  to  con- 
centrate the  rays  of  light,  with  a  lens  of  low  power,  on  to  the 
outside  of  the  sclerotic  just  behind  the  cornea  ;  the  light  in  this 
case  emanates  from  the  illuminated  si)0t  on  the  sclerotic  and  pass- 
ing straight  through  the  vitreous  humour  throws  a  tiirect  shadow 
of  the  vessels  on  to  the  retina.  Thus  the  rays  passing  through 
the  sclerotic  at  b,  Fig.  54,  in  the  direction  bv,  will  throw  a  shadow 


Fig.  s4-     Diagram  illustrating  the  For.mation  of  Purkinje's  Figures  when  the 
Illumination  is  directed  through  the  Sclerotic. 

of  the  vessel  v  on  to  the  retina  at  /8 ;  this  will  appear  as  a  dark 
line  at  B  in  the  glare  of  the  field  of  vision.  This  proves  that  the 
structures  in  which  visual  impulses  originate  must  lie  behind  the 
retinal  vessels,  otherwise  the  shadows  of  these  could  not  be 
perceived. 

If  the  light  be  moved  from  b  to  a,  the  shadow  on  the  retina  will 
move  from  i;i  to  a,  and  the  dark  line  in  the  field  of  vision  will  move  from 
B  to  A.     If  the  distance  BA  be  measured  when  the  whole  image  is 

.34—2 


532  VISUAL   SENSATIONS.  [BOOK   III. 

projected  at  a  known  distance,  kh  from  the  eye,  k  being  the  optical 
centre',  then,  knowing  the  distance,  /&/3  in  the  diagrammatic  eye,  the 
distance  jSa  can  be  calculated.  But  if  the  distance  j3a  be  thus  estimated, 
and  the  distance  ia  be  directly  measured,  the  distances  ^v,  av,  bv,  av 
can  be  calculated,  and  if  the  appearance  in  the  field  of  vision  is  really 
caused  by  the  shadow  of  v  falling  on  /3,  these  distances  ought  to  corre- 
spond to  the  distances  of  the  retinal  vessels  v  from  the  sclerotic  b  on 
the  one  hand,  and  from  that  part  of  the  retina  /3  where  visual  impre- 
sions  begin,  on  the  other.  H.  Miiller  found  that  the  distance  ^v  thus 
calculated  corresponded  to  the  distance  of  the  retinal  vessels  from  the 
layer  of  rods  and  cones.  Thus  Purkinje's  figures  prove  in  the  first 
place  that  the  sensory  impulses  which  form  the  commencement  of 
visual  sensations  originate  in  some  part  of  the  retina  behind  the  retinal 
vessels,  i.e.  somewhere  between  them  and  the  choroid  coat ;  and  H. 
Miiller's  calculations  go  far  to  show  that  they  originate  at  the  most 
posterior  or  external  part  of  the  retina,  viz.  the  layer  of  rods  and  cones. 
It  must  be  admitted  however  that  H.  Midler's  results  were  not 
sufficiently  exact  to  allow  any  great  stress  to  be  placed  on  this 
argument. 

It  is  desirable  in  these  cases  to  move  the  light  to  and  fro, 
especially  in  the  first  method,  as  the  retina  soon  becomes  tired,  and 
the  image  fades  away.  Some  observers  can  recognize  in  the  axis 
of  vision,  a  faint  shadow  corresponding  to  the  edge  of  the  de- 
pression of  the  fovea  centralis. 

In  the  second  method  of  experimenting,  the  image  always  moves 
in  the  same  direction  as  the  light,  as  it  obviously  must  do.  In  the  first 
method,  where  the  light  enters  through  the  cornea,  the  image  moves  in 
the  same  direction  as  the  light  when  the  light  is  moved  from  right  to 
left,  provided  the  movement  does  not  extend  beyond  the  middle  of  the 
cornea,  but  in  the  opposite  direction  to  the  light  when  the  latter  is 
moved  up  and  down.  In  Fig.  55,  which  represents  a  horizontal  section 
of  an  eye,  if  a  be  moved  to  a,  b  will  move  to  /3,  the  shadow  on  the 
retina  c  to  y,  and  the  image  d  to  5.  If  on  the  other  hand  a  be  sup- 
posed to  move  above  the  plane  of  the  paper,  b  will  move  below,  in 
consequence  c  will  move  above,  and  d  will  appear  to  move  below,  i.e. 
d  will  sink  as  a  rises. 

The  retinal  vessels  may  also  be  rendered  visible  by  looking  through 
a  small  orifice  at  a  bright  field  such  as  the  sky,  and  moving  the  orifice 
very  rapidly  from  side  to  side  or  up  and  down.  If  the  movement  be 
from  side  to  side,  the  vessels  which  run  vertical  will  be  seen  ;  if  up 
and  down,  the  horizontal  vessels.     The  fine  capillary  vessels  are  seen 

^  For  the  properties  of  the  optical  centre,  we  must  refer  the  reader  to  the 
various  treatises  on  optics.  The  optical  centre  of  a  lens  is  the  point  through 
which  all  the  principal  rays,  of  the  various  pencils  of  rays  falling  on  the  lens, 
pas-i.  The  diagrammatic  eye  of  Listing  (p.  512)  has  two  optical  centres,  but 
these  may,  without  serious  error,  be  further  i-educed  for  practical  purposes  to 
one  lying  in  the  lens  near  its  posterior  surfjSe,  at  about  15  mm.  distance  from 
the  retina. 


CHAP.   II. J  SIGHT.  533 

more  easily  in  this  way  than  by  Piirkinje's  metlind.  The  same  ap- 
pearances may  also  be  j^roduced  by  looking  tlirough  a  microscope  from 
which  the  objective  has  been  removed  and  the  eye-piece  only  left  (or 
in  which  at  least  there  is  no  object  distinctly  in  focus  in  the  field),  and 
moving  the  head  rapidly  from  side  to  side  or  backwards  and  forwards. 
Or  the  microscope  itself  may  be  moved  ;  a  circular  movement  of  the 
field  will  then  bring  both  the  vertical  and  horizontally  directed  vessels 
into  view  at  the  same  time. 


Fi'"..  55.     Diagram  illustrating  the  Fokmation  of  Pukkinje's  Figures  when  thb 
Illumination  is  directed  through  the  Cornea. 

The  Photochemistry  of  the  Retina.  In  seeking  to  under- 
stand how  it  is  that  rays  of  light  falling  upon  the  region  of  the  rods 
and  cones  can  give  rise  to  visual  impulses  in  the  optic  nerve  we 
naturally  turn  to  a  chemical  explanation.  We  are  familiar  with  the 
fact  that  rays  of  light  are  able  to  bring  about  the  decomposition  of 
very  many  chemical  substances  ;  and  we  accordingly  speak  of 
these  substances  as  being  sensitive  to  light.  All  the  facts  dwelt 
on  in  this  book  illustrate  the  great  complexity  and  corresponding 
instability  of  the  composition  of  protoplasm.  And  we  might 
reasonably  suj^pose  that  protoplasm  itself  would  be  sensitive  to 
light;  that  is  to  say  that  rays  of  light  falling  on  even  undifferen- 
tiated protoplasm  might  set  up  a  decomposition  of  that  protoplasm 
and  so  inaugurate  a  molecular  disturbance  ;  in  order  words,  that 
light  might  act  as  a  direct  stimulus  to  protoplasm.  As  a  matter 
of  fact,  however,  such  evidence  as  we  at  ])resent  possess  goes  to 
shew  that  native  undifferentiated  protoplasm  is  not  sensitive  to 
light  (that  is,  to  those  particular  wa^'es  which  when  they  fall  on 
our  retina  give  rise  in  us  to  the  sensation  of  light),  though  in  at 
least  one  instance  a  lowly  organism,  whose  protoplasm  exhibits 
very  little  differentiation  and  in  particular  contains  no  pigment, 
does  manifest  a  sensitiveness  to  light'.  Nor  can  we  be  surprised 
'  Engelmann,  Pfliiger's  Archiv,  xix.  (1879)  p.  i. 


534  VISUAL   SENSATIONS.  [BOOK   III. 

at  this  indifference  to  protoplasm  when  we  reflect  that  what  we 
may  call  pure  protoplasm  is  remarkable  for  its  transparency,  that 
is  to  say,  the  rays  of  light  pass  through  it  with  the  slightest  possible 
absorption.  But  in  order  that  light  may  produce  chemical  effects, 
it  must  be  absorbed  ;  it  must  be  spent  in  doing  the  chemical  work. 
Accordingly  the  first  step  towards  the  formation  of  an  organ  of 
vision  is  the  differentiation  of  a  portion  of  protoplasm  into  a 
pigment  at  once  capable  of  absorbing  light  and  sensitive  to  hght. 
I.e.  undergoing  decomposition  upon  exposure  to  light.  An 
organism,  a  portion  of  whose  protoplasm  had  thus  become  differ- 
entiated into  such  a  pigment  would  be  able  to  react  towards  light. 
The  light  falling  on  the  organism  would  be  in  part  absorbed  by 
the  pigment,  and  the  rays  thus  absorbed  would  produce  a  chemical 
action  and  set  free  chemical  substances  which  before  were  not 
present.  We  have  only  to  suppose  that  the  chemical  substances 
are  of  such  a  nature  as  to  act  as  a  stimulus  to  the  protoplasm  of 
other  parts  of  the  organism,  (and  we  have  manifold  evidence  of 
the  exquisite  sensitiveness  of  protoplasm  in  general  to  chemical 
stimuli),  in  order  to  see  how  rays  of  light  falling  on  the  organism 
might  excite  movements  in  it,  or  modify  movements  which  were 
being  carried  on,  or  might  otherwise  affect  the  organism  in  whole 
or  in  part  ^. 

Such  considerations  as  the  foregoing  may  be  applied  to 
even  the  complex  organ  of  vision  of  the  higher  animals.  If 
we  suppose  that  the  actual  terminations  of  the  optic  nerve  are 
surrounded  by  substances  sensitive  to  light,  then  it  becomes  easy 
to  imagine  how  light  falling  on  these  sensitive  substances  should 
set  free  chemical  bodies  possessed  of  the  property  of  acting  as 
stimuli  to  the  actual  nerve-endings  and  thus  give  rise  to  visual 
impulses  in  the  optic  fibres.  We  say  'easy  to  imagine,'  but  we 
are,  at  present,  far  from  being  able  to  give  definite  proofs  that  such 
an  explanation  of  the  origin  of  visual  impulses  is  the  true  one, 
probable  and  enticing  as  it  may  appear.  One  of  the  most 
striking  features  in  the  structure  of  the  retina  is  the  abundance  of 
pigment  in  the  retinal  or  as  it  is  sometimes  called  choroidal  epithe- 
lium. It  is  difficult  to  suppose  that  the  sole  function  of  this  pigment 
is  to  absorb  the  superfluous  rays  of  light,  and  that  the  rays  thus 
absorbed  are  put  to  no  use  but  simply  wasted ;  and  Kiihne  ^ 
indeed  has  shewn  that  the  p^ment  is  sensitive  to  light ;  but  the 
changes  in  it  induced  by  light  are  excessively  slow,  and  vision  is 
not  only  possible  but  fairly  distinct  with  albinos  in  which  this 
pigment  is  absent. 

'  Cf.  Kiihne,  Zur  PhotochUnie  der  Netzhaut. 
'  Journal  of  Physiology,  I.  (1878)  pp.  109,  189. 


CHAP.    II. J  SIGHT.  535 

Then  again,  in  the  vast  majority  of  vertebrate  animals,  the 
outer  limbs  of  the  rods  are  sulTuscd  wiih  a  purplish  red  pigment, 
the  so-calle<l  visual  purple,  which  is  so  eminently  sensitive  to  light 
that  images  of  external  objects  may  by  api)ropriate  means  be 
pholDgraphed  in  it  on  the  retina.  And  upon  the  first  discovery 
of  this  visual  purple  we  seemed  to  have  found  the  substance  of 
which  we  are  in  search.  But  unfortunately  this  pigment  is  absent 
from  the  cones,  and  from  the,  fovea  centralis,  which  as  we  shall 
see  is  the  region  of  distinct  vision  ;  it  is  further  entirely  wanting 
in  some  animals  which  undoubtedly  see  very  well,  and  lastly 
animals,  such  as  the  frog,  naturally  possessing  the  pigment,  con- 
tinue to  see  very  well  when  it  has  been  absolutely  bleached,  as  it 
may  be  by  prolonged  exposure  of  the  eyes  to  strong  light.  We 
cannot  therefore  at  present  at  least  explain  the  origin  of  visual 
impulses  by  the  help  of  visual  purple.  But  at  the  same  time  it  must 
be  remembered  that  the  discovery  of  its  existence  is  a  step  in  the 
desired  direction  ;  though  it  has  failed  us  now,  it  gives  promise  of 
success  in  the  future. 

That  in  the  retina  there  does  e.xist  a  substance  or  do  exist  sub- 
stances, presumably  of  the  sensitive  nature  which  we  have  indicated, 
which  are  used  up  in  vision,  has  been  urged  by  Exner^'  to  be  proved  by 
the  following  experiment. 

It  is  well  known  that  when  pressure  is  forcibly  applied  to  the  eye- 
ball, the  retina  speedily  becomes  insensible  to  light.  If  a  sheet  of 
paper,  one  half  of  which  is  white,  and  the  other  black,  but  having  in 
its  middle  a  white  patch  covered  temporarily  with  black,  be  held  before 
the  eyes,  and  if  while  looking  at  the  sheet,  the  eyeball  be  pressed  till 
.  the  white  half  is  no  longer  visible,  and  then  the  cover  of  the  white 
patch  in  the  black  half  be  suddenly  withdrawn,  the  white  patch  is 
recognized  for  a  while  though  the  white  half  is  invisible  ;  very  soon 
however  the  white  patch  fades  away  too.  Exner's  argument  is  that 
the  blindness  due  to  pressure  must  be  caused  not  by  a  mere  loss  of 
conductivity  of  the  nervous  structures,  but  by  a  consumption  of  visual 
substance  which,  owing  to  the  pressure  checking  the  nutritive  supply, 
cannot  be  furnished  rapidly'enough.  Thus  in  the  retina  correspondmg 
to  the  white  half  of  the  sheet  loo.<ed  at  this  visual  substance  is  being 
used  up,  while  in  that  part  which  corresponds  to  the  white  patch,  there 
is  no  consumption  as  long  as  the  black  cover  is  kept  on.  When  the 
black  cover  is  removed,  the  rays  from  the  white  patch  accordingly  find 
some  visual  substance  to  work  upon,  and  hence  the  patch  is  visible 
until  the  supply  of  visual  substance  here  also  is  in  turn  exhausted. 
Kiahne-"  however,  urges  that  Exner's  interpretation  is  not  valid  and 
that  the  phenomena  may  be  explained  on  the  Law  of  Contrast,  of 
which  wc  shall  treat  presently,  manifested  in  a  not  wholly  exhausted 
retina. 

'  Pfliiger's  Archiv,  XVI.  (187S)  p.  407. 

»  Unterstuh.  Physiol.  Inst.  Heidi!.,  Bd.il.  (1878)  p.  46. 


53^  VISUAL   SENSATIONS.  [BOOK   III. 

But  even  admitting  as  probable  the  existence  of  sensitive 
visual  substances,  the  products  of  whose  decomposition  act  as 
stimuli  to  the  real  endings  of  the  retinal  nervous  mechanism,  we 
cannot  at  present  state  anything  definite  concerning  those  nerve- 
endings  or  the  manner  of  their  stimulation.  It  may  be  that%ven 
the  outer  limbs  of  the  rods  and  cones  in  spite  of  the  apparent 
break  of  continuity  between  the  outer  and  inner  limbs,  are  really 
nervous  in  nature.  It  may  be  on  the  other  hand  that  the  outer 
limbs  are  either  purely  dioptric  in  function  or  are  in  some  way 
associated  with  the  sensitive  visual  substances,  so  that  the  nervous 
structures  must  be  considered  as  extending  at  least  no  further  than 
the  inner  limbs.  We  cannot  as  yet  make  any  definite  statement 
in  the  one  direction  or  the  other. 

Visual  Purple.  As  long  ago  as  1839  Krohn  called  attention  to  the 
rose  colour  of  the  retinas  of  cephalopods  ;  but  though  his  observations 
were  confirmed  by  Max  Schultze  and  others,  and  though  some  years 
afterwards  H.  Miiller,  and  Leydig  and  Max  Schultze,  found  a  similar 
colouration  in  the  retinas  of  frogs  and  other  vertebrates,  the  matter  did 
not  attract  any  great  interest  until  BoU^  disco^^ered  that  this  colour 
was  in  the  living  animal  susceptible  to  light,  being  bleached  when  the 
animal  was  exposed  to  light  but  returning  again  when  the  animal  was 
kept  in  the  dark.  He  found  that  when  the  eye  of  a  frog  which  had 
been  kept  for  some  time  in  the  dark  was  rapidly  opened,  the  outer 
limbs  of  the  rods  of  the  retina  presented  a  very  beautiful  purple,  or 
(as  he  afterwards  preferred  to  call  it)  red  colour,  which  after  a  few 
seconds  changed  into  a  yellow  and  finally  disappeared,  leaving  the  rods 
colourless.  Scattered  among  these  red  or  purple  rods  were  a  number 
of  bright  green  rods,  the  colour  of  which  also  faded  on  exposure  to 
light.  If  the  frog  had  previously  been  exposed  for  some  time  to  a 
bright  light,  the  retina,  even  with  the  most  rapid  manipulation,  was 
found  to  be  colourless.  And  by  examining  at  intervals  the  eyes  of  a 
series  of  frogs  which  after  being  kept  in  the  dark  had  been  exposed  to 
li^ht  for  variable  periods,  and  conversely  of  frogs  which,  after  an  ex- 
posure to  bright  light,  had  been  kept  in  the  dark  for  variable  periods, 
Boll  was  enabled  to  satisfy  himself  that,  in  the  living  eye  the  colour  of 
the  rods  was  destroyed  by  exposure  to  light  and  restored  by  rest  in  the 
dark.  Using  under  similar  circumstances  monochromatic  instead  of 
white  light,  he  came  to  the  conclusion  that  under  exposure  to  green 
ligat  the  retina  became  first  purple,  then  violet,  and  finally  colourless  ; 
unier  blue  and  violet  light,  it  first  suffered  a  change  to  violet  and  finally 
lost  all  colour ;  while  under  red  light  it  became  a  deeper  red,  under 
yellow  light  a  brighter  red,  and  when  exposed  to  the  ultra-violet  rays 
underwent  very  little  change.  He  found  this  visual  purple  or  visual 
red  in  the  outer  limbs  of  the  rods  not  only  of  the  frog,  but  of  all  other 
vertebrates,  including  mammalia,  whose  retinas    contain  sufficiently 

'^  Berlin.    Sitzungsberichte,    1876,   Sitzung  Nov.    12;   l877»  Sitzung  Jan  II. 
Du  Bois-Reymond's  Archiv,  1877,  p.  4. 


CHAP.   II.J  SICIIT.  537 

conspicuous    rods.     He  concluded    that   the  colour  must  be  largely 
concerned  in  the  act  of  vision. 

Kiiline'  t;ikinjj  up  and  lirgcly  extending  Boll's  discovery  has  been 
led  to  the  followinii  results  : 

The  colour  of  the  rods  is  susceptible  to  light  not  only  during  life 
but  also  after  death,  the  fading  which  occurs  after  the  removal  and 
opening  of  an  eye  being  due  not  to  post  mortem  changes  but  to  the 
action  of  lii^ht. 

The  colour  of  the  rods  is  due  to  the  presence  of  a  distinct  pigment, 
the  visual  purple,  which  may  be  extracted  from  the  substance  of  the 
rods  by  dissolving  these  in  an  aqueous  solution  of  bile  salts.  A  clear 
purple  solution  is  thus  obtained,  which  is  capable  of  being  bleached 
by  the  action  of  light,  and  in  its  general  features  and  behaviour  is 
similar  to  the  pigment  as  it  naturally  exists  in  the  retina. 

Visual  purple  is  found  exclusively  in  the  outer  limbs  of  the  rods  ;  it 
has  never  yet  been  found  in  the  cones,  and  it  is  accordingly  absent 
from  the  retinas  of  animals  (such  as  those  of  snakes)  which  are  com- 
posed of  cones  only,  and  from  the  macula  lutea  and  fovea  centralis  of 
the  retinas  of  man  and  the  ape.  The  intensity  of  the  colouration  varies 
in  different  animals,  and  the  retinas  even  of  some  animals  possessing 
rods  (bat,  dove,  hen)  seem  to  be  wholly  devoid  of  the  visual  purple  ; 
it  is  generally  well  marked  in  retinas  in  which  the  outer  limbs  of  the 
rods  are  well  developed.  Its  absence  or  presence  is  not  dependent  on 
no:turnal  habits,  since  the  intense  colour  of  the  retina  of  the  owl  is  in 
strong  contrast  to  the  absence  of  colour  in  the  bat.  It  has  been  found 
in  the  retina  of  a  sheep's  embryo.  As  a  general  rule  the  amount  of 
pigment  present  may  be  said  to  be  in  inverse  ratio  to  the  development 
of  coloured  'globules'  or  '  lenses'  in  the  rods  and  cones  ;  but  it  would 
be  prem  iture  to  insist  on  any  exact  relation. 

The  visual  purple  is  bleached  not  only  by  white  but  also  by  mono- 
chromatic light  ;  the  change  however  in  the  latter  is  slower  than  in  the 
former.  Of  the  various  prismatic  rays  the  most  active  are  the  greenish 
yellow  rays,  those  to  the  blue  side  of  these  coming  next,  the  least 
active  being  the  red.  Now  it  is  precisely  the  greenish  yellow  rays 
which  are  most  readily  absorbed  by  the  colour  itself.  A  natural 
coloured  retina  or  a  solution  of  visual  purple  gives  a  diffuse  spectrum 
without  any  defined  absorption  bands,  and  according  to  the  amount  of 
colouring  material  through  which  the  light  passes,  absorption  is  seen 
either  to  be  limited  to  the  greenish  yellow  part  of  the  spectrum  or  to 
spread  thence  towards  the  blue  and  to  a  much  less  extent  towards  the 
red.  Thus  the  various  prismatic  rays  produce  a  photochemical  effect 
on  the  visual  purple  in  proportion  as  they  are  absorbed  by  it.  Under 
the  action  of  light  the  visual  purple,  whether  in.  solution,  or  in  its 
natural  condition  in  the  rods,  passes  through  what  Kiihne  calls  a 
chamois  colour  {i.e.  the  purplish  orange  seen  on  the  chamois)  to  a 
yellow,  and  finally  becomes  colourless  ;  and  Kiihne  believes  that  he  is 

'  Ztir  Pholochemie  der  Nelzhaitt .  '  Ueber  den  Sehpurpur,'  Vcrhaiidl.  d. 
naturhistorjschmed.  Vereins  in  Heidelberg,  Iki.  I.  1S77.  '  .Sehen  ohne 
Purpur,'  Untcrsuck.  physiol.  Instit.  Heidelberg,  Bd.  I.  1877.  Ewald  and  Kiihne, 
'  Uebcr  den  Sehpurpur,'  ibid. 


S3^  VISUAL   SENSATIONS.  [BOOK   III. 

Justified  in  speaking  of  a  visual  yellow  and  visual  white  as  products  of 
the  photochemical  changes  undergone  by  the  visual  purple. 

For  the  restoration  of  the  visual  purple,  after  it  has  been  destroyed 
by  light,  the  maintenance  of  the  circulation  of  the  blood  through  the 
tissues  of  the  eye  is  not  essential.  The  choroidal  epithelium  has  by 
itself,  provided  that  it  still  retains  its  tissue  life,  the  power  of  regenera- 
ting the  purple.  If  a  portion  of  the  retina  of  an  excised  eye  be  raised 
from  its  epithelial  bed,  bleached,  and  then  carefully  restored  to  its 
natural  position,  the  purple  will  return  if  the  eye  be  kept  in  the  dark. 
The  choroidal  epithelium  may  in  fact  be  spoken  of  as  a  '  purpuro- 
genous '  membrane. 

If  an  excised  eye,  a  portion  of  the  retina  of  which  has  been 
bleached  by  light,  be  treated  with  a  4  p.  c.  solution  of  potash  alum 
before  the  choroidal  epithehum  has  had  time  to  obliterate  the  bleaching 
effects,  the  retina  may  remain  permanently  in  that  condition,  the 
photochemical  effect  may,  as  the  photographers  say,  be  fixed.  In  this 
way  Kiihne  succeeded  in  obtaining  promising  '  optograms'. 

The  above  facts  leave  no  room  for  doubt  that  the  visual  purple  is 
in  some  way  concerned  in  vision,  but  it  is  impossible  at  present  to  say 
what  is  its  exact  function.  Its  conspicuous  absence  from  the  cones, 
and  especially  its  absence  from  the  fovea  centralis  of  man,  shew  that 
vision,  indeed  the  best  and  most  exact  vision,  may  take  place  without 
it  ;  and  Kiihne  has  satisfied  himself  that  frogs  whose  retinas  have  been 
wholly  and  thoroughly  bleached  by  exposure  to  light  can  see  perfectly 
well.  It  is  very  tempting  to  connect  the  pitrple  in  some  way  with 
colour  vision,  but  we  know  that  our  colour  vision  is  most  exact  in  the 
fovea  centralis,  and  the  frogs  just  spoken  of  seemed  to  be  as  susceptible 
to  colour  as  normal  frogs. 

Kiihne  and  Ewald  ^  have  called  attention  to  the  remarkable  changes 
which  the  cells  of  the  retinal  pigment  epithelium  undergo  under  the 
influence  of  light.  When  an  eye  has  been  shut  off  from  all  light  for 
some  little  time  the  pigment  is  concentrated  in  the  body  of  the  cells, 
and  the  remarkable  fringes  of  filamentous  processes  of  the  cells,  with 
the  pigment  granules  or  crystals  which  these  carry,  extend  a  slight 
distance  only  between  the  limbs  of  the  rods  and  cones  (about  one- 
third  down  the  length  of  the  outer  limbs  of  the  rods).  Under  the 
influence  of  light  these  processes  loaded  with  pigment  thrust  them- 
selves a  much  longer  way  down  towards  the  external  Hmiting  mem- 
brane ;  in  consequence  a  considerable  quantity  of  pigment  is  found 
massed  between  the  outer  and  even  the  inner  limbs  of  the  rods  and 
cones  ;  indeed  the  outer  limbs  of  the  rods  swelling  at  the  same  time 
become  jammed  as  it  were  between  the  m.isses  of  pigment,  causing 
the  epithelial  layer,  to  adhere  very  closely  to  the  layer  of  rods  and 
cones. 

Retinal  Currents.  HtDlmgren  '^  and  Dewar  and  Mc  Kendrick  3 
have  shewn  that  an  electrical  change  takes  place  in  the  retina  and 

^   Untirsuch.  Physiol.  Inst.  Heidel.,  Bd.  I.  1877-8. 

^  Centrbt.  Med.  Wiss.,  1871,  pp.  423,  438  :  an  earlier  notice  was  published 
m  1865. 

3   Trans.  Roy.  Soc.  Edin.,  1873. 


ciiAi'.  II. I  SIGHT.  539 

optic  nerve  whenever  the  former  is  affected  by  light.  When  the 
electrodes  of  a  galvanometer  arc  placed  one  on  the  cornea  and  the 
other  on  the  posterior  surface  of  the  eyeball,  or  on  the  transverse 
section  of  the  opiic  nerve,  the  galvanometer  indicates  the  existence  of 
a  current  corresponding  to  the  so-called  natural  nerve-currents,  the 
cornea  being  positive  ;  and  this  current  undergoes  a  variation  when 
light  falls  upon  or  is  withdrawn  from  the  eye.  To  eliminate  currents 
proceeding  from  the  iri-,  the  front  half  of  the  bulb  may  be  cut  away 
and  the  electrodes  pl-Kcd  one  on  the  retina  and  the  other  on  the 
hinder  surface  of  the  eyeball  or  on  the  optic  nerve  or  on  the  surface 
of  the  brain  ;  in  this  case  also  the  incidence  or  withdrawal  of  light 
produ(--es  variations  in  the  'natural'  currents;  and  Dewar  and 
Mc  Kendrick  find  that  these  variations  due  to  the  action  of  light  may  be 
shewn  in  the  intact  body,  by  simply  placing  one  electrode  on  the 
cornea  and  the  other  on  some  portion  of  the  surface  of  the  body.  The 
variations  observed  are  sometimes  positive,  sometimes  negative,  or 
according  to  Dewar  and  Mc  Kendrick,  always  positive  at  first,  becoming 
ne;4ative  as  the  action  of  light  continues  (exhaustion)  with  a  positive 
rebound  upon  the  withdrawal  of  the  light  Currents  may  be  observed 
between  the  sclerotic  and  optic  nerve  after  the  removal  of  the  retina, 
but  these  are  wholly  unaffected  by  light ;  and  the  variations  just 
described  as  brought  about  by  light  appear  to  be  in  proportion  to  the 
functional  activity  of  the  retina.  It  would  thus  appear  that  the  inci- 
dence of  light  on  the  retina  produces  electrical  changes  comparable  to 
those  resulting  from  the  stimulation  of  an  ordinary  nerve  ;  the  fact 
that  the  changes  frequently  appear  in  the  form  of  a  '  positive'  instead 
of  a  '  negative  variation '  may  in  the  present  state  of  our  knowledge  of 
nerve-currents  be  fairly  considered  as  of  secondary  importance. 

Holmgren'  has  shewn  that  these  retinal  currents  arc  manifested 
with  undiminished  energy  in  eyes  in  which  the  visual  purple  has  been 
completely  bleached,  and  on  the  other  hand  that  the  visual  purple  may 
continue  to  exist  and  to  remain  purple  long  after  the  retinal  currents 
have  disappeared. 

Siviple  Sensations. 

Relations  of  the  Sensation  to  the  Stimulus.  If  we 
put  asiile  for  the  present  all  questions  of  colour,  we  may  say  that 
light,  viewed  as  a  stimulus  affecting  the  retina,  varies  in  intensity, 
that  is,  in  the  energy  of  the  luminous  vibrations  as  manifested  by 
their  amplitude,  and  in  duration,  that  is,  in  the  length  of  time  a 
succession  of  waves  continue  to  fall  upon  the  retina.  The  effect 
of  the  light  will  also  depend  on  the  extent  of  retinal  surface 
exposed  to  the  luminous  vibratioiis  at  the  same  time.  Taking  a 
luminous  point,  in  order  to  eliminate  the  latter  circumstance,  we 
may  make  the  following  statements. 

The  sensation  has  a  duration  much  greater  than  that  of  the 

'  Untersuch.  Physiol,  hut.  Hcidd.,  Bd.  ii.  (1S7S)  p.  81. 


540  VISUAL   SENSATIONS.  [BOOK   III. 

stimulus,  and  in  this  respect  is  comparable  to  a  muscular  con- 
traction caused  by  such  a  stimulus  as  a  single  induction  shock. 
The  sensation  of  a  flash  of  light  for  instance  lasts  for  a  much 
longer  time  than  that  during  which  luminous  vibrations  are  falling 
on  the  retina.  Hence  when  two  stimuli,  such  as  two  flashes  of 
light,  follow  each  other  at  a  sufficiently  short  interval,  the  two 
sensations  are  fused  into  one ;  and  a  luminous  point  moving 
rapidly  round  in  a  circle  gives  rise  to  the  sensation  of  a  continuous 
circle  of  light.  This  again  is  quite  comparable  to  muscular 
tetanus.  The  interval  at  which  fusion  takes  place,  that  is  the 
interval  between  successive  stimuli  which  must  be  exceeded  in 
order  that  successive  distinct  sensations  may  be  produced,  varies 
according  to  the  intensity  of  the  light,  being  shorter  with  the 
stronger  light ;  with  a  faint  light  it  is  about  ^o  ^^c-)  '^^^^'^  ^  strong 
light  ^Q  or  Jq-  sec.  This  may  be  shewn  by  rotating  rapidly  before 
the  eye  a  disc  arranged  with  alternate  black  and  white  sectors  of 
equal  width.  With  a  faint  illumination,  the  flickering  indicative 
of  the  successive  sensations  from  the  white  sectors  not  being 
completely  fused,  ceases  when  the  rotation  becomes  so  rapid  that 
each  pair  of  black  and  white  sectors  takes  only  —^  sec.  in  passing 
before  the  eye.  When  a  brighter  illumination  is  used  the  rapidity 
must  be  increased  before  the  flickering  disappears.  That  part  of 
the  sensation  which  is  recognized  as  lasting  after  the  cessation  of 
the  stimulus  is  frequently  spoken  of  as  the  '  after-image.' 

Though  the  sensation  is  longer  with  a  stronger  light  (that  from 
looking  at  the  sun  lasting  for  some  time)  the  commencement  of  the 
decline  begins  relatively  earlier,  hence  the  greater  difficulty  in  the 
complete  fusion  of  successive  sensations  with  the  brighter  light.  The 
interval  at  which  fusion  takes  place  differs  with  different  colours, 
being  shortest  with  yellow,  intermediate  with  red,  and  longest  with 
blue. 

The  duration  of  a  stimulus  necessary  to  call  forth  a  sensation 
is  exceedingly  short,  that  is  to  say,  the  number  of  vibrations 
which  must  fall  on  the  retina  in  order  to  atfect  consciousness  may 
be  exceedingly  small.  Thus  the  shortest  possible  flash,  such  as 
that  of  an  electric  spark,  gives  rise  to  a  sensation  of  light. 

Objects  in  motion  when  illuminated  by  a  single  electric  spark 
appear  motionless,  the  stimulus  of  the  light  reflected  from  them 
ceasing  before  they  can  make  an  appreciable  change  in  their  position. 
When  a  moving  body  is  illuminated  by  several  rapid  flashes  in  succes- 
sion, several  distinct  images  corresponding  to  the  positions  of  the 
body  during  the  several  flashes  are  generated  :  the  images  of  the 
body  corresponding  to  the  several  flashes  fall  on  different  parts  of  the 
retina. 


^"A''-   "1  SIGHT.  ^^I 

f.nP^  f",^""!-  °^  '^'^  sensation  varies  with  the  luminous  in- 
tcns  ty  of  the  ol.ject;  a  wax  cndle  appears  brighter  than  a  rush- 
light. I  he  ratio  however,  of  the  sensation  to  the  stimulus  is  not 
a  smiplc  one.     If  the  luminosity  of  an  object  be  gradually  in- 

founf  t  aTth  ""'  '^"^"^^  r^'  ^°  '  '^'y  ^^'S»^^  °-'  i^  -ifl  be 
to  <  hat  the  corresponding  sensations,  though  they  likewise 
gradually  increase,  mcrease  less  and  less  slowly  than  the  lumi- 
nosity;  and  at  last  an  mcrease  of  the  luminosity  produces  no 
certl'l  ',;■"""''  °f  «---tion;  a  light  when  it  reaches  a 
certain  brightness   appears  so  bright  that  we  cannot  tell  when  it 

slight  difference  ot  brightness  between  two  feeble  lights  tiian  the 
same  difterence  between  two  bright  lights;  we  can  Easily  tell  the 
diflerence  between  a  rushlight  and  a  wax  candle;  but  two  suns 
one  of  which  differed  from  tlie  other  merely  by  jlist  the  numbe; 
of  luminous  rays  which  a  wax  candle  emits  in  addition  to  those 
sent  forth  by  a  rushlight,  would  appear  to  us  to  have  exactly  the 
T.7u  ''''?  ;^""^-  I"  ^  ^^'^^^^^^^  ^oom  an  object  placed  before  a 
candle  will  throw  what  we  consider  a  deep  shadow  on  a  sheet  of 

m 'fnli'  o  '  ?K ^        '"  ''^' u""-     ^^'  ^^"■^^■^^'  ^'^e  ^""''S'^t  be  allowed 
o  tall  on  the  paper  at  the  same  time  from  the  opposite  side,  the 

tu  rV\''^ f'"'^^''.  "^''^''-  ^^'  ^'"■^^^"^'^  l^^twe^"  the  'total 
light  reflected  from  that  part  of  the  paper  where  the  sliadow  was, 

th^rt  f  ;^^>llt'mmated  by  the  sun  alone,  and  that  reflected  fronJ 
h.  .K  ^''■^^'  '7''^^'^  ''  illuminated  by  the  candle  as  well  as 

tha  difference"""  """  ^  '"''''  ^^"  "^  ^°"^'^^  '-^1^1^^--^^ 

on  a  Vhito^W.';""'^'  'f  "''"^  '^"°  rushlights  we  throw  two  shadows 
on  a  \hite  buifacc  and  move  one  rushlight  away  until  the  shadow 
Sit  LdToh?''^  be  v,sible;  and,  having  noted  thj  distance  to 
Snd  4  •  :  .^  c.  ur''Tu'  'T""^  '^"  '^""^  experiment  with  two  wax 
as  tl  eVus  li' n  {"'V'^f  '''"-^"Y  ^^"^'<^  ^^'  '°  be  moved  just  as  far 
Sthintoe  h  ■  "r^'''''  ''u''  ^'^""^  ^y  ^'-^'-^^"^'l  observation,  that 
within  toleiably  wide  limits,  the  smallest  difference  of  IJc^ht  which  we 

TZ^ZT^  "'^  •'"""'  sensations  is  a  constant  fraction  (alou'Lh^ 
?e^ard  to  hi  l^j^'nos.ty  employed.  The  same  law  holds  good"w  th 
regard  to  the  other  senses  as  well.  The  smallest  difference  in  len-h 
m  le   I'ii'^h''  '^'^^^^■^^"/".•°  li"-^.  one  an  inch  long  and  t'le  ofc  a 

simlh  1  di  r  '"  ''"  "J'^^'  1'  ^'"'-^  ^^'"''^  f'-'^'^^'""  °f  '-^n  inch,  that  the 
smallest  d  iferen-e  in  length  wc  can  detect  between  a  line  a  foot  Ion- 
and  one  ah  tie  less  than  a  foot,  is  of  a  foot.  Put  in  a  more  "cneral 
form  then  the  law,  which  is  often  called  Weber's  la^"  Is  as  fallows 
Tn  wh.'-hTo  c^."  continually  increased,  the  smallest  increase  of  e'sa^ 
on  \Mi.h  we  can  appreciate  remains  the  same  so  Ion-  as  the  nrouor- 
tion  which  the  increase  of  the  stimulus  bears  to  the  who  e  s  nu  us 
remains  the  same  ;  that  is  to  say,  the  one  varies  directly  as  the  other! 


542  VISUAL   SENSATIONS.  [BOOK  III. 

Fechner,  regarding  sensation  as  the  summation  of  a  series  of  incre- 
ments of  sensation  corresponding  to  increments  of  stimulus,  made 
use  of  the  fact  that  when  the  stimulus  is  continually  diminished  a 
point  is  reached  at  which  no  sensation  whatever  follows,  or  in  other 
words,  that  there  is  a  certain  strength  of  the  stimulus  which  must  be 
exceeded  before  any  sensation  at  all  can  be  produced.  By  the  intro- 
duction of  this  'liminal  intensity' of  the  stimulus,  he  transformed, 
with  the  help  of  the  mathematical  operation  of  integration  Weber's  law, 
which  is  only  an  expression  .of  the  relation  of  increments  of  stimulus 
and  sensation,  into  a  formula  spoken  of  as  Fechner's  formula  or 
Fechner's  law,  which  is  offered  as  a  measure  of  the  sensation  in  terms 
of  the  stimulus  in  the  general  form  that  '  the  sensation  varies  as  the 
logarithm  of  the  stimulus".  Independent  however  of  the  important 
fact  that  Weber's  Jaw  ceases  to  hold  good  when  the  stimulus  is  either 
very  small  or  very  great,  i.e.  fails  exactly  at  the  point  at  which  Fechner 
makes  use  of  it,  there  are  serious  objections  to  the  validity  of  Fechner's 
formula  ^ 

Distinction  and  Fusion  of  Sensations.  When  light 
falls  on  a  large  portion  of  the  retina  the  total  sensation  produced 
is  greater  m'amotmt  than  when  a  small  portion  only  of  the  retina 
is  affected ;  a  large  piece  of  white  paper  produces  a  greater  total 
effect  on  our  consciousness  than  a  small  one,  though,  if  the 
surfaces  be  uniformly  and  equally  illuminated,  the  inteJisity  of  the 
sensation  is  in  each  case  the  same ;  the  small  piece  of  paper 
appears  as  bright  or  as  'white'  as  the  large  one.  If  the_ images 
of  two  luminous  objects  fall  on  the  retina  at  sufficient  distances 
apart,  the  consequent  sensations  are  distinct,  and  the  intensity  of 
each  sensation  will  depend  solely  upon  the  luminosity  of  the 
corresponding  object.  If  however  the  two  objects  are  made  to 
approach  each  other,  a  point  will  be  reached  at  which  the  two 
sensations  are  fused  into  one.     When  this  occurs  the  intensity  of 

^  Weber's  law  may  be  stated  mathematically  as  a6"  =  -K—,  where  AS  is  the 

smallest  appreciable  increment  of  sensation  caused  by  Ax,  the  corresponding 
increment  of  the  -timulus  x,  and  A' is  a  constant, 

If  the  increment  be  regarded  as  indefinitely  small  and  the  equation  then  be 

integrated  we  eet 

S  -  Klogx  ^  c. 
If  ;»:  be  diminished  there  will  be  a  certain  value   (liminal  intensity)  of  x  at 
which  all  sensation  ceases  ;  if  this  be  x',  then 
o  —  K  log  x'  +  c, 
or  c  -   -  K\og  xf, 

whence  S  -  K\ogx  -  K log  x'. 

X 

.5'  = /nog-,, 

which  is  Fechner's  more  complete  formula. 

^  Cf.  Coutts  Trotter,  Journ.  Physiol.,  I.  (1878)  p.  60, 


CMAl'.   II.]  SIGHT.  543 

the  total  sensation  produced  will  be  greater  than  that  of  either  of 
the  sensations  caused  by  tlie  single  objects.  A  number  of 
luminous  points  scattered  over  a  wide  surface  would  appear  eacli 
to  have  a  certain  brightness ;  each  would  give  rise  to  a  sensation 
of  a  certain  intensity.  If  they  were  all  gathered  into  one  spot, 
that  sput  would  appear  far  brighter  than  any  of  the  previous 
points ;  the  intensity  of  the  sensation  would  be  greater.  We  may 
therefore  suppose  the  retina  to  be  divided  into  areas  corresponding 
to  sensational  units.  If  the  images  from  two  luminous  objects 
fall  on  separate  visual  areas,  if  we  may  so  call  them,  two  distinct 
sensations  will  be  produced ;  if,  on  the  contrary,  they  both  fall  on 
the  same  visual  area,  one  sensation  only  will  be  produced.  Where 
the  sensations  are  separate,  the  intensity  of  the  one  (with  ex- 
ceptions hereafter  to  be  mentioned)  is  not  aftected  by  the  presence 
of  the  other ;  but  where  they  become  fused  the  intensity  of  the 
united  sensations  is  greater  tiian  either  of,  though  not  equal  to  the 
sum  of,  the  single  sensations.  The  existence  of  these  sensational 
units  is  the  basis  of  distinct  vision.  When  we  speak  of  the 
smallest  size  visible  or  distinguishable,  we  are  referring  to  the 
dimensions  of  the  retinal  areas  corresponding  to  these  sensational 
units.  The  retinal  area  must  be  carefully  distinguished  from  the 
sensational  unit,  for  the  sensation  is,  as  we  have  seen,  a  process 
whose  arena  stretches  from  the  retina  to  certain  parts  of  the  brain, 
and  the  circumscription  of  the  sensational  unit,  though  it  must 
begin  as  a  retinal  area,  must  also  be  continued  as  a  cerebral  area 
in  the  brain,  the  latter  corresponding  to,  and  being  as  it  were  the 
projection  of,  the  former.  With  most  people  two  stars  appear  as 
a  single  star  when  the  distance  between  them  subtends  an  angle 
of  less  than  60  seconds ;  and  Weber  found  that  the  best  eyes 
failed  to  distinguish  two  parallel  white  streaks  when  the  distance 
between  the  two,  measured  from  the  middle  of  each,  subtended 
an  angle  of  less  than  73  seconds.  Hirschmann'  could  distinguish 
objects  50  seconds  distant  from  each  other.  An  angle  of  73 
seconds  in  an  object  corresponds  in  the  diagrammatic  eye  (see 
p.  512)  to  the  length  of  5*36  fx  in  the  retinal  imaged  and  one  of 
50  seconds  to  yO^  p. 

Max  Schultzc^  counted  in  the  human  eye  50  cones  along  a  line  of 
200 /z  i/i  icn^^'th  drawn  through  the  centre  of  the  yellow  spot  ;  this  would 
give  4/x  for  the  distance  between  the  centres  of  two  adjoining  cones  in 
the  yellow  spot,  the  average  diameter  of  a  cone  at  its  widest  part  being 
3  H  and   there  being   slight   intervals    between  neighbouring    cones. 

'  Quoted  by  Hclinhollz,  P/tys.  Optik,  p   S41. 
'  by  ^  is  meant  one-thousandth  of  a  millimetre. 
•''  Strieker,  Han.ibuch,  p.  1023. 


544  VISUAL   SENSATIONS.  [BOOK   III. 

Hence  if  we  take  the  centre  of  a  cone  as  the  centre  of  an  anatomical 
retinal  area,  these  anatomical  areas  correspond  very  fairly  to  the 
physiological  visual  areas  as  determined  above.  That  is  to  say,  if  two 
points  of  the  retinal  image  are  less  than  4.fjL  apart,  they  may  both  lie 
within  the  area  of  a  single  cone  ;  and  it  is  just  wheii  they  are  less  than 
about  4/i  apart  that  they  cease  to  give  rise  to  two  distinct  sensations. 
It  must  be  remembered,  however,  that  the  fusion  or  distinction  of  the 
sensations  is  ultimately  determined  by  the  brain  and  not  by  the  retina. 
Two  points  of  the  retinal  image  less  than  4 /x  apart  might  lie  both 
within  the  area  of  a  single  cone  ;  but  the  reason  why,  under  such 
circumstances,  they  give  rise  to  one  sensation  only  is  not  because  one 
cone-fibre  only  is  stimulated.  Two  points  of  a  retinal  image  might  lie, 
one  on  the  area  of  one  cone  and  another  on  the  area  of  an  adjoining 
cone,  and  still  be  less  than  4.^  apart  ;  in  such  a  case  two  cone-fibrco 
would  be  stimulated,  and  yet  only  one  sensation  would  be  produced. 
So  also  in  the  less  sensitive  pei'ipheral  parts  of  the  retina  two  points  of 
the  retinal  image  might  stimulate  two  cones  a  considerable  distance 
apart,  and  yet  give  rise  to  one  sensation  only. 

In  the  case  where  the  tv/o  points  lie  entirely  within  the  area  of  a 
single  cone,  it  is  exceedingly  probable  that,  even  if  the  adjacent  cones 
or  cone-fibres  in  the  retina  are  not  at  the  same  time  stimulated, 
impulses  radiate  from  the  cerebral  ending  of  the  excited  cone  into  the 
neighbouring  cerebral  endings  of  the  neighbouring  cones  ;  in  other 
words,  the  sensation-area  in  the  brain  does  not  exactly  correspond  to 
and  is  not  sharply  defined  like  the  retinal  area,  but  gradually  fades 
away  into  neighbouring  sensation-areas.  We  may  imagine  two  points 
of  the  retinal  image  so  far  apart  that  even  the  extreme  margins  of 
their  respective  cerebral  sensation  areas  do  not  touch  each  other  in  the 
least  ;  in  such  a  case  there  can  be  no  doubt  about  the  two  points 
giving  rise  to  two  sensations.  We  might,  however,  imagine  a  second 
case  where  two  points  were  just  so  far  a,part  that  their  respective 
sensation-areas  should  coalesce  at  their  margins,  and  yet  that  in 
passing  from  the  centre  of  one  sensation-area  to  the  centre  of  the 
other,  we  should  find  on  examination  a  considerable  fall  of  sensation 
at  the  junction  of  the  two  areas ;  and  in  a  third  case  we  might  imagine 
the  two  centres  to  be  so  close  to  each  other  that  in  passing  from  one  to 
the  other  no  appreciable  diminution  of  sensation  could  be  discovered. 
In  the  last  case  there  would  be  but  one  sensation,  in  the  second  there 
might  still  be  two  sensations  if  the  marginal  fall  were  great  enough, 
even  though  the  areas  partially  coalesced.  Thus,  though  the  mosaic  of 
rods  and  cones  is  the  basis  of  distinct  vision,  the  distinction  or  fusion  of 
two  visual  impulses  is  ultimately  determined  by  the  disposition  and 
condition  of  the  cerebral  centres.  Hence  the  possibility  of  increasing 
by  exercise  the  faculty  of  distinguishing  two  sensations,  since  by 
use  the  cerebral  sensation-areas  become  more  and  more  differentiated. 
This  however  is  even  more  strikingly  shewn  in  touch  than  in  sight. 

Colour  Sensationss 

When  we  allow  sunlight  reflected  from  a  cloud  or  sheet  of 
paper  to  fall  into  the  eye  we  have  a  sensation  which  we  call  a 


CIIAr.   II.]  SIGHT.  545 

sensation  of  while  lii^ht.  Wiien  we  look  at  the  same  light  through 
a  prism,  and  aUow  different  parts  of  the  spectrum  to  fall  in  suc- 
cession into  the  eye,  we  have  sensations  which  we  call  respectively 
sensations  of  red,  yello\v,  green  and  blue  light.  In  other  words, 
rays  of  li.nht  falling  on  the  retina  give  rise  to  different  sensations, 
according  to  tlie  wave-lengths  of  the  rays.  Though  we  speak  of 
the  spectrum  as  consisting  of  a  few  colours — red,  green,  &c.,  there 
are  an  almost  infinite  number  of  intermediate  tints  in  the  spectrum 
itself;  and  we  jjcrceive  in  external  nature  a  large  number  of 
colours,  such  as  purple,  brown,  grey,  &c.,  which  do  not  correspond 
to  any  of  the  colour  sensations  gained  by  regarding  the  successive 
parts  of  the  spectrum.  We  find  however,  on  examination,  that 
many  apparently  distinct  colour  sensations  may  be  obtained  by 
the  fusion  of  two  or  more  other  colour  sensations.  Thus  purplo, 
which  is  not  present  in  the  spectrum,  may  be  at  once  produced 
by  fusing  the  sensations  of  blue  and  red  in  proper  proportions ; 
and  the  various  tints  and  shades  of  nature  may  be  imitated  by 
fusing  a  particular  colour  sensation  with  the  sensation  of  white,  or 
by  allowing  a  certain  quantity  of  light  of  a  particular  colour  to 
fall  sparsely  over  the  area  of  the  retina,  which  is  at  the  same  time 
protected  from  the  access  of  any  other  light,  i.e.  as  we  say,  by 
mixing  the  colour  with  black.  Thus  the  browns  of  nature  result 
from  various  admixtures  of  yellow,  red,  white  and  black ;  and  a 
small  quantity  of  white  light,  scattered  over  a  large  area  of  the 
retina,  i.e.  white  largely  mixed  with  black,  forms  a  grey.  In  fact, 
the  qualities  of  a  colour  depend  (i)  on  the  nature  of  the  prismatic 
colour  or  colours  falling  on  a  given  area  of  the  retina,  i.e.  on  the 
wave-lengths  of  the  constituent  rays;  (2)  on  the  amount  of  this 
coloured  light  which  falls  on  the  area  of  the  retina  in  a  given 
time;  and  (3)  on  the  amount  of  white  light  fldling  on  tlie  same 
area  at  the  same  time.  When  rays  corresi)onding  to  a  prismatic 
colour  fall  upon  the  retina  unaccompanied  by  any  white  light,  the 
colour  is  said  to  be  'saturated';  and  a  colour  is  spoken  of  as 
more  or  less  saturated  according  as  it  is  mixed  with  less  or  more 
white  light.  We  are  guided  by  the  first  of  the  above  conditions 
when  we  describe  a  colour  as  being  of  such  a  tint  or  hue.  But 
we  have  no  common  phrases  by  which  we  distinguish  the  second 
of  the  above  conditions  from  the  third.  The  word  '  pale,'  it  is 
true,  is  most  frequently  used  to  express  a  colour  very  slightly 
saturated;  but  the  words  'rich'  or  'deep'  are  used  sometimes  as 
meaning  highly  saturated,  sometimes  as  meaning  simply  that  a 
large  quantity  of  light  of  the  particular  hue  is  passing  into  the 
eye.  So  also  with  the  phrase  '  bright ' ;  this  we  often  use  when  a 
large  amoimt  of  coloured  and  white  light  fall  at  the  same  time  on 
F-  1^  35 


546  COLOUR   SENSATIONS.  [BOOK  III. 

the  same  retinal  area,  but  we  sometimes  also  use  it  to  express  the 
mere  intensity  of  the  sensation. 

The  best  method  of  fusing  colour  sensations  is  that  adopted  by- 
Maxwell,  of  allowing  two  different  parts  of  the  spectrum  to  fall  on  the 
same  part  of  the  retina  at  the  same  time.  The  use  of  the  pure 
prismatic  colours  eliminates  errors  which  arise  when  pigments,  the 
colours  of  which  are  not  pure,  but  mixed,  are  employed.  And  where 
pigments  are  used,  it  is  the  sensations  which  must  be  mixed  and  not  the 
pigments  themselves.  Thus  while  the  sensations  of  yellow  and  indigo 
when  fused  give  rise  to  a  sensation  of  white,  yellow  and  indigo 
pigments  when  mixed  appear  green  on  account  of  tlieir  reciprocally 
absorbing  part  of  each  other's  colour  ;  the  indigo  particles  absorb  the 
red  of  the  yellow,  and  the  yellow  particles  absorb  the  blue  of  the 
indigo,  so  that  only  gi'een  is  left  for  both  to  reflect.  When  pure 
pigments,  i.e.  pigments  corresponding  as  closely  as  possible  to  the 
prismatic  colours,  are  used,  satisfactory  results  may  be  gained,  either 
by  using  the  reflection  of  the  image  of  one  pigment  so  that  it  falls  on 
the  retina  at  the  same  spot  as  the  direct  image  of  the  other,  or  bj' 
allowing  the  image  of  one  pigment  to  fall  on  the  retina  before  the 
sensation  produced  by  the  other  has  passed  away.  The  first  result  is 
easily  reached  by  Helmholtz's  simple  method  of  placing  two  pieces  of 
coloured  paper  a  little  distance  apart  on  a  table,  one  on  each  side  of  a 
glass  plate  inclined  at  an  angle.  By  looking  down  with  one  eye  on 
the  glass  plate  the  reflected  image  of  the  one  paper  may  be  made  to 
coincide  with  the  direct  image  of  the  other,  the  angle  which  the  glass 
plate  makes  with  the  table  being  adjusted  to  the  distaxce  between  the 
pieces  of  paper.  In  the  second  method,  the  '  colour  top '  is  used  ; 
sectors  of  the  colours  to  be  investigated  are  placed  on  a  disc  made  to 
rotate  very  rapidly,  and  the  image  of  one  colour  is  thus  brought  to 
bear  on  the  retina  so  soon  after  the  image  of  another,  that  the  two 
sensations  are  fused  into  one. 

When  the  sensations  corresponding  to  the  several  prismatic 
colours  are  fused  together  in  various  combinations,  the  following 
remarkable  results  are  brought  about. 

I,  When  red  and  yellow  in  certain  proportions  are  mixed 
together  the  result  is  a  sensation  of  orange,  quite  indistinguishable 
from  the  orange  of  the  spectrum  itself.  Now  the  latter  is  produced 
by  rays  of  certain  wave-length,  whereas  the  rays  of  red  and  of 
yellow  are  respectively  of  quite  a  different  wave-length.  The 
orange  of  the  spectrum  cannot  be  made  up  by  any  mixture  of  tlie 
red  and  the  yellozu  of  the  spectrum  in  the  sense  that  the  red  and 
yellow  rays  can  unite  together  to  form  rays  of  the  same  wave- 
length as  the  orange  rays ;  the  three  things  are  absolutely  different. 
It  is  simply  the  mixed  sensation  of  the  red  and  yellow  which  is  so 
like  the  sensation  of  orange ;  the  mixture  is  entirely  and  absolutely 
a  physiological  one.     And  since  we  must  suppose  that  rays  of 


CHAP.  II.]  siciFT.  5.17 

different  wave-length  give  rise  to  different  sensory  impulses,  and 
that  tlic  sensory  inipuLscs  generated  by  orange  rays  are  different 
from  those  generated  by  red  and  by  yellow  rays,  we  are  led  to 
infer  either  that  the  sensory  impulses  which  rays  of  a  given  wave- 
length originate  are  themselves  of  a  nii.vcd  cliaractcr,  or  that  the 
mixture  takes  place  at  the  time  wlien  the  sensory  impulses  are 
becoming  converted  into  sensations.  The  first  of  these  views  is 
the  one  generally  adopted. 

2.  When  certain  colours  are  mi.xed  together  in  pairs  in  certain 
definite  projjortions,  the  result  is  white.     These  colours  are 

Red  (near  a)^,  and  Blue-Green  (near  F), 

Orange  (near  C),  and  Blue  (between  F  and  G), 

Yellow  (near  D),  and  Indigo- Blue  (near  G), 

Green-Yellow  (near  E),  and  Violet  (between  G  and  H), 

and  are  said  to  be  *  complementary '  to  each  other.  To  these 
might  be  added  the  peculiar  non-prismatic  colour  purple,  which 
with  green  also  gives  white. 

3.  If  we  select  arbitrarily  any  three  distinct  colours,  i.e.  any 
three  parts  of  the  spectrum  sufficiently  far  apart,  .say  red,  green, 
and  blue,  we  can,  by  a  proper  adjustment  of  the  i)roportions  of 
each,  produce  white.  Further,  by  a  proper  addition  of  white, 
these  three  colours  can  be  taken  in  such  proportions  as  to  produce 
the  sensations  of  all  other  colours.  That  is  to  say,  given  three 
standard  sensations,  all  the  other  sensations  may  be  gained  by  the 
proper  mixture  of  these. 

If  we  suppose  that  the  visual  apparatus  is  so  constructed  that 
we  possess  three  standard  sensations,  and  that  rays  of  different 
wave-length  produce  all  three  of  these  sensations  to  a  dift'erent 
extent  according  to  their  wave-length,  we  can  easily  regard  the 
whole  of  our  sensations  of  colour  as  compounds  of  three  "primary 
colour  sensations.'  We  might  thus  represent  our  colour  sensations 
by  such  a  diagram  as  that  given  in  Fig.  56,  where  one  jjrimary  sensa- 
tion is  seen  to  be  produced  in  greatest  intensity  by  the  rays  at  the 
red  end  of  the  spectrum,  the  second  by  those  near  the  middle,  and 
the  third  by  those  at  the  violet  end  of  the  spectrum.  Under  this 
view  orange  rays  are  those  which  produce  much  of  the  first  sensa- 
tion, less  of  the  second,  and  hardly  any  of  the  third  ;  whereas  blue 
rays  produce  much  of  the  third,  less  of  the  second,  and  hardly 
any  of  the  first ;  and  so  on. 

'  TlicbL-  letters  refer  to  Frauenliofer's  lines. 

35—2 


548 


COLOUR   SENSATIONS. 


[BOOK   III. 


This  theory  of  three  primary  colour  sensations  we  owe  to  Young  ; 
but  since  its  general  acceptance  has  been  largely  due  to  the  labours  of 
Helmholtz,  it  is  frequently  spoken  of  as  the  Young-Hehnholtz  theory 
Young's  view  took  the  form  of  the  hypothesis  that  there  were  present 
in  the  retina  three  sets  of  fibres,  each  set  correspondmg  to  a  pnmary 
colour  sensation,  and  beiiTg  sensitive  in  a  different  degree  to  the  various 
rays  of  lic^ht.  In  the  retina  itself  no  such  distinction  of  fibres  can  be 
found  We  are  entirely  in  the  dark  concerning  the  anatomical  basis 
not  only  of  colour  sensations  but  also  of  vision  as  a  whole.  We  have 
reason  to  think,  as  we  have  seen  (p.  529)  that  visual  opuses  are 
started  in  that  part  of  the  retina  which  lies  beyond  the  retinal  blood- 
vessels ;  but  in  the  generation  of  those  impulses  we  can  assign  no 


Fig.  56.    Diagram  of  Three  Primary  Colour  Sensations. 
X  is  the  so-called  '  red,'  2  '  green.'  arrd  3  '  violet '  P"'"^'^  colour  sensation^^O^K.&c^represe^^ 

respectively  excited  by  vibrations  of  different  wave-lengths. 

exact  functions  to  rods  or  cones,  to  rod  fibres  or  cone  fibres  or  to  the 
various  bodies  constituting  the  external  nuclear  layer.  1  he  view  tt^at 
the  cones  rather  than  the  rods  of  the  retina  are  concemed  m  coloui 
lision  cannot  be  regarded  as  established.  The  -,f -^^^^f  • -."^g 
are  absent  from  the  retinas  of  nocturnal  a^"^^f^^'/^7,X%nd7he 
until  it  has  been  proved  that  these  animals  are  colour-blind  and  he 
argument  that  in  the  fovea  centrahs  cones  only  ex  st  may  be  usea 
eSXwell  to  prove  that  the  rods  are  of  no  use  at  all  in  distinct  vision 
iTteTcs  of  Birds,  Reptiles  and  Amphibia,  coloured  globules  are 
lound  in-the  cones  at  the  junction  of  the  inner  and  outer  limbs.  In 
the  fowHlese  c.  obules  occur  in  three  colours,  ruby-red,  orange-yellow 
and  °ixensh  yellow,  and  Kuhne^  has  extracted  three  distinct  p.gmen 
(rhodophane,'xanthophane  and  chlorophane)  which  however  are  but 
verv  feebly  sensitive  to  light.  It  has  been  suggested  that  these 
Sured  /lobules  are  connected  with  ^frJ'T^T.^sTtlZl 
red  globufes,  for  instance,  allowing  red  light  only  to  pass  through 

'  Journal  of  Physiology,  i.  (1878)  pp.  109-189. 


CHAP.   II.]  SIGHT.  549 

the  inher  limb  and  impinge  on  the  outer  limb,  so  that  these 
conc5  would  serve  as  organs  for  seeing  red.  But  this  is  very 
doubtful. 

The  Young- Hclmholtz  theory  has  not  been  accepted  by  all  in- 
quirers. Its  most  serious  opponent  at  the  present  time  is  Hcring', 
who,  following  Aubert*,  and  indeed  Leonardo  da  Vinci,  maintains 
that  the  primary  visuil  sensations  are  white,  black,  red,  yellow,  green, 
and  blue.  He  considers  that  these  several  sensations  arise  as  the 
results  of  changes  in  what  may  be  called  the  visual  substance  of  the 
visual  nervous  apparatus  (see  p.  535),  those  changes  which  give  rise  to 
black,  green,  and  blue  being  essentially  processes  of  assimilation  or 
construction  of  the  visual  substance,  while  those  which  give  rise  to 
white,  red,  and  yellow  arc  processes  of  dissimilation,  or  destruction  of 
the  visual  substance.  Black  and  white,  green  and  reel,  blue  and  yellow, 
form  accordingly  antagonistic  rather  than  complementary  pairs,  and 
the  visual  organ  is  conceived  of  as  never  existing  during  life  in  a  state 
of  complete  rest.  A  satisfactory  discussion  of  the  relative  merits  of 
this  and  of  the  generally  accepted  view,  would  lead  us  beyond  the 
proper  limits  of  this  work,  but  llering  uses  his  view  with  great  ability 
to  explain  the  obscure  phenomena  of  'contrasts'  (see  p.  555)  and 
' negative  images '  (p.  551). 

Admitting,  however,  tliat  the  hypothesis  of  three  primary  colour 
sensations  explains  many  of  tlie  phenomena  of  colour  vision,  there 
still  remains  the  question,  '  What  are  the  three  primary  colour  sen- 
sations ?  '  We  have  spoken  of  any  three  arbitrarily  selected  colour 
sensations  producing  by  manipulation  all  the  other  colour  sensa- 
tions ;  but,  of  what  kind  are  the  three  sensations  which  may  be 
considered  as  the  actual  primary  sensations  ?  We  cannot  enter 
here  into  the  discussion  of  this  question  ;  and  may  simply  state 
that  the  most  generally  accepted  view  is,  that,  the  three  primary 
sensations  correspond  to  what  we  call  red,  green,  and  violet;  and 
in  the  diagram.  Fig.  56,  the  upper  figure  represents  this  primary 
red  sensation,  the  middle  figure  green,  and  the  lower  violet. 

Colour  Blindness.  All  persons  vary  much  in  their  power 
of  discriminating  and  appreciating  colour,  i.e.  in  the  intensity  and 
accuracy  of  their  colour  sensations  ;  but  some  people  regard  as 
similar,  colours  which  to  most  people  are  glaringly  distinct,  and 
these  jjersons  are  said  to  be  'colour  blind.'  The  most  common 
form  of  colour  blindness  is  that  of  persons  unable  to  distinguish 
green  and  red  from  each  other.  As  in  the  case  of  Dalton,  they 
tell  a  red  gown  lying  on  a  green  grass  plot,  or  a  red  cherry  among 
the    green   leaves,    by  its  form,   and    not    by   its    colour.       lliey 

^  Zur  Lehre  vom  Lichtsinnc.      Wicn.   Sitztiiigshcncht,   Lxvi.    (1872)  LXVlil. 
LXIX.    I.XX. 

"  PItysiolooie  ,i^r  Netzliaut.      1865. 


550  COLOUR   SENSATIONS.'  [BOOK   III. 

confound  not  only  red,  brown,  and  green,  but  also  rose,  purple,  and 
blue.  They  cannot  see  the  red  end  of  the  spectrum,  all  this  part 
appearing  to  them  dark.  Their  vision  is  best  explained  by 
supposing  that  they  lack  altogether  the  primary  sensation  of  red. 

Hence  they  probably  see  in  the  spectrum  only  two  colours,  blue 
and  green,  with  various  tints  ;  our  red,  orange,  yellow  and  green 
appearing  green,  and  all  the  rest  blue,  green-blue  being  to  them  a  kind 
of  grey.  Since  the  sensation  of  green  seems  to  be  absolutely  most 
intense  in  that  part  of  the  spectrum  which  we  call  yellow,  though  of 
course  relatively  to  the  other  two  primary  sensations  most  intense  in 
the  green,  our  yellow  probably  corresponds  in  them  to  the  sensation  of 
a  bright  deep  green.  All  the  colours  they  see  can,  in  fact,  be  produced 
by  mixtures  of  yellow  and  blue. 

Cases  in  which  the  other  primary  sensations  may  be  supposed 
to  be  absent,  i.e.  green  blindness  and  violet  blindness  are  much 
more  rare,  and  have  not  as  yet  been  examined  with  sufficient 
completeness. 

Influence  of  the  pigment  of  the  yellow  spot.  In  the  macula  lutea, 
which  part  of  the  retina  we  use  chiefly  for  vision,  images  falhng  on 
other  parts  of  the  retina  being  said  to  give  rise  to  'indirect  vision,' 
the  yellow  pigment  absorbs  some  of  the  greenish-blue  rays.  Hence 
all  that  which  we  are  in  the  habit  of  calling  white  is  in  reality  more 
or  less  yellow.  We  may  use  this  feature  of  the  yellow  spot  for  the 
purpose  of  making  the  spot,  so  to  speak,  visible  to  ourselves,  by  an 
experiment  suggested  by  Maxwell.  A  solution  of  chrome  alum, 
which  only  transmits  red  and  greenish-blue  rays,  is  held  up  between 
the  eye  and  a  white  cloud.  The  greenish-blue  rays'  are  absorbed 
by  the  yellow  spot,  and  here  the  light  gives  rise  to  a  sensation  of 
red  ;  -whereas  in  the  rest  of  the  field  of  vision,  the  sensation  is  that 
ordinarily  produced  by  the  purplish  solution.  The  yellow  spot  is 
consequently  marked  out  as  a  rosy  patch.  This  very  soon  however 
dies  away. 

In  speaking  of  sensation  as  a  function  of  the  stimulus,  p.  539,  we 
referred  to  white  light  only  ;  but  the  different  colours  are  unequal  in 
the  relations  borne  by  the  intensity  of  the  stimulus  to  the  amount  of 
sensation  produced.  Thus  the  more  refrangible  blue  rays  produce  a 
sensation  more  readily  than  the  yellow  or  red  rays.  Hence  in  dim 
lights,  as  those  of  evening  and  moonlight,  the  blues  preponderate,  and 
the  reds  and  yellows  are  less,  obvious.  So  also  when  a  landscape  is 
viewed  through  a  yellow  glass,  the  yellow  hue  suggests  to  the  mind 
bright  sunlight  and  summer  wea'her,  although  the  actual  illumination 
which  reaches  the  eye  is  diminished  by  the  glass.  Conversely  when 
the  same  landscape  is  viewed  through  a  blue  glass  the  idea  of 
moonlight  or  winter  is  suggested. 

The  theory  of  primary  colour  sensations  may  be  used  to  explain 
why  any  coloured  light,  if  made  sufficiently  intense,  appears  white. 
Thus  a  violet  light  of  moderate  intensity  appears  violet  because  it- 
excites  the  primary  sensation  of  violet  much  more  than  those  of  gieen 


CHAP.   II.]  SIGHT.  551 

and  red.  If  llic  stinnilus  be  increased  the  maximum  of  violet 
stimulation  will  be  reached,  while  the  stimulation  of  f,'rccn  will  con- 
tinue to  be  increased  and  oven  that  of  red  to  a  slight  de;4ree.  The 
result  will  be  that  the  light  appears  violet  mixed  with  green,  that 
is  blue.  If  the  stimulus  be  still  further  increased  while  the  green 
and  violet  are  both  excited  to  the  maximum,  the  red  stimulation 
may  be  increased  until  the  result  is  violet,  green  and  red  in  the 
proportions  which  make  white  light.  And  so  with  light  of  other 
colours. 

After-images.  Wc  have  already  seen  that  in  vision  the 
sensation  lasts  much  longer  than  the  stimulus.  Under  certain 
circumstances,  such  as  condition  of  the  eye,  intensity  of  the  stimu- 
lus, &c.,  the  sensation  is  so  prolonged,  that  it  is  spoken  of  as  an 
after-image.  Thus,  if  the  eye  be  directed  to  the  sun,  the  image 
of  that  body  is  present  for  a  long  while  after;  and  if,  on  early 
waking,  the  eye  be  directed  to  the  window  for  an  instant  and  then 
closed,  an  image  of  the  window^  with  its  bright  panes  and  darker 
sashes,  the  various  parts  being  of  the  same  colour  as  the  object, 
will  remain  for  an  appreciable  time.  These  images,  which  are 
simply  continuations  of  the  sensation,  are  spoken  of  as  positive 
aftcr-iinages.  They  are  best  seen  after  a  momentary  exposure  of 
the  eye  to  the  stimulus. 

When,  however,  the  eye  has  been  for  some  time  subject  to  a 
stimulus,  the  sensation  which  follows  the  withdrawal  of  the  stimu- 
lus is  of  a  different  kind  ;  what  is  called  a  negative  afier-image,  or 
negative  image,  is  produced.  If,  after  looking  steadfastly  at  a  white 
patch  on  a  black  ground,  the  eye  be  turned  to  a  white  ground,  a 
grey  patch  is  seen  for  some  little  time.  A  black  patch  on  a  white 
ground  similarly  gives  rise  on  a  grey  ground  to  a  negative  image 
of  a  white  patch.  This  may  be  explained  as  the  result  of  exhaus- 
tion. When  the  white  patch  has  been  looked  at  steadily  for  some 
time,  that  part  of  the  retina  on  which  the  image  of  the  patch  fell 
becomes  tired ;  hence  the  white  light  coming  from  the  white 
ground  subsec][uently  looked  at,  which  falls  on  this  part  of  the 
retina,  does  not  produce  so  much  sensation  as  in  other  parts  of 
the  retina  ;  and  the  image,  consequently,  appears  grey.  And  so 
in  the  other  instance,  the  whole  of  the  retina  is  tired,  except  at  the 
patch;  here  the  retina  is  for  a  while  most  sensitive,  and  hence  the 
white  negative  image. 

When  a  red  patch  is  looked  at,  the  negative  image  is  a  green 
blue,  that  is,  the  colour  of  the  negative  image  is  complementary 
to  that  of  the  object.  Thus  also  orange  produces  a  blue,  green  a 
pink,  yellow  an  indigo-blue,  negative  image;  and  so  on.  This 
too  can  be  explained  as  a  result  of  exhaustion.   When  the  coloured 


552  VISUAL   PERCEPTIONS.  [BOOK   III. 

patch  is  looked  at,  one  of  the  primary  colour  sensations  is  much 
exhausted,  and  the  other  two  less  so,  in  varying  proportions,  ac- 
cording to  the  exact  nature  of  the  colour  of  the  patch  ;  and  the 
less  exhausted  sensations  become  prominent  in  the  after-image. 
Thus,  the  red  patch  exhausts  the  red  sensation,  and  the  negative 
image  is  made  up  chiefly  of  green  and  blue  sensations,  that  is, 
appears  to  be  greenish  blue,  or  bluish  green,  according  to  the  tint 
of  the  red.  Similarly,  when  the  eye,  after  looking  at  a  coloured 
patch,  is  turned  to  a  coloured  ground,  the  effects  may  easily  be 
explained  by  reference  to  the  comparative  exhaustion  of  the  colour 
sensations  excited  by  the  patch  and  the  ground  respectively ;  if  a 
yellow  (i.e.  a  green  and  red)  ground  be  chosen  after  looking  at  a 
green  object,  the  negative  image  will  appear  of  a  reddish  yellow, 
and  so  on. 

What  is  not  so  clear  is  why  negative  images,  should  make  their 
appearance  without  any  subsequent  stimulation  of  the  retina.  When 
the  eyes  are  shut  and  all  excess  of  light,  even  through  the  eyelids, 
carefully  avoided,  the  field  of  vision  is  not  absolutely  dark;  there  is  still 
a  sensation  of  light,  the  so-called  'proper  light'  of  the  retina.  If  a 
white  patch  on  a  black  ground  be  looked  at  for  some  time,  and  the 
eyes  then  shut,  a  negative  (black)  image  of  the  spot  will  be  seen  on 
the  ground  of  the  '  proper  light '  of  the  retina,  having  in  its  immediate 
neighbourhood  a  specially  bright  corona.  So  also,  if  a  window  be 
looked  at  and  the  eyes  then  closed,  the  positive  after-image  with 
bright  panes  and  dark  sashes  gives  rise  to  a  negative  after-image 
with  bright  sashes  and  dark  panes  ;  and  similar  effects  appear  with 
colours.  Plateau'  has  attempted  to  explain  the  various  pheno- 
mena of  after-images  by  supposing  oscillations  to  take  place  in  some 
part  of  the  visual  apparatus ;  but  the  matter  is  surrounded  with 
difficulties^ 

Sec.  3.     Visual  Perceptions. 

Hitherto  we  have  studied  sensations  only,  and  have  considered 
an  external  object,  such  as  a  tree,  as  simply  a  source  of  so  many 
distinct  sensations,  differing  from  each  other  in  intensity  and  kind 
(colour).  In  the  mind  these  sensations  are  coordinated  into  a  per- 
ception. We  are  not  only  conscious  of  a  number  of  sensations  of 
bright  and  dim  lights,  of  green,  brown,  black,  &c.,  but  these 
sensations  are  so  related  to  each  other  and  by  virtue  of  cerebral 
processes  so  fashioned  into  a  whole,  that  we  '  see  a  tree.'  We 
sometimes,  in  illustration  of  such  an  effect  speak  of  an  image  or 
picture  in  the  mind  corresponding  to  the  physical  image  on  the 
retina. 

'   Theorie  gdn.  des  Apparences  visitelles.     Bruxelles,  1834. 
'  Cf.  Hering,  op.  cit. 


CllAl'.    II.]  SIGHT.  553 

When  we  look  upon  the  external  world,  a  variety  of  images  are 
formed  at  the  same  time  on  the  retina,  and  give  rise  to  a  nimiber 
of  contemporaneous  visiKil  sensations.  The  sum  of  these  sensa- 
tions constitutes  '  the  field  of  vision,'  which  varies  of  course  with 
every  movement  of  the  eye.  This  field  of  vision,  being  in  reality 
an  aggregate  of  sensations,  is  of  course  a  subjective  matter  ;  but  we 
are  in  the  habit  of  using  the  same  phrase  to  denote  the  sum  of 
e.xternal  objects  which  give  rise  to  the  aggregate  of  visual  sensa- 
tions;  in  common  language  the  field  of  vision  is  'all  that  we  can 
see '  m  any  position  of  the  eye,  and  we  have  a  field  of  vision 
for  each  eye  separately  and  for  the  two  eyes  combined. 

Using  for  the  present  the  words  in  their  subjective  sense,  we 
may  remark,  that  we  are  able  to  assign  to  each  constituent  sensa- 
tion its  place  among  the  aggregate  of  sensations  constituting  the 
field  of  vision ;  we  can,  as  we  say,  localise  the  sensation.  We  can 
say  whether  it  belongs  to  (what  we  regard  as)  the  right-hand  or 
left-hand,  the  upper  or  the  lower  part,  of  the  field  of  vision.  We 
are  able  to  distmguish  the  relative  positions  of  any  two  distinct 
Sensations  ;  and  the  relative  positions,  together  with  the  relative 
intensities  and  qualities  (colour)  of  the  sensations  arising  from 
any  object  deierniine  our  perception  of  the  object.  It  need  hardly 
be  remarked  that  this  localisation  is  purely  subjective.  We  simply 
determine  the  position  of  the  sensation  in  the  field  of  vision 
(which  is  itself  a  wholly  subjective  matter) ;  we  do  not  determine 
the  position  of  the  object.  The  connection  between  the  position 
of  the  object  in  the  external  world  and  the  position  of  the  sensa- 
tion in  the  field  of  vision,  cannot  be  determined  by  visual  observa- 
tion alone.  All  the  information  which  can  be  gained  by  the  eye 
is  limited  to  the  field  of  vision,  and  provided  that  the  relative 
position  of  the  sensations  in  the  field  of  vision  remained  the  same, 
the  actual  position  of  external  objects  might,  as  far  as  vision  is 
concerned,  be  changed  without  our  being  aware  of  it. 

As  a  matter  of  f;ict  the  field  of  vision  in  one  important  particular 
docs  not  correspond  to  the  field  of  e.xternal  objects.  The  image  on 
the  retina  is  inverted  ;  the  rays  of  light  proceeding  from  an  object 
which  by  touch  we  know  to  be  on  what  we  call  our  right  hand,  faJl  on 
the  left-hand  side  of  the  retina.  It  therefore  the  field  of  vision  corre- 
sponded to  the  retinal  image,  the  object  would  be  seen  on  the  left 
hand.  We  however  sec  it  on  the  right  hand,  because  we  invariably 
associate  right-hand  tactile  localisation  with  left-hand  visual  localisa- 
tion;  that  is  to  say,  our  field  of  vision,  when  interpreted  by  touch,  is 
a  re-inversion  of  the  retinal  image. 

The  dimensions  of  the  field  of  vision  of  a  single  eye  are  about 
145°  for  the  horizontal  and    100°  from  the  vertical  meridian,  the 


554  VISUAL   PERCEPTIONS.  [BOOK   III. 

former  being  distinctly  greater  than  tiie  latter.  The  horizontal 
dimension  of  the  field  of  vision  for  the  two  eyes  is  about  iJ5o°. 
By  movements  of  the  eyes,  however,  apart  from  those  of  the  head, 
the  extent  may  be  increased  to  260°  in  the  horizontal  and  200°  in 
tire  vertical  direction. 

The  satisfactory  perception  of  external  objects  requires  distinct 
vision  ;  and  of  this,  as  we  have  already  said,  the  formation  of  a 
distinct  image  on  the  retina  is  an  essential  condition.  We  can 
receive  visual  sensations  of  all  kinds  with  the  most  imperfec- 
dioptric  apparatus,  but  our  perception  of  an  object  is  precise  in 
proportion  to  the  clearness  of  the  image  on  the  retina. 

Region  of  Distinct  Vision.  If  we  take  two  points,  such 
as  two  black  dots,  only  just  so  far  apart  that  they  can  be  seen  dis- 
tinctly as  two  when  placed  near  the  axis  of  vision,  and  then, 
keeping  the  axis  fixed,  move  the  two  points  out  into  the  circum- 
ferential parts  of  the  field  of  vision,  it  will  be  found  that  the  two 
soon  appear  as  one.  The  two  sensations  become  fused,  as  they 
would  do  if  brought  nearer  to  each  other  in  the  centre  of  the  field. 
The  farther  away  from  the  centre  of  the  field,  the  farther  apart 
must  two  points  be  in  order  that  they  may  be  seen  as  two.  In 
other  words,  vision  is  much  more  distinct  in  the  centre  of  the  field 
than  towards  the  circumference.  Practically  the  region  of  distinct 
vision  may  be  said  to  be  limited  to  the  macula  lutea,  or  even  to 
the  fovea  centralis ;  by  continual  movements  of  the  eye  we  are 
constantly  bringing  any  object  wliich  we  wish  to  see  in  such  a 
position  that  its  nnage  falls  on  this  region  of  the  retina. 

The  diminution  of  distinctness  does  not  take  place  equally  from 
the  centre  to  the  circumference  along  all  meridians.  The  outline 
described  by  a  line  uniting  the  points  where  two  spots  cease  to  be  seen 
as  two  when  moved  along  different  radii  from  the  centre,  is  a  very 
irregular  figure. 

The  sensations  of  colour  are  much  more  distinct  in  the  centre  of 
the  retina,  than  towards  the  circumference.  If  the  visual  axis  be 
fixed  and  a  piece  of  coloured  paper  be  moved  towards  the  outside  of 
the  field  of  vision,  the  colour  undergoes  changes  and  is  eventually 
lost,  red  disappearing  first,  then  green,  and  blue  last.  A  purple  colour 
becomes  blue,  and  a  rose  colour  a  bluish  white.  In  fact,  there  seems 
to  be  a  certain  amount  of  red-blindness  in  the  peripheral  parts  of  all 
retinas. 

Modified  Perceptions. 

Since  our  perception  of  external  objects  is  based  on  the  distinct- 
ness of  the  sensations  which  go  to  form  the  perception,  it  might 
be  expected  that  when  an  image  of  an  object  is  formed  on  the 


ciiAi'.  ii.J  sicirr.  555 

retina  the  sensory  impulses  will  correspond  to  the  retinal  image, 
the  sensations  corrcs])onfl  (o  the  sensory  impulses  and  the  percep- 
tion corresponding  to  the  sensations,  and  that  therefore  the  mental 
condition  resultint^  from  our  looking  at  any  object  or  view  would 
corrcsjwnd  exactly  to  the  retinal  image.  We  find,  however,  that 
this  is  not  the  case.  The  sensations  and  probably  even  the  sim[)le 
sensory  impulses  produced  by  an  image  react  upon  each  other, 
and  these  reactions  modify  our  perceptions,  independently  of  the 
jihysical  conditions  of  the  retinal  image.  There  arise  certain  dis- 
crepancies between  the  retinal  image  and  the  perception,  some 
having  their  source  in  the  retina,  some  in  the  brain,  and  others 
being  of  such  a  nature,  that  it  is  difficult  to  say  where  the 
irrelevancy  is  introduced. 

Irradiation.  A  white  patch  on  a  dark  ground  appears  larger, 
and  a  dark  patch  on  a  white  ground  smaller,  than  it  really  is.  This 
is  especially  so  when  the  object  is  somewhat  out  of  focus,  and 
may,  in  this  case,  be  partly  explained  by  the  diffusion  circles 
which,  in  each  case,  encroach  from  the  white  upon  the  dark. 
Bat  over  and  beyond  this,  any  sensation,  coming  from  a  given 
retinal  area,  occupies  a  larger  share  of  the  field  of  vision,  when 
the  rest  of  the  retina  and  central  visual  apparatus  are  at  rest,  than 
when  diey  are  simultaneously  excited.  It  is  as  if  the  neighbourmg, 
either  retinal  or  cerebral,  structures  were  sympathetically  thrown 
into  action  at  the  same  time. 

Contrast.  If  a  white  strip  be  placed  between  the  two  black 
strips,  the  edges  of  the  white  strip,  near  to  the  black,  will  appear 
whiter  than  its  median  portion  ;  and  if  a  white  cross  be  placed  on 
a  black  background,  the  centre  of  the  cross  will  appear  sometimes 
.so  dim,  com]jared  with  the  parts  close  to  the  black,  as  to  seem 
shaded.  This  occurs  even  when  the  object  is  well  in  focus  ;  the 
increased  sensation  of  light  which  causes  the  apparent  greater 
whiteness  of  the  borders  of  the  cross  is  the  result  of  the  '  contrast ' 
with  the  black  placed  immediately  close  to  it.  Still  more  curious 
results  arc  seen  with  coloured  objects.  If  a  small  piece  of  grey 
l^aper  be  placed  en  a  sheet  of  green  paper,  and  both  covered  with 
a  sheet  of  thin  tissue  paper,  the  grey  paper  will  appear  of  a  pink 
colour,  the  complementary  of  the  green.  This  effect  of  contrast 
is  far  less  striking,  or  even  wholly  absent,  when  the  small  piece  of 
paper  is  white  [instead  of  grey,  and  generally  disappears  when  the 
thin  covering  of  tissue  paper  is  removed.  It  also  vanishes  if  a  bold 
broad  black  line  be  drawn  round  the  small  piece  of  paper,  so  as 
to  isolate  it  from  the  ground  colour.     If  a  book,  or  pencil,  be 


556  VISUAL   PERCEPTIONS.  [BOOK  III. 

placed  vertically  on  a  sheet  of  white  paper,  and  illuminated  on 
one  side  by  the  sun,  and  on  the  other  by  a  candle,  two  shadows 
will  be  produced,  one  from  the  sun  which  will  be  illuminated  by 
the  yellowish  light  of  the  candle,  and  the  other  from  the  candle 
which  will  in  turn  be  illuminated  by  the  white  light  of  the  sun. 
The  former  naturally  appears  yellow ;  the  latter,  however,  appears 
not  white  but  blue;  it  assumes,  by  contrast,  a  colour  complemen- 
tary to  that  of  the  candle-light  which  surrounds  it.  If  the  candle 
be  removed,  or  its  light  shut  off  by  a  screen,  the  blue  tint  disap- 
pears, but  returns  when  the  candle  is  again  allowed  to  produce 
its  shadow.  If,  before  the  candle  is  brought  back,  vision  be 
directed  through  a  narrow  blackened  tube  at  some  part  falling 
entirely  within  the  area  of  what  will  be  the  candle's  shadow,  the 
area,  which  in  the  absence  of  the  candle  appears  white,  will  con- 
tinue to  appear  white  when  the  candle  is  made  to  cast  its  shadow, 
and  it  is  not  until  the  direction  of  the  tube  is  changed  so  as  to 
cover  part  of  the  ground  outside  the  shadow,  as  well  as  part  of 
the  shadow,  that  the  latter  assumes  its  blue  tint '. 

Filling  up  the  Blind  Spot.  Though,  as  we  have  seen, 
that  part  of  the  retina  which  corresponds  to  the  entrance  of  the 
optic  nerve  is  quite  insensible  to  light,  we  are  conscious  of  no 
blank  in  the  field  of  vision.  When  in  looking  at  a  page  of  print 
we  fix  the  visual  axis  so  that  some  of  the  print  must  fall  on  the 
blind  spot,  no  gap  is  perceived.  We  could  not  expect  to  see  a 
black  patch,  because  what  we  call  black  is  the  absence  of  the 
sensation  of  light  from  structures  which  are  sensitive  to  light ;  we 
inust  have  visual  organs  to  see  black.  But  there  are  no  visual 
organs  in  the  blind  spot,  and  consequently  we  are  in  no  way  at  all 
affected  by  the  rays  of  light  which  fall  on  it.  There  is  in  our 
subjective  field  of  vision  no  gap  corresponding  to  the  gap  in  the 
retinal  image.  We  refer  the  sensations  coming  from  two  points 
of  the  retina  lying  on  opposite  margins  of  the  blind  spot  to  two 
points  lying  close  together,  since  we  have  no  indication  of  the 
space  which  separates  them.  Concerning  the  effects  which  are 
produced  when  an  object  in  the  field  of  view  passes  into  the 
region  of  the  blind  spot  there  has  been  much  discussion.  In 
ordinary  vision,  of  course,  the  existence  of  the  bhnd  spot  is  of  little 
moment  since  it  is  outside  the  region  used  for  distinct  vision,  and 
besides  the  image  of  an  object  does  not  fall  on  the  blind  spots  of 
both  eyes  at  the  same  time. 

Ocular  Spectra.  So  far  from  our  perceptions  exactly  cor- 
responding to  the  arrangements  of  the  luminous  rays  which  fall  on 

'  Cf.  Hering,  loc.  cii. 


LllAP.   II.]  SIGHT.  557 

the  retina,  we  may  have  visual  sensations  and  perceptions  in  the 
entire  absence  of  light.  Any  stimulation  of  llie  retina  or  of  the 
optic  nerve  sufficiently  intense  will  give  rise  to  a  visual  sensation. 
Gradual  pressure  on  the  eyeball  causes  a  sensation  of  rings  of 
coloured  light,  the  so-called  j)hosphenes ;  a  sudden  blow  on  the 
eye  causes  a  sensation  of  flasht^s  of  light,  and  the  seeming  identity 
of  the  visual  sensations  so  brought  about  with  visual  sensations 
])roduccd  by  liglit  is  well  illustrated  by  the  statement  once  gravely 
made  in  a  German  court  of  law,  by  a  witness  who  asserted  that  on 
a  pitch  dark  night  he  recognised  an  assailant  by  help  of  the  flash 
of  light  caused  by  the  assailant's  hand  coming  in  violent  contact 
with  liis  eye.  Electrical  stimulation  of  the  eye  or  optic  nerve  will 
also  give  rise  to  visual  sensations. 

The  sensations  which  may  arise  without  any  light  falling  on 
the  retina  need  not  necessarily  be  undefined  ;  on  the  contrary 
they  may  be  most  clearly  defined.  Complex  and  coherent  visual 
images  or  perceptions  may  arise  in  the  brain  without  any  corre- 
sponding objective  luminous  cause.  These  so-called  ocular  spectra 
or  phantoms,  which  are  the  result  of  an  intrinsic  stimulation  of 
some  (probably  cerebral)  part  of  the  visual  apparatus,  have  a 
distinctness  which  gives  them  an  apparent  objective  reality  quite 
as  striking  as  that  of  ordinary  visual  perceptions'.  They  may 
occasionally  be  seen  with  the  eyes  open  (and  therefore  while 
ordinaiy  visual  perceptions  are  being  generated)  as  well  as  when 
the  eyes  are  closed.  I'hey  sometimes  become  so  frequent  and 
obtrusive  as  to  be  distressing,  and  form  an  important  element  in 
some  kinds  of  delirium,  such  as  delirium  tremens. 

Appreciation  of  apparent  size.  By  the  eye  alone  we 
can  only  estimate  the  apparoit  size  of  an  object,  we  can  only  tell 
what  space  it  takes  in  the  field  of  vision,  we  can  only  perceive  the 
dimensions  of  the  retinal  image,  and  therefore  have  a  right  only  to 
speak  of  the  angle  which  the  diameter  of  the  object  subtends. 
The  real  size  of  an  object  must  be  determined  by  other  means. 
But  our  perception  of  even  the  apparent  size  of  an  object  is  so 
modified  by  concurrent  circumstances  that  in  many  cases  it  cannot 
be  relied  on.  The  apparent  size  of  the  moon  must  be  the  same 
to  every  eye,  and  yet,  while  some  persons  will  be  found  ready  to 
compare  the  moon  in  mid  heavens  with  a  threepenny  piece,  others 
will  liken  it  to  a  cart-wheel ;  that  is  to  say,  the  angle  subtended 
by  the  moon  seems  to  the  one  to  be  about  equal  to  that  subtended 

'  I  am  acquainted  with  a  ca^e  in  which  ocular  spectra  of  a  jileasing  and 
gorgeous  character,  such  as  visions  of  flowers,  and  landscapes,  can  be  brought 
on  at  once  by  compressing  the  eyeballs  with  the  orbicularis  muscle. 


558  VISUAL   PERCEPTIONS."  [BOOK   III. 

by  a  threepenny  piece  held  at  the  distance  from  the  eye  at  which 
it  is  most  commonly  looked  at,  and  to  the  other  about  equal  to 
that  subtended  by  a  cart-wheel  similarly  viewed,  at  the  distance  at 
which  it  is  most  commonly  looked  at.  If  a  line  such  as  AC, 
Fig.  57,  be  divided  into  two  equal  parts  AB,  BC,  and  AB  be 


9    ®    ®    ©    ^    @  ^ 

A  B  c 

Fig.  57. 

divided  by  distinct  marks  into  several  parts,  as  is  shewn  in  the 
figure,  while  BC  he  left  entire,  the  distance  AB  will  always  appear 
greater  than  CB.  So  also,  if  two  equal  squares  be  marked,  one 
with  horizontal  and  the  other  with  vertical  alternate  dark  and 
light  bands,  the  former  will  appear  higher,  and  the  latter  broader, 
than  it  really  is.  Hence  short  persons  affect  dresses  horizontally 
striped  in  order  to  increase  their  apparent  height,  and  very  stout 
persons  avoid  longitudinal  stripes.  Two  perfectly  parallel  lines  or 
iDajids,  each  of  which  is  crossed  by  slanting  parallel  short  lines, 
will  appear  not  parahel,  but  diverging  or  converging  according  to 
the  directio-n  of  the  cross-lines. 

Again,  when  a  short  person  is  placed  side  by  side  with  a  tall 
person,  the  former  appears  shorter  and  the  latter  taller  than  each 
really  is.  The  moon  on  the  horizon  appears  larger  than  when  at 
the  zenith,  partly  because  it  can  then  be  most  easily  compared 
with  terrestrial  objects,  and  partly  perhaps  because,  from  a  con- 
ception we  have  of  the  heavens  being  flattened,  we  judge  the 
moon  to  be  farther  off  at  the  horizon  than  at  the  zenith;  and 
being  farther  off,  and  yet  subtending  the  same  angle,  must  needs 
be  judged  larger.  The  absence  of  comparison  may,  however, 
have  an  opposite  effect,  as  when  a  person  looks  larger  in  a  fog; 
being  seen  indistinctly,  he  is  judged  to  be  farther  off  than  he  really 
is,  and  so  appears  to  be  proportionately  larger,  just  as  conversely 
distant  mountains  appear  small,  when  in  a  clear  atmosphere  they 
are  seen  distinctly  and  so  judged  to  be  near.  Indeed,  our  daily 
life  is  full  of  instances  in  which  our  direct  perception  is  modified 
by  circumstances.  Among  those  circumstances  previous  experience 
is  one  of  the  most  jDotent,  and  thus  simple  perceptions  become 
mingled  with  what  are  in  reality  judgments,  though  frequently 
made  unconsciously.  But  this  mtrusion  of  past  experience  into 
present  perceptions  and  sensations  is  most  obvious  in  binocular 
vision,  to  which  we  now  turn. 


CHAP.   II.] 


SIGHT. 


559 


Sec.  4.     Binocular  Vision. 
Corresponding  or  Identical  Points. 

Though  we  have  two  eyes,  and  must  therefore  receive  from 
every  object  two  sets  of  sensations,  our  perception  of  any  object 
is  under  ordinary  circumstances  a  single  one;  we  see  one  object, 
not  two.  By  putting  either  eye  into  an  unusual  position,  as  by 
squinting,  we  can  render  the  perception  double ;  we  see  two 
objects  where  one  only  exists.  From  which  it  is  evident  that 
singleness  of  perception  depends  on  the  image  of  the  object 
falling  on  certain  parts  of  each  retina  at  the  same  time,  these  parts 
being  so  related  to  each  other,  that  the  sensations  from  each  are 
blended  into  one  perception  ;  and  it  is  also  evident  that  the 
movements  of  the  eyeballs  are  adapted  to  bring  the  image  of  the 
object  to  fall  on  these  'corresponding'  or  'identical'  parts,  as 
they  are  called,  of  each  retina. 

When  we  look  at  an  object  with  one  eye  the  visual  axis  of  that 
eye  is  directed  to  the  object,  and  when  we  use  two  eyes  the  visual 
axes  of  the  two  eyes  converge  at  the  object,  the  eyeballs  moving 
accordingly.  The  corresponding  points  of  the  two  retinas  are 
those  on  which  the  two  images  of  the  object  fall  when  the  visual 
axes  converge  at  the  object.     Thus  in  Fig.  58,  if  Cc,  Cc-^  be  the 


Fig.  58.    Diagram  illustkating  Cokresponding  Points. 
L  the  left,  R  the  ri'^ht  eye.  A'  the  optical  centre,  <i,,  3,,  f ,  are  points  in  lhe_  right  eye 
i»tTes|i  nJinj  lo  the  points  a.  6,  c  in  the  left  eye.    The  two  figures  below  are  projections  of 
'  tlie  lift  .-uii  R  the  right  retina.     It  will  be  seen  that  a  on  the  malar  side  of  L  corresponds 
ic  <:„  OK  the  M<U'>/&ide  of  R. 


56o  BINOCULAR   VISION.  [BOOK   III. 

two  visual  axes,  r,  c^  being  the  centres  of  the  fovese  centrales  of 
the  two  eyes,  then,  the  object  ACB  being  seen  single,  the  point  a 
on  the  one  retina  will  'correspond  '  to  or  be  '  identical'  with  the 
point  a-^  on  the  other,  and  the  point  /'  in  the  one  to  the  point  b^  in 
the  other.  Hence  a  point  lying  anywhere  on  the  right  side  of  one 
retina  has  its  corresponding  point  on  the  right  side  of  the  other 
retina,  and  the  points  on  the  left  of  one  correspond  with  those  on 
the  left  of  the  other.  Thus,  while  the  upper  half  of  the  retina  of 
the  left  eye  corresponds  to  the  upper  half  of  the  retina  of  the 
right  eye,  and  the  lower  to  the  lower,  the  nasal  side  of  the  left  eye 
corresponds  with  the  malar  side  of  the  right,  and  the  malar  of 
the  left  with  the  nasal  side  of  the  right. 

Since  the  blending  of  the  two  sensations  into  one  only  occurs 
when  the  two  images  of  an  object  fall  on  these  corresponding 
points  of  the  two  retinas,  it  is  obvious  that  in  single  vision  with 
two  eyes  the  ordinary  movements  of  the  eyeballs  must  be  such  as 
to  bring  the  visual  axes  to  converge  at  the  object  so  that  the  two 
images  may  fall  on  corresponding  points.  When  the  visual  axes 
do  not  so  converge,  and  when  therefore  the  images  do  not  fall  on 
corresponding  points,  the  two  sensations  are  not  blended  into  one 
perception  and  vision  becomes  double. 

Movements  of  the  Eyeballs. 

The  eye  is  virtually  a  ball  placed  in  a  socket,  the  orbit  and  the 
bulb  forming  a  ball  and  socket-joint.  In  its  socket-joint  the  optic 
ball  is  capable  of  a  variety  of  movements,  but  it  cannot  by  any 
voluntary  effort  be  moved  out  of  its  socket. 

It  is  stated  that  by  a  very  forcible  opening  of  the  eyelids  the  ev^ 
ball  may  be  slightly  protruded  ;  but  this  trifling  locomotion  may  be 
neglected.  By  disease,  however,  the  position  of  the  eyeball  in  the 
socket  may  be  materially  changed. 

Each  eyeball  is  capable  of  rotating  round  an  immobile  centre 
of  rotation,  which  has  been  found  to  be  placed  a  little  (177  mm.) 
behind  the  centre  of  the  eye  ;  but  the  movements  of  the  eye 
round  the  centre  are  limited  in  a  peculiar  way.  The  shoulder- 
joint  is  a  similar  ball  and  socket-joint ;  and  we  know  that  we 
can  not  only  move  the  arm  up  and  down  round  a  horizontal 
axis  passing  through  the  centre  of  rotation  of  the  head  of  the 
humerus,  and  from  side  to  side  round  a  vertical  axis,  but  we  can 
also  rotate  it  round  its  own  longitudinal  axis.  When,  however,  we 
come  to  examine  closely  the  movements  of  the  eyeball  we  find,  as 
was  shewn  by  Donders,  that  though  we  can  move  it  up  and  down 


CUAV.   II.]  SIGHT.  561 

round  a  horizontal  axis,  as  when  witli  fixed  liead  we  direct  our 
vision  to  the  heavens  or  to  the  ground,  and  from  side  to  side,  as 
when  wo  look  to  left  or  right,  and  though  by  combining  these  two 
movements  we  can  give  the  eyeball  a  variety  of  inclinations,  we 
cannot,  by  a  voluntary  effort,  rotate  tlie  eyeball  round  its  longi- 
tudinal visunl  axis.  The  arrangement  of  the  muscle  of  the  eyeball 
would  permit  of  such  a  movement,  but  we  cannot  by  any  direct 
effort  of  will  bring  it  about  by  itself;  we  can  only  effect  it  in- 
directly when  we  attempt  to  move  the  eyeballs  in  certain  special 
ways. 

If,  when  vision  is  directed  to  any  object,  the  head  be  moved 
from  side  to  side,  the  eyes  do  not  move  with  it;  they  appear  to 
remain  stationary,  very  much  as  the  needle  of  a  ship's  compass 
remains  stationary  when  the  head  of  the  ship  is  turned.  The 
change  in  the  position  of  the  visual  axis  to  which  the  movement 
of  the  head  would  naturally  give  rise  is  met  by  compensating 
movements  of  the  eyeballs;  were  it  not  so,  steadiness  of  vision 
would  be  impossible. 

There  is  one  position  of  the  eyes  which  has  been  called  ihepn'mary 
position.  It  corresponds  to  that  which  may  be  attained  by  looking  at 
the  distant  horizon  with  the  head  vertical  and  the  body  upright  ;  but 
its  exact  determination  requires  special  precautions.  The  visual  axes 
are  then  parallel  to  each  other  and  to  the  median  plane  of  the  head. 
All  other  positions  of  the  eyes  are  called  secondary  positions.  In  a 
secondary  position  the  visual  line  takes  a  new  direction,  and  a  plane 
drawn  through  the  centre  of  rotation  at  right  angles  to  the  primary 
direction  of  the  visual  line  acquires  importance;  for  it  was  suggested 
by  Listing,  and  proved  by  Donders  and  Helmholts,  that  the  change 
from  the  primary  to  any  secondary  position  is  brought  about  by  a  rota- 
tion of  the  eye  round  an  axis  lying  in  this  plane.  This  law  of  the 
movements  of  the  eye  is  known  as  Listing's  law.  The  chief  axes  in 
this  plane  are  the  transverse  axis  of  the  eye,  rotation  round  which 
causes  the  eye  to  move  up  and  down,  and  the  vertical  axis,  rotation 
round  which  causes  the  eye  to  move  from  side  to  side ;  rotation  round 
other  axes  in  the  plane  causes  oblique  movements.  When,  one  eye 
being  closed,  we  look  with  the  other  in  the  primary  position  at  a  ver- 
tical coloured  stripe  on  a  giey  wall  until  a  negative  image  of  the  stripe 
is  produced,  and  then  move  the  eye  away  from  the  strips,  the  negative 
image  remains  vertical,  however  much  the  eye  is  moved  either  hori- 
zontally from  side  to  side,  or  vertically  up  and  down  ;  in  these  move- 
ments, which  are  rotations  round  the  vertical  and  transverse  axes  re- 
spectively, the  relations  of  the  retina  to  the  visual  line  are  unchanged  ; 
the  meridian  in  which  the  negative  image  lies  and  which  was  vertical 
in  the  primary  position,  remains  vertical  in  the  new  positions.  A 
horizontal  negative  image  similarly  remains  horizontal.  If  theeye  be 
moved  from  the  primary  position  in  an  oblique  direction,  the  nega- 
tive image,  whether  horizontal  or  vertical,  becomes  inclined  ;  but 
P.  P.  36 


562  BINOCULAR   VISION.  [BOOK   III. 

Helmholtz^  shewed  that  an  oblique  linear  negative  image  also  maintains 
its  inclination  when  the  eye  is  moved  from  the  primary  position,  in 
the  direction  of  the  line  of  (or  at  right  angles  to  the  line  of)  the  nega- 
tive image  ;  that  here  too  the  meridian  passing  through  the  visual  line 
and  the  negative  image  remains  unchanged  ;  and  that  therefore  the 
movement  m  this  case  also  must  be  brought  about  by  rotation  round  an 
axis  at  right  angles  to  the  plane  passing  through  the  meridian  of  the 
negative  image  {i.e.  the  visual  line  in  its  new  direction)  and  the  visual 
line  in  the  primary  position.  In  other  words,  just  as  a  vertical  or  hori- 
zontal movement  of  the  eye  is  a  rotation  round  a  horizontal  or  vertical 
axis  in  the  plane  of  rotation  spoken  of  above,  so  an  oblique  movement 
is  a  rotation  round  an  oblique  axis  in  the  same  plane  and  not  in  any 
way  a  rotation  round  the  visual  axis  itself.  When  the  horizontal  or 
vertical  negative  image  in  the  above  experiment  becomes  inclined  in  an 
oblique  movement  of  eye,  its  motion  is  similar  to  that  of  the  spokes  of 
a  wheel  ;  but  this  change  of  position  of  the  meridians  of  the  retina 
must  not  be  confounded  with  the  actual  rotation  of  the  eyeball  on  its 
visual  axis. 

All  movements  then  starting  from  the  primary  position,  whether 
rectangular  or  obhque,  are  executed  without  rotation  of  the  eyeball ; 
but  this  is  not  the  case  in  moving  from  one  secondary  position  to 
another.  Moreover  Listing's  law  holds  good  only  so  long  as  the  visual 
axes  remain  parallel.  When  the  visual  axes  are  made  to  converge, 
some  amount  of  rotation  occurs,  and  that  even  when  their  horizontal 
direction,  proper  to  them  in  the  primary  position,  is  maintained.  The 
rotation  is,  with  the  exception  of  a  particular  position,  still  more 
marked  when,  as  is  usually  the  case  during  the  convergence,  the  eyes 
are  directed  downwards. 

It  was  once  thought  that  the  maintenance  of  the  position  of  the  eye- 
balls when  the  head  was  turned  to  the  shoulders,  while  vision  was 
directed  to  an  object  in  front,  was  effected  by  means  of  a  rotation  of 
the  eyeballs.  This  Bonders  proved  to  be  an  error,  though  some  slight 
amount  of  rotation  does  take  place.  In  various  other  movements  of 
the  eye  too  rotation  occurs  to  a  variable  extent. 

Muscles  of  the  Eyeball.  The  eyeball  is  moved  by  six 
muscles,  the  recti  inferior,  superior,  interims,  and  externus,  and  the 
obliqui  inferior  and  superior.  It  is  found  by  calculation  from  the 
attachments  and  directions  of  the  muscles,  and  confirmed  by 
actual  observation,  that  the  six  muscles  may  be  considered  as  three 
pairs,  each  pair  rotating  the  eye  round  a  partictilar  axis.  The 
relative  attachments  and  the  axes  of  rotation  are  diagrammatically 
shewn  in  Fig.  59.  Thus  the  rectus  superior  and  the  rectus  inferior 
rotate  the  eye  round  a  horizontal  axis,  which  is  directed  from  the 
upper  end  of  the  nose  to  the  temple  ;  the  obliquus  superior  and 
obliquus  inferior  round  a  horizontal  axis  directed  from  the  centre  of 

*  Proc;  Roy,  Soc,  XIII.  {1864)  p.  186. 


CHAP.    II.] 


SIGHT. 


563 


the  eyeball  to  the  occiput  ;  and  the  rectus  intemtis  and  rectus 
cxtcrnus  round  a  vertical  axis  (which,  being  at  right  angles  to  the 
plane  of  the  paper,  cannot  be  shewn  in  the  diagram),  passing 
through  the  centre  of  rotation  of  the  eyeball  parallel  to  the  medium 
plane  of  the  head  when  the  head  is  vertical.  Thus  the  latter  pair 
acting  alone  would  turn  the  eye  from  side  to  side,  the  other 
straight  pair  acting  alonj  would  move  the  eye  up  and  round,  while 
the  oblique  muscles  acting  alone  would  give  the  eye  an  oblique 
movement.     The  rectus  externus  acting  alone  would  turn  the  eye 


cibLsup. 


xyfi. 


3TIJ1, 


r.iTit 


r.exl.    r.sup.  r.int 
r.i/if. 

Fig.  59.  Diagram  OF  THE  Attachments  of  the  Muscles  of  the  Eve,  and  op  their 
AxE<  OF  Rotation,  the  latter  being  represented  by  dotted  lines.  The  axis  of  rotation 
of  the  rectus  extcmiis  and  intemus,  being  perpendicular  to  the  plane  of  the  paper,  cannot 
be  shewn.    (After  Fick.) 

to  the  malar  side,  the  intemus  to  the  nasal  side,  the  rectus  superior 
upwards,  the  rectus  inferior  downwards,  the  oblique  superior 
downwards  and  outwards,  and  the  inferior  upwards  and  outwards. 
The  recti  superior  and  inferior  in  moving  the  eye  up  and  down 
also  turn  it  somewhat  inward  and  at  the  same  time  give  it  a  slight 
amount  of  rotation  ;  but  this  is  corrected  if  the  oblique  muscles  act 
at  '.he  same  time  ;  and  it  is  found  that  the  rectus  superior  acting 
with  the  obliquus  inferior  moves  the  eye  upwards,  and  the  rectus 
inferior  with  the  obliquus  superior  downwards  in  a  vertical  direction. 
In  oblique  movements  also,  the  obliqui  are  always  associated  with 

36—2 


564 


BINOCULAR   VISION. 


[book  III. 


the  recti.     Hence  the  various  movements  of  the  eyeball  may  be 
arranged  as  follows  : 


•^a 


'  Elevation. 
Depression. 
Adduction  to 

nasal  side. 
Adduction  to 

malar  side. 


Rectus  superior  and  obliquus  inferior. 
Rectus  inferior  and  obliquus  superior. 

Rectus  internus. 
Rectus  externus. 


2  ^ 


Elevation  with  Rectus  superior  and  internus  with  obliqutis 

adduction.  inferior. 

Depression      Rectus  inferior  and  internus  with  obliquus 
with  adduction.       superior. 
Elevation  with   Rectus  superior  and  externus  with  obliquus 

abduction.  inferior. 

Depression      Rectus  inferior  and  externus  with  obliquus 
^  with  abduction.      superior. 


Coordination  of  Visual  Movements.  Thus  even  in  the 
movements  of  a  single  eye,  a  considerable  amount  of  coordina- 
tion takes  place.  When  the  eye  is  moved  in  any  other  than  the 
vertical  and  horizontal  meridians,  impulses  must  descend  to  at 
least  three  muscles,  and  in  such  relative  energy  to  each  of  the 
three_  as  to  produce  the  required  inclination  of  the  visual  axis. 
But  the  coordination  observed  in  binocular  vision  is  more  striking 
still.  If  the  movements  of  any  person's  eyes  be  watched  it  will  be 
seen  that  the  two  eyes  move  alike.  If  tke  right  eye  moves  to  tlie 
right,  so  does  also  the  left ;  and,  if  the  object  looked  at  be  a  distant 
one,  exactly  to  the  same  extent ;  if  the  right  eye  looks  up,  the  left 
eye  looks  up  also,  and  so  in  every  other  direction.  Very  few 
persons  are  able  by  a  direct  effort  of  the  will  to  move  one  eye  in- 
dependently of  the  other ;  though  some,  and  among  them  one 
distinguished  both  as  a  physiologist  and  an  oculist,  have  acquired 
this  power.  In  fact,  the  movements  of  the  two  eyes  are  so  ar- 
ranged that  in  the  various  movements  the  images  of  any  object 
should  fall  on  the  corresponding  points  of  the  two  retinte,  and  that 
thus  single  vision  should  result.  We  cannot  by  any  direct  effort  of 
our  will  place  our  eyes  in  such  a  position  that  the  rays  of  light  pro- 
ceeding from  any  object  shall  fall  on  parts  of  the  retina  which  do 
not  correspond,  and  thus  give  rise  to  two  distinct  visual  images. 
We  can  bring  the  visual  axes  of  the  two  eyes  from  a  condition  of 
parallelism  to  one  of  great  convergence,  but  we  cannot,  without 


CHAl".   II.J  SIGHT.  565 

special  assistance,  bring  them  from  a  condition  of  parallelism  to 
one  of  divergence. 

The  stereoscope  will  en.iblc  us  to  create  a  divergence.  If  in  a 
stereoicopic  piniirc  the  distance  between  the  pictures  be  increased  so 
gradually  that  the  impression  of  a  single  object  be  not  lost,  the  visual 
axes  may  be  brought  to  diverge.  Hehnholtz,  while  looking  at  a  dis- 
tant object  with  a  prism  before  one  eye,  with  the  angle  of  the  prism 
directed  towards  the  nose  and  the  vision  of  the  object  kept  carefully 
single,  found  after  turning  the  angle  very  slowly  up  or  down,  and  keep- 
ing the  image  of  the  obje:t  single  all  the  time,  that  on  removing  the 
jirism  a  double  image  was  for  a  moment  seen  ;  shewing  that  the  eye 
before  which  the  prism  was  placed  had  moved  in  disaccordance  with 
the  other.  The  double  image  however  in  a  few  seconds  after  the 
removal  ot  the  prism  became  single,  on  account  of  the  eyes  coming 
into  accordance. 

It  is  only  when  loss  of  coordination  occurs,  as  in  various  dis- 
eases and  in  alcoholic  or  other  poisoning,  that  the  movements  of 
the  two  eyes  cease  to  agree  with  each  other.  It  is  evident  then 
that  when  we  look  at  an  object  to  the  right,  since  we  thereby 
abduct  the  right  eye  and  adduct  the  left,  we  throw  into  action  the 
rectus  cxternus  of  the  right  eye  and  the  rectus  internus  of  the 
left ;  and  similarly  when  we  look  to  the  left  we  use  the  rectus 
externus  of  the  left  and  the  rectus  internus  of  the  right  eye.  When 
we  look  at  a  near  object,  and  therefore  converge  the  visual  axes, 
we  use  the  recti  interni  of  both  eyes  ;  and  when  we  look  at  a 
distant  object,  and  bring  the  axes  from  convergence  towards  paral- 
lelism, we  use  the  recti  externi  of  both  eyes.  In  the  various 
movements  of  the  eye  there  is  therefore,  so  to  speak,  the  most 
delicate  picking  and  choosing  of  the  muscular  instruments.  Bear- 
ing this  in  mind,  it  cannot  be  wondered  at  that  thj  various  move- 
ments of  the  eye  are  dependent  for  their  causation  on  v  sual 
sensations.  In  order  to  move  our  eyes,  we  must  either  look  at  or 
for  an  object ;  when  we  wish  to  converge  our  axes,  we  look  at 
some  near  object  real  or  imaginary,  and  the  convergence  of  the 
axes  is  usually  accompanied  by  all  the  conditions  of  near  vision, 
such  as  increased  accommodation  and  contraction  of  the  pupil. 
And  so  with  other  movements. 

The  close  association  of  the  movements  of  the  eye  may  be  illus- 
trated by  the  following  case.  Suppose  the  eyes,  to  start  with,  directed 
for  the  tar  distance,  and  that  it  is  desired  to  direct  attentioijto  a  nearer 
point  lying  in  the  visud  line  of  the  right  eye.  In  this  case  no  move- 
meat  of  the  rig'it  eye  is  required  ;  all  that  is  necessary  is  for  the  left 
eye  to  be  turned  to  the  right,  that  is,  for  the  rectus  internus  of  the  left 
eye  to  be  thrown  into  action.  But  in  ordinary  movements  the  contrac- 
tion of  this  muscle  is  always  associated  with  either  the  rectus  externus 


566  BINOCULAR   VISION,  [BOOK   III. 

of  the  right  eye  (as  when  both  eyes  are  turned  to  the  right)  or  the 
rectus  internus  of  that  eye,  as  in  convergence  ;  the  muscle  is  quite  un- 
accustomed to  act  alone.  This  would  lead  us  to  suppose  that  in  the 
case  in  question  the  contraction  of  the  rectus  internus  of  the  left  eye  is 
accompanied  by  a  contraction  of  both  recti  externus  and  internus  of 
the  right  eye,  keeping  that  efe  in  lateral  equilibrium.  And  when  we 
come  to  examine  our  own  consciousness,  we  feel  a  sense  of  effort  in 
the  right  as  well  as  in  the  left  eye,  and  the  slight  amount  of  rotation 
which  accompanies  convergence  (see  p.  562)  may  be  discovered  also  in 
the  right  as  well  as  in  the  left  eye. 

Such  a  complex  coordination  requires  for  its  carrying  out  a  dis- 
tinct nervous  machinery ;  and  we  have  reasons  for  thinking  that 
such  a  machinery  exists  in  certain  parts  of  the  corpora  quadri- 
gemina  or  in  the  underlying  structures  (see  p.  525).  In  the  nates, 
Adamuk  finds  a  common  centre  for  both  eyes,  stimulation  of  the 
right  side  producing  movements  of  both  eyes  to  the  left,  of  the  left 
side  movements  to  the  right ;  while  stimulation  in  the  middle  line 
behind  causes  a  downward  movement  of  both  eyes  with  con- 
vergence of  the  axes,  and  in  the  front  an  upward  movement  with 
return  to  parallelism,  both  accompanied  by  the  naturally  associated 
movements  of  the  pupil.  Stimulation  of  various  parts  of  the 
nates  causes  various  movements,  depending  on  the  position  of  the 
spot  stimulated.  After  an  incision  in  the  middle  line,  stimulation 
of  the  nervous  centre  on  one  side  produces  movements  in  the  eye 
of  the  same  side  only. 

T/ie  Horopter. 

When  we  look  at  any  object  we  direct  to  it  the  visual  axes,,  so 
that  when  the  object  is  small,  the  '  corresponding'  parts  of  the  two 
retinae,  on  which  the  two  images  of  the  object  fall,  lie  in  their 
respective  fovese  centrales.  But  while  we  are  looking  at  the 
particular  object  the  images  of  other  objects  surrounding  it  fall  on 
the  retina  surrounding  the  fovea,  and  thus  go  to  form  what  is  called 
indirect  vision.  And  it  is  obviously  of  advantage  that  these  images 
also  should  fall  on  '  corresponding  '  parts  in  the  two  eyes.  Now 
for  any  given  position  of  the  eyes  there  exists  in  the  field  of  vision 
a  certain  line  or  surface  of  such  a  kind  that  the  images  of  the  points 
in  it  all  fall  on  corresponding  points  of  the  retina.  A  line  or 
surface  having  this  property  is  called  a  Horopter.  The  horopter 
is  in  fact^he  aggregate  of  all  those  points  in  space  which  are  pro- 
jected on  to  corresponding  points  of  the  retina ;  hence  its 
determination  in  any  particular  case  is  simply  a  matter  of 
geometrical  calculation.  In  some  instances  it  becomes  a  very 
comphcated  figure.      The  case  whose  features  are   most   easily 


ClIAl'.    Il.J 


SI  (J  111'. 


507 


grasped,  is  a  circle  drawn  in  the  plane  of  the  two  visual  axes 
through  the  point  of  tiie  convergence  of  the  axes  and  tlie  optic 
centres  of  the  two  eyes.  It  is  olnious  from  geometrical  relations 
that  in  Fig.  60  the  images  of  any  point  in  the  circle  will  fall  on 
corresponding  points  of  tlie  two  retinae.  When  we  stand  upright 
and  look  at  the  distant  horizon  the  horopter  is  (approximately,  for 
normal  long-sighted  persons)  a  plane  drawn  through  our  feet,  that 
is  to  say,  is  the  ground  on  which  we  stand  ;  the  advantage  of  this 
is  obvious. 


Fig.  60.    Diagram  illustrating  a  simhle  Horopter. 

When  the  visual  axes  converge  at  C.  the  images  a  a  of  any  point  A  on  the  circle  drawn 
through  C  and  the  optical  centres  M  k,  will  fall  on  corresponding  points. 


In  determining  the  position  of  corresponding  points  it  must  be  re- 
memberei,  as  Helinholtz'  has  shewn,  that  while  the  horizontal  meri- 
dians of  the  two  fields  really  correspond,  it  is  the  apparent -xviA  not  the 
ri?^?/ vertical  meridians  which  are  combined  into  one  image  in  binocular 
vision,  and  it  is  therefore  by  these  that  the  corresponding  points  must 
be  determined.  If  two  areas  be  mar'^ed  with  lines  ncarlv  but  not  quite 
vertical,  those  on  the  right  side  inclining  to  the  left,  and  those  on  the 
left  to  the  right,  the  former  when  judged  by  the  right  eye  will  appear 
vertical,  though  their  slant  will  be  apparent  to  the  left  eye,  and  the 
latter  will  appear  vertical  to  the  left  eye  but  not  to  the  right.  When 
combined  in  a  stereoscope  picture,  the  lines  in  spite  of  their  not  being 
parallel  will  appear  (.ompletcly  to  coincide,  shewing  that  it  is  the 
apfyarciit  position  of  the  vertical  lines  which  must  be  taken  into 
consideration  in  determining  corresponding  points. 

'  Froc.  Koy.  -W.,  xiii.  (1S64)  \\  96. 


568  VISUAL  JUDGMENTS.  [BOOK  III. 

Sec.  5.      Visual  Judgments. 

Binocular  visibn  is  of  use  to  us  inasmuch  as  the  one  eye  is 
able  to  fill  up  the  gaps  and  imperfections  of  the  other.  For 
example,  over  and  above  the  monocular  filling  up  of  the  blind 
spot,  of  which  we  spoke  in  page  556,  since  the  two  blind  spots  of 
the  two  eyes,  being  each  on  the  nasal  side,  are  not  'corresponding' 
parts,  the  one  eye  supplies  that  part  of  the  field  of  vision  which 
is  lacking  in  the  other.  And  other  imperfections  are  similarly 
made  good.  But  the  great  use  of  binocular  vision  is  to  afford  us 
means  of  forming  visual  judgments  concerning  the  form,  size,  and 
distance  of  objects. 

Judgment  of  Distance  and  Size.  The  perceptions  which 
we  gain  simply  and  solely  by  our  field  of  vision  concern  two 
dimensions  only.  We  can  become  aware  of  the  apparent  size 
of  any  part  of  the  field  corresponding  to  any  particular  object, 
and  of  its  topographical  relations  to  the  rest  of  the  field,  but  no 
more.  Had  we  nothing  more  to  depend  on,  our  sight  would  be 
almost  valueless  as  far  as  any  exact  information  of  the  external 
world  was  concerned.  By  association  of  the  visual  sensations 
with  sensations  of  touch,  and  with  sensations  derived  from  the 
movements  of  the  eyeballs  required  to  make  any  such  part  of  the 
field  as  corresponds  to  a  particular  object  distinct,  we  are  led  to 
form  judgments,  i.e.  to  draw  conclusions  concerning  the  external 
world  by  means  of  an  interpretation  of  our  visual  perceptions. 
Looking  before  us,  we  say  we  see  a  certain  object  of  a  certain 
colour  nearly  in  front  of  us,  or  much  on  our  right  hand  or  much 
on  our  left;  that  is  to  say,  we  judge  such  an  object  to  be  in  such 
a  position  because  from  the  constitution  of  our  brain,  strengthened 
by  all  our  experience,  we  associate  such  a  part  of  our  field  of 
vision  with  such  an  object.  The  subjective  visual  complex 
sensation  or  perception  is  to  us  ■  a  symbol  of  the  external 
object. 

Even  with  one  eye  we  can,  to  a  certain  extent,  form  a  judg- 
ment, not  only  as  to  the  position  of  the  object  in  a  plane  at 
right  angles  to  our  visual  axis,  but  also  as  to  its  distance  from 
us  along  the  visual  axis.  If  the  object  is  near  to  us,  we  have 
to  accommodate  for  near  vision  ;  if  far  from  us,  to  relax  our 
accommodation  mechanism  so  that  the  eye  becomes  adjusted  for 
distance.  The  muscular  sense  (see  chap.  iv.  sec.  4)  of  this 
effort  enables  us  to  form  a  judgment  whether  the  object  is 
far  or  near.  Seeing  the  narrow  range  of  our  accommodation, 
and  the   slight  muscular  effort  which  it  entails,  all  monocular 


CHAF.    11. j  SIGHT.  569 

judgments  of  distance  must  be  subject  to  much  error.  Every 
one  who  has  tried  to  thread  a  needle  without  using  both  eyes, 
knows  how  great  these  errors  may  be.  When,  on  the  other  hand, 
we  use  two  eyes,  we  have  still  the  variations  in  accommodation, 
and  in  addition  have  all  the  assistance  which  arises  from  the 
muscular  effort  of  so  directing  the  two  eyes  on  the  object  that 
single  vision  shall  result.  When  the  object  is  near,  we  converge 
our  visual  axes ;  when  distant,  we  bring  them  back  towards 
parallelism.  This  necessary  contraction  of  the  ocular  muscles 
affords  a  muscular  sense,  by  the  help  of  which  we  form  a  judg- 
ment as  to  the  distance  of  the  object.  Hence,  when  by  any 
means  the  convergence  which  is  necessary  to  bring  the  object 
into  single  vision  is  lessened,  the  object  seems  to  become  more 
distant ;  when  increased,  to  move  towards  us,  as  may  be  seen  in 
the  stereoscope. 

The  judgment  of  size  is  closely  connected  with  that  of  distance. 
Our  perceptions,  gained  exclusively  from  the  field  of  vision,  go  no 
farther  than  the  appai-ent  si/e  of  the  image,  i.e.  of  the  angle  sub- 
tended by  the  object.  The  real  size  of  the  object  can  only  be 
gathered  from  the  apparent  size  of  the  image  when  the  distance 
of  the  object  from  the  eye  is  known.  Thus  perceiving  directly 
the  apparent  size  of  the  image,  we  judge  the  distance  of  the 
object  giving  the  image,  and  upon  that  come  to  a  conclusion  as  to 
its  size.  And  conversely,  when  we  see  an  object,  of  whose  real 
size  we  are  otherwise  aware,  or  are  led  to  think  we  are  aware,  our 
judgment  of  its  distance  is  influenced  by  its  apparent  size.  Thus 
when  in  our  field  of  vision  there  appears  the  image  of  a  man, 
knowing  otherwise  the  ordinary  size  of  man,  we  infer,  if  the  image 
be  very  small,  that  the  man  is  far  off.  The  reason  of  the  image 
being  small  may  be  because  the  man  is  far  off,  in  which  case 
our  judgment  is  correct ;  it  may  be,  however,  because  the  image 
has  been  lessened  by  artificial  dioptric  means,  as  when  the  man 
is  looked  at  through  an  inverted  telescope,  in  which  case  our 
judgment  becomes  a  delusion.  So  also  an  image  on  a  screen 
when  gradually  enlarged  seems  to  come  forward,  when  gradually 
diminished  seems  to  recede.  In  these  cases  the  influ-nce  on 
our  judgment  of  the  muscular  sense  of  binocular  adjustment, 
or  monocular  accommodation,  is  thwarteil  by  the  more  direct 
influence  of  the  association  between  size  and  distance. 

Judgment  of  Solidity.  When  we  look  at  a  small  circle 
all  parts  of  the  circle  are  at  the  same  distance  from  us,  all  parts 
are  equally  distinct  at  the  same  time,  whether  we  look  at  it  with 
one  eye  or  with  two  eyes.     When,  on  the  other  hand,  we  look  at 


570 


VISUAL  JUDGMENTS. 


[book   III. 


a  sphere,  the  various  parts  of  which  are  at  different  distances  from 
us,  a  sense  of  the  accommodation,  but  much  more  a  sense  of  the 
binocular  adjustment,  of  the  convergence  or  the  opposite  of  the 
two  eyes,  required  to  make  the  various  parts  successively  distinct, 
makes  us  aware  that  the  various  parts  of  the  sphere  are  unequally 
distant  :  and  from  that  we  form  a  judgment  of  its  solidity.  As 
with  distance  of  objects,  so  with  solidity,  which  is  at  bottom  a 
matter  of  distance  of  the  parts  of  an  object,  we  can  form  a  judg- 
ment with  one  eye  alone ;  but  our  ideas  become  much  more  exact 
and  trustworthy  when  two  eyes  are  used.  And  we  are  much 
assisted  by  the  effects  produced  by  the  reflection  of  light  from  the 
various  surfaces  of  a  solid  object ,  so  much  so,  that  raised  surfaces 
may  be  made  to  appear  depressed,  or  vice  versa,  and  flat  surfaces 
either  raised  or  depressed,  by  appropriate  arrangements  of  shadings 
and  shadow. 


X 

/ 

/ 

\ 

y 

B 

/" 

\ 

/ 

/ 

\ 

Fig.  6i. 


Binocular  vision,  moreover,  affords  us  a  means  of  judging  of 
the  solidity  of  objects,  inasmuch  as  the  image  of  any  solid  object 
which  falls  on  to  the  right  eye  cannot  be  exactly  hke  that  which 
falls  on  the  left,  though  both  are  combined  in  the  single  percep- 
tion of  the  two  eyes.  Thus,  when  we  look  at  a  truncated  pyramid 
placed  in  the  middle  line  before  us,  the  image  which  falls  on  the 
right  eye  is  of  the  kind  represented  in  Fig.  61  R,  while  that  which 
falls  on  the  left  eye  has  the  form  of  Fig.  61  L;  yet  the  perception 
gained  from  the  two  images  together  corresponds  to  the  form  of 
which  Fig.  61  B,  is  the  projection.  Whenever  we  thus  combine 
in  one  perception  two  dissimilar  images,  one  of  the  one,  and  the 
other  of  the  other  eye,  we  judge  that  the  object  giving  rise  to  the 
images  is  solid. 

This  is  the  simple  principle  of  the  stereoscope,  in  which  two 
slightly  dissimilar  pictures,  such  as  would  correspond  to  the  vision 
of  each  eye  separately,  are,  by  means  of  reflecting  mirrors,  as  in 
Wheatstone's  original  instrument,  or  by  prisms,  as  in  the  form 
introduced  by  Brewster,  made  to  cast  images  on  corresponding 
parts  of  the  two  retinas  so  as  to  produce  a  single  perception. 
Though  each  picture  is  a  surface  of  two  dimensions  only,  the 


CHAT.    II. J  SIGHT. 


3/ 


resulting  perception  is  the  same  as  if  a  single  oi)ject,  or  group  of 
objects,  of  three  dimensions  had  been  looked  at. 

It  might  be  supposed  that  the  judgment  of  solidity  which  arises 
when  two  dissimilar  images  are  thus  combined  in  one  perception, 
was  due  to  the  fact  that  all  parts  of  the  two  images  cannot  fall  on 
corresponding  parts  of  the  two  retinas  at  the  same  time,  and  that 
therefore  the  combination  of  tlie  two  needs  some  movement  of  the 
eyes.  Thus,  if  we  superimpose  R  on  L  (Fig.  6i),  it  is  evident 
that  when  the  bases  coincide  the  truncated  apices  will  not,  and 
vice  versa  ;  hence,  when  thj  bases  fall  on  corresponding  parts,  the 
apices  will  not  be  combined  into  one  image,  and  vice  versa ;  in 
order  that  both  may  be  combined,  there  must  be  a  slight  rapid 
movement  of  the  eyes  from  the  one  to  the  other.  That,  however, 
no  such  movement  is  necessary  for  each  particular  case  is  shewn 
by  the  fact  that  solid  objects  appear  as  such  when  illuminated  by 
an  electric  spark,  the  duration  of  which  is  too  short  to  permit  of 
any  movements  of  the  eyes.  If  the  flash  occurred  at  the  moment 
that  the  eyes  were  binocularly  adjusted  for  the  bases  of  the  pyra- 
mids, the  two  apices  not  falling  on  exactly  corresponding  parts 
would  give  rise  to  two  perceptions,  and  the  whole  object  ought  to 
appear  confused.  That  it  does  not,  but,  on  the  contrary,  appears 
a  single  solid,  must  be  the  result  of  cerebral  operations,  resulting 
in  what  we  have  called  a  judgment. 

Struggle  of  the  two  Fields  of  Vision.  If  the  images 
of  two  surfaces,  onj  black  and  the  other  white,  are  made  to  fall 
on  corresponding  parts  of  the  eye,  so  as  to  be  united  into  a  single 
perception,  the  result  is  not  always  a  mixture  of  the  two  impres- 
sions, that  is  a  grey,  but,  in  many  cases,  a  sensation  similar  to  that 
proiluced  when  a  polished  surface,  such  as  plumbago,  is  looked 
at ;  the  surface  appears  brilliant.  Tlie  reason  probably  is  becau.se 
when  we  look  at  a  polished  surface  the  amount  of  reflected  light 
which  falls  upon  the  retina  is  generally  ditiferent  in  the  two  eyes  ; 
and  hence  we  associate  an  une(iual  stimulation  of  the  two  retinas 
with  the  idea  of  a  polished  surface.  So  also  when  the  impressions 
of  two  colours  are  united  in  binocular  vision,  the  result  is  in  most 
cases  not  a  mixture  of  the  two  colours,  as  when  the  same  two  im- 
pressions are  brought  to  bear  together  at  the  same  time  on  a  single 
retina,  but  a  struggle  between  the  two  colours,  now  one,  and  now 
the  other,  becoming  prominent,  intermediate  tints  however  being 
frequentlv  passed  through.  This  may  arise  from  the  difficulty  of 
accommodating  at  the  same  time  for  the  two  different  colours 
(see  p.  520);  if  two  eyes,  one  of  which  is  looking  at  red,  and 
the  other  at  blue,  be  both  accommodated  for  red  rays,  the  red 


572  TEARS.  [BOOK   III. 

sensation  will  overpower  the  blue,  and  vice  versa.  It  may  be  however 
that  the  tendency  to  rhythmic  action,  so  manifest  in  other  simpler 
manifestations  of  protoplasmic  activity,  makes  its  appearance  also 
in  the  higher  cerebral  labours  of  binocular  vision. 

Sec.  6.     The  Protective  Mechanisms  of  the  Eye. 

The  eyeball  is  protected  by  the  eyelids,  which  are  capable  of 
movements  called  respectively  opening  and  shutting  the  eye.  The 
eye  is  shut  by  the  contraction  of  the  orbicularis  muscle,  carried 
out  either  as  a  reflex  or  voluntary  act,  by  means  of  the  facial 
nerve.  The  eye  is  opened  chiefly  by  the  raising  of  the  upper 
eyelid,  through  the  contraction  of  the  levator  palpebrse  carried  out 
by  means  of  the  third  nerve.  The  upper  eyelid  is  also  raised  and 
the  lower  depressed,  the  eye  being  thus  opened,  by  means  of 
plain  muscular  fibres  existing  in  the  two  eyelids  and  governed  by 
the  cervical  sympathetic.  The  shutting  of  the  eye  as  in  winking 
is  in  general  effected  more  rapidly  than  the  opening. 

The  eye  is  kept  continually  moist  partly  by  the  secretion  of 
the  glands  in  the  conjunctiva,  and  of  the  Meibomian  glands,  but 
chiefly  by  the  secretion  of  the  lachrymal  gland.  Under  ordinary 
circumstances  the  fluid  thus  formed  is  carried  away  by  the  lachry- 
mal canals  into  the  nasal  sac  and  thus  into  the  cavity  of  the  nose. 
When  the  secretion  becomes  too  abundant  to  escape  in  this  way  it 
overflows  on  to  the  cheeks  in  the  form  of  tears. 

If  a  quantity  of  tears  be  collected,  they  are  found  to  form  a 
clear  faintly  alkaline  fluid,  in  many  respects  like  saliva,  containing 
about  I  p.c.  of  solids,  of  which  a  small  part  is  proteid  in  nature. 
Among  the  salts  present  sodium  chloride  is  conspicuous. 

The  nervous  mechanism  of  the  secretion  of  tears,  in  many 
respects,  resembles  that  of  the  secretion  of  saliva.  A  flow  is 
usually  brought  about  either  in  a  reflex  manner  by  stimuli  applied 
to  the  conjunctiva,  the  nasal  mucous  membrane,  tongue,  optic 
nerve,  &c.  or  m.ore  directly  by  emotions.  Venous  congestion 
of  the  head  is  also  said  to  cause  a  flow.  The  efferent  nerves 
belong  either  to  the  cerebro-spinal  system,  (the  lachrymal  and 
orbital  branches  of  the  fifth  nerve,)  or  arise  from  the  cervical 
sympathetic,  the  afferent  nerves  varying  according  to  the  exciting 
cause. 

Herzenstein'  and  Wolferz^  shewed  that  stimulation  of  the  peripheral 
end  of  the  divided  lachrymal  branch  of  the  fifth  nerve  produced  a 
copious  flow  of  tears.     After  division  of  this  branch  stimulation  of  the 

'  Du  Bois-Reymond's  Archiv,  1867,  p.  651. 

^  Dissertatio.     Henle  and  Meissner's  Bericht,  1871,  p.  245. 


CHAP.  II.]  SIGHT.  573 

nasal  mucous  membrane  produced  no  increased  flow  :  the  reflex  act 
could  not  be  carried  out.  Stimul.ition  of  the  orbital  (subcutaiicou- 
milar)  branch  also  pro.luccd  an  increased  flow  but  not  to  ->o  marked  an 
extent,  or  so  constantly  as  did  stimul  :tion  of  the  lachrymal  branch. 
According  to  Wolfcrz'  and  Reich",  stimulation  of  the  upper  cnl  of  the 
divided  cervical  sympathetic  also  produces  an  increased  flow,  even 
after  division  of  tiie  lachrymal  nerve  ;  Hcrzenstcin's  results  on  this 
point  were  uncertain  or  ne^'ative.  Reich  also  maintains  that  stimula- 
tion of  the  ])eripheral  portion  of  the  divided  roo/  of  the  fiftii  nerve  docs 
not  excite  the  gland,  but  that,  after  such  a  division,  the  flow  of  tears 
may  be  excited  in  a  reflex  manner  as  usual.  This  would  shew  that 
the  secretory  fibres  in  the  lachrymal  branch  do  nut  belong  properly  to 
the  fifth  nerve.  Reich  believes  that  they  come  however  not  from  the 
facial,  as  might  by  analogy  with  the  submaxillary  gland  be  supposed, 
but  from  the  sympathetic. 

The  act  of  winking  undoubtedly  favours  the  passage  of  tears 
through  the  lachrj-nial  canals  into  the  nasal  sac,  and  hence  when  the 
orbicularis  is  paralysed  tears  do  not  pass  so  readily  as  usual  into 
the  nose  ;  but  the  exact  mechanism  by  which  this  is  effected  has 
been  much  disputed.  According  to  some  authors,  the  contraction 
of  the  orbicularis  presses  the  fluid  onwards  out  of  the  canals, 
which,  upon  the  relaxation  of  the  orbicularis,  dilate  and  receive  a 
fresh  quantity.  DenitschL-nko  3  states  that  a  special  arrangement 
of  muscular  fibres  keeps  the  canals  open  even  during  the  closing 
of  the  lids,  so  that  the  pressure  of  the  contraction  of  tlie  orbi- 
cularis is  able  to  have  full  effect  in  driving  the  tears  through  the 
canals. 

'  C/.  cii. 

'  Archivf.  Ophthalmol.,  Xix.  (1873)  ]'•  S^- 

3  Hofmanii  and  Schwalbe's  Bericht,  1S73,  p.  530. 


CHAPTER  III. 
HEARING,  SMELL,  AND  TASTE. 

Sec.   1.     Hearing. 

As  in  the  eye,  so  in  the  ear,  we  have  to  deal  first  with  a  nerve  of 
special  sense,  the  stimulation  of  which  gives  rise  to  a  special 
sensation ;  secondly  with  terminal  organs  through  which  the 
physical  changes  proper  to  the  special  sense  are  enabled  to  act  on 
the  nerve ;  and  thirdly  vv^ith  subsidiary  apparatus,  by  which  the 
usefulness  of  the  sense  is  increased.  The  central  connections  of 
the  auditory  nerve  are  such  that  whenever  the  auditory  fibres  are 
stimulated,  whether  by  means  of  the  terminal  organs  in  the  usual 
way  or  by  the  direct  application  of  stimuli,  electrical,  mechanical, 
&c.,  the  result  is  always  a  sensation  of  sound.  Just  as  stimulation 
of  the  optic  fibres  produces  no  other  sensation  than  that  of  light, 
so  stimulation  of  the  auditory  fibres  produces  no  other  sensation 
than  that  of  sound\  The  terminal  organs  of  the  auditory  nerve 
are  of  two  kinds  :  the  complicated  organ  of  Corti  in  the  cochlea, 
and  the  epithelial  arrangements  of  the  maculae  and  cristas  acousticse 
in  other  parts  of  the  labyrinth.  Waves  of  sound  falling  on  the 
auditory  nerve  itself,  produce  no  efiect  whatever ;  it  is  only  when 
by  the  medium  of  the  endolymph  they  are  brought  to  bear  on  the 
delicate  and  peculiar  epithelium  cells  which  constitute  the  peri- 
pheral terminations  of  the  nerve,  that  sensations  of  sound  arise. 
Such  dehcate  structures  are  for  the  sake  of  protection  naturally 
withdrawn  from  the  surface  of  the  body  where  they  would  be 
subject  to  injury.  Hence  the  necessity  of  an  acoustic  apparatus, 
forming  the  middle  and  external  ear,  by  which  the  waves  of  sound 
are  most  advantageously  conveyed  to  the  terminal  organs. 

'  It  will  be  seen  later  on  that  there  are  reasons  for  thinking  that  impulses 
passing  along  the  auditory  nerve  may  give  rise  to  other  effects  than  auditory 
sensations. 


CIIAI'.    IIJ.]         HKAKING,    SMLLl,,    ANU    TASIK.  575 

The  Acoustic  Apparatus. 

Waves  of  sound  can  and  do  reach  the  endolymph  of  the  laby- 
rinth by  direct  conduction  tlirough  the  skull.  Since  however 
sonorous  vibrations  are  transmitted  with  great  difficulty  from  the 
air  to  solids  and  liquids,  and  most  sounds  come  to  us  through  the 
air,  some  special  apparatus  is  required  to  transfer  the  aerial 
vibrations  to  the  liquids,  of  the  internal  ear.  This  apparatus  is 
supplied  by  the  tympanum  and  its  appendages 

The  concha.  The  use  of  this,  as  far  as  hearing  is  con- 
cerned, is  to  collect  the  waves  of  sound  coming  in  various 
directions,  and  to  direct  them  on  to  the  membrana  tympani.  In 
ourselves  of  moderate  service  only,  in  many  animals  it  is  of  great 
importance. 

The  membrana  tympani.  It  is  a  characteristic  property 
of  stretched  membranes  that  they  are  readily  thrown  into  vibration 
by  aerial  waves  of  sound.  'Ihe  membrana  tympani,  from  its 
peculiar  conformation,  being  funnel-shaped  with  a  depressed 
centre  surrounded  by  sides  gently  convex  outwards,  is  peculiarly 
susceptible  to  sonorous  vibrations,  and  is  most  readily  thrown 
into  corresponding  movements  when  waves  of  sound  reach  it  by 
the  meatus.  It  has  moreover  this  useful  feature,  that  unlike 
other  stretched  membranes,  it  has  no  marked  note  of  its  own.  It 
is  not  thrown  into  vibrations  by  waves  of  a  particular  length  more 
readily  than  by  others.  It  answers  equally  well  within  a  consider- 
able range,  to  vibrations  of  very  different  wave-lengths.  Had  it  a 
fundamental  tone  of  its  own,  we  should  be  distracted  by  the 
prominence  of  this  note  in  most  of  the  sounds  we  hear. 

The  auditory  ossicles.  The  malleus,  the  handle  of  which 
descending  forwards  and  inwards,  is  attached  to  the  membrana 
tympani,  and  the  incus,  whose  long  process  is  connected  by  means 
of  its  OS  orbiculare  or  lenticular  process  and  the  stapes  to  the 
fenestra  ovalis,  form  together  a  body  which  rotates  round  an  axis, 
passing  through  the  short  process  of  the  incus,  the  bodies  of  the 
incus  and  malleus,  and  the  processus  gracilis  of  the  malleus. 
When  the  malleus  is  carried  inwards,  the  incus  moves  inwards  too, 
^nd  when  the  malleus  returns  to  its  position,  the  incus  returns 
with  it,  the  peculiar  saddle-sh.iped  joint  \vith  its  catch  teeth  per- 
miting  this  movement  readily,  but  preventing  the  stapes  being 
pulled  back  when  the  membrana  tympani  with  the  malleus  is,  for 
any  reason,  pushed  outwards  more  than  usual ;  the  joint  then 
gapes,  so  as  to  permit  the  malleus  to  I)e  moved  alone.  Various 
ligaments,  the  superior  or  suspensory,  anterior,  and  external,  also 


57^  THE   TYMPANUM.  [BOOK   III. 

serve  to  keep  the  malleus  in  place.  The  whole  series  of  ossicles 
may  be  regarded  as  a  lever,  the  fulcrum  of  which  is  situated  at 
the  ligamental  attachment  of  the  short  processus  of  the  incus  to 
the  posterior  wall  of  the  tympanum.  The  long,  malleal  arm  of 
this  lever  is  about  g^  mm.,  the  short,  stapedial,  6|-  mm.  in  length; 
hence  the  movements  of  the  stapes  are  less  than  those  of  the 
tympanum ;  but  the  loss  in  amplitude  is  made  up  by  a  gain  of 
force,  which  is  in  itself  an  obvious  advantage. 

Thus  every  movement  of  the  tympanic  membrane  is  trans- 
mitted through  this  chain  of  ossicles  to  the  membrane  of  the 
fenestra  ovalis,  and  so  to  the  perilymph  of  the  labyrinth ;  the 
vibrations  of  the  tympanic  membrane  are  conveyed  with  increased 
intensity,  though  with  diminished  amplitude,  to  the  latter.  That 
the  bones  thus  move  en  masse  has  been  proved  by  recording  their 
movements  in  the  usual  graphic  method.  A  very  light  style 
attached  to  the  incus  or  stapes  is  made  to  write  on  a  travelling 
surface  ;  when  the  membrana  tympani  is  thrown  into  vibrations 
by  a  sound,  the  curves  described  by  the  style  indicate  that  the 
chain  of  bones  moves  with  every  vibration  of  the  tympanum. 
On  the  other  hand,  the  comparatively  loose  attachments  of  the 
several  bones  is  an  obstacle  to  the  molecular  transmission  of 
sonorous  vibrations  through  them.  Moreover,  sonorous  vibrations 
can  only  be  transmitted  to  or  pass  along  such  bodies  as  either  are 
very  long  compared  to  the  length  of  the  sound-waves,  or,  as  in  the 
case  of  membranes  and  strings,  have  one  dimension  very  much 
smaller  than  the  others.  Now  the  bones  in  question  are  not 
especially  thin  in  any  one  dimension,  but  are  in  all  their 
dimensions  exceedingly  small  compared  with  the  length  of  the 
vibrations  of  even  the  shrillest  sounds  we  are  capable  of  hearing ; 
hence  they  must  be  useless  for  the  molecular  propagation  of 
vibrations. 

The  tensor  tympani  muscle  even  in  a  quiescent  state  is 
of  use  in  preventing  the  membrana  tympani  being  pushed  out  far. 
When  it  contracts,  it  renders  the  membrana  tympani  more  tense 
and  hence  has  been  supposed  to  act  either  as  a  damper  lessening 
the  amount  of  vibration  of  the  membrane  in  the  case  of  two 
powerful  sounds,  or  as  a  sort  of  accommodation  mechanism  attuning 
the  membrane  to  the  sounds  which  fall  upon  it.  Its  activity  in 
this  direction  is  regulated  by  a  reflex  action.  In  some  persons 
the  muscle  seems  to  be  partly  under  the  dominion  of  the  will, 
since  a  peculiar  craclding  noise  which  these  persons  can  produce 
at  pleasure  appears  to  be  caused  by  a  contraction  of  the  tensor 
tympani. 


CHAK    III. J        IIEAkliNt;,   SMELL,   AND    TASTK.  377 

Hensen'  has  directly  observed  the  action  of  the  tensor  tympani 
in  the  dog  and  cat,  :;nd  finds  that  while  the  mus?le  is  readily  thrown 
into  contraction  at  the  commencement  of  every  sound  or  noise,  it 
returns  to  rest  and  becomes  rclixcd  agiin  during  the  continuance  of  a 
prolonged  note.  He  suggests  that  by  tlirowing  the  muscle  into  activity 
the  sound  of  a  consonant  muy  make  the  mcmbrana  tympani  tense  and 
thus  render  it  better  adapted  to  carry  on  the  vibntions  of  the  vowel 
sound  following  the  consonant. 

The  stapedius  muscle  is  supposed  to  regulate  the 
movements  of  the  stai)es,  and  especially  to  prevent  its  base  being 
driven  too  far  into  the  fenestra  ovalis  during  large  or  sudden 
movements  of  the  membrana  tympani. 

A  contraction  of  the  stapedius  by  itself  would  have  the  effe:rt  of 
pulling  the  hinder  end  of  the  base  of  the  stapes  out  of,  and  of  pushing 
the  front  end  into,  the  fenestra  ovalis,  and  this  might  give  rise  to  a 
wave  in  the  perilymph.  For  speculations  on  this  and  on  the  reason 
why  the  stapedius  is  governed  by  the  facial  and  the  tensor  tympani  by 
the  fifth  nerve,  see  Budge-. 

The  so-cilled  laxator  tympani  is  considered  ^  to  be  not  a  muscle  at 
all,  but  a  part  of  the  ligamentous  supports  of  the  malleus. 

The  Eustachian  Tube.  This  serves  to  maintain  an  equi- 
librium of  pressure  between  the  external  air  and  that  within  the 
tympanum,  and  to  serve  as  an  exit  for  the  secretions  of  that  cavity. 
Were  the  tympanum  permanently  closed  the  vibrations  of  the 
membrana  tympani  would  be  injuriously  affected  by  variations  of 
pressure  occurring  either  inside  or  outside. 

The  Eustachian  tube  is  undoubtedly  open  during  swallowing  but  it 
is  still  disputed  whether  it  remains  permanently  open,  or  is  opened 
only  at  intervals. 

Auditory  Sensations. 

Each  vibration  communicated  by  the  stapes  to  the  perilymph 
travels  as  a  wave  over  the  vestibule,  the  semi-circular  canals,  and 
other  parts  of  the  labyrinth,  and  is  there  transmitted  to  the  endo- 
lymph  ;  it  passes  on  from  the  vestibule  into  the  scala  vestibuli  of 
the  cochlea,  and  descending  the  scala  tympani,  ends  as  an  impulse 
against  the  membrane  of  the  fenestra  rotunda.  In  the  maculce 
and  crista:  the  vibrations  of  the  enilolymph  are  supposed  to  throw 
into  correspondln^  vibrations  the  so-called  auiiitory  hairs.  In  the 
cochlea  the  vibrations  of  the  perilymph  arc  supposed  to  throw 
into  vibrations  the  basilar  membrane  with  the  superimposed  organ 

'  Arch  f.  Anal.  u.  P'lys.,  iSjS  (Phys.  Ab[h.),-p.  312. 

■  Plliiger's  Aic/iir  (1874)  IX.  460. 

3  Hclmholtz,  Ptliijer's  ArcJth',  i.  (1S68)  i.      Ilenlc,  Anatomu,  II.  746. 

F.  P  37 


578  AUDITORY   SENSATIONS,  [BOOK  III. 

of  Corti,  consisting  of  the  rods  of  Corti  with  the  inner  and  outer 
hair-cells.  The  vibrations  thus  transmitted  to  these  structures'  give 
rise  to  nervous  impulses  in  the  terminations  of  the  auditory  nerves, 
and  these  impulses  reaching  certain  parts  of  the  brain  produce 
what  we  call  auditory  sensations.  We  are  accustomed  to  divide 
our  auditory  sensations  into  those  caused  by  noises  and  those 
caused  by  musical  sounds.  It  is  the  characteristic  of  the  latter  that 
the  vibrations  which  constitute  them  are  periodical ;  they  occur 
and  recur  at  regular  intervals.  When  no  periodicity  is  present  in 
the  vibrations,  when  the  repetition  of  the  several  vibrations  is 
irregular,  or  the  period  so  complex  as  not  to  be  readily  appreciated, 
the  sensation  produced  is  that  of  a  noise.  There  is  however  no 
abrupt  line  between  the  two.  Between  a  pure  and  simple  musical 
sound  produced  by  a  series  of  vibrations  each  of  which  has  exactly 
the  same  wave-length,  and  a  harsh  noise  in  which  no  consecutive 
vibrations  may  be  alike,  there  are  numerous  intermediate  stages. 

In  both  noises  and  musical  sounds  we  recognise  a  character 
which  we  call  loudness.  This  is  determined  by  the  amplitude 
of  the  vibrations ;  the  greater  the  disturbance  of  the  air  (or  other 
medium)  the  louder  the  sound.  In  a  musical  sound  we  recog- 
nise also  a  character  which  we  call  pitch.  This  is  determined  by 
the  wave-length  of  the  vibrations  ;  the  shorter  the  wave-length, 
the  larger  the  number  of  consecutive  vibrations  which  fall  upon 
the  ear  in  a  second,  the  higher  the  pitch.  We  are  able  to  speak 
of  a  whole  series  of  tones  or  musical  sounds  of  different  pitch,  from 
the  lowest  to  the  highest  audible  tone.  And  even  in  many  noises 
we  can,  to  a  certain  extent,  recognise  a  pitch,  indicating  that  among 
the  multifarious  vibrations  there  is  a  periodicity  with  fixed  intervals. 

Lastly,  we  distinguish  musical  sounds  by  their  quality;  the 
same  note  sounded  on  a  piano  and  on  a  violin  produce  very 
different  sensations,  even  when  a  series  of  vibrations  having  in 
each  case  the  same  period  of  repetition  is  set  going.  This  arises 
from  the  fact  that  the  musical  sounds  generated  by  most  musical 
instruments  are  not  simple  but  compound  vibrations.  When  the 
note  C  in  the  treble  for  instance  is  struck  on  the  piano,  it  is 
perfectly  true  that  a  series  of  vibrations  with  a  period  characteristic 
of  the  pure  tone  of  the  treble  C  are  started,  but  it  is  also  true  that 
those  vibrations  are  accompanied  by  other  vibrations  with  periods 
characteristic  of  the  C  in  the  octave  above,  of  the  G  above  that, 
of  the  C  in  the  next  octave,  and  of  the  E  above  that.  And  it  is 
the  effect  of  all  these  vibrations  together  on  the  ear  which  causes 
the  sensation  which  we  associate  with  the  sound  of  the  treble  C 
on  the  piano.  Almost  all  musical  sounds  are  thus  composed  of 
what  is  called  a  '  fundamental  tone  '  accompanied  by  a  number  of 


CHAP.   Ill]        TIEARINC,    SMKI.L.    AND   TASTE.  579 

'overtones.'  And  tlic  overtones  varying  in  number  and  relative 
prominence  in  different  instruniencs,  give  rise  to  a  difference  in 
the  sensation  caused  by  the  whole  tone.  So  tiiat  while  the 
fundamental  tone  determines  the  pitch  of  the  sound,  the 
quality  of  the  sound  is  determined  by  the  number  and  relative 
prominence  of  the  overtones.  In  a  similar  way  we  distinguish 
the  quality  of  noises,  such  as  a  banging,  crackling,  or  rustling 
noi.se,  by  the  predominance  of  vibrations  having  a  less  orderly 
character,  and  recurring  less  regularly  than  those  of  a  musical 
sound. 

Since  we  have  a  very  considerable  appreciation,  capable  by 
exercise  of  astonishing  enlargement,  of  the  loudness,  pitch,  and 
quality  of  a  wide  range  of  noises  and  musical  sounds,  it  is  clear 
that,  within  the  limits  of  hearing,  each  vibration  or  series  of 
vibrations  must  produce  its  effect  on  the  auditory  nerves,  according 
to  the  measure  of  its  intensity  and  period.  Out  of  those  effects, 
out  of  the  sensory  impulses  to  wliich  the  several  vibrations 
thus  give  rise,  are  generated  our  sensations  of  the  noise  or  of 
the  sound. 

The  vibrations  of  a  musical  sound  (and  since  noises  are  so 
imperfectly  understood,  we  may,  with  benefit,  chiefly  confine 
ourselves  to  musical  sounds)  as  they  pass  through  the  air  (or 
other  medium)  are  not  discrete  ;  the  vibrations  corresponding  to 
the  fundamental  tone  antl  overtones  do  not  travel  as  so  many 
separate  waves ;  they  all  together  form  one  complex  disturbance 
of  the  medium  ;  and  it  is  as  one  coriposite  wave  that  the  sound 
falls  on  the  membrana  tympani,  and  passing  through  the  auditory 
apparatus,  breaks  on  the  terminations  of  the  auditory  nerve.  And 
when  two  or  more  musical  sounds  are  heard  at  the  same  time, 
the  same,  fusion  of  the  waves  occurs.  Since  wc  can  distinguish 
several  tones  reaching  our  ear  at  the  same  time,  it  is  clear  that  we 
must  possess  in  our  minds  or  in  our  ears  some  means  of  analysing 
these  composite  waves  of  sound  which  fall  on  our  acoustic  organs, 
and  of  sorting  out  their  constituent  vibrations. 

'I'here  is  at  hand  a  simple  and  easy  physical  method  of 
analysing  composite  sounds.  If  a  person  standing  before  an  open 
piano  sings  out  any  note,  it  will  be  observed  that  a  number  of 
the  strings  of  the  piano  will  be  thrown  into  vibration,  and  on 
examination  it  will  be  found  that  those  strings  which  are  thus  set 
going  correspond  in  pitch  to  the  fundamental  tone  and  to  the 
several  overtones  of  the  note  sung.  The  note  sung  reaches  the 
strings  as  a  complex  wave,  but  these  strings  are  able  to  analyse 
the  wave  into  its  constituent  vibrations,  each  string  taking  up 
those  vibrations  and  those  vibrations  only  which  belong  to  the 


580  AUDITORY   SENSATIONS.  [BOOK  III. 

tone  given  forth  by  itself  when  struck.  If  we  suppose  that  each 
terminal  fibril  of  the  auditory  nerve  is  connected  with  an  organ  so 
far  like  a  piano-string  that  it  will  readily  vibrate  in  response  to  a 
series  of  vibrating  impulses  of  a  given  period  and  to  none  other, 
and  that  we  possess  a  number  of  such  terminal  organs  sufficient 
for  the  analysis  of  all  the  sounds  which  we  can  analyse,  and  thdt 
each  terminal  organ  so  affected  by  particular  vibrations  gives  rise  to 
a  sensory  impulse  and  thus  to  a  sensation  of  a  distinct  character 
— if  we  suppose  these  organs  to  exist,  our  appreciation  of  sounds 
is  in  a  large  measure  explained.  In  the  organ  of  Corti  we  find 
structures,  the  arrangement  of  which  irresistibly  suggests  to  us 
that  these  are  the  organs  we  are  seeking.  We  have  only  to  suppose 
that  of  the  long  series  of  rods  of  Corti,  varying  regularly  as  these 
do  from  the  bottom  to  the  top  of  the  spiral,  in  length  and  in  the 
span  of  their  arch,  each  pair  will  vibrate  in  response  to  a  particular 
tone,  and  the  whole  matter  seems  explained.  But  .the  more  the 
subject  is  inquired  into,  the  more  complex  and  difficult  it  appears; 
and  we  are  obliged  to  conclude  that  the  part  played  by  the  rods 
of  Corti  is  only  a  subordinate  part  of  the  function  of  the  whole 
organ  of  Corti. 

In  the  first  place,  it  is  difficult  to  see  how  the  rods  of  Corti,  even  if 
they  are  thrown  into  vibration,  can  originate  sensory  impulses,  for  the 
fibrils  of  the  auditory  nerve  terminate  in  the  inner  and  outer  hair-cells, 
and  it  is  in  these  cells,  and  not  along  the  course  of  the  fibrils  as  they 
pass  under  and  between  the  rods  of  Corti,  that  the  sensory  impulses 
must  begin.  In  the  second  place,  the  variation  in  length  of  the  fibres 
along  the  series  is  insufficient  for  the  work  assigned  to  them.  More- 
over, they  appear  not  to  be  elastic.  Lastly,  they  are  wholly  absent  in 
birds,  who  very  clearly  can  appreciate  musical  sounds.  This  last  fact 
proves  indubitably  that  the  rods  in  question  are  not  absolutely  essential 
for  the  recognition  of  tones.  In  the  face  of  these  difficulties  it  has  been 
suggested  that  the  basilar  membrane,  which  is  present  in  birds,  and 
■whi:h,  being  tense  radially  but  loose  longitudinally,  i.e.  along  the  spiral 
of  the  cochlea, may,as  physical  investigations  shew,  be  consideredas  con- 
sisting of  a  number  of  parallel  radial  strings,  each  capable  of  independent 
vibrations,  is  the  sought-for  organ  of  analysis.  According  to  this  view, 
a  particular  vibration  reaching  the  scala  tympani  of  the  cochlea  throws 
into  sympathic  vibrations  a  small  portion  of  the  basilar  membrane,  the 
vibrations  of  which  in  turn  so  affect  the  structures  overlying  it,  that 
sensory  impulses  are  generated.  These  sensory  impulses  reaching  the 
brain  give  rise  to  a  corresponding  sensation  of  a  particular  tone. 
According  to  Hensen  the  radial  dimensions  of  the  basilar  membrane 
in  man  diminish  downwards  from  "495  mm.  at  the  hamulus  to  •04125 
mm.  near  the  bottom  of  the  spiral,  giving  a  much  greater  range  than 
the  rods  of  Corti,  the  difference  in  length  of  which  is  simply  that 
between  "048  and  -085  mm.  for  the  inner,  and  between  "019  and  "085 
for  the  outer,  fibres. 


CHAP.   III.]        HEARING,   SMELL,   AND   TASTE.  58I 

The  remarkable  reticular  membrane  which  has  such  peculiar  rela- 
tions with  the  hair-cells,  and  through  them  with  the  basilar  membrane, 
must,  one  might  imagine,  have  some  special  function  ;  but  it  is  impos- 
sible to  assign  to  it  any  satisf  ictory  duty.  The  structural  arrangements 
seem,  if  anything,  to  indicate  that  wh.n  a  segment  of  t!ie  basilar  mem- 
brane is  thrown  into  vibrations,  the  overlying  hair-cells,  reticular 
me  nbrane,  and  rods  of  Corti  vibrate  en  masse  together  with  it.  But 
this  renders  the  whole  matter  still  more  difficult.  Indeed  the  whole 
subject  is  in  the  highest  degree  obscure,  and  the  most  we  can  say  is 
that  the  organ  of  Corti  as  a  whole  seems  to  be  in  some  way  con- 
nected with  the  appreciation  of  tones,  but  that  at  present  it  is  very 
hazardous  to  attempt  to  explain  how  it  acts,  or  to  assign  particular 
functions  to  particular  parts.  The  distinction  between  the  inner  and 
outer  hair-cells  seems  to  be  very  parallel  to  that  between  the  rods  and 
the  cones  of  the  retina ;  but  even  this  analogy  may  be  a  fallacious 
one. 

Hensen  has  observed  that  among  the  auditory  hairs  of  the  Crustacea, 
some  will  vibrate  to  particular  notes  ;  but  the  auditory  hairs  of  the 
mammal  are  far  too  much  of  the  same  length  to  permit  the  supposition 
that  they  can  act  as  organs  of  analysis. 

If  the  organ  of  Corti  is  the  means  by  which  we  appreciate  tones,  it 
is  evident  that  by  it  also  we  must  be  able  to  estimate  loudness,  for  the 
quality  of  a  musical  sound  is  dependent  on  the  relative  intensity,  as 
well  as  on  the  nature,  of  the  overtones.  And  since  noise  is  at  best  but 
confused  music,  the  cochlea  must  be  a  means  of  appreciating  noises 
as  well  as  sounds.  But  this  would  leave  nothing  whatever  for  the  rest 
of  the  labyrinth  to  do  as  far  as  the  appreciation  of  sound  is  concerned. 
We  have  no  reason  to  think  that  any  impulse  which  could  affect  the  hair- 
cells  of  the  maculre  and  crista;  could  not  aftect  the  hair-cells  of  the 
organ  of  Corti.  That  this  p  irt  of  the  ear  is  however  concerned  in 
he  ;ring  is  shewn  by  its  being  the  only  auditory  organ  in  the  i:hthyo- 
psida,  unless  we  suppose  that  in  the  higher  vertebrates  its  function  has 
been  wholly  transferred  to  the  cochlea.  That  the  semicircular  canals 
have  duties  apart  from  hearing  we  shall  shew  later  on. 

Concerning  the  function  of  the  other  parts  of  the  internal  ear  we 
know  very  little.  The  otoliths  have  been  supposed  to  intensify  the 
vibrations  of  the  endolymph  ;  but  since  apparently  they  are  lodged  in 
a  quantity  of  mucus  it  is  probable  that  they  really  act  as  dampers.  A 
similar  damping  action  has  been  suggested  for  the  membrane  of  Corti 
{menibrana  teciorin)  overhanging  the  fibres  and  hair-cells  ;  and  some 
writers  have  supposed  that  muscular  fibres  present  in  the  planum 
semilunare  may  by  tightening  the  basilar  membrane  serve  as  a  sort  of 
accommodation  mechanism. 

It  must  however  be  borne  in  mind  that  even  making  the 
fullest  allowance  for  the  assistance  afforded  us  by  the  organ  of 
Corti,  the  appreciation  of  any  sound  is  ultimately  a  mental  act. 
The  analysis  of  the  vibrations  by  the  fibres  of  Corti  or  the  basilar 
membrane  is  simply  preliminary  to  a  synthesis  of  the  sensory 
impulses    so  generated  into  a  complex  sensation.      We  do  not 


582  AUDITORY   SENSATIONS.  [BOOK   III. 

receive  a  distinct  series  of  specific  auditory  impulses  resulting  in 
a  specific  sensation  for  every  possible  variation  in  the  wave-length  , 
of  sonorous  vibrations  any  more  than  we  receive  a  distinct  series 
of  specific  visual  impulses  for  every  possible  wave-length  of 
luminous  vibrations.  In  each  case  we  have  probably  a  number 
of  primary  sensations,  from  the  various  mingling  of  which,  in 
different  proportions,  our  varied  complex  sensations  arise  ;  the 
difference  between  the  eye  and  the  ear  being  that  whereas  in  the 
former  the  number  of  primary  sensations  appears  to  be  limited  to 
three,  viz.  red,  green,  and  violet ;  in  the'  latter,  thanks  to  the 
organ  of  Corti,  the  number  is  very  large ;  what  the  exact  number 
is  we  cannot  at  present  tell.  Our  appreciation  of  a  sound  is  at 
bottom  an  appreciation  of  the  combined  effect  produced  by  the 
relative  intensities  to  which  the  primary  auditory  sensations  are, 
with  the  help  of  the  organ  of  Corti,  excited  by  the  sound. 

Whatever  be  the  explanation  of  the  manner  in  which  our 
distinct  auditory  sensations  arise,  the  range  and  precision  of  our 
appreciation  of  musical  sounds  is  very  great.  Vibrations  with  a 
recurrence  below  30  a  second  are  unable  to  produce  a  sensation 
of  sound  ;  if  the  waves  are  powerful  enough  we  may  feel  them, 
but  we  do  not  hear  them  if  the  vibrations  are  simple,  and  such 
as  would  give  rise  to  a  pure  tone  ;  if  the  fundamental  tone  is 
accompanied  by  overtones  we  may  hear  these  and  are  thus  apt  to 
say  we  hear  the  former  when  in  reality  we  only  hear  the  latter. 
The  note  of  the  i6-feet  organ  pipe,  ^;^  vibrations  a  second,  gives 
us  the  sensation  of  a  dronmg  sound.  A  tone  of  40  vibrations  is 
however  quite  distinct.  In  the  other  direction  it  is  possible  to 
hear  a  note  caused  by  38,000  vibrations  a  second,  though  the 
limit  for  most  persons  is  far  lower,  about  16,000'.  Some  persons 
hear  grave  sounds  more  easily  than  high  ones,  and  mce  versa. 
This  may  be  so  pronounced  as  to  justify  the  subjects  being 
spoken  of  as  deaf  to  grave  or  high  tones  respectively. 

The  power  of  distmguishing  one  note  from  another  varies,  as 
is  well  known,  in  different  individuals,  according  as  they  have 
or  have  not  a  '  musical  ear.'  A  well-trained  ear  can  distinguish 
the  difference  of  a  single  or  even  of  a  half  vibration  a  second, 
and  that  through  a  long  range  of  notes,  the  sensation  not  obeying 
Weber's  law^  The  range  of  an  ordinary  appreciation  of  tones 
lies  between  40  and  4000  vibrations  a  second,  i.e.  between  the 

'  Helmholtz,  Toneiiipfindungeti,  p.  30.  Cf.  Preyer  \Grenzen  der  Ton- 
"wahrnehmung,  Physiolog.  Abhandlungen,  I.  I,  1876),  who  places  the  grave  limit 
as  varying  from  15  to  24,  and  the  acute  limit  from  16,000  to  40,000  vibrations 
per  sec. 

*  Cf.  Preyer,  op.  cit.  and  Acustische  Untersuch.,  ibid.  II.  4  (1879). 


CHAI'.    III.]        HEARlfIG,   SMKLL,   AND   TASTE.  5S3 

lowest  bass  C  (C,  33  vibrations)  and  the  highest  treble  C  (C54224 
vilirations)  of  the  piano  j  tones  above  and  below  these,  even 
when  audible,  being  distinguished  from  each  other  with  great 
difficulty. 

When  the  two  consecutive  sounds  follow  each  other  at  a 
sufticiently  short  interval  the  sensations  are  fused  into  one.  In 
this  respect  auditory  sensations  are  of  shorter  duration  than 
ocular  sensations.  When  ocular  sensations  are  repeated  ten 
times  in  a  second  they  become  fused  (p.  542),  whereas  the  ticks 
of  a  pendulum  beating  100  in  a  second  are  readily  audible  as 
distinct  sounds.  When  two  tuning-forks  not  quite  in  tune  are 
struck  together  the  interference  of  the  vibrations  gives  rise  to  an 
alternating  rise  and  fall  of  the  sound,  known  as  '  beats.'  When 
the  beats  follow  each  other  as  rapidly  as  132  in  a  second  they 
cease  to  be  recognised,  that  is  to  say,  the  sensations  which  they 
cause  become  fused.  Just  before  they  disappear  they  give  a 
peculiar  disagreeable  roughness  to  the  sound.  The  pleasure  given 
by  musical  sounds  depends  largely  on  the  absence  of  this 
incomplete  fusion  of  sensations. 

Corresponding  to  entoptic  phenomena  there  are  various  entotic 
phenomena,  sensations  or  modifications  of  sensations  originating 
in  the  tympanum  or  in  the  labyrinth ;  moreover  sensations  of 
sound  may  rise  in  the  auditory  nerve  or  in  the  brain  itself,  without 
any  vibration  whatever  falling  on  the  labyrinth. 

Auditory  Judgments. 

In  seeking  for  the  cause  of  our  visual  sensations  we  invariably 
refer  to  the  external  world.  The  sensation  caused  by  a  direct 
stimulation  of  the  optic  nerve  or  retina  by  a  blow  or  a  galvanic 
current,  we  identify  with  that  caused  by  a  flash  of  light,  A 
sensation  arising  from  any  stimulation  of  the  left  side  of  our 
retina  we  regard  as  caused  by  some  object  on  the  right-hand  side 
of  our  external  visible  world.  In  a  similar  way,  but  to  a  less 
extent,  we  project  our  auditory  sensations  into  the  world  outside 
us,  and  when  the  auditory  nerve  is  atitected  we  seek  the  cause  in 
vibrations  starting  at  a  greater  or  less  distance  from  us.  We  do 
not  tiiink  of  the  sound  as  originating  in  the  ear  itself. 

This  mental  projection  of  the  sound  is  much  more  complete 
when  the  ear  is  stimulated  by  vibrations  reaching  it  through  the 
membrana  tympani  than  when  the  \ibrations  are  conducted  by 
the  solids  of  the  head  directly  to  the  perilymph  of  the  labyrinth. 
When  the  meatus  externus  is  filled  with  fluid  and  the  vibrations 
of  the  membrana  tympani  are  in  consequence  interfered  with,  the 


584  AUDITORY  JUDGMENTS.  [BOOK    III. 

apparent  outwardness  01'  sounds  is  to  a  very  large  extent  lost ; 
sounds,  however  caused,  seem  under  these  circumstances  to  arise 
in  the  ear.  Hence  it  would  seem  that  our  judgment  of  the 
objectiveness  of  sounds  is  largely  dependent  on  coincident 
sensations  derived  in  some  way  or  other  from  the  tympanum. 

When  sounds  impinge  on  the  solids  of  the  head,  as  when  a  watch 
is  held  between  the  teeth,  the  membrana  tympani  is  still  functional. 
Vibrations  are  conveyed  from  the  temporal  bone  to  it  and  hence  pass 
in  the  usual  way,  in  addition  to  those  transmitted  directly  from  the 
bone  to  the  perilymph. 

Our  judgment  of  the  distance  of  sounds  is  very  limited.  A 
sound  whose  characters  we  know  appears  to  us  near  when  it  is 
loud,  and  far  off  when  it  is  faint.  A  blindfold  person  will  be 
unable  to  distinguish  between  the  difference  of  intensity  produced 
by  a  tuning-fork  being  held  before  him,  first  with  the  broad  edge 
of  the  fork  toward  him  and  then  with  the  narrow  edge,  and  the 
difference  caused  by  the  removal  of  the  tuning-fork  to  a  distance. 
We  can  on  the  whole  better  appreciate  the  distance  of  noises  than 
of  musical  sounds. 

Our  judgment  of  the  direction  of  sounds  is  also  very 
limited.  Our  chief  aid  in  this  is  the  position  in  which  we  have 
to  place  the  head  in  order  that  we  may  hear  the  sound  to  the 
best  advantage.  If  a  tuning-fork  be  held  in  the  median  vertical 
plane  over  the  head,  though  it  is  easy  to  recognize  it  as  being  in 
the  median  plane,  it  becomes  very  difficult  when  the  eyes  are  shut 
to  say  what  is  its  position  in  that  plane,  i.e.  whether  it  is  more 
towards  the  front  or  back  of  the  head.  In  this  respect,  too,  our 
appreciation  is  more  accurate  in  the  case  of  noises  than  of 
musical  sounds,  with  the  exception  of  those  given  out  by  the 
human  voice,  the  direction  of  which  can  judged  better  than  even 
that  of  a  noise. 


Sec.  2.     Smell. 

Odorous  particles  present  in  the  inspired  air  passing  through 
the  lower  nasal  chambers  diffuse  into  the  upper  nasal  chambers, 
and  falling  on  the  olfactory  epithelium  produce  sensory  impulses 
which,  ascending  to  the  brain,  give  rise  to  sensations  of  smell. 
We  may  presume  that  the  sensory  impulses  are  originated  by  the 
contact  of  the  odorous  particles  with  the  peculiar  rod-shaped 
olfactory  cells  described  by  Max  Schultze  \  but  we  are  as  much 
in  the  dark  about  this  matter  as  about  the  development  of  visual 


CHAP.   III.]        HEARING,   SMELL,   AND   TASTE.  585 

sensory  impulses  in  the  rods  and  cones  or  of  auditory  sensory 
impulses  in  the  organ  of  Corti. 

The  subsidiary  apparatus  of  smell  is  exceedingly  meagre.  By 
the  forced  nasal  inspiration,  called  sniffing,  \vc  draw  air  so  forcibly 
through  the  nostrils  that  currents  pass  up  into  the  upper  as  well  as 
the  lower  nasal  chambers ;  and  thus  a  more  complete  contact  of 
the  odorous  particles  with  the  olfactory  membrane  than  that 
supplied  by  mere  diffusion  is  provided  for. 

We  have  every  reason  to  think  that  any  stimulus  applied  to 
the  olfactory  nerve  will  produce  the  sensation  of  smell ;  but  the 
proof  of  this  is  not  so  clear  as  in  the  case  of  the  optic  and 
auditory  nerves.  We  are,  however,  subject  to  sensations  of  smell 
not  caused  by  objective  odours.  The  olfactory  membrane  is  the 
onlv  part  of  the  body  in  which  odours  as  such  can  give  rise  to  any 
sensations  ;  and  the  sensations  to  which  they  give  rise  are  always 
those  of  smell.  The  mucous  membrane  of  the  nose  is  however 
also  an  instrument  for  the  development  of  afferent  impulses 
other  than  the  specific  olfactory  ones.  Chemical  stimulation  of 
the  olfactory  membrane  by  pungent  substances  such  as  ammonia 
gives  rise  to  a  sensation  distinct  from  that  of  smell,  a  sensation 
which  affords  us  no  information  concerning  the  chemical  nature  of 
the  stimulus,  and  which  is  indistinguishable  from  the  sensations 
j^roduced  by  chemical  stimulation  of  other  parts  of  the  nasal 
membrane  as  well  as  of  other  surfaces  equally  sensitive  to  chemical 
action.  It  is  probable  that  these  two  kinds  of  sensations  thus 
arising  in  the  olfactory  membrane  are  conveyed  by  different  nerves, 
the  former  by  the  olfactory,  the  latter  by  the  fifth  nerve.  • 

For  the  development  of  smell  it  appears  necessary  that  the 
odorous  particles  should  be  conveyed  to  the  nasal  membrane  in 
a  gaseous  medium,  or  at  least  that  the  surface  of  the  membrane 
should  not  be  e.xposed  at  the  same  time  to  the  action  of  fluids. 
Thus  when  the  nostril  is  filled  with  rose-water,  the  odour  of  roses 
is  not  perceived  ;  and  simply  filling  the  nostrils  with  distilled 
water  suspends  for  a  time  all  smell,  the  sense  returning  gradually 
after  the  water  has  been  removed  ;  the  water  apparently  acts 
injuriously  on  the  delicate  olfactory  cells. 

Each  substance  that  we  smell  causes  a  specific  sensation,  and 
we  are  not  only  able  to  recognize  a  multitude  of  distinct  odours, 
but  also  to  distinguish  individual  odours  in  a  mixed  smell. 

As  in  the  previous  senses,  we  project  our  sensation  into  the 
external  world  ;  the  smell  appears  to  be  not  in  our  nose,  but  some- 
where outside  us.  We  can  judge  of  the  position  of  the  odour 
however  even  less  definitely  than  we  can  of  that  of  a  sound. 

The  sensation  takes  some  time  to  develope  after  the  contact  of 


586  TASTE.  -       [book  III. 

the  stimulus  with  the  olfactory  membrane,  and  may  last  very  long. 
When  the  stimulus  is  repeated  the  sensation  very  soon  dies  out ; 
the  sensory  terminal  organs  speedily  become  exhausted.  Mental 
associations  cluster  more  strongly  round  sensations  of  smell  than 
round  any  other  impressions  we  receive  from  without.  And  reflex 
effects  are  very  frequent,  many  people  fainting  in  consequence  of 
the  contact  of  a  few  odorous  particles  with  their  olfactory  cells. 

Apparently  the  larger  the  surface  the  more  intense  the  sensa- 
tion ;  animals  with  acute  scent  having  a  proportionately  large  area 
of  olfactory  membrane.  The  quantity  of  material  required  to 
produce  an  olfactory  sensation  may  be,  as  in  the  case  of  musk, 
almost  immeasurably  small. 

When  two  different  odours  are  presented  to  the  two  nostrils, 
an  oscillation  of  sensation  similar  to  that  spoken  of  in  binocular 
vision  (p.  571)  takes  place. 

The  assertion  that  the  olfactory  nerve  is  the  nerve  of  smell  has 
been  disputed.  Cases  have  been  recorded '  of  persons  who  appeared 
to  have  possessed  the  sense  of  smell,  and  yet  in  whom  the  olfactory 
lobes  were  found  after  death  to  be  absent.  Majendie  asserted  that 
animals  could  still  smell  after  the  removal  of  the  olfactory  lobes  ;  but 
the  stimulus  which  he  applied  was  ammonia,  in  no  way  a  test  of  smell. 
Biffi,  operating  on  blind  puppies,  came  to  the  conclusion  that  true  smell 
disappeared  after  destruction  of  the  olfactory  lobes,  and  Prevost°  also 
found  that  in  dogs  smell  disappeared  after  section  of  the  olfactory 
nerves.  On  the  other  hand,  it  is  stated  that  section  or  injury  of  the 
fifth  nerve  causes  a  loss  of  smell  though  the  olfactory  nerve  remains 
intact ;  but  in  these  cases  it  has  not  been  shewn  that  the  olfactory 
membrane  remains  intact,  and  it  is  quite  possible  that,  as  in  the  case 
of  the  eye,  changes  may  take  place  in  the  nasal  membrane  as  the  result 
of  injury  to  the  fifth  nerve,  sufficient  to  prevent  its  performing  its  usual 
functions. 

Sec.  3.     Taste. 

The  word  taste  is  frequently  used  when  the  word  smell  ought 
to  be  employed.  We  speak  of  '  tasting '  odoriferous  substances, 
such  as  an  onion,  wines,  &c.,  when  in  reality  we  only  smell  them 
as  we  hold  them  in  our  mouth  ;  this  is  proved  by  the  fact  that  the 
so-called  taste  of  these  things  is  lost  when  the  nose  is  held,  or  the 
nasal  membrane  rendered  inert  by  a  catarrli. 

The  terminal  organs  of  the  sense  of  taste  thus  more  strictly  de- 
fined, are  the  endings  of  the  glossopharyngeal  and  lingual  nerves 
in  the  mucous  membrane  of  the  tongue  and  palate,  those  nerves 

»  Bernard,  CI.,  SysL  New.,  11.  p.  228. 

2  Archives  d.  Set.  Phys.  et  Nat.,  187 1,  p.  209. 


CHAP.    III.]         IIKAkING,   SMKLL,    AND   TASTK.  587 

serving  as  the  special  nerves  of  taste.  The  subsidiary  apparatus 
IS  confined  to  the  "tongue  and  lips,  which  by  their  movements 
assist  in  l)r'nging  the  sapid  substances  into  contact  with  the  mucous 
membrane  of  the  mouth. 

The  so-called  gustatory  buds  cannot  be  regarded  as  specific  organs 
of  taste,  since  they  occur  in  places  {e.g.  epiglottis)  wholly  devoid  of 
taste. 

Though  we  can  hardly  be  said  to  project  our  sensation  of  taste 
into  the  external  world,  we  assign  to  it  no  subjective  localisation. 
When  we  place  quinine  in  our  mouth,  the  resulting  sensation  of 
taste  gives  us  no  information  as  to  svhere  the  quinine  is,  though 
we  may  learn  that  by  concomitant  general  sensations  arising  in  tlie 
buccal  mucous  membrane. 

We  recognize  a  multitude  of  distinct  tastes,  which  may  be 
broadly  classified  into  acid,  saline,  bitter  and  sweet  tastes.  Sapid 
substances  have  the  power  of  producing  these  sensations  by 
virtue  of  their  chemical  nature.  But  other  stimuli  will  also  give 
rise  to  sensations  of  taste.  When  the  tongue  is  tapped,  a  taste 
is  felt ;  and  when  a  constant  current  is  passed  through  the  mouth, 
an  alkaline  or,  according  to  Vintschgau',  a  bitter  metallic  taste 
is  developed  when  the  anode,  and  an  acid  taste  when  the 
kathode,  is  placed  on  the  tongue.  It  is  probable  that  in  these 
cases  the  terminal  organs  are  indirectly  affected  by  the  current. 
When  hot  or  pungent  substances  are  introduced  into  the  mouth, 
sensations  of  general  feeling  are  excited,  which  obscure  any 
strictly  gustatory  sensations  which  may  be  present  at  the  same 
time. 

Though  analogy  would  lead  us  to  suppose  that  a  stimulus- 
applied  to  any  part  of  the  course  of  the  real  gustatory  fibres  of 
either  the  glossopharyngeal  or  lingual  nerves,  would  give  rise  to  a 
sensation  of  taste  and  nothing  else,  the  proof  is  not  forthcoming ; 
since  both  these  nerves  are  mixed  nerves  containing  other  afferent 
fibres  as  well  as  those  of  taste. 

When  the  constant  current  is  used  as  a  means  of  exciting  taste, 
gustatory  sensations  are  found  to  be  developed  in  the  back,  edges 
and  tip  of  the  tongue,  the  soft  palate,  the  anterior  pillar  of  the 
fauces,  and  a  small  tract  of  the  posterior  part  of  the  hard  palate. 
They  are  absent  from  the  anterior  and  middle  dorsum,  and  under 
surface  of  the  tongue,  the  front  portion  of  the  hard  palate,  the 
posterior  pillars  of  tlie  fauces,  the  gums  and  the  lips.  Sapid  sub- 
stances are  unsuitable  as  a  test  for  this  purpose,  on  account  of 
their  rapid  diffusion.     Bitter  substances  produce  most  effect  when 

'  Pfliigcr's  .'Irchiv,  XX.   (1S79)  p.  Si. 


588  TASTE.  [book   III. 

placed  on  the  back  of,  and  sweet  substances  when  placed  on  the 
tip  of  the  tongue ;  but  the  tasting  power  of  the  tip  of  the  tongue 
varies  very  much  in  different  individuals  and  in  many  seems  almost 
entirely  absents  It  is  said  that  acids  are  best  appreciated  by  the 
edge  of  the  tongue. 

It  is  essential  for  the  development  of  taste,  that  the  substance 
to  be  tasted  should  be  dissolved ;  and  the  effect  is  increased  by 
friction.  The  larger  the  surface  the  more  intense  the  sensation. 
The  sensation  takes  some  time  to  develope,  and  endures  for  a 
long  time,  though  this  may  be  in  fact  due  to  the  stimulus  remain- 
ing in  contact  with  the  terminal  organs.  A  temperature  of  about 
40°  is  the  one  most  favourable  for  the  production  of  the  sensation. 
At  temperatures  much  above  or  below  this,  taste  is  much  impaired. 
The  nerves  of  taste  are,  as  we  have  said,  the  glossopharyngeal 
and  the  lingual  or  gustatory.  The  former  supplies  the  back  of 
the  tongue,  and  section  of  it  destroys  taste  in  that  region.  The 
latter  is  distributed  to  the  front  of  the  tongue,  and  section  of  it 
similarly  deprives  the  tip  of  the  tongue  of  taste.  There  is  no 
reason  for  doubting  that  the  gustatory  fibres  in  the  glossopharyn- 
geal are  proper  fibres  of  that  nerve ;  but  it  has  been  urged  by 
many,  that  the  gustatory  fibres  of  the  lingual  are  derived  from  the 
chorda  tympani,  and  that  those  fibres  of  the  lingual  which  come 
from  the  fifth  are  employed  exclusively  in  the  sensations  of  touch 
and  feeling. 

The  arguments  in  favour  of  this  latter  view  are  as  follows.  Cases 
have  been  observed  in  which  the  fifth  nerve  has  been  destroyed  in  the 
cranium,  and  yet  taste  in  the  front  of  the  tongue  has  not  been  lost.. 
Cases  have  been  observed  where  the  chorda  tympani  has  been  diseased, 
or  injured  in  the  tympanum,  and  where  taste  has  been  impaired.  It  is 
asserted  that  when  the  lingual  is  divided  above  the  junction  of  the 
chorda,  taste  in  the  front  of  the  tongue  is  not  lost,  while  it  disappears 
after  section  of  the  united  lingual  and  chorda.  It  is  also  stated  that  the 
glossopharyngeal  having  been  divided,  and  taste  in  consequence  con- 
fined to  the  front  part  of  the  tongue,  subsequent  section  of  the  chorda 
within  the  tympanum  has  removed  taste  altogether.  On  the  other  hand, 
cases  have  been  observed  where  the  fifth  was  alone  diseased  and  yet 
taste  was  lost  (in  the  front  of  the  tongue)  ;  and  it  is  moreover  urged 
that  while  stimulation  of  the  central  end  of  a  divided  chorda  gives  rise 
to  no  sensation  of  taste,  stimulation  of  an  undivided  chorda  miglit  give 
rise  to  such  sensations  by  simply  promoting  a  flow  of  saliva,  and  that 
divison  of  the  chorda  might  affect  taste  by  interfering  with  the  normal 
flow  of  saliva.  And  even  if  the  chorda  contain  gustatory  fibres  these 
might  have  their  ultimate  origin  in  the  fifth,  coming  from  that  nerve 
to  the  facial  by  the  spheno-palatine  ganglion  and  superficial  petrosal 
nerve. 

.    '  Of.  Vintschgau,  Pfliiger's  Archiv,  xix.  (1879)  p.  236. 


CHAPTER   IV. 
FEELING  AND   TOUCH. 

Sec.  1.     General  Sensibility  and  Tactile  Perceptions. 

We  have  taken  the  foregoing  senses  first  in  the  order  of  discussion 
on  account  of  their  being  eminently  specific.  The  eye  gives  us 
only  visual  sensations,  the  ear  only  auditory  sensations.  The 
sensations  are  produced  in  each  case  by  specific  stimuli ;  the  eye 
is  only  affected  by  light  and  the  ear  by  sound.  Moreover,  the 
information  they  afford  us  is  confined  to  the  external  world ;  they 
tell  us  nothing  about  ourselves.  The  various  visual  sensations 
which  arise  in  our  retina  are  referred  by  us  not  to  the  retina  itself, 
but  to  some  real  or  imaginary  object  in  the  world  without  (in- 
cluding as  part  of  the  external  world  such  portions  of  our 
own  bodies  as  are  visible  to  ourselves).  Such  also  with  diminish- 
ing precision  is  the  information  gained  by  hearing,  taste  and 
smell. 

All  the  other  afferent  nerves  of  the  body,  centripetal  im- 
pulses along  which  are  able  to  affect  our  consciousness,  are  the 
means  of  conveying  to  us  information  concerning  ourselves. 
The  sensations,  arising  in  them  from  the  action  of  various 
slimuli,  are  referred  by  us  to  appropriate  parts  of  our  own  body. 
When  any  body  comes  in  contact  with  our  finger,  we  know 
that  it  is  our  finger  which  has  been  touched ;  frum  the  resul- 
tant sensation  wc  not  only  learn  the  existence  of  certain  qualities 
in  the  object  touched,  but  we  also  are  led  to  connect  the 
cognizance  of  those  qualities  with  a  particular  part  of  our  own 
body. 

Like  the  more  si:«tcific  senses  previously  studied,  the  sensa- 
tions of  which  we  are  now  speaking,  and  which  may  be  referred 
to  under  the  name  of  touch,  using  that  word  for  the  present  in  a 
wide  meaning,  require  for  their  production  terminal  organs;  and 


590  TACTILE   SENSATIONS.  [BGOK   III. 

the  chief  but  not  exclusive  organ  of  touch  is  to  be  found  in  the 
epidermis  of  the  skin  and  certain  underlying  nervous  structures. 
For  the  development  of  specific  tactile  sensations  these  terminal 
organs  are  as  essential  as  are  the  terminal  organs  of  the  eye  for 
sight  or  of  the  ear  for  hearing.  Contact  of  the  skin  with  a  hard 
or  with  a  hot  body  gives  rise  to  a  distinct  sensation,  whereby  we 
recognize  that  we  have  touched  a  hard  or  a  hot  body.  But  the 
application  of  either  body  or- of  any  other  stimulus  to  a  nerve- 
trunk  gives  rise  to  a  sensation  of  general  feeling  only,  correspond- 
ing to  the  simple  sensation  of  light  which  is  produced  by  direct 
stimulation  of  the  optic  nerve.  We  have  no  more  tactile  percep- 
tion of  a  body  which  is  in  contact  with  a  nerve-trunk  than  we 
could  have  visual  perception  of  any  luminous  object,  the  rays 
proceeding  from  which  were  strong  enough  to  excite  sensory 
impulses  when  directed  on  to  the  optic  nerve  instead  of  on  to 
the  retina,  supposing  such  a  thing  to  be  possible.  It  is  further 
characteristic  of  these  ordinary  nerves  of  general  feeling,  that 
the  sensations  caused  by  any  stimulation  of  them  beyond  a 
certain  degree  develope  that  state  of  consciousness  which  we  are 
in  the  habit  of  speaking  of  as  '  pain.'  Putting  aside  the  general 
feeling  which  many  parts  of  the  eye  possess,  a  very  strong 
luminous  stimulation  of  the  retina  is  required  to  produce  a 
sensation  of  pain,  if  indeed  it  can  be  at  all  brought  about ; 
whereas  a  very  moderate  stimulation  of  the  skin,  and  almost 
every  stimulation  of  an  ordinary  nerve-trunk,  is  said  by  us  to 
be  painful. 

Though  the  skin  is  the  chief  organ  of  touch,  the  mucous 
membrane  lining  the  various  passages  of  the  body  also  serves  as 
an  instrument  for  the  same  sense,  but  only  for  a  short  distance 
from  the  respective  orifices.  We  can  recognize  hard  or  hot 
bodies  with  our  lips  or  mouth,  but  a  hot  liquid  when  it  has 
reached  the  oesophagus  or  stomach,  simply  gives  rise  to  a  sensa- 
tion of  pain :  we  cannot  distinguish  the  sensation  caused 
by  it  from  the  sensation  caused  by  a  draught  of  a  too  acid 
fluid. 

The  stimuli  which,  when  applied  to  the  skin,  give  rise  to 
tactile  perceptions  are  of  two  kinds  only  :  (i)  mechanical,  that  is, 
the  contact  of  bodies  with  varying  degrees  of  pressure  ;  and  (2) 
thermal,  i.e.  the  raising  or  lowering  of  the  temperature  of  the  skin 
by  the  approach  or  contact  of  hot  or  cold  bodies.  We  can  judge 
of  the  weight  and  of  the  temperature  of  a  body,  because  we  can, 
through  touch,  perceive  how  much  it  presses  when  allowed  to 
rest  on  our  skin  or  how  hot  it  is.  But  we  can  through  touch 
derive  no  other  perceptions  and  form  no  other  judgments.     An 


CHAP.   IV.]  FEELING   AND   TOUCH.  59 1 

electric  shock  sent  through  the  skin  will  give  rise  to  a  sensation, 
but  the  sensation  is  an  indefinite  one,  because  the  electric  current 
acts  not  on  the  terminal  organs  of  touch,  but  on  the  fine  nerve- 
branches  of  the  skin.  We  cannot  distinguish  the  sensation  so 
caused  from  a  mechanical  prick  of  similar  intensity,  we  cannot 
perceive  that  the  sensation  is  caused  by  an  electric  current. 
Similarly  certain  chemical  substances  such  as  a  strong  acid  will 
give  rise  to  a  sensation,  but  we  cannot  perceive  the  acid,  we  can 
form  no  judgment  of  its  nature  such  as  we  could  if  we  tasted  it; 
and  if  the  acid  does  not  permeate  the  skin  so  as  to  act  directly 
and  chemically  on  the  fine  nerve-fibres,  we  cannot  distinguish  the 
acid  from  any  other  liquid  giving  rise  to  the  same  simple  contact 
impressions.  The  terminal  organs  of  the  skin  are  such  as  are  only 
affected  by  pressure  or  by  temperature.  Conversely  pressure  or  a 
variation  in  temperature  brought  to  bear  on  a  nerve  trunk,  instead 
of  on  the  terminal  organs,  produces  no  specific  tactile  sensations 
of  pressure  or  temperature,  but  merely  general  sensations  of 
feeling  rapidly  rising  into  pain. 

Sec.  2.     Tactile  Sensations. 
Sensations  of  Pressure. 

As  with  visual,  so  with  tactile  and  indeed  with  all  other  sensa- 
tions, the  intensity  of  the  sensation  maintains  that  general  rela- 
tion to  the  intensity  of  the  stimulus  which  we  spoke  of  at  p.  541 
as  being  formulated  under  Weber's  law.  We  can  distinguish  the 
ditTerence  of  pressure  between  one  and  two  grammes  as  readily  as 
we  can  that  between  ten  and  twenty  or  one  hundred  and  two 
hundred. 

When  two  sensations  follow  each  other  in  the  same  spot  at  a 
sufficiently  short  interval  they  are  fused  into  one  ;  thus,  if  the 
finger  be  brought  to  bear  hghtly  on  a  rotating  card  having  a  series 
of  holes  in  it,  the  holes  cease  to  be  felt  as  such  when  they  follow 
each  other  at  a  rapidity  of  about  1500  in  a  second.  The  vibra- 
tions of  a  cord  cease  to  be  appreciable  by  touch  when  they  reach 
the  same  rapidity.  When  sensations  are  generated  at  points  of 
the  skin  too  close  together,  they  become  fused  into  one ;  but  to 
this  point  we  shall  return  presently. 

The  sensation  caused  by  pressure  is  at  its  maximum  soon  afier 
its  beginning,  and  thenceforward  diminishes.  The  more  suddenly 
the  pressure  is  increased,  the  greater  the  sensation  ;  and  if  the 
increase  be  sufficiently  gradual,  even  very  great  pressure  may  be 
applied  without  giving  rise  to  any  sensation.     A  sensation  in  any 


592  TACTILE   SENSATIONS.  [BOOK   III. 

spot  is  increased  by  contrast  with  surrounding  areas  not  subject 
to  pressure.  Thus  if  the  finger  be  dipped  into  mercury  the 
pressure  will  be  felt  most  at  the  surface  of  the  fluid ;  and  if  the 
finger  be  drawn  up  and  down,  the  sensation  caused  will  be  that 
of  a  ring  moving  along  the  finger. 

All  parts  of  the  skin  are  not  equally  sensitive  to  pressure ; 
small  differences  of  simple  pressure  are  more  readily  appreciated 
when  brought  to  bear  on  the  palmar  surface  of  the  finger,  or  on 
the  forehead,  than  on  the  arm  or  on  the  sole  of  the  foot.  In 
making  these  determinations  all  muscular  movement  should  be 
avoided  in  order  to  eliminate  the  muscular  sense  of  which  we 
shall  speak  presently ;  and  the  area  stimulated  should  be  as 
small  and  the  surfaces  in  contact  as  uniform  as  possible.  In 
a  similar  manner  small  consecutive  variations  of  pressure,  as  in 
counting  a  pulse,  are  more  readily  appreciated  by  certain  parts  of 
the  skin  than  by  others  ;  and  the  minimum  of  pressure  which  can 
be  felt  diff"ers  in  diflierent  parts.  In  all  cases  variations  of  pressure 
are  more  easily  distinguished  when  they  are  successive  than  when 
they  are  simultaneous. 

Sensations  of  Tempei-ature. 

When  the  temperature  of  the  skin  is  raised  or  lowered  in  any 
spot  we  receive  sensations  of  heat  and  cold  respectively ;  and  by 
these  sensations  of  the  temperature  of  our  own  skin  we  form 
judgments  of  the  temperature  of  bodies  in  contact  with  it. 
Bodies  of  exactly  the  same  temperature  as  the  region  of  the  skin 
to  which  they  are  applied  produce  no  such  thermal  sensations, 
though  we  can,  from  the  very  absence  of  sensations,  form  a  judg- 
ment as  to  their  temperature  ;  and  good  conductors  of  heat  appear 
respectively  hotter  and  colder  than  bad  conductors  raised  to  the 
same  temperature. 

We  may  consider  the  skin  as  having  at  any  given  time  and  in  any 
given  spot  a  normal  temperature  at  which  the  sensation  of  temperature 
is  at  zero  ;  for  under  ordinary  circumstances  we  are  not  directly 
conscious  of  the  temperature  of  our  skin  ;  it  is  only  when  the  normal 
temperature  at  the  spot  is  raised  or  lowered  that  we  have  a  sensation 
of  heat  or  cold  respectively.  This  normal  temperature  may  be  at  the 
same  time  different  in  different  parts  of  the  body;  thus  at  a  time  when 
neither  the  forehead  nor  the  hand  are  giving  rise  to  any  sensation  of 
temperature,  we  may,  by  putting  the  hand  to  the  forehead,  frequently 
feel  the  former  hot  or  cold  because  the  normal  temperatures  of  the  two 
parts  differ.  The  normal  tem.perature  in  any  spot  may  also  vary  from 
time  to  time.  Thus  when  the  hand  is  placed  in  a  warm  medium  for 
some  time,  the  sensation  of  warmth  ceases  ;  a  new  normal  tempera- 
ture is  established  with   the  zero  of  sensation  at   a  higher  level,  a 


CHAP.   IV.]  FEELING    AND   TOUCH.  593 

depression  or  elevation  of  this  new  temperature  giving  rise  however 
as  before  to  sensations  of  heat  and  cold  respectively.  That  it  is  the 
chanj;cd  condition,  and  not  the  change  itself,  of  which  we  are 
conscious  is  shewn  by  the  lact  that  when  a  portion  of  skin  is  cooled, 
by  brief  contact  with  a  cold  metal  for  instance,  we  are  still  conscious 
of  the  spot  being  cold  after  the  cooling  agent  has  been  removed,  that 
is  at  a  time  w!icn  the  cooled  spot  is  in  reality  being  heated  by  the 
surrounding  warmer  tissues '. 

The  change  in  temperature  of  the  skin  necessary  to  produce  a 
sensation  must  have  a  certain  rapidity  ;  and  the  more  gradual  the 
change  the  less  intense  the  sensation.  The  repeated  dipping  of 
the  hand  into  hot  water  produces  a  greater  sensation  than  when 
the  hand  is  allowed  to  remain  all  the  time  in  the  water,  though  in 
the  latter  case  the  temperature  of  the  skin  is  most  affected.  The 
same  ctTect  of  contrast  is  seen  in  these  sensations  as  in  those  of 
pressure. 

We  can  with  some  accuracy  distinguish  variations  of  temper- 
ature, especially  those  lying  near  the  normal  temperature  of  the 
skin.  These  sensations,  in  fact,  follow  Weber's  law,  though 
apparently  sensations  of  slight  cold  are  more  vivid  than  those  of 
slight  heat,  the  range  of  most  accurate  sensation  seeming  to  lie 
between  27°  and  ^2°-  ^  ^e  regions  of  the  skin  most  sensitive  to 
variations  in  temperature  arc  not  identical  with  those  most  sensitive 
to  variations  in  pressure.  Thus  the  cheeks,  eyelids,  temples  and 
lips,  are  more  sensitive  than  the  hands.  The  least  sensitive  parts 
are  the  legs,  and  front  and  back  of  the  trunk. 

The  simplest  view  which  can  be  taken  with  regard  to  the  distinc- 
tion between  pressure  and  temperature  sensations  is  to  suppose  that 
two  distinct  kinds  of  terminal  organs  exist  in  the  skin,  one  of  which  is 
aftected  only  by  pressure,  and  the  other  only  by  variations  in  tempera- 
ture ;  and  that  the  two  kinds  of  peripheral  organs  are  connected  with 
different  parts  of  the  central  sensory  organs  by  separate  nerve-fibres. 
Certain  pathological  cases  have  been  quoted''  as  shewing  not  only  that 
this  is  the  case,  but  that  the  two  sets  of  fibres  pursue  ditferent  courses 
in  the  spinal  cord.  Thus  in  certain  diseases  or  injuries  to  the  brain  or 
spinal  cord,  hyperaesthcsia  as  regards  temperature  has  been  observed 
unaccompanied  by  an  augmentation  of  sensitiveness  to  pressure  ;  and 
conversely  instances  have  been  seen  where  the  patient  could  tell  when 
he  was  touched,  but  could  not  distinguish  between  hot  and  cold. 
Against  this  view  it  might  be  urged  that  these  pathological  cases  have 
not  received  the  critical  examination  which  they  demand  ;  and  that 
there  are  facts  which  shew  a  close  dependence  between  the  sensations  of 
pressure  and  temperature.     When  each  stimulus  is  brought  to  bear  on 

'  Hering,   IViftt.  SUtungsbetichi,  LXXV.  (1877). 

»  Browu-Sequard,  Jotirn.  d.  Phys.,    1863,  Vol.  VIII.     Archives  de  Fhys., 
1868,  Vol.  I. 

F.  P  3^ 


594  TACTILE   PERCEPTIONS.  [BOOK   III. 

a  very  limited  area,  the  two  sensations  are  frequently  confounded,  and 
Weber  has  pointed  out  that  cold  bodies  feel  heavier  than  hot  bodies  of 
the  same  weight.  No  case  has  yet  been  recorded  where  a  hot  body, 
a  cold  body,  and  a  body  of  the  temperature  of  the  skin,  all  felt  exactly 
alike,  when  each  was  applied  with  the  same  pressure  ;  and  the  cases 
where  a  hot  sponge  or  spoon  was  felt  (because  it  was  hot),  and  yet  the 
sensation  was  confounded  with  one  of  pressure,  indicate  that  the  same 
terminal  organs  are  affected  by  both  stimuli. 

With  regard  to  the  nature  of  the  terminal  organs  in  the  skin, 
it  may  be  stated  that  the  corpuscula  tadus  were  regarded  by  their 
discoverers  as  specific  organs  of  touch.  The  end-bulbs  of  Krause 
have  also  been  regarded  in  the  same  light.  But  the  evidence  we 
possess  concerning  this  matter  is  at  present  inconclusive. 

Sec.  3.'    Tactile  Perceptions  and  Judgments. 

When  a  body  presses  on  any  spot  of  our  skin,  or  when  the  tem- 
perature of  the  skin  at  that  spot  is  raised,  we  are  not  only  conscious 
of  pressure  or  of  heat,  but  perceive  that  a  particular  part  of  our 
body  has  been  touched  or  heated.  We  refer  the  sensations  to  their 
place  of  origin,  and  we  thus  by  touch  perceive  the  relations  to 
ourselves  of  the  body  which  gives  rise  to  the  tactile  sensations,  in 
the  same  way  as  in  our  visual  perception  of  external  objects  we 
refer  to  external  nature  the  sensations  originating  in  certain  parts 
of  the  retina.  When  we  are  touched  on  the  finger  and  on  the 
back  we  refer  the  sensations  to  the  finger  and  to  the  back  respec- 
tively, and  when  we  are  touched  at  two  places  on  the  same  finger 
at  the  same  time  we  refer  the  sensations  to  two  points  of  the  finger. 
In  this  way  we  can  localise  our  sensations,  and  are  thus  assisted 
in  perceiving  the  space  relations  of  objects  with  which  we  come  in 
contact. 

This  power  of  localising  pressure-sensations  varies  in  different 
parts  of  the  body.  The  following  table  from  Weber  gives  the 
distance  at  which  two  points  of  a  pair  of  compasses  must  be  lield 
apart,  so  that  when  the  two  points  are  in  contact  with  the  skin, 
the  two  consequent  sensations  can  be  localised  with  sufficient 
accuracy  to  be  referred  to  two  points  of  the  body,  and  not 
confounded  together  as  one. 


Tip  of  tongue    ... 

Palm  of  last  phalanx  of  finger... 

Palm  of  second... 

I'l  mm. 

2*2     „ 
4'4     » 

Tip  of  nose        

White  part  of  lips 

Back  of  second  phalanx  of  finger 

..       6-6     „ 
..       8-8     „ 

..       TI'I       „ 

CHAP     I  V.J  FKELING   AND   TOUCH.  595 

Skin  over  malar  bone  ...  ...  ...  154  nun. 

Back  of  hand     ...  ...  ...  ...  sq'S  „ 

Forearm...          ...  ...  ...  ...  39-6  „ 

Sternum...          ...  ...  ...  ...  440  ,, 

Back       ...          ...  ...  ...  ...  660  „ 

And  a  very  similar  distribution  has  been  observed  in  reference 
to  the  localisation  of  sensations  of  temperature.  As  a  general 
rule  it  may  be  said  that  the  more  mobile  parts  are  those  by  which 
we  can  thus  discriminate  sensations  most  readily.  The  lighter  the 
pressure  used  to  give  rise  to  the  sensations,  the  more  easily  are 
two  sensations  distinguished  ;  thus  two  points  which,  when  touch- 
ing lightly,  appear  as  two,  may,  when  tirmly  pressed,  give  rise  to 
one  sensation  only.  The  distinction  between  the  sensations  is 
obscured  by  neighbouring  sensations  arising  at  the  same  time. 
Thus  two  points  brought  to  bear  within  a  ring  of  heavy  metal 
pressing  on  the  skin,  are  readily  confused  into  one.  And  it  need 
hardly  be  said  that  these  tactile  perceptions,  like  all  other 
perceptions,  are  immensely  increased  by  being  exercised. 

Our  '  field  of  touch,'  if  we  may  be  allowed  the  expression,  is  com- 
posed of  tactile  areas  or  units,  in  the  same  way  that  our  field  of  vision 
is  composed  of  visual  areas  or  units.  The  tactile  sensation  is,  like  the 
visual  sensation,  a  symbol  to  us  of  some  external  event,  and  we  refer 
the  sensation  to  its  appropriate  place  in  the  field  of  touch.  All  that 
has  been  said  (p.  543)  concerning  the  subjective  nature  of  the  limits  of 
visual  areas,  applies  ecjiially  well,  mutatis  tnutandis,  to  tactile  areas. 
When  two  points  of  the  compasses  are  felt  as  two  distinct  sensations, 
it  is  not  necessary  that  two  and  only  two  nerve-fibres  should  be 
stimulated  ;  all  that  is  necessary  is  that  the  two  cerebral  sensation- 
areas  should  not  be  too  completely  fused  together.  The  improvement 
by  exercise  of  the  sense  of  touch  must  be  explained  not  by  an  increased 
development  of  the  terminal  organs,  not  by  a  growth  of  new  nerve- 
fibres  in  the  skin,  but  by  a  more  exact  limitation  of  the  sensational 
areas  in  the  brain,  by  the  development  of  a  resistance  which 
limits  the  radiation  taking  place  from  the  centres  of  the  several 
areas. 

By  a  multitude  of  simultaneous  and  consecutive  tactile  sensa- 
tions thus  converted  into  perceptions  we  are  able  to  make 
ourselves  acquainted  with  the  form  of  external  objects.  We  can 
tell  by  variations  of  pressure  whether  a  surface  is  rough  or  smooth, 
plane  or  curved,  what  variations  of  surface  a  body  presents,  and 
how  far  it  is  heavy  or  light ;  and  from  the  information  thus  gained 
we  build  up  judgments  as  to  the  form  and  nature  of  objects, 
judgments  however  which  are  most  intimately  bound  up  with 
visual  judgments,  the  knowledge  derived  by  one  sense  correcting 

38—2 


-596  MUSCULAR   SENSE.  [BOOK   III. 

and  completing  that  obtained  by  the  other.  As  in  other  senses 
so  in  this,  our  sensations  may  mislead  us  and  cause  us  to  form 
erroneous  judgments.  This  is  well  illustrated  by  the  so-called 
experiment  of  Aristotle.  It  is  impossible  in  an  ordinary  position 
of  the  fingers  to  bring  the  radial  side  of  the  middle  finger  and  the 
ulnar  side  of  the  ring  finger  to  bear  at  the  same  time  on  a  small 
object,  such  as  a  marble.  Hence  when  with  the  eyes  shut  we  cross 
one  finger  over  the  other,  and  place  a  marble  between  them  so 
that  it  touches  the  radial  side  of  the  one  and  the  ulnar  side  of  the 
other,  we  recognise  that  the  object  is  such  as  could  not  under 
ordinary  conditions  be  touched  at  the  same  time  by  these  two 
portions  of  our  skin,  and  therefore  judge  that  we  are  touching  not 
one  but  two  marbles. 

Distinct  tactile  sensations  are,  as  we  have  seen,  produced  only 
when  a  stimulus  is  applied  to  a  terminal  organ.  When  sensations 
or  affections  of  general  sensibility  other  than  the  distinct  tactile 
sensations  are  developed  in  the  termination  of  a  nerve,  we  are 
able,  though  with  less  exactitude,  to  refer  the  sensation  to  a  par- 
ticular part  of  the  body.  Thus  when  we  are  pricked  or  burnt,  we 
can  feel  where  the  prick  or  burn  is.  When  a  sensory  nerve  trunk 
is  stimulated,  the  sensation  is  always  referred  to  the  peripheral 
terminations  of  the  nerve.  A  blow  on  the  ulnar  nerve  at  the 
elbow  is  felt  as  a  tingling  in  the  little  and  ring  fingers  correspond- 
ing to  the  distribution  of  the  nerve.  Sensations  started  in  the 
stump  of  an  amputated  limb  are  referred  to  the  absent  member. 

Stimulation  of  a  nerve  trunk  gives  rise  to  general  sensations 
only;  no  distinct  tactile  perceptions  can  thus  be  produced. 
When  cold  is  applied  to  the  elbow  it  is  felt  as  cold  in  the  skin  of 
the  elbow ;  but  a  cooling  of  the  ulnar  nerve  at  this  spot  simply 
gives  rise  to  pain  which  is  referred  to  the  ulnar  side  of  the  hand 
and  arm. 

Sec.  4.     The  Muscular  Sense. 

When  we  come  into  contact  with  external  bodies  we  are  con- 
scious not  only  of  the  pressure  exerted  by  the  object  on  our  skin, 
but  also  of  the  pressure  which  we  exert  on  the  object.  If  we 
place  the  hand  and  arm  flat  on  a  table,  we  can  estimate  the 
pressure  exerted  by  bodies  resting  on  the  palm  of  the  hand,  and 
so  come  to  a  conclusion  as  to  their  weights  ;  in  this  case  we  are 
conscious  only  of  the  pressure  exerted  by  the  body  on  our  skin. 
If  however  we  hold  the  body  in  the  hand,  we  not  only  feel  the 
pressure  of  the  body,  but  we  are  also  aware  of  the  muscular 
exertion  required  to  support  and  lift  the  body.     We  are  conscious 


CHAP.   IV.J  FEELING   AND   TOUCH.  597 

of  a  nuisciilar  sense ;  and  we  find  by  experience  that  when  we 
trust  to  lliis  imiscular  sense  as  well  as  to  the  .sensation  of  pressure, 
we  can  form  much  more  accurate  judgments  concerning  the  weight 
of  bodies  than  when  we  rely  on  pressure  alone.  When  we 
want  to  tell  how  heavy  a  body  is,  we  are  not  in  the  habit  of 
allowing  it  simply  to  press  on  the  hand  laid  flat  on  a  table  ;  we 
hold  it  in  our  hand  and  lift  it  up  and  down.  We  appeal  to  our 
muscular  sense  to  inform  us  of  the  amount  of  exertion  necessary 
to  move  it,  and  by  hel[)  of  that,  judge  of  its  weight.  And  in  all 
the  movements  of  our  body  we  are  conscious,  even  to  an  astonish- 
ingly accurate  degree,  as  is  well  seen  in  the  discussions  concerning 
vision,  of  the  amount  of  the  contraction  to  which  we  are  putting 
our  muscles.  In  some  way  or  other  we  are  made  aware  of  what 
particular  muscles  or  groui)s  of  muscles  are  being  thrown  into 
action,  and  to  what  extent  that  action  is  being  carried.  We  are 
also  conscious  of  the  varying  condition  of  our  muscles,  even  when 
they  are  at  rest ;  the  tired  and  especially  the  paralysed  limb  is  said 
to  'feel'  heavy.  In  this  way  the  state  of  our  muscles  largely 
determines  our  general  feeling  of  health  and  vigour,  of  weariness, 
ill  health  and  feebleness. 

It  has  been  suggested  that  since  muscle  possesses  little  or  no 
general  sensibility,  comparatively  little  pain  being  felt  for  instance 
when  muscles  are  cut,  our  muscular  sense  is  chiefly  derived  from  the 
traction  of  the  contracting  muscle  on  its  attachments  ;  and  un- 
doubtedly in  cramp,  when  it  can  be  localised,  the  pain  is  chiefly  felt 
at  the  joints  ;  and,  as  we  know.  Pacinian  bodies  are  abundant  around 
the  joints.  The  investigations  of  Sachs,  however',  seem  to  shew  that 
afferent  nerves,  having  a  different  disposition  from  the  ordinary  motor 
nerves  which  terminate  in  end-plates,  are  present  in  muscle  ;  and 
analogy  would  lead  us  to  suppose  that  these  afferent  fibres,  though 
possessing  a  low  general  sensibility,  might  be  easily  excited  by  a 
muscular  contraction  ;  but  further  investigations  are  necessary  before 
these  can  be  accepted  as  the  true  nerves  of  the  muscular  sense  ". 

In  favour  of  the  view  that  the  muscular  sense  is  peripheral  and  not 
central  in  origin,  may  be  urged  the  fact  that  the  sense  is  felt  when  the 
muscles  are  thrown  into  contraction  by  direct  galvanic  stimulation 
inste.id  of  by  the  agency  of  the  will.  Many  authors,  even  while 
admitting  the  existence  of  a  muscular  sense  of  peripheral  origin, 
contend  that  we  also  possess  and  are  very  largely  guided  in  our 
movements  by  what  might  be  called  'neural'  sense  of  central  origin. 
That  is  to  say  the  changes  in  the  central  nervous  system  involved  in 
initialing  and  carrying  out  a  movement  of  the  body,  so  affect  our 
consciousness,  that  we  have  a  sense  of  the  effort  itself. 

It  has  been  observed  that  when  the  posterior  roots  are  divided, 

'  Kcichert  and  du  Bois-Reymond's  Arc/iiv,  1S74,  p.  175. 
■  Cf.  Tschiriew,  Archives  de  Physiol.,  vi.  {1879)  p.  89. 


598  MUSCULAR   SENSE.  [BOOK   III. 

movements  become  less  orderly,  as  if  they  lacked  the  guidance  of  a 
muscular  sense  ;  and  although  the  impairment  of  the  movements  may 
be  due  in  part  to  the  coincident  loss  of  tactile  sensations,  it  is  probable 
that  it  is  increased  by  the  loss  of  the  muscular  sense.  There  is  a 
malady  or  rather  a  condition  attending  various  diseased  states  of  the 
central  nervous  system  called  locomotor  ataxy,  the  characteristic 
feature  of  which  is  that,  though  there  is  no  loss  of  direct  power  over 
the  muscles,  the  various  bodily  movements  are  effected  imperfectly 
and  with  difficulty,  from  want  of  proper  co-ordination.  In  such 
diseases  the  pathological  mischief  is  frequently  found  in  the  posterior 
columns  of  the  spinal  cord  and  the  posterior  roots  of  the  spinal  nerves, 
that  is  in  distinctly  afferent  structures  ;  and  the  phenomena  seem  in 
certain  cases  at  least  due  to  inefficient  co-ordination  caused  by  the 
loss  both  of  the  muscular  sense  and  of  ordinary  tactile  sensations. 
The  patients  walk  with  difficulty,  because  they  have  imperfect  sensa- 
tions both  of  the  condition  of  their  muscles  and  of  the  contact  of  their 
feet  with  the  ground.  In  many  of  their  movements  they  have  to 
depend  largely  on  visual  sensations  ;  hence  when  their  eyes  are  shut 
they  become  singularly  helpless.  In  other  cases  again  ataxy  may  be 
present  without  any  impairment  of  touch ;  but  a  discussion  of  the 
varied  phenomena  of  this  class  of  maladies  cannot  be  entered  into 
here. 

Ainong  the  names  of  those  who  have  contributed  largely  to  our 
knowledge  of  the  physiology  of  the  various  senses,  the  following  (the 
more  purely  physical  inquirers  being  passed  over)  call  for  special 
mention.  In  vision,  the  labours  of  Young^  on  accommodation  and 
colour  sensations,  of  Purkinje^  on  subjective  phenomena,  of  Bonders^ 
and  Helmholtz''  on  the  various  dioptric  features  of  the  eye  and  the 
movements  of  the  eyeballs,  and  of  Wheatstone  on  binocular  vision, 
were  of  first  importance  ;  and  to  these,  on  the  psychological  side  may 
be  added  the  speculations  of  Berkeley s.  It  need  hardly  be  said  that 
in  his  Physiological  Optics  Helmholtz  has  treated  the  whole  subject 
in  such  a  complete  and  masterly  way  as  to  make  it  almost  entirely  his 
own.  In  both  sight  and  hearing,  and  indeed  in  the  senses  in  general, 
we  owe  much  to  Johannes  Miiller^.  The  physiology  of  touch,  and  the 
relations  obtaining  in  the  senses  in  general  between  the  stimulus  and 
the  sensation,  was  largely  advanced  by  the  labours  of  Weber 7.  Lastly, 
the  researches  of  Helmholtz s  on  musical  sounds  mark  an  epoch  in  the 
history  of  the  physiology  of  hearing. 

'  Phil.  Trans.  l8oi. 

^  Beobacht.  u.  Verstuh.  zur  Physiol,  d.  Sinne,  1825,  and  other  papers. 

3  Numerous  papers  from  1846  onwards. 

*  Numerous  papers,  and  Ha7idbuch  der  Physiol.  Optik,  1867, 

5   Theory  of  Vision,  1709. 

^  Phys.  d.  Gesichtssinns,  1^26,  a.ndi  Handb.  der  Physiol.  1835. 

'  De  Aure,  &c.  1820,      Wagner's  Handworterbuch,  Art.  Tastsinn. 

'  Tonempjindungen,  1870. 


CHAPTER  V. 
THE  SPINAL  CORD. 

Sec.  I.     As  a  Centre  of  Reflex  Action. 

We  have  already  discussed  (Book  i.  Chap,  iii.)  the  general 
features  of  reflex  action,  so  that  we  can  now  confine  ourselves 
to  special  points  of  particular  interest.  Since  the  frog  and  the 
mamtnal  difter  very  markedly  from  each  other  in  respect  of  their 
reflex  spinal  phenomena,  it  will  be  convenient  to  consider  them 
separately. 

In  the  Frog. 

The  salient  feature  of  the  ordinary  reflex  actions  of  the  frog 
is  their  purposeful  character,  though  every  variety  of  movement 
may  be  witnessed,  from  a  simple  spasm  to  a  most  complex 
muscular  manoeuvre.  The  nature  of  any  movement  called  forth 
is  determined  : 

I.  By  the  nature  of  the  afferent  impulses.  Simple  nervous 
impulses  generated  by  the  direct  stimulation  of  afferent  nerve- 
fibres  evoke  as  reflex  movements  merely  irregular  spasms  in  a  few 
muscles ;  whereas  the  more  complicated  differentiated  sensory 
impulses  generated  by  the  application  of  the  stimulus  to  the  skin, 
give  rise  to  large  and  purposeful  movements.  It  is  much  more 
easy  to  produce  a  reflex  action  by  a  slight  pressure  on  the  skin 
than  by  even  strong  induction-shocks  applied  directly  to  a  nerve- 
trunk.  If,  in  a  brainless  frog,  the  area  of  skin  supplied  by  one 
of  the  dorsal  cutaneous  nerves  be  separated  by  section  from  the 
rest  of  the  skin  of  the  back,  the  nerve  being  left  attached  to  the 
piece  of  skin  and  carefully  protected  from  injury,  it  will  be  found 
that  slight  stimuli  applied  to  the  surface  of  the  piece  of  skin 
easily  evoke  reflex  actions,  whereas  the  trunk  of  the  nerve  may  be 
stimulated  with  even  strong  currents  without  producing  anything 
more  than  irregular  movements. 


600  REFLEX   ACTIONS.  [BOOK   III. 

In  ordinary  mechanical  and  chemical  stimulation  of  the  skin 
it  is  a  series  of  impulses  and  not  a  single  impulse  which  passes 
upwards  along  the  sensory  nerve,  the  changes  in  which  may  be 
compared  to  the  changes  in  a  motor  nerve  during  tetanus.  In 
every  reflex  action,  in  fact,  the  central  mechanism  may  be  looked 
upon  as  being  thrown  into  activity  through  a  summation  of  the 
afferent  impulses  reaching  it^. 

When  a  muscle  is  thrown  into  contraction  in  a  reflex  action, 
the  note  which  it  gives  forth  does  not  vary  with  the  stimulus,  but 
is  constant,  being  the  same  as  that  given  forth  by  a  muscle  thrown 
into  contraction  by  the  will.  From  which  we  inler  that  in  a  reflex 
action  the  afferent  impulses  do  not  simply  pass  through  the  centre 
in  the  same  way  that  they  pa^s  along  afferent  nerves,  but  are 
profoundly  modilied.  And  this  explains  why  a  reflex  action  takes 
always  a  considerable  time,  and  frequently  a  very  long  time,  for  its 
development.  When  the  toes  of  a  brainless  frog  are  dipped  in 
dilute  sulphuric  acid,  several  seconds  may  elapse  before  the  feet 
are  withdrawn.  Making  every  allowance  for  the  time  needed  for 
the  acid  to  develope  sensory  impulses  in  the  peripheral  endings  of 
the  afierent  nerve,  a  very  large  fraction  of  the  period  must  be 
taken  up  by  the  molecular  actions  going  on  in  the  nerve-cells. 
In  other  words,  the  interval  between  the  advent  at  the  central 
organ  of  afferent,  and  the  exit  from  it  of  efferent  impulses,  is  a 
busy  time  for  the  nerve-cells  of  that  organ  ;  during  it  many 
processes,  of  which  at  present  we  know  little  or  nothing,  are  being 
carried  on. 

2.  By  the  intensity  of  the  stimulus.  We  have  already  pointed 
out  (p.  130)  that  while  the  effects  of  a  weak  stimulus  applied  to 
an  afferent  nerve  are  limited  to  a  few,  those  of  a  strong  stimulus 
may  spread  to  many  efferent  nerves.  Granting  that  any  particular 
afferent  nerve  is  more  particularly  associated  with  certain  efferent 
nerves  than  with  any  others,  so  that  the  reflex  impulses  generated 
by  impulses  entering  the  cord  by  the  former,  pass  with  the  least 
resistance  down  the  latter,  we  must  evidently  admit  further  that 
other  efferent  nerves  are  also,  though  less  directly,  connected  with 
the  same  afferent  nerve,  the  passage  into  the  second  efferent 
nerve  meeting  with  an  increased  but  not  insuperable  resistance. 
When  a  frog  is  poisoned  with  strychnia,  a  slight  touch  on  any 
part  of  the  skin  may  cause  convulsions  of  the  whole  body  ,;  that 
is  to  say,  the  afferent  impulses  passing  along  any  single  afferent 
nerve  may  give  rise  to  the  discharge  of  efferent  impulses  along  any 
or  all  of  the  eft'erent  nerves.     This  proves  that  a  physiological  if 

'  Cf.  Stirling,  Ludwig's  Arbeiien,  1874. 


CHAP,   v.]  THE   SPINAL   CORD.  6oi 

not  an  anatomical  continuity  obtains  between  all  the  nerve-cells  of 
tlie  spinal  cord  which  are  concerned  in  reflex  action,  that  the 
nerve-cells  with  their  processes  form  a  functionally  continuous 
jirotoplasniic  network.  This  network  however  is  marked  out  into 
tracts  presenting  greater  or  less  resistance  to  the  progress  of  the 
imiJiiises  into  which  afferent  impulses,  coming  from  this  or  that 
afferent  nerve,  are  transformed  on  their  advent  at  the  network  ; 
and  accordingly  the  path  of  any  series  of  impulses  in  the  network 
will  be  determined  largely  by  the  energy  of  the  afferent  impulses. 
And  the  action  of  strychnia  is  most  easily  explained  by  supposing 
that  it  reduces  and  equalises  the  normal  resistance  of  this  network, 
so  that  even  weak  impulses  travel  over  all  its  tracts  witii  great 
ease. 

3.  By  the  locality  where  the  stimulus  is  applied.  Pinching^ 
the  folds  of  skin  surrounding  the  anus  of  the  frog  produces 
different  effects  from  those  witnessed  when  the  flank  or  toe  is 
pinched  ;  and,  speaking  generally,  the  stimulation  of  a  particular 
spot  calls  forth  particular  movements.  From  this  we  may  infer 
that  the  protoplasmic  network  spoken  of  above  is,  so  to  speak, 
mapped  out  into  nervous  mechanisms  by  the  establishment  of 
lines  of  greater  or  less  resistance,  so  that  the  disturbances  in  it 
generated  by  certain  afferent  impulses  are  directed  into  certain 
efferent  channels.  But  the  arrangement  of  these  mechanisms  is 
not  a  fixed  and  rigid  one.  We  cannot  predict  exactly  the  nature 
of  the  movement  which  will  result  from  the  stimulation  of  any 
particular  spot.  Moreover,  under  a  change  of  circumstances  a 
movement  quite  different  from  the  normal  one  may  make  its 
appearance.  Thus  when  a  drop  of  acid  is  placed  on  the  right 
flank  of  a  frog,  the  right  foot  is  almost  invariably  used  to  rub  off 
the  acid;  in  this  there  appears  nothing  more  than  a  mere 
'  mechanical '  reflex  action.  If  however  the  right  leg  be  cut  off, 
or  the  right  foot  be  otherwise  hindered  from  rubbing  off  the  acid, 
the  left  foot  is,  under  the  exceptional  circumstances,  used  for  the 
purpose.  This  at  first  sight  looks  like  an  intelligent  choice.  A 
choice  it  evidently  is ;  and  were  there  many  instances  of  similar 
choice,  and  were  there  any  evidence  of  a  variable  automatism, 
like  that  of  a  conscious  volition,  being  manifested  by  the  spinal 
cord  of  the  frog,  we  should  be  justified  in  supposing  that  the 
choice  was  determined  by  an  intelligence.  It  is  however,  on  the 
other  hand,  quite  possible  to  suppose  that  the  lines  of  resistance 
in  the  spinal  protoplasm  are  so  arranged  as  to  admit  of  an 
alternative  action ;  and  seeing  how  few  and  simple  are  the 
ai>[j«irent   instances  of   choice  witnessed  in  a  brainless  frog,  and 


602  REFLEX   ACTIONS.  [BOOK   III. 

how  absolutely  devoid  of  spontaneity  or  irregular  automatism 
is  the  spinal  cord  of  the  frog,  this  seems  the  more  probable 
view'. 

Moreover  to  this  often  quoted  behaviour  of  the  frog  may  be 
opposed  the  behaviour  of  the  snake.  This  animal  when  decapitated 
executes  movements  the  purpose  of  which  is  obviously  to  twine  the 
body  round  any  object  with  which  it  comes  in  contact ;  thus  it  very 
speedily  twists  itself  round  an  arm  or  a  stick  presented  to  it.  It  will 
however  with  equal  and  fatal  readiness  twine  itself  round  a  red-hot 
bar  of  iron  or  lump  of  live  coal^ 

It  may  be  remarked  that  two  entirely  different  questions  are  started 
by  this  exhibition  of  choice  on  the  part  of  the  frog  ;  the  one  is  whether 
the  spinal  cord  of  the  frog  possesses  intelligence,  the  other  is  whether  it 
possesses  consciousness  ;  and  care  must  be  taken  to  keep  the  two 
questions  apart.  Intelligence  in  the  ordinary  meaning  of  that  word 
undoubtedly  presupposes  consciousness  ;  but  we  are  not  at  liberty  to 
say  that  consciousness  may  not  exist  without  intelligence.  It  is  quite 
possible  to  conceive  of  the  simplest  and  most  'mechanical'  reflex 
action  being  accompanied  by  consciousness  ;  the  coexistence  of  the 
consciousness  being  merely  an  adjunct  to,  and  in  no  appreciable  way 
modifying  the  mechanical  elaboration  of,  the  act.  On  the  other  hand, 
though  it  is  possible  to  conceive  of  such  a  concomitant  and  appa7'ently 
useless  consciousness,  and  though  if  we  admit  an  evolution  of  conscious- 
ness we  must  suppose  such  forms  of  consciousness  to  exist,  yet  inasmuch 
as  our  reason  for  believing  in  the  possession  by  any  being  of  a  conscious- 
ness like  our  own  is  based  on  the  similarity  of  the  behaviour  of  that 
being  with  our  own  behaviour,  we  are  precluded  from  distinctly 
predicating  consciousness  except  in  the  cases  where  an  intelligence 
similar  to  our  own  is  manifested.  But  the  discussion  of  this  subject 
would  lead  us  too  far  away  from  the  object  of  the  present  book. 

It  may  be  added  that  the  movements  evoked  by  even  a 
segment  of  the  cord  may  be  purposeful  in  character;  hence  we 
must  conclude  that  every  segment  of  the  protoplasmic  network  is 
mapped  out  into  mechanisms. 

4.  By  the  condition  of  the  cord.  The  action  of  strychnia 
just  alluded  to  is  an  instance  of  an  apparent  augmentation  of  reflex 
action  best  explained  by  supposing  that  the  resistances  in  the  cord 
are  lessened.  There  are  probably  hov/ever  cases  in  which  the 
explosive  energy  of  the  nerve-cells  is  positively  increased  above 
the  normal.  Conversely,  by  various  influences  of  a  depressing 
character,  as  by  various  ansesthetics,  reflex  action  may  be  lessened 
or  prevented ;  and  this  again  may  arise  either  from  an  increase  of 

'  Pfluger,  Die  sensorische  Function  des  Riickenviarks,    1853.     Sanders-Ezn, 
Ludwig's  Arbeiten,  1867.     Gergens,  Pfliiger's  Archiv,  XIII.  (1876)  p.  61.   ' 
^  Osawa  and  Tiegel,  Pfliiger's  Archiv,  xvi.  (1877)  p.  90.  • 


CHAP,   v.]  THE  SPINAL   CORD.  603 

resistance,  or  from  a  diminished  action  of  the  nerve-cells  them- 
selves. In  the  mammal  the  condition  of  apnoea  is  antagonistic, 
not  only  to  the  convulsions  proceeding  from  the  convulsive  centre 
in  the  medulla,  but  also  to  rcllex  actions  arising  in  any  part  of  the 
cord,  such  as  those  produced  by  strychnia. 

Inhibition  of  Reflex  Action.  When  the  brain  of  a  frog 
is  removed,  reflex  actions  are  developed  to  a  much  greater  degree 
than  in  the  entire  animal.  We  ourselves  are  conscious  of  being 
able  by  an  effort  of  the  will  to  stop  reflex  movements,  such  for 
instance  as  are  induced  by  tickling.  There  must  therefore  be  in 
the  brain  some  mechanism  or  other  for  preventing  the  normal 
development  of  the  spinal  reflex  actions.  And  we  learn  by  ex- 
periment that  stimulation  of  certain  parts  of  the  brain  has  a 
remarkable  effect  on  reflex  action.  In  a  frog,  from  which  the 
cerebral  hemispheres  only  have  been  removed,  the  optic  thalami, 
cptic  lobes,  medulla  oblongata  and  spinal  cord  being  left  intact,  a 
certain  average  time  will  (see  p.  600)  be  found  to  elapse  between 
the  dipping  of  the  toe  into  very  dilute  sulphuric  acid,  and  the 
resulting'  withdrawal  of  the  foot.  If,  however,  the  optic  lobes  or 
optic  thalami  be  stimulated,  as  by  putting  a  crystal  of  sodium 
chloride  on  them,  it  will  be  found  on  repeating  the  experiment 
while  these  structures  are  still  under  the  influence  of  the  stimula- 
tion, that  the  time  intervening  between  the  action  of  the  acid  on 
the  toe  and  the  withdrawal  of  the  foot  is  very  much  prolonged. 
That  is  to  say,  the  stimulation  of  the  optic  lobes  has  caused 
impulses  to  descend  to  the  cord,  which  have  there  so  interfered 
with  the  action  of  the  nerve-cells  engaged  in  reflex  action  as 
greatly  to  retard  the  generation  of  reflex  impulses  ;  in  other  words, 
the  stimulation  of  the  optic  lobes  has  inhibited  the  reflex  action  of 
the  cord '. 

It  is  worthy  of  notice  that  the  inhibitory  action  of  the  optic  lobes 
spoken  of  above,  bears  exclusively  on  the  length  of  the  period  of 
incubation.  We  have  no  evidence  that  it  diminishes  the  minimum 
intensity  of  stimulation  required  to  produce  a  reflex  action.  On  the 
other  hand,  the  augmenting  effect  of  strychnia  may  manifest  itself 
without  any  change  in  the  latent  period  or  period  of  incubation,  if  we 
may  use  the  phrase.  When  a  frog  is  poisoned  with  small  doses  of 
strychnia  the  reflex  movement-;  caused  by  a  very  slight  stimulus  may 
be  very  great,  I)ut  the  period  of  incubation  may  be  the  same  as  that  of 
a  frog  in  a  normal  condition  ;  when  the  dose  is  increased,  the  period 

'  Setschcnow,  Uchcr  die  FJentmuftgsmechanismeti  fiir  die  ReflexthHligkeil  des 
Riickeuinarks,  1S63.  SetscheiT>\v  and  Pascliutin,  Neue  Vi^iuc/u;  1S65. 
Herzcn,  Exp   sw  Us  Centra  modcrateurs  de  Inaction  rffltxe,  1864. 


604  REFLEX   ACTIONS.  [BOOK  III. 

instead  of  being  diminished  is  increased,  the  increase  being  very  con- 
siderable when  minimum  stimuh  are  employed,  but  much  less  marked 
with  strong  stimuli'. 

If  quinine-  be  injected  under  the  skin  of  the  back  of  a  frog  the 
period  of  incubation  of  reflex  action  will  be  much  prolonged.  If  after 
the  retardation  has  become  clearly  developed,  the  brain  be  removed, 
the  period  of  incubation  rapidly  returns  to  the  normal.  And  if  the 
quinine  is  similarly  injected  beneath  the  skin  of  a  frog  from  which  the 
brain  has  previously  been  removed,  no  such  retardation  makes  its 
appearance.  From  this  we  may  infer  that  the  injection  of  the  quinine 
inhibits  the  reflex  actions  of  the  spinal  cord  by  stimulating  an  inhibitory 
mechanism  in  the  brain.  The  difference  is  however  said  not  to  be 
manifested  when  mechanical  instead  of  chemical  or  thermal  stimuli 
are  used  ;  and  indeed  the  experiment  is  one  requiring  further 
investigation. 

Langendorf3  concludes  that  in  frogs  the  inhibitory  action  of  one 
side  of  the  brain  is  exerted  on  the  reflex  actions  of  the  opposite  side  of 
the  body,  the  inhibitory  impulses  crossing  in  the  medulla  oblongata. 

Such  an  inhibitory  effect  is  however  not  confined  to  the  optic 
lobes.  Stimuli,  if  sufficiently  strong,  applied  to  any  afferent  nerve 
will  inhibit,  i.e.  will  retard  or  even  wholly  prevent  reflex  action. 
If  the  toes  of  one  leg  are  dipped  into  dilute  sulphuric  acid  at  a 
time  when  the  sciatic  of  the  other  leg  is  being  powerfully  stimu- 
lated with  an  interrupted  current,  the  period  of  incubation  will  be 
found  to  be  much  prolonged,  and  in  some  cases  the  reflex  with- 
drawal of  the  foot  will  not  take  place  at  all.  And  this  holds  good, 
not  only  in  the  complete  absence  of  the  optic  lobes  and  medulla 
oblongata,  but  also  when  only  a  portion  of  the  spinal  cord,, 
sutticient  to  carry  out  the  reflex  action  in  the  usual  way,  is  left. 
There  can  be  no  question  here  of  any  specific  inhibitory  centres, 
such  as  have  been  supposed  to  exist  in  the  optic  lobes.  We 
have  already  seen  that  the  action  of  such  nervous  centres,  auto- 
malic  or  reflex,  as  the  respiratory  and  vaso-motor  centres,  may 
be  either  inhibited  or  augmented  by  afferent  impulses.  The 
micturition-centre  in  the  mammal  may  be  easily  inhibited  by 
impulses  passing  downward  to  the  lumbar  cord  from  the  brain,  or 
upwards  along  the  sciatic  nerves.  Goltz  observed  that  in  the  case 
of  the  dog  (see  p.  421),  micturition  set  up  as  a  reflex  act  by 
simple  pressure  on  the  abdomen,  or  by  sponging  the  anus,  was  at 
once  stopped  by  sharply  pinching  the  skin  of  the  leg.  And  it  is  a 
matter  of  common  experience  that  micturition  may  be  suddenly 
checked  by  an  emotion  or  other  cerebral  event.  The  erection 
centre  in  the  lumbar  cord  is  also  susceptible  of  being  inhibited  by 

'   Wundt,  Llechanik  der  Nervcn,  II.  (1876)  p.  70. 
^  Chaper  m,  Pfluger's  Archiv,  il.  (1869)  p.  293. 
3  ]ju  Bois-Reyiaond's  Archiu,  1877,  p.  95. 


CHAP,   v.]  THE   SPINAL   CORD.  605 

impulses  reaching  it  from  various  sources.  And  though  the  reflex 
mechanism  of  croaking  belongs  to  the  optic  lobes,  and  not  to  the 
spinal  cord,  this  may  be  quoted  in  reference  to  the  inhibition  of 
reflex  action,  since  the  croaking  which,  as  we  shall  shortly  see,  in 
a  frog  deprived  of  its  cerebral  hemispheres,  invariably  follows  the 
stroking  of  the  flanks  in  a  particular  way,  fails  to  appear  if  a 
sensory  nerve  such  as  the  sciatic  be  powerfully  stimulated  at  the 
same  time. 

These  various  facts  clearly  shew  that  the  spinal  cord,  and 
indeed  the  whole  cerebral  nervous  system,  may  be  regarded  as  an 
intricate  mechanism  in  which  the  direct  effects  of  stimulation  or 
automatic  activity  are  modified  and  governed  by  the  checks  of 
inhibitory  influences ;  but  we  have  as  yet  much  to  learn  before  we 
can  speak  with  certainty  as  to  the  exact  manner  in  which  inhibition 
is  brought  about.  Seeing  that  in  the  ordinary  actions  of  life  the 
spinal  cord  is  to  a  large  extent  a  mere  instrument  of  the  cerebral 
hemispheres,  we  may  readily  expect  that  regulative  inhibitory 
impulses  passing  from  the  latter  to  the  former  would  be  of  frequent 
occurrence  ;  and  the  experiments  quoted  above  shew  that  the 
optic  lobes  when  stimulated  are  especially  prone  to  give  rise  to 
such  inhibitory  impulses  ;  but  facts  do  not  at  present  justify  us  in 
speaking  of  the  optic  lobes  as  being  the  organ  for  the  inhibition 
of  reflex  action  or  in  regarding  their  absence  as  the  cause  of  the 
exaltation  of  reflex  activity  which  is  so  obvious  in  the  brainless 
frog. 

The  inhibitory  action  of  the  cerebral  hemispheres  is  illustrated  by 
the  'croaking  frog'  alluded  to  above.  An  entire  frog  when  stroked  on 
the  flanks  in  a  particular  way  may  or  may  not  '  croak' :  a  frog  from 
which  the  cerebral  hemispheres  alone  have  been  removed,  all  other 
parts,  including  the  optic  lobes,  having  been  left  intact,  will  invariably 
croak  when  stroked  in  the  same  way.  But  Langendorf^  finds  that  the 
same  regular  response  to  stimulation,  i.e.  the  same  absence  of  inhibi- 
tion, is  witnessed  in  a  frog  which  has  been  merely  blinded,  for  instance 
by  section  of  both  optic  nerves,  the  cerebral  hemispheres  being  left 
intact.  From  this  it  might  be  inferred  that  the  inhibitory  activity  ot 
the  cerebral  hemispheres  was  so  to  speak  furnished  by  the  sense  of 
sights  Langley^  on  the  other  hand  finds  that  ordinary  reflex  action 
produced  by  the  stimulation  of  one  sciatic  is  diminished  by  section  of 
the  other  sciatic,  and  he  regards  the  result  as  indicating  not  that  the 
mere  section  acts  as  a  stimulus  exciting  an  inhibitory  mechanism  or 

'  Archivf.  Anat.  u.  Phys.,  1877  (Phys.  Abth.)  p.  435. 

^  Cf.  V.  Boetticher,  '  Ueber  Reflexhemmung,'  Preyer's  Abhandl.,  11.  3 
(1S78) ;  and  his  critic,  Spode,  Archiv  f.  Anat.  u.  Phys.,  1879  (Phys.  Abth.), 
p.  113. 

3  Proc.  Cambridge  P/iilos.  Soc  ,  .1879. 


6o6  REFLEX   ACTIONS.  [BOOK   III. 

producing  an  inhibitory  result,  but  that  in  a  normal  state  of  things 
afferent  impulses  passing  up  the  sciatic  nerve  maintain  the  activity  of 
the  spinal  cord,  keep  it  so  to  speak  awake,  and  hence  when  these 
are  interrupted  by  the  section  of  the  nerve,  the  spinal  cord  is  more 
difficult  to  move  by  impulses  reaching  it  from  other  nerves. 

We  may  put  the  whole  matter  in  a  somewhat  general  way  as 
follows.  In  treating  of  the  senses,  we  have  seen  that  two  sensory 
impulses  may,  according  to  circumstances,  unite  in  producing  a  sensa- 
tion greater  than  that  caused  by  either  alone,  or  they  may  lessen  each 
other's  influence,  or  they  may  have  no  effect  on  each  other  at  all,  each 
sensory  impulse  producing  its  effects  quite  independent  of  the  other. 
We  have  moreover  seen  that  the  various  automatic  centres,  whether 
sporadic  or  belonging  to  the  central  nervous  system,  may  in  reference 
to  any  given  afferent  impulse  be  affected  in  the  way  of  inhibition  or  of 
augmentation,  or  may  not  be  affected  at  all.  Indeed  we  may  say 
probably  of  any  mass  of  active  living  protoplasm,  whether  automatic 
or  reflex,  whether  concerned  in  consciousness  or  not,  that  it  is  so 
related  to  other  parts  of  the  body,  that  its  activity  may  be  diminished 
or  exalted  or  unaffected  by  events  occurring  in  those  parts.  Whether 
inhibition  or  exaltation  or  indifference  is  in  any  given  case  predo- 
minant will  depend  on  circumstances  and  arrangements,  the  nature  of 
which  we  at  present  understand  in  a  very  imperfect  manner.  And  the 
difficulties  are  increased  rather  than  diminished  by  presupposing  the 
existence  of  an  unlimited  number  of  inhibitory  and  augmenting  fibres. 


In  the  Mammal. 

In  the  frog  the  shock  which  follows  upon  division  of  the 
spinal  cord,  and  which  for  a  while  inhibits  reflex  activity,  soon 
passes  away ;  within  a  very  short  time  after  the  medulla  oblongata 
for  instance  has  been  divided  the  most  complicated  reflex  move- 
ments can  be  carried  on  by  the  spinal  cord  when  the  appropriate 
stimuli  are  applied.  With  the  mammal  the  case  is  very  different. 
For  days  even  after  division  of  the  spinal  cord  the  parts  of  the 
body  supplied  by  nerves  springing  from  the  cord  below  the  section 
exhibit  very  feeble  reactions  only.  In  the  dog  for  instance  after 
division  of  the  spinal  cord  in  the  lower  dorsal  region,  the  hind 
limbs  hang  flaccid  and  motionless,  and  pinching  the  hind  foot 
evokes  as  a  response  either  slight  irregular  movements  or  none  at 
all.  Indeed  were  our  observations  limited  to  this  period  we  might 
infer  that  the  reflex  actions  of  the  spinal  cord  in  the  mammal 
were  but  feeble  and  insignificant.  If  however  the  animal  be  kept 
alive  for  a  longer  period,  for  weeks,  or  better  still  for  months, 
though  no  union  or  regeneration  of  the  spinal  cord  takes  place, 
reflex  movements  of  a  powerful,  varied  and  complex  character 
manifest  themselves  in  the  hind  limbs  and  hinder  parts  of  the 


CHAP,   v.]  TIIK   SPINAL   CORD.  607 

body  ;  a  very  feeble  sliimiliis  apiilied  to  the  skin  of  these  regions 
promptly  gives  rise  to  extensive  and  yet  coordinate  movements. 
Conii)arcd  with  the  reflex  actions  of  the  frog,  the  movements 
carried  out  l)y  the  lower  jiortion  of  tlie  spinal  cord  of  the  mammal 
while  they  are  more  energetic  may  perhaps  be  regarded  as  less 
definite  and  comj^Iete  and  less  purposeful ;  though  even  this  is 
not  admitted  by  r.oltz  '  and  his  pupils,  to  whom  we  are  largely 
indebted  for  information  on  this  subject.  A  striking  feature  in 
the  phenomena  attendant  on  this  isolation  of  the  lumbar  cord  in 
the  mammal  is  the  occurrence  of  apparently  spontaneous  move- 
ments in  the  parts  which  it  governs.  When  the  animal  has 
thoroughly  recovered  from  the  operation  the  hind  limbs  rarely 
remain  at  rest  for  any  long  period ;  they  move  restlessly  in 
various  ways ;  and  when  the  animal  is  suspended  by  the  upper 
part  of  the  body,  the  pendent  hind  limbs  are  continually  being 
drawn  up  and  let  down  again  with  a  monotonous  rhythmic 
regularity,  highly  but  perhaps  falsely  suggestive  of  automatic 
rhythmic  discharges  from  the  central  mechanisms  of  the  cord. 
This  greater  proneness  to  activity  is  however  just  what  might  be 
exj)ected,  when  we  take  into  consideration  the  more  rapid  meta- 
l)olic  changes  and  the  consequent  greater  molecular  mobility  of 
the  whole  nervous  system  of  the  mammal.  Another  fact  worthy 
of  attention  is  that  the  reflex  jjhenomena  in  mammals  (dogs)  vary 
very  much  both  in  different  individuals  and  in  the  same  individual 
under  different  circumstances.  Race,  age,  and  previous  training, 
seem  to  have  a  marked  effect  in  determining  the  extent  and 
character  of  the  reflex  actions  which  the  lumbar  cord  is  capable 
of  carrying  out;  and  these  seem  also  to  be  largely  influenced  by 
passing  circumstances,  such  as  whether  food  has  been  recently 
taken  or  no.  It  is  evident  diat  the  reflex  as  well  as  other 
phenomena  of  the  mammalian  spinal  cord  present  a  large  field 
for  inquiry,  being  much  more  varied  and  extensive  than  previous 
experience  had  led  us  to  suppose. 

Vicarious  reflex  movements  may  also  be  witnessed  in  mammals, 
though  not  perha|)S  to  such  a  striking  extent  as  in  frogs.  In  dogs, 
in  which  partial  removal  of  the  cerebral  hemispheres  has 
apparently  heightened  the  reflex  excitability  of  the  spinal  cord, 
the  remarkable  scratching  movements  of  the  hind  leg  which  are 
called  forth  by  stimulating  particular  spots  on  the  side  of  the 
body,  are  executed  by  the  leg  of  the  opposite  side,  when  the  leg 
of  the  same  side  is,  even  without  any  great  force  being  applied, 
prevented  from  carrying  them  out '.     Here  too  the  absence  of  a 

■  Pfliiger's  Wn7/iz',  vim.  (1S74)  ]■.  460  ;   ix.  (1874)  p.  358. 
•  Gergens,  Pfliiger's  Archiv,  xiv.  (1877)  p.  340. 


6o8  REFLEX   ACTIONS.  [BOOK   III. 

truly  purposeful  character  of  the  movements  is  very  marked,  and 
the  phenomena  afford  a  strong  support  to  the  '  mechanical ' 
explanation  of  the  more  complicated  behaviour  of  the  frog. 

According  to  Cwsjannikow^,  if  in  the  rabbit  the  spinal  cord  be 
divided  at  the  calamus  scriptorius,  a  moderate  stimulus  applied  to  the 
hind  foot  causes  movements  in  one  or  other  or  both  hind  legs,  but 
none  in  the  fore  legs,  and  a  stimulation  of  the  fore  foot  causes  move- 
ments in  the  fore  but  not  in  the  hind  legs  ;  whereas  if  a  zone  of 
nervous  tissue  only  6  to  5  mm.  in  height  be  left  above  the  calamus 
scriptorius,  stimulation  of  either  foot  may  produce  a  movement  in  any 
part  of  the  body.  This  would  seem  to  shew  that  the  mechanisms  co- 
ordinating the  movements  of  the  fore  limbs  with  those  of  the  hind  limbs, 
which  in  the  frog  are  scattered  over  the  whole  spinal  cord,  are  in  the 
mammal  (rabbit)  gathered  into  the  medulla  oblongata.  The  region 
referred  to  above  lies,  it  may  be  remarked,  near  to  the  '  convulsive 
centre '  (see  p.  388).  Woroschiloff"  has  observed  that  in  the  rabbit 
direct  stimulation  with  an  interrupted  current  of  the  cervical  cord, 
down  as  far  as  the  origin  of  the  sixth  cervical  nerve,  causes  co- 
ordinated rhythmic  springing  movements  of  the  body,  whereas  when 
the  same  stimulus  is  applied  to  lower  regions  of  the  cord,  a  rigid 
tetanus  results  ;  this  too  indicates  the  existence  in  the  cei^vical  cord  of 
peculiar  co-ordinating  mechanisms. 

Muscular  movements,  as  parts  of  a  reflex  action,  may  occur 
on  stimulation  of  not  only  the  ordinary  spinal  and  cranial  sensory 
nerves,  but  also  of  the  nerves  of  special  sense.  A  sound  or  a. 
flash  of  light  readily  produces  a  start,  a  bright  light  causes  many 
persons  to  sneeze,  and  reflex  movements  may  even  result  from 
a  taste  or  smell. 


T/ie  Time  required  for  Reflex  Actions. 

When  we  stimulate  one  of  our  eyelids  with  a  sharp  electrical  shock, 
both  eyelids  blink.  Hence,  if  the  length  of  time  intervening  between 
the  stimulation  of  the  right  eyelid  and  the  movement  of  the  left  eyelid 
be  carefully  measured,  this  will  give  the  time  required  for  the  develop- 
ment of  a  reflex  action.  Exner^  found  this  to  be  from  "0662  to  '0578 
sec,  being  less  for  the  stronger  stimulus.  Deducting  from  these  figures 
the  time  required  for  the  passage  of  afferent  and  efferent  impulses 
along  the  fifth  and  facial  nerves  to  and  from  the  medulla,  and  for  the 
latent  period  of  the  muscular  contraction  of  the  orbicularis,  there 
would  remain  '0555  to  '0471  sec.  for  the  time  consumed  in  the  central 
operations  of  the  reflex  act.  The  calculations,  however,  necessary  for 
this  reduction,  it  need  not  be  said,  are  open  to  sources  of  error.    Exner 

'  Ludwig's  Arbeiten,  1874,  p.  308. 

^  Ludwig's  Arbeiten,  1874,  p,  99. 

3  Pfliiger's  Archiv,  VIII.  (1874)  P«  526. 


CHAP,   v.]  THE  SPINAL  CORD.  609 

louticl  that  when  he  used  a  visual  stimuUis,  viz.  a  flash  of  light, 
the  time  was  not  only  exceedingly  prolonged,  •2168  sec,  but  very 
variable. 

The  time  required  for  any  reflex  act  varies,  according  to  Rosenthal', 
very  considerably  with  the  strength  of  the  stimulus  employed,  being 
less  for  the  stronger  stimuli  ;  it  is  greater  in  transverse  than  in 
longitudinal  conduction,  and  is  much  increased  by  exhaustion  of  the 
cord.  It  has  been  stated  that  the  central  pro?esses  of  a  reflex  action 
are  propagated  in  the  frog  at  the  rate  of  about  8  metres  a  second  ; 
but  this  value  cannot  be  depended  on.  The  time  thus  occupied  by 
purely  reflex  actions  must  not  be  confounded  with  the  interval  required 
for  mental  operations  ;  of  the  latter  we  shall  speak  presently. 

Sec.  2.  As  A  Centre  or  Group  of  Centres  of  Automatic 

Action. 

Irregular  automatism,  i.e.  a  spontaneity  comparable  to  our 
own  volition,  is  wholly  absent  from  the  spinal  cord.  A  brainless 
frog  placed  in  a  condition  of  complete  equilibrium  in  which  no 
stimulus  is  brought  to  bear  on  it,  remains  perfectly  motionless 
till  it  dies. 

Of  the  various  regular  automatic  centres,  both  the  numerous 
ones  in  the  medulla  oblongata,  such  as  the  vaso-motor,  respiratory, 
&c.,  and  the  more  sparse  ones  in  other  regions  of  the  cord,  such 
as  those  connected  with  micturition  (p.  421),  defaecation  (p.  302), 
erection,  parturition,  and  so  on,  we  have  treated  or  sliall  have  to 
treat  so  fully  in  reference  to  their  respective  mechanisms,  and 
discussed  how  far  they  are  purely  automatic,  or  in  reality  merely 
reflex  in  nature,  that  nothing  more  need  be  said  liere. 

The  connection  between  the  spinal  cord  and  the  automatic  move- 
ments of  the  lymph-hearts  of  the  frog  has  also  (p.  127)  been  briefly 
referred  to.  Volkmann-  was  the  first  to  obsei-ve  that  the  destruction 
of  even  a  small  portion  of  special  regions  of  the  spinal  cord  puts  an 
end  to  the  pulsations  of  these  organs,  the  region  or  centre  for  the 
anterior  pair  of  hearts  being  opposite  the  third  vertebra,  and  that  for 
the  posterior  pair  being  opposite  the  seventh,  or  according  to 
Priestley^  sixth,  vertebra.  Eckhard-  however  observed  that  the  pulsa- 
tion':,  though  ceasing  upon  the  destruction  of  the  regions  of  the 
spinal  cord  above  mentioned,  after  a  while  returned  ;  still  the 
pulsations  thus  independent  of  the  spinal  cord  differed  in  character 

'  M <natsbericht  d.  Berlin.  Acad.  1873,  p.  104.  See  also  Sitzungsberuht  d. 
phys.  vied.  Ges,  Erlangcn,  1875,  and  Wundt,  Mcchanik  der  I^ erven,  &c.  Abth. 
II.  (1876). 

=  Miiller's  Archiv,  1844,  p.  419. 

3  Journal,  of  Phys.  I.  (187S)  pp.  I  and  19. 

*  Zt.  f.  rat.  Med.  viii.  p.  24,  and  Exp.  Phys.  Nerv.  System,  lS66,  p.  259. 

F.  P.  39 


6lO  LYMPH-HEARTS.  [BOOK  III. 

from,  being  mo.  e  partial  and  irregular  than,  those  witnessed  when 
the  spinal  cord  was  intact.  Goltz'  saw  the  pulsations  return  in  about 
three  weeks  after  they  had  been  stopped  by  section  of  the  tenth 
(coccygeal)  spinal  nerve,  though  no  regeneration  of  the  nervous  tract 
had  taken  place ;  and  he  states  that  with  care  the  hearts  may  then 
be  wholly  removed  from  the  body  without  arresting  their  pulsations. 
Waldeyer%  though  he  described  ganglionic  cells  in  the  neighbourhood 
of  the  hearts,  found  the  return  of  pulsations  after  division  of  the 
coccygeal  nerve  or  destruction  of  the  spinal  cord  too  inconstant  to 
prove  their  independence  of  the  spinal  cord,  and  Heidenhain^  arrived 
at  a  similar  conclusion. 

According  to  some  authors  stimulation  of  the  coccygeal  nerves 
with  the  interrupted  current  brings  about  a  tetanic  systole  of  the 
posterior  lymph-hearts,  but  stimulation  with  a  strong  constant  current 
causes  a  standstill  in  diastole  1  Priestley  ^  however  finds  that  the 
interrupted  current  applied  to  the  spinal  centre  produces  a  slowing  of 
the  lymph-hearts  passing  on  to  complete  arrest  as  the  strength  of  the 
current  is  increased.  If  the  current  be  made  still  stronger,  the  inhibi- 
tion gives  ^yay  to  tetanic  contraction.  The  effects  of  the  constant 
cun-ent  vary  according  to  circumstances.  Goltz*  found  that  the 
lymph-hearts  might  like  the  blood-heart  be  inhibited,  and  brought 
to  a  diastolic  standstill  in  a  reflex  manner,  by  striking  sharply  the 
exposed  intestines,  and  that  they  might  also  be  similarly  inhibited  by 
pinching  the  auricles  of  the  blood-heart ;  the  centre  of  this  reflex 
inhibition  appeared  to  be  in  the  medulla  and  the  afferent  impulses  to 
pass  along  the  vagus.  Suslovva'  traced  these  afferent  inhibitory  im- 
pulses from  the  intestine  through  the  rami  communicantes.  He  found 
that  after  destruction  of  all  the  posterior  sensory  spinal  roots,  the 
lymph-hearts  remained  in  a  (diastolic)  still-stand,  which  however  gave 
place  to  a  return  of  pulsatile  activity  as  soon  as  the  rami  communi- 
cantes were  also  divided,  the  experiment  in  his  opinion  indicating  that 
the  inhibitory  impulses  passing  along  the  latter  channel  from  the 
intestine  are  of  a  tonic  character.  Suslowa  also  found  that  stimula- 
tion of  a  transverse  section  of  the  optic  thalami  or  optic  lobes  produced 
a  diastolic  standstill  of  the  lymph-hearts,  whereas  stimulation  of  a 
transverse  section  of  the  spinal  cord  itself  increased  their  activity ; 
that  the  inhibitory  centres  of  Setschenow  in  fact  govern  also  the 
lymph-hearts. 

It  has  been  maintained  that  the  spinal  cord  exercises  over  the 
skeletal  muscles  a  tonic  action  comparable  to  that  of  the  vaso- 
motor centres  over  the  smooth  muscles  of  the  arteries.  There  is, 
however,  no  adequate  support  to  this  view.  When  a  muscle  is 
cut  across  in  the  living  body,  the  section  gapes,  because  all  the 

^  Cbl.f.  Med.  Wiss.,  1863,  p.  497. 

=  Stud.  Bresl.  Inst.,  III.  p.  71. 

3  DisqiAisitiones  de  nii~vis  organisque  centralibus  coi'dis  cordiumve,  &c.,  1864, 

4  Eckhard,  loc.  cit.     Waldeyer,  loc.  cit.  s   Op.  at. 
^  Cbl.f.  Med.  Wiss.,  1863.  pp.  17  and  497  ;   1864,  p.  690. 

^  Cbl.f.  Med.  Wiss.,  1S67,  p.  833.     Zt.  J.  rat.  Med.  31  (i868)  p.  224. 


CHAP,  v.]  THE   SPIxVAL  COKD.  6l  I 

muscles  of  the  body  arc  slightly  stretched  beyond  their  normal 
length.  When  one  side  of  the  face  is  paralysed  the  mouth  is 
drawn  to  the  opposite  side,  not  because  the  paralysed  muscles 
have  lost  their  tone,  but  because  there  are  on  the  paralysed  side 
no  contractions  to  antagonise  the  effect  of  the  continually  re- 
peated contractions  of  the  sound  side.  And  the  view  is 
distinctly  disproved  by  the  fact  that,  according  to  most  observers, 
when  in  the  living  body  the  nerve  going  to  a  muscle  is  cut  no 
permanent  lengthening  of  the  muscle  is  caused.  After  the  sciatic 
plexus  of  one  leg  of  a  brainless  frog  has  been  cut,  that  leg  hangs 
down  more  helplessly  than  the  other  when  the  animal  is  suspended. 
This  might  at  first  sight  be  considered  as  the  result  of  loss  of 
tone  ;  but  the  same  flaccidity  is  observed  in  a  leg  in  which  the 
posterior  roots  only  of  tiie  sciatic  i)lexus  have  been  divided.  The 
difference  between  the  leg  of  the  one  side  and  that  of  the  other  in 
these  cases  is  that  the  sound  leg  is  rather  more  flexed  than  the 
other ;  and  evidently  this  slight  flexion,  since  it  disappears  on 
section  of  the  posterior  roots,  is  the  result  of  a  reflex  and  not  of 
an  automatic  action. 

Tschiriew'  affirms  that  with  a  certain  degree  of  tension,  section  of 
the  nerve  in  the  living  body  is  followed  by  a  lengthening  of  the 
muscle,  and  he  contends  for  the  existence  of  a  muscular  tone  not  of 
automatic  but  of  reflex  nature,  originating  in  afferent  impulses  started 
in  the  nerves  of  the  tendon  of  the  muscle  whenever  the  tendon  is 
subjected  to  a  certain  degree  of  tension.  He  believes  that  the  nerve- 
fibres,  which  he  has  traced  to  the  tendons  and  aponeuroses  of  muscles, 
and  which  he  reg:irds  as  identical  with  the  fibres  described  by  Sachs 
(see  p.  597),  are  the  only  afferent  fibres  belonging  to  muscle  and  are 
simple  afferent  nerves,  not  specific  nerves  of  muscular  sense.  He 
explains*  the  so-called  tendon  reflex  or  knee  phenomena,  i.e.  the  con- 
tractions in  the  muscles  of  the  thigh  caused  by  sharply  striking  the 
patellar  tendon,  as  reflex  movements  started  by  afferent  impulses 
passing  along  the  same  nerves. 


Sec.    3.      As   a  Conductor     of    Afferent    and   Efferent 

Impulses. 

When  we  move  our  foot,  or  feel  something  touching  our  foot, 
efferent  or  afterent  impulses  must  evidently  pass  along  the  whole 
length  of  the  spinal  cord  on  their  way  from  and  to  the  brain.  We 
might  suppose  that  in  such  cases  sensory  impulses  are  conveyed 
straight  along  a  fibre  from   the  periphery  to  the  sensorium,  and 

'  Archivf.  Anal.  u.  Phvs.,  r879  (Phys.  Abth.)  p.  78b 
•  Archivf.  Psych.,  VIII.'  (187S)  Hft.  3. 

39—2 


6l2  CONDUCTION   OF   IMPULSES.  [BOOK    III. 

volitional  impulses  straight  along  a  fibre  from  the  '  organ  of  the 
will '  to  the  muscular  fibre.  Or  we  might  suppose  that  the  con- 
duction is  not  simple,  but  carried  out  by  a  more  or  less  com- 
plicated system  of  relays.  Both  anatomical  and  physiological 
considerations  shew  that  the  latter  view  is  the  correct  one. 

The  phenomena  of  reflex  action  have  shewn  us  that  the  cord 
contains  a  number  of  more  or  less  complicated  mechanisms 
capable  of  producing,  as  reflex  results,  coordinated  movements 
altogether  similar  to  those  which  are  called  forth  by  the  will.  Now 
it  must  be  an  economy  to  the  body,  that  the  will  should  make 
use  of  these  mechanisms  already  present,  by  acting  directly  on 
their  centres,  rather  than  that  it  should  have  recourse  to  a  special 
apparatus  of  its  own  of  a  similar  kind.  And  from  an  anatomical 
point  of  view,  it  is  clear  that  the  white  matter  of  the  upper 
cervical  cord  does  not  contain  a  suflicient  number  of  fibres,  even 
of  attenuated  dimensions,  to  connect  the  brain,  by  afferent  or 
efferent  ties,  with  every  sensory  or  motor  nerve-ending  of  the 
trunk  and  limbs. 

Regarded  in  a  genetic  aspect,  the  spinal  cord  is  a  series  of 
cemented  segments,  having  mutual  relations  one  with  the  other,  and 
all  being  governed  by  the  dominant  cerebral  segments.  And  we 
might  fairly  expect  to  find  that  in  each  segment  of  the  cord  part  of 
the  structures  are  purely  segmental,  and  serve  as  a  nervous  centre  for 
the  afferent  and  eflerent  nerves  corresponding  to  a  portion  of  the  body, 
while  part  are  commissural  structures  connecting  the  segment  with 
other  segments  and  the  remainder  are  structures  connecting  the 
governed  segment  with  the  governing  cerebral  organs.  Some  such 
arrangement  as  this  is  indicated  by  the  directions  taken  by  the  fibres 
of  the  roots  of  the  spinal  nerve  ;  and  the  view  is  supported  by  the 
results  gained  by  comparing  sections  of  the  spinal  cord  taken  at 
different  points  of  its  length.  If  a  curve  be  constructed  representing 
the  sectional  area  of  the  nerve-roots  entering  the  spinal  coi'd,  at  their 
respective  points,  along  its  whole  length  from  the  first  cervical  to  the 
last  sacral  nerve,  some  such  form  as  that  shewn  in  Fig.  62  would  be 
obtained.  If  instead  of  the  sectional  area  of  each  pair  of  roots  the 
continued  summation  of  the  roots  were  used  to  construct  the  curve, 
the  form  would  be  that  of  Fig.  63.  If  the  variations  of  the  sectional 
area  of  the  grey  matter  at  different  points  of  its  length  were  thrown 
into  a  curve,  the  form  would  be  that  of  Fig.  64.  If  the  variations  of 
the  sectional  area  of  the  lateral  columns  were  taken,  the  curve  would 
take  the  form  of  Fig.  65.  The  anterior  columns  similarly  treated 
would  give  Fig.  66,  and  the  posterior  Fig.  67.  A  comparison  of  these 
several  figures  suggests  the  view  that  the  grey  matter  of  the  cord  is 
preeminently  segmental,  falling  and  rising  as  it  does  with  the  amount 
of  nerve-fibre  passing  into  each  part  of  the  cord,  and  that  the  lateral 
columns,  increasing  as  they  do  from  below  upward,  much  more 
steadily  than  either  the  grey  matter  or  the  anterior  and   posterior 


CHAP,    v.] 


THE   SPINAL  CORD. 


^>'3 


columns,  are  the  chief  means  by  which  the  brain  is  brought  into  con- 
nection with  the  several  segments  of  the  cord,  and  thus  with  the 
nerves  of  the  body  at  large. 


IV    lU     II      IV    W    III     11     I    XII  XI    X    IX   VIII  VII   VI    V    IV    III    II     I    VIII  VII  VI    V    IV   111     'I     I 
Fig.  62.      DiAGRA.M  skewing  the  relative  sectional  areas  op  the  Spinal  Nerves, 

AS   THEV   JOIN    the   ShINAL   CoRD. 

(To  be  read  from  left  to  right.) 

In  this  and  the  succeeding  figures  taken  from  WonschiloflTs  paper  in  Ludwig's  Arbeiten, 
1874,  and  constructed  from  Slilling's  data  of  the  human  spinal  cord,  the  cervical,  dirsal, 
lumbar,  and  s.icral  nerves  are  used  as  abscissa;  ;  3  mm.  to  the  interval  between  each  two 
nerve-roots.  The  ordinates  are  in  millimetres,  each  mm.  corresponding  to  a  square  unit 
of  surface  of  nerve-root-section,  of  grey  substance,  or  of  white  substance. 


V    IV  III    II    I    V    IV  III   II     I    XII  XI   X   IXVUIVII  VI    V    IV  III    II    I  VIUVII  VI  V   IV  III    II     I 
Fig.  (13.      Diagram   shewing  the   united  sectio'Nal  areas  of  the  Spinal  Nerves, 
puocEEDiNG  FROM  BELOW  UPWARDS.     The  ordinates  in  this  figure  are  smaller  than  in 
the  preceding. 


I    XU  XI    X  IX  VIU  VU  VI   V   IV  IB    a    t   VU  VU  VI   V  IV  III    U    I 


Fig.  64.      Diagram  shewing   the  Variations   in  the  sectional  area  of  the  Grey 
Matter  of  the  Spinal  Cord,  along  its  length. 


xn  XI  X  IX  vin  vu  VI  v  iv  m  ii    i  vni  vn  vi  v  iv  in  ii    i 


Fig.  65.     Diagram  shewing  thb  Variations  in  the  sectional  area  of  thk  Lateral 
Columns  op  thb  Spinal  G>rd  along  its  lkngth. 


6l4  CONDUCTION   OF   IMPULSES.  [BOOK   III. 


V   IV  111    II     I    V    IV  111    II     I    XII  XI   X   IX  VIII  VII  Vi   V    IV    III    II     I    VIII  VII  VI    V    IV    III    II     I 

Fig.  66.    Diagram  shewing  the  Variations  in  the  sectional  area  of  the  Anterior 
Columns  of  the  Spinal  Cord,  along  its  length. 


I       V    IV   III    II     I     V    !V   III    II     I    XII  XI    X    IX  VIII  VII  VI    V    IV   III    II     I   VIU   VII  VI    V    IV    III    II     9 


Fig.  67.     Diagram  shewing  the  Variations  in  the  sectional  area,  of  the  Posterior 
Colu.vins  of  the  Spinal  Cord,  along  its  length. 

Our  information  concerning  the  conduction  of  impulses  along 
the  spinal  cord  is  derived  partly  from  experiment  and  partly  from 
pathological  observation.  Both  these  methods  have  their  advan- 
tages and  disadvantages.  In  experiments  there  is  danger  of  con- 
founding the  immediate  and  temporary  effects  of  the  operation, 
such  as  those  produced  by  shock,  with  the  more  real  and  lasting 
effects.  It  is  difficult  too  in  such  cases  to  determine  the  ex- 
istence of  sensations,  and  to  distinguish  between  reflex  and  purely 
voluntary  movements.  In  pathological  cases  we  have  the  advan- 
tage of  being  able  clearly  to  define  sensation  and  volition,  but 
this  is  frequently  more  than  counterbalanced  by  the  diffuse  nature 
of  the  injury  or  disease,  and  the  want  of  exact  anatomical  verifi- 
cation. When  these  facts  are  borne  in  mind,  it  will  easily  be 
understood  that  in  no  part  of  physiology  are  the  statements  of 
investigators  more  conflicting  and  unsatisfactory. 

According  to  the  views  put  forward  by  Brown-Sequard  and 
others,  transverse  division  of  the  lateral  half  of  the  cord  is 
followed  on  the  same  side,  below  the  injury,  by  loss  of  voluntary 
movement,  accompanied,  not  by  loss  of  sensation,  but  by 
hyperaesthesia,  and  on  the  opposite  side  by  loss  of  sensation 
without  any  affection  of  voluntary  movement ;  whereas  a  longi- 
tudinal median  incision  through  the  cord  causes  on  both  sides 
loss  of  sensation  in  an  area  corresponding  to  the  length  of  the 
incision,  without  any  impairment  of  voluntary  movement.  That 
is  to  say,  sensory  impulses  entering  into  the  cord  at  its  posterior 


CHAT,   v.]  THE   SPINAL   CORD.  615 

root  immediately  cross  to  the  other  side  of  the  cord  and  so 
a'scend  to  the  brain,  whereas  efferent  impulses  of  volition,  though 
they  cross  in  the  region  of  the  medulla  oblongata  or  higher  up 
(and  hence  in  cases  of  paralysis  from  cerebral  mischief,  the  right 
side  loses  the  ])0\ver  of  voluntary  movement  when  the  left  hemi- 
sphere is  affected,  and  vice  versa),  keep  to  the  same  side  of  the 
cord  along  its  whole  length.  The  paths  may  be  somewhat  more 
closely  defined  by  stating  that  the  sensory  impulses  pass  from  the 
posterior  roots  along  a  certain  length  of  the  posterior  columns, 
and  then  cross  over  to  the  grey  matter  of  the  opposite  side,  in 
which  they  ascend  to  the  brain,  while  volitional  impulses,  having 
crossed  in  the  pons  Varolii  and  medulla  oblongata  before  their 
entrance  into  the  cord,  descend  in  the  antero-lateral  columns, 
keeping  to  the  same  side  throughout,  and  leave  the  cord  by  the 
anterior  roots.  According  to  Vulpian '  and  others,  the  volitional 
impulses  are  confined  in  the  cervical  region  to  the  lateral  columns, 
though  in  the  dorsal  and  lumbar  regions  they  travel  in  the  anterior 
columns  as  well,  and  the  decussation  is  not  confined  to  or  com- 
pleted in  tlie  region  of  the  medulla,  but  is  continued  some  way 
down  ;  and  similarly  the  decussation  of  the  sensoiy  impulses  is 
not  sudden  but  gradual,  so  that  section  of  a  lateral  half  of  the 
cord  affects  sensation  on  both  sides,  though  most  on  the 
opposite  side. 

Schiff,  and  others  with  him,  make  a  distinction  between  the 
conduction  of  distinct  tactile  sensations  and  that  of  general 
sensibility,  as  well  as  between  the  conduction  of  volitional  im- 
pulses anil  that  of  impulses  merely  forming  part  of  a  reflex  action. 
They  hold  that  purely  volitional  impulses  pass  exclusively  along 
the  antero-lateral  columns,  and  purely  tactile  sensations  along  the 
posterior  columns  of  the  same  side,  and  that  the  grey  matter  is 
capable  of  transmitting  in  all  directions  such  afferent  impulses  as 
only  give  rise  to  affections  of  general  sensibility,  and  such  efferent 
impulses  as  are  parts  of  reflex  actions.  Hence,  according  to 
them,  when  at  any  part  of  the  cord  the  continuity  of  the  white 
matter  is  wholly  broken,  so  that  the  parts  above  the  injury  are 
connected  with  those  below  by  grey  matter  only,  tactile  sensa- 
tions and  voluntary  movements  are  entirely  absent  in  the  parts 
below  the  injury,  though  violent  stimulation  of  those  parts  will 
give  rise  to  pain,  and  reflex  actions  in  them  may  be  induced  by 
stimuli  applied  to  parts  above  the  injury.  Conversely,  when  at 
any  point  the  grey  matter  is  destroyed  but  the  white  left  •intact, 
voluntary  movements  and  tactile  sensations  remain  in  the  parts 
below  the  injury,  though  even  violent  stimuli  applied  to  those 
'  Syst.  Nerv.  Le^.  xvii. 


6l6  CONDUCTION   OF   IMPULSE  :  [BOOK   III. 

parts  give  rise  to  no  pain,  and  reflex  actions  cannot  be   induced 
in  them  by  stimuli  applied  to  the  parts  above  the  seat  of  injury. 

Schiff'  states  that  when  in  any  part  of  the  cord  the  posterior 
columns  only  are  left,  all  the  rest  of  the  white  and  the  grey  matter 
being  removed,  tactile  sensations  remain  though  no  pain  i;;  felt  :  there 
is  analgesia  but  not  anesthesia  ;  a  rabbit  thus  operated  on  is  readily 
awakened  for  a  moment  from  sleep  (artihcially  induced  by  bleeding) 
when  the  hind  limbs,  or  parts  below  the  seat  of  injury,  are  even 
lightly  touched,  but  exhibits  no  sign  of  pain  when  the  nerves  are  laid 
bare  and  pinched,  or  when  needles  are  driven  through  the  skin.  This 
experiment  however,  on  which  Schiff  rests  his  theory  of  analgesia, 
does  not  prove  the  existence  of  tactile  sensations  ;  it  simply  shews 
that  a  peculiar  condition  may  be  brought  about  in  which  a  sensory 
impulse  produces  a  maximum  initial  result  and  then  ceases  to  have 
any  effect.  The  animal  moved  at  every  fresh  stimulus,  whether  slight 
or  strong,  whether  applied  to  the  skin  or  to  a  bare  nerve,  but  after  the 
first  explosion  the  central  organs  concerned  in  the  matter,  whatever 
they  were,  appeared  to  be  exhausted.  The  condition  is  certainly  a 
remarkable  one,  and  may  bear  many  interpretations. 

To  make  these  views  logically  complete,  we  must  suppose  that 
after  section  of  a  lateral  half  of  the  cord,  tactile  sensations  and 
voluntary  movements  would  be  entirely  lost  on  the  same  side 
below  the  seat  of  injury,  but  that  pain  would  still  be  felt,  and  the 
parts  would  still  be  capable  of  being  thrown  into  movements  by 
reflex  action. 

Such  are  the  two  chief  opinions  held  on  this  subject,  and  it  must 
be  confessed  that  neither  is  satisfactory.  Much  confusion  has  probably 
arisen  from  different  kinds  of  animals  being  used,  and  different  parts 
of  the  cord  operated  on,  and  from  the  want  of  a  searching  micro- 
scopic examination  of  the  results  of  the  various  operations.  These 
objections  cannot  be  urged  against  the  inquiries  of  Miescher^  and 
Woroschiloff3,  in  so  far  as  their  experiments  were  all  conducted  on 
rabbits,  and  on  the  same  dorsal  part  of  the  cord.  Miescher  found 
that  the  afferent  impulses  which,  starting  from  the  sciatic  nerve  and 
travelling  up  to  the  medullary  vaso-motor  centre,  caused  a  rise  in 
blood-pressure  by  acting  on  that  centre,  passed  almost  exclusively  by 
the  lateral  columns.  When  one  lateral  column  was  divided,  stimula- 
tion of  either  sciatic  produced  much  less  than  the  normal  effect ;  when 
both  columns  were  divided,  no  effect  at  all  was  produced.  When  only 
the  lateral  columms  were  left,  the  other  parts  being  destroyed,  the 
vaso-motor  influences  of  the  sciatic  stimulation  appeared  to  be  quite 
normal.  From  which  it  would  appear  that  afferent  impulses,  such  as 
affect  the  vaso-motor  centre,  pass  from  one  sciatic  up  ^oi/i  lateral 
columns;  and  Miescher  came  to  the  conclusion  that  they  passed  more 

'  LeArd.,  p.  251.  '   Ludwig's  Arbeiten,  1870,  p.  172. 

3  Ibid.  1874,  p.  99. 


CHAP,   v.]  THE   SPINAL   CORD.  617 

on  the  opposite  than  on  the  same  side.  He  also  thought  that  im- 
pulses coming  from  more  distant  parts  travelled  more  to  the  outside 
of  the  columns  than  those  from  nearer  parts.  It  need  hardly  be  urged 
that  one  set  of  experiments  of  this  kind,  the  result  of  which  can  be 
detiniiely  slated  in  millimetres  of  mercury,  as  measurements  of  the 
rise  of  blood-prcs^ure,  arc  worth  a  score  of  others,  in  which  trust  has 
to  be  placed  in  variable  and  illusory  signs  of  sensation.  On  the  other 
hand,  it  is  obvious  that  the  path  of  the  afferent  impulses  which  affect 
the  vaso-motor  centre  mii^ht  be  quite  difTcrcnt  from  that  of  the  afferent 
impulses  giving  rise  to  sensations.  Woros'hiloff  however  has  repeated. 
Mioscher  s  experiments,  using  the  ordinary  signs  of  sensation  instead 
of  blood-pressure,  and  has  come  to  t!ie  conclusion  that  both  the 
afferent  impulses,  which,  starling  in  the  hind  limbs,  give  rise,  either 
by  developing  into  sensations  or  by  originating  rctiex  actions,  to 
movements  in  the  head  and  fore  limbs,  and  the  efferent  impulses, 
which,  starting  in  the  brain  or  upper  part  of  the  spinal  cord,  either  by 
volition  or  as  the  result  of  stimulation,  produce  movements  in  the  hind 
limbs,  pass  also  exclusively  through  the  lateral  columns.  The  course 
of  the  afferent  impulses  difters  however  from  that  of  the  efferent 
impulses,  in  so  far  that  the  former  crois  over  largely  from  one  side  of 
the  cord  to  the  other,  while  the  latter,  though  they  also  cross,  do  so  to 
a  small  extent  only.  The  results  of  both  these  inquirers  then  lead  to 
the  conclusion,  that  in  the  dorsal  spinal  cord  of  the  rabbit  the  lateral 
columns  form  the  chief  bridge  between  the  fore  and  hind  part  of  the 
body  for  the  conduction  of  impulses  of  all  kinds. 

We  must  of  course  be  cautious  in  inferring  that  what  has  been 
found  to  be  true  of  the  dorsal  cord  is  also  true  of  other  parts  of  the 
cord  ;  still  the  experimental  results  just  described,  when  compared 
with  the  anatomical  facts  mentioned  at  p.  612,  with  which  they 
wonderfully  agree,  enable  us  perhaps,  to  a  certain  extent,  to  interpret 
the  observations  of  others  in  some  such  way  as  follows.  In  the  first 
place,  if  there  be  any  truth  in  our  interpretation  of  the  phenomena  of 
strychnia  poisoning,  the  grey  matter  must  be  physiologically  con- 
tinuous, and  a  stimulus  of  sufficient  strength  may  cause  impulses  to 
travel  in  every  direction  along  its  whole  length.  In  the  second  place, 
this  protoplasmic  network  is  marked  out  by  barriers  of  resistance  into 
nervous  mechanisms  for  the  carrying  out  of  coordinated  muscular 
movements  and  for  the  associ  Uion  of  affjrent  impulses  with  these 
niovements.  If  we  suppose,  as  we  have  already  urged,  that  volition 
makes  use  of  these  already  existing  mechanisms  instead  of  requiring 
separate  coordinating  mechanisms  in  many  respects  exactly  like  them, 
we  should  expect  to  find  that  a  volitional  impulse,  tending  towards 
any  movement,  in  descending  from  the  brain,  passes  into  the  grey 
matter  of  the  cord,  at  the  spot  where  the  appropriate  mechanism 
exists,  before  it  emerges  in  the  anterior  rout ;  and  conversely,  that  an 
afferent  impulse  passes  first  into  the  mechanism,  with  which  it  is 
naturally  associated  for  the  production  of  the  frequently  occurring 
reflex  action,  before  it  travels  up  to  the  brain  by  some  tract  more 
direct  than  the  grey  matter.  And  we  should  look  also  for  similar 
arrangements  connecting  any  group  of  nerves,  not  only  with  the  brain, 
but  with  distant  parts  of  the  cord.     In  harmony  with  ihe:,c  functional 


6l8  CONDUCTION   OF   IMPULSES.  [BOOK  III. 

requirements  we  should  be  prepared  to  find  that  the  entrance  of  any- 
large  group  of  nerves  into  the  spinal  cord  was  associated  with  a  large 
development  of  grey  matter  for  the  local  coordinating  mechanisms, 
and  with  a  corresponding  increase  of  certain  parts  of  the  white 
matter,  whose  function  was  to  bring  these  mechanisms  into  connection 
with  both  the  afferent  and  efferent  nerves  ;  on  the  other  hand  we 
should  expect  to  find  that  the  longitudinal  connecting  tracts  of  white 
matter  would  steadih'  increase  from  below  upwards,  inasmuch  as  a 
larger  and  larger  number  of  mechanisms  had  to  be  connected  with 
the  brain,  though  the  increase  would  not  be  so  rapid  or  uniform  as 
that  of  the  united  sectional  areas  of  the  nerves,  since  some  part  of 
these  connecting  tracts  would  serve  to  connect  distant  parts  of  the 
spinal  cord  itself.  In  other  words,  we  should  anticipate  some  such  an 
anatomical  variation  of  the  cord,  as  we  actually  do  find  to  be  the 
case  :  the  grey  matter  varying  directly  in  proportion  to  the  nerves 
entering  into  it  (Figs.  62,  64),  and  the  anterior  and  posterior  columns 
following  the  grey  matter  very  closely  (Figs.  66,  67),  while  the  lateral 
columns  (Fig.  65),  though  not  exactly  parallel  to  the  united  sectional 
areas  of  the  nerves  (Fig.  63),  steadily  increase  from  below  upwards. 

For  the  present  we  may  be  content  with  some  such  general  exposi- 
tion as  the  above,  but  we  already  possess  the  beginnings  of  a  more 
exact  analysis.  -The  Wallerian  method  has  been  applied  to  the  spinal 
cord  with  some  striking  results.  Tiirck '  long  ago  shewed  that  in 
cases  of  disease  of  the  brain  certain  definite  tracts  of  degenerated 
nerves  may  be  traced  downwards  along  the  spinal  cord  in  the  anterior 
and  lateral  columns,  while  in  cases  of  localized  spinal  disease  similadf 
tracts  appear  above  the  seat  of  disease  in  the  posterior  and  lateral 
columns.  Similar  results  have  been  obtained  by  subsequent  inquirers  ; 
and  Schiefferdecker  ^,  studying  with  care  the  condition  of  the  cord 
consequent  upon  its  complete  division  at  any  point  (chiefly  at  the 
junction  of  the  lumbar  and  dorsal  regions),  finds  tracts  of  degenerated 
fibres  which  run  above  the  seat  of  injury  chiefly  in  the  posterior,  but 
also  to  a  less  extent  in  the  hinder  circumferential  parts  of  the  lateral 
columns,  and  below  the  seat  of  injury  in  the  anterior  columns,  and  as 
scattered  bundles  in  the  lateral  columns.  The  former,  having  their 
'trophic  centres'  below,  maybe  regarded  as  fibres  carrying  impulses 
upward,  the  latter  as  carrying  impulses  downwards  ;  both  are  most 
abundant  in  the  immediate  neighbourhood  of  the  cicatrix  where  the 
cord  was  divided,  and,  though  they  may  be  traced  a  long  way  in  their 
respective  directions,  diminish  more  or  less  gradually.  These  facts 
may  fairly  be  taken  as  shewing  that  a  region  of  the  spinal  cord  is 
connected  by  afferent  fibres  with  regions  higher  up,  and  by  efferent 
fibres  with  regions  lower  down,  the  fibres  running  in  the  tracts  de- 
scribed above  ;  but  it  would  be  hazardous*  to  venture  a  more  exact 
opinion  as  to  the  exact  function  of  the  respective  tracts  until  our 
■  knowledge  of  similar  degenerations  has  been  greatly  enlarged.  Schief- 
ferdecker  is  himself  struck  by  the  fact  that  the  great  mass  of  the 
lateral  columns  is  unaffected  by  the  section  ;  this  he  explains  by  the 

-    Wien.  Sitzungshei-icht,  Bd.  VI.  (1851). 
'  »  Virchow's  Archiv,  Bd.  67  (1876),  p.  542. 


CHAP,    v.]  Tin:   SriNAL   CORD.  GlQ 

hypothesis  that  the  larger  number  of  the  fibres  of  these  columns 
being  connected  at  both  ends  with  homologous  nerve-cells,  conduct 
equally  in  both  directions,  and  hold  both  tlicir  terminal  cells  as  '  trophic 
centres,'  so  that  whjn  they  arc  cut  off  from  the  one  set  they  can  still 
depend  on  the  other.  Flcchsig'  has  obtained  some  noteworthy  results 
by  the  embryolo;.,Mcal  method.  Observing  that  the  fibres  of  different 
tracts  acquire  their  medullary  sheaths  at  different  times,  he  has  been 
enabled  to  differentiate  the  longitudinal  fibres  of  the  spinal  cord  into 
separate  tracts,  some  of  which  appear  to  pass  on  into  or  down  from 
the  crura  cerebri,  some  to  end  or  begin  in  the  medulla  oblongata,  and 
others  to  end  and  begin  in  the  spinal  chord  itself  Hi?  results  in 
many  points  coincide  with  those  of  Tiirck  and  Schiefferdecker,  and  in 
jome  respects  are  inconsistent  with  the  general  view  given  above  ;  but 
further  inquiries  are  necessary  before  these  various  anatomical  data 
and  the  results  of  physiological  experiment  and  observation  can  be 
united  in  a  consistent  exposition. 

In  an  ordinary  state  of  things,  with  the  cord  quite  intact,  we  should 
expect  to  find  that  both  voluntary  and  sensory  impulses  spread  into 
the  grey  matter  as  little  as  was  consistent  with  their  due  propagation, 
and  that  they  passed  chiefly  along  their  own  side  ;  but  we  can  also 
readily  imagine  that  when  the  ordinary  tracts  were  interfered  with,  as 
after  section  of  the  white  matter,  powerful  impulses  (and  these  would 
naturally  be  sensory  ones,  since  the  generation  of  sensory  but  not  of 
volitional  impulses  is  in  the  hands  of  the  experimenter,  and  moreover 
is  of  almost  unlimited  range)  might  spread  in  many  directions  over 
the  grey  matter.  Such  errant  impulses  would  of  necessity,  when  they 
reached  the  conscious  centre,  appear  not  as  tactile,  but  simply  as  the 
diffused  sensations  which  we  call  pain.  Hence  it  would  be  said  that 
the  grey  matter  conveyed  the  sensory  impulses,  not  of  touch,  but 
of  pain. 

Moreover  we  must  bear  in  mind  that  the  barriers  of  resistance  in 
the  protoplasm  of  the  grey  matter  are  not  wholly  even  if  largely 
structural.  We  have  seen  that  the  whole  cord  may  be  inhibited  in 
reference  to  reflex  action.  This  total  inhibition  is  probably  made  up 
of  individual  inhibitions  ;  and  in  studying  the  effects  of  section  or 
injury  of  the  spinal  cord  we  must  bear  in  mind  that  the  change  caused 
by  the  operation  most  probably  affe:ts  the  transmission  of  impulses, 
not  only  negatively  by  breaking  down  accustomed  tracts,  but  also 
positively  by  altering  the  action  of  inhibitory  impulses.  We  have  in 
all  probability  an  instance  of  this  in  the  remarkable  hyper^esthesia 
which  is  a  constant  effect  of  a  lateral  section  of  the  cord.  Since  it 
appears  immediately  after  the  operation,  it  cannot  be  due  to  any 
inflammatory  process.  Nor  can  it  be  explained  as  simply  the  result 
of  the  increased  supply  of  blood  to  the  peripheral  terminations  of  the 
sensory  nerves,  caused  by  the  section  involving  vaso-motor  tracts  ; 
since  the  simple  section  of  a  vaso-motor  tract,  as  when  the  cervical 
sympathetic  is  divided,  does  not  give  rise  to  hypera;sthesia.  Nor  can 
we  explain  it  as  due  to  a  one-sided  hyperha^mia  of  the  spinal  cord 

'  Die  Leitungsbahne  im   Gehiin  ttitJ  Kiicl-c'tniiark  des  Mtitschfn.     Leipzig, 
lS.>6. 


620  >  CONDUCTION    OF   IMPULSES.  [BOOK   III. 

itself,  for  we  have  no  evidence  that  such  a  state  of  things  is  brought 
about.  Since  it  lasts  for  a  very  considerable  time  it  cannot  be  due  to 
any  passing  exciting  effect  of  the  opt  ration.  In  the  frog,  after  hemi- 
section  of  the  cord  below  the  brachial  plexus,  this  hypersesthesia  is 
manifested  by  increased  reflex  movements  occurring  in  the  lower  limbs 
as  well  as  in  the  upper  when  the  lower  limbs  are  stimulated  ;  and 
when  the  hemisection  is  converted  into  a  complete  section  an  hyper- 
assthesia  still  remains  in  both  lower  limbs,  but  it  is  then  spoken  of 
simply  as  increased  reflex  action,  due  to  the  isolation  of  the  lower 
cord  from  an  inhibitory  centre  placed  higher  up.  In  the  rabbit, 
according  to  Woroschiloff,  hyperaesthesia,  after  baemisection  of  the 
dorsal  cord,  manifests  itself,  not  so  much  in  increased  reflex  actions  in 
the  lower  limbs  as  in  increased  movements  of  the  upper  part  of  the 
body  when  a  stimulus  is  appHed  to  the  lower  limbs.  This  may  be 
interpreted  as  indicating  that  in  the  rabbit  the  hemisection  removes 
inhibitory  influences  which  previously  were  checking  not  so  much  the 
so  to  speak  direct  reflex  conversion  of  afferent  into  efferent  impulses, 
as  the  propagation  of  the  afferent  impulses  to  higher  parts  of  the  spinal 
cord  and  so  upwards  to  the  brain.  We  have  already  insisted  on  the 
probable  complexity  of  the  central  processes  involved  in  a  reflex  action 
of  even  the  simplest  kind.  And  of  the  long  chain  of  molecular  events 
intervening  in  the  central  (reflex)  mechanism  between  the  advent  of 
the  simple  afferent  impulse  and  the  issue  of  the  simple  efferent  im- 
pulses, we  may,  without  too  great  a  presumption,  suppose  that  those 
on  what  we  may  call  the  afferent  side  of  the  chain  might  be  affected 
by  extrinsic  (inhibitory  or  other)  influences  more  than  those  on  the 
efferent  side  or  than  those  more  central  ;  and  vice  versa.  Hence, 
adopting  the  view  already  urged,  that  the  spinal  mechanisms  Avhich 
serve  for  reflex  actions  are  also  the  instruments  of  the  higher  cerebral 
operations,  the  afferent  side  of  the  mechanism  being  more  especially 
connected  with  sensation,  and  the  efferent  with  volition,  we  see  the 
possibility  of  the  removal  of  certain  inhibitory  influences  manifesting 
itself  especially  as  an  apparent  increase  of  sensibility.  And  this  natu- 
rally would  occur  more  readily  in  the  rabbit,  where  the  reflex  actions 
of  the  cord  are  so  largely  subordinated  to  the  operations  of  the  brain, 
than  in  the  frog,  where  they  still  retain  so  much  of  their  primitive 
independence.  When  the  section  passes  through  the  whole  cord 
instead  of  half,  the  absence  of  inhibition  can  of  course  only  be  shewn 
by  increased  reflex  action  in  both  cases.  When  these  obscure  inhibi- 
tory mechanisms  have  been  more  completely  worked  out,  many  of  the 
at  present  discordant  results  of  operations  and  injuries  will  probably 
be  explained  away. 

Much  discussion  has  arisen  on  the  question  whether  the  spinal 
cord  itself  is  irritable,  that  is  whether  it  can  be  excited  by  stimuli 
applied  directly  to  it.  Undoubtedly,  the  cord,  as  a  whole,  is  irrita- 
ble ;  if  two  electrodes  be  plunged  into  it,  and  a  current  sent  through 
it,  muscular  movements,  arterial  constriction,  and  other  results, 
follow.  But  in  such  a  case,  the  current  may  fall  into  nerve-roots, 
.which  are  as  irritable,  at  least,  as  the  nerve-trunks.     But  even  if 


CHAl'.  v.]  THE   SPINAL   CuKD.  62 1 

the  nerve-roots  be  cliniinatcd,  the  white  matter  at  least  is  irritable  ; 
for  Fick  and  Engelken'  found  that  movements  resulted  when  the 
anterior  columns  were  isolated  for  some  way  down  and  stimulated 
with  an  electric  current.  With  regard  to  the  grey  matter  Van  Deen 
anil  Schift"  maintain  that  though  it  will  convey  both  motor  and 
sensory  impulses,  it  cannot  originate  them.  They  speak  of  it 
accordingly  as  kinesodic  and  ccsthesodic,  as  simply  affording  paths 
for  motor  and  sensory  iiiipulses.  But  their  arguments  cannot  be 
regarded  as  conclusive,  and  Miescher*  found  that  when  after  division 
of  the  spinal  cord  he  removed  the  posterior  coknnns  for  a  certam 
distance,  so  as  to  get  rid  of  all  afferent  nerve-fibres,  the  exposed 
grey  matter,  as  tested  by  the  effects  on  blood-pressure,  still 
remained  sensitive,  especially  to  mechanical  stimulation. 

»  Du   Bois-Reymond's  Archiv,  1867,  p.  198.     Pfliiger's  Arc/iiv,   11.  {1869), 
p.  414. 
'  Op.cit. 


CHAPTER   Vr. 

THE  BRAIN. 

Sec.  I.  On  the  Phenomena  exhibited  by  an  Animal  deprived 
OF  ITS  Cerebral  Hemispheres. 

A  FROG  from  which  the  cerebral  lobes  have  been  removed,  even 
though  all  the  rest  of  the  brain  has  been  left  intact,  seems  to  possess 
no  volition.  The  apparently  spontaneous  movements  which  it 
executes  are  so  few  and  seldom  that  it  is  much  more  rational  to 
attribute  those  which  do  occur  to  the  action  of  some  stimulus  which 
has  escaped  observation,  than  to  suppose  that  they  are  the  products 
of  a  will  acting  only  at  long  intervals  and  in  a  feeble  manner. 

By  the  application  however  of  appropriate  stimuli,  such  an 
animal  can  be  induced  to  perform  all  the  movements  which  an 
entire  frog  is  capable  of  executing.  It  can  be  made  to  swim,  to 
leap,  and  to  ciawl.  When  placed  on  its  back,  it  immediately 
regains  its  natural  position.  When  placed  on  a  board,  it  does  not 
fall  from  the  board  when  the  latter  is  tilted  up  so  as  to  displace  the 
animal's  centre  of  gravity  :  it  crawls  up  the  board  until  it  gains  a 
new  position  in  which  its  centre  of  gravity  is  restored  to  its  proper 
place.  Its  movements  are  exactly  those  of  an  entire  frog  except 
that  they  need  an  external  stimulus  to  call  them  forth.  They 
inevitably  follow  when  the  stimulus  is  applied;  they  come  to  an 
end  when  the  stimulus  ceases  to  act.  By  continually  varying  the 
inclination  of  a  board  on  which  it  is  placed,  the  frog  may  be  made 
to  continue  crawling  almost  indefinitely ;  but  directly  the  board  is 
made  to  assume  such  a  position  that  the  body  of  the  frog  is  in 
equilibrmm,  the  crawling  ceases ;  and  if  the  position  be  not 
disturbed  the  animal  will  remain  impassive  and  quiet  for  an  almost 
indefinite  time.  When  thrown  into  water,  the  creature  begins  at 
once  to  swim  about  in  the  most  regular  manner,  and  will  continue 
to  swim  till  it  is  exhausted,  if  there  be  nothing  present  on  which  it 
can  come  to  rest.     If  a  small  piece  of  wood  be  placed  on  the 


CHAP.   VI.]  THE   BRAIN.  Ojj 

water  the  frog  will  when  it  comes  in  contact  with  ihe  wood  crawl 
upon  it,  and  so  come  to  rest.  Such'a  fnjg,  if  its  flanks  be  gently 
stroked,  will  croak  ;  and  the  croaks  follow  so  regularly  and  surely 
upon  the  strokes  tliat  the  animal  may  almost  be  played  upon  like  a 
musical  instrument.  Moreover,  the  movements  of  the  animal  are 
influenced  by  light ;  if  it  be  urged  to  move  in  any  i)arlicular  direction 
it  will  avoid  in  its  progress  objects  casting  a  strong  shadow.  In 
fact,  even  to  a  careful  observer  the  differences  between  such  a  frog 
and  an  entire  frog  which  was  simj^ly  very  stupid  or  very  obstinate, 
would  appear  sliglit  and  unimportant  except  in  one  point,  viz.  that 
the  animal  without  its  cerebral  hemispheres  was  obedient  to  every 
stimulus,  and  that  each  stimulus  evoked  an  appropriate  movement, 
whereas  with  the  entire  animal  it  would  be  impossible  to  predict 
whether  any  result  at  all,  and  if  so  what  result,  would  follow  the 
application  of  this  or  that  stimulus.  Both  are  machines  ;  buc  the 
one  is  a  machine  and  nothing  more,  the  other  is  a  machine 
governed  and  checked  by  a  dominant  volition. 

Now  such  movements  as  crawling,  leaping,  swimming,  and 
indeed,  to  a  greater  or  less  extent,  all  bodily  movements,  are 
carried  out  by  means  of  coordinate  nervous  motor  impulses, 
influenced,  arrangecT,  and  governjd  by  coincident  sensory  or 
afferent  impulses.  We  have  already  seen  that  muscular  move- 
ments are  determined  b)  the  muscular  sense ;  they  are  also 
directed  by  means  of  sensory  impulses  passing  centripetally  along 
the  sensory  nerves  of  the  skin,  the  eye,  the  ear,  and  other  organs. 
Independently  of  the  afferent  impulses,  which  acting  as  a  stimulus 
call  forth  the  movement,  all  manner  of  other  afferent  impulses  are 
concerned  in  the  generation  and  coordination  of  the  resultant 
motor  impulses.  Every  bodily  movement  such  as  those  of 
which  we  are  speaking  is  the  work  of  a  more  or  less  compli- 
cated nervous  mechanism,  in  which  there  are  not  only  central 
and  efferent,  but  also  afferent  factors.  And,  putting  aside  the 
question  of  consciousness,  with  which  we  have  here  no  occasion 
to  deal,  it  is  evident  that  in  the  frog  deprived  of  its  cerebral 
hemispheres  all  these  fiictors  are  present,  the  afferent  no  less  than 
the  central  and  the  efferent.  The  machinery  for  all  the  necessary 
and  usual  bodily  movements  is  present  in  all  its  completeness. 
The  share  therefore  which  the  cerebral  hemispheres  take  in 
executing  the  movements  of  which  the  entire  animal  is  capable, 
is  simply  that  of  putting  this  machinery  into  action.  The  relation 
which  the  higher  nervous  changes  concerned  in  volition  bear  to 
this  machinery  is  not  unlike  that  of  a  stimulus.  We  might 
almost  speak  of  the  will  as  an  intrinsic  stimulus.  Its  operations 
are   limited    by  the  machinery  at  its  command.     The   cerebral 


624  THE   BRAINLESS   FROG.  [BOOK  III. 

hemispheres  in  their  action  can  only  give  shape  to  a  bodily- 
movement  by  throwing  into  activity  particular  parts  of  the 
nervous  machinery  situated  in  the  lower  encephalic  structures  ; 
and  precisely  the  same  movement  may  be  initiated  in  their 
absence,  by  applying  such  stimuli  as  shall  throw  precisely  the 
same  parts  of  that  machinery  into  the  same  activity. 

Very  marked  is  the  contrast  between  a  frog  which,  though 
deprived  of  its  cerebral  hemispheres,  still  retains  the  optic  lobes, 
cerebellum  and  medulla  oblongata,  and  one  which  possesses  a 
spinal  cord  only.  The  latter  when  placed  on  its  back  makes  no 
attempt  to  regain  its  normal  position ;  in  fact,  it  may  be  said  to 
have  completely  lost  its  normal  position,  for  even  when  placed  on 
its  feet  it  does  not  stand  with  its  fore  feet  erect,  as  does  the  other 
animal,  but  lies  flat  on  the  ground.  When  thrown  into  water, 
instead  of  swimming  it  sinks  like  a  lump  of  lead.  When  pinched, 
or  otherwise  stimulated,  it  does  not  crawl  or  leap  forwards ;  it 
simply  throws  out  its  limbs  in  various  ways.  When  its  flanks  are 
stroked  it  does  not  croak ;  and  when  a  board  on  which  it  is 
placed  is  inclined  sufiiciently  to  displace  its  centre  of  gravity 
it  makes  no  effort  to  regain  its  balance,  but  falls  off"  the  board 
like  a  lifeless  mass.  Though,  as  we  have  -seen,  there  is  in  all 
parts  of  the  spinal  cord  of  the  frog  a  large  amount  of  coordinating 
machinery,  it  is  evident  that  a  great  deal  of  the  mpre  complex 
machinery  of  this  kind,  especially  all  that  which  has  to  deal  with 
the  body  as  a  whole,  and  all  that  which  is  concerned  with  equili- 
brium and  is  specially  governed  by  the  higher  senses,  is  seated 
not  in  the  spinal  cord  but  in  the  brain  and  medulla  oblongata. 
We  shall  presently  see  that  in  the  frog  a  great  deal  of  this  more 
complex  machinery  is  concentrated  in  the  optic  lobes.  The 
point  however  to  which  we  wish  now  to  call  special  attention 
is  that  the  nervous  machinery  required  for  the  execution,  as 
distinguished  from  the  origination,  of  bodily  movements  even 
of  the  most  complicated  kind,  is  present  after  complete  removal 
of  the  cerebral  hemispheres,  though  these  movements  may  require 
the  cooperation  of  highly  diff"erentiated  afferent  impulses'. 

Our  knowledge  of  the  phenomena  .presented  by  the  bird  or 
mammal  from  which  the  cerebral  hemispheres  have  been  removed 
is  not  so  exact  as  in  the  case  of  the  frog.  We  may  however  assert 
that  volition  is  absent,  though  movements  apparently  spontaneous 
in  character  are  more  common  with  the  mammal  than  with  the 
frog,  as  might  be  expected,  seeing  that  the  more  complicated 
brain  of  the  former  affords,  even  in  the  absence  of  the  cerebral 
hemispheres,  much  more  opportunity  for  the  origination  of 
*  Cf.  Goltz,  Functionen  d.  Nervencentren  des  Frosches,  1869. 


CI  I A  I".    VI.]  TIIK    BRAIN.  625 

Stimuli  within  the  nervous  system  itself,  and  for  the  play  of 
stimuli  however  originating,  than  does  that  of  the  latter. 

When  the  cerebral  heiiiisplieres  are  removed  from  a  bird  the 
animal  is  able  to  maintain  a  completely  normal  posture,  and  that 
too  when  the  corpora  striata  and  optic  thalami  are  taken  away  at 
the  same  time.  Jt  will  balance  itself  on  one  leg,  after  the  fashion 
of  a  bird  which  has  in  a  natural  way  gone  to  sleep.  In  fact,  the 
appearance  and  behaviour  of  a  bird  which  lias  been  deprived  of 
its  cerebral  hemispheres  are  strikingly  similar  to  those  of  a  bird 
sleepy  and  stupid.  Left  alone  in  perfect  quiet,  it  will  remain 
impassive  a^d  motionless  for  a  long,  it  may  be  for  an  almost 
indefinite  time.  When  stirred  it  moves,  shifts  its  position ;  and 
tlien  on  being  left  alone  returns  to  a  natural,  easy  posture.  Placed 
on  its  side  or  its  back  it  will  regain  its  feet ;  thrown  into  the  air, 
it  flies  with  considerable  precision  for  some  distance  before  it 
returns  to  rest.  It  frequently  tucks  its  head  under  its  wings,  and 
if  by  judicious  feeding  it  has  been  kept  alive  for  some  time  after 
the  operation,  it  may  be  seen  to  clean  its  feathers  and  to  pick  up 
corn  or  to  drink  water  presented  to  its  beak'.  It  may  be  induced 
to  move  not  only  by  ordinary  stimuli  applied  to  the  skin,  but  also 
by  sudden  sharp  sounds,  or  flashes  of  light ;  and  it  is  evident  that 
its  movements  are  to  a  certain  extent  guided  by  visual  sensations, 
for  in  its  flight  it  will,  though  imperfectly,  avoid  obstacles.  Save 
that  all  signs  of  distinct  volitioa  are  absent,  that  all  satisfactory 
indications  of  intelligence  are  wanting,  and  that  the  movements 
are  on  the  whole  clumsy,  resembling  rather  those  of  a  stupid 
drowsy  bird  than  those  of  one  quite  wide  awake,  there  is  very 
little  to  distinguish  such  a  bird  from  one  in  full  possession  of  its 
cerebral  hemispheres. 

Even  in  a  mammal,  during  the  few  hours  which  intervene 
between  the  removal  of  the  hemispheres  and  death,  very  much 
the  same  phenomena  may  be  observed.  The  rabbit,  or  rat, 
operated  on,  can  stand,  run  and  leap  ;  placed  on  its  side  or  back 
it  at  once  regains  its  feet.  Left  alone,  it  remains  as  motionless 
and  impassive  as  a  statue,  save  now  and  then  when  a  passing 
unpulse  seems  to  stir  it  to  a  sudden  but  brief  movement.  Such 
a  rabbit  will  remain  for  minutes  together  utterly  heedless  of  a 
carrot  or  cabbage-leaf  placed  just  before  its  nose,  though  if 
a  morsel  be  placed  in  its  mouth  it  at  once  begins  to  gnaw  and 
eat.  When  stirred,  it  will  \yith  perfect  ease  and  steadiness  run  or 
leap  forward  ;  and  obstacles  in  its  course  are  very  frequently,  with 
more  or  less  success,  avoided.     It  will  often  follow  by  movements 

'  Bischoflf  and  Voit,  Silzungsf>erichle  Acad.  Wiss.  Miinchen^  1S63,  pp.  479, 
469 ;   1868,  p.  105. 

F.  P.  40 


626  THE   BRAINLESS   MAMMAL.  [BOOK   III. 

of  the  head  a  bright  light  held  in  front  of  it  (provided  that  the 
optic  nerves  and  tracts  have  not  been  injured  during  the  opera- 
tion), and  starts  when  a  shrill  and  loud  noise  is  made  near  it. 
When  pinched  it  cries,  often  with  a  long  and  seemingly  plaintive 
scream.  Evidently  its  movements  are  guided  and  may  be  origi- 
nated by  tactile,  visual,  and  auditory  sensations  \  But  there  is  no 
evidence  that  it  possesses  either  visual  or  other  perceptions,  while 
there  is  almost  clear  proof  that  the  sensations  it  experiences  give 
rise  to  no  ideas.  Its  avoidance  of  objects  depends  not  so  much 
on  the  form  of  these  as  on  their  interference  with  light.  No 
image,  whether  pleasant  or  terrible,  whether  of  fot)d  or  of  an 
enemy,  produces  an  effect  on  it,  other  than  that  of  an  object 
reflecting  more  or  less  light.  And  though  the  plaintive  character 
of  the  cry  which  it  gives  forth  when  pinched  suggests  to  the 
observer  the  existence  of  passion,  it  is  probable  that  this  is 
a  wrong  interpretation  of  a  vocal  action ;  the  cry  appears  plain- 
tive simply  because,  in  consequence  of  the  completeness  of  the 
reflex  nervous  machinery  and  the  absence  of  the  usual  restraints, 
it  is  prolonged.  The  animal  is  able  to  execute  all  its  ordinary 
bodily  movements,  but  in  its  performances  nothing  is  ever  seen  to 
indicate  the  retention  of  an  educated  intelligence. 

These  phenomena  are  witnessed  in  some  mammals  at  least 
not  only  after  the  cerebral  convolutions  have  been  removed,  but 
also  when  the  corpora  striata  and  optic  thalami  are  taken  away  at 
the  same  time-,  so  that  the  brain  is  reduced  to  the  corpora  quadri- 
gemina  and  cerebellum  with  the  crura  cerebri  and  pons  Varolii. 
In  removing  the  corpora  striata,  however,  various  forced  move- 
ments, of  which  we  shall  speak  presently,  frequently  make  their 
appearance,  and  interfere  with  the  observation  of  the  phenomena 
we  have  just  described ;  and  it  is  stated  by  some  observers  that, 

'  Here  we  come  upon  a  difficulty,  which  we  shall  meet  with  again  in  the 
present  chapter.  Are  we'justified  in  speaking  of  '  sensation '  in  cases  where  we 
have  reason  to  think  that  consciousness  is  absent,  or  where,  as  in  the  present 
instance,  we  have  no  evidence  to  shew  whether  consciousness  is  present  or  not? 
In  treating  of  the  senses  we  called  attention  to  the  fact,  that  we  must  suppose 
in  the  case,  for  instance,  of  vision,  the  visual  peripheral  organ  to  be  connected 
with  a  visual  central  organ  in  such  a  way  that  the  sensory  impulses  originating 
in  the  former  become  modified  in  the  latter  before  they  affect  consciousness. 
In  the  peripheral  organ  and  along  the  nerve  of  sense,  the  affection  of  the 
nervous  tissue  miy  be  spoken  of  as  a  sensory  impulse  ;  but  after  the  affection 
has  traversed  the  central  organ  and  become  modified  it  is  no  longer  a  simple 
sensory  impulse.  We  must  then  either  call  it  a  sensation  irrespective  of  whether 
any  change  of  consciousness  intervenes  or  no,  or  we  must  give  it  a  new  name. 
Not  wishing  to  introduce  a  new  name,  we  have  ventured  to  use  the  word 
'  sensation '  in  a  sense  which  neither  affirms  nor  denies  the  coexistence  of 
consciousness. 


CHAP.   VI.]  THE   BRAIN.  627 

even  when  these  do  not  occur,  the  scope  of  the  various  move- 
ments of  which  the  animal  remains  capable  is  much  limited. 

Vulpian  insists' that  all  the  phenomena  above  described  maybe 
observed  in  the  total  absence  both  of  the  corpora  striata  and  optic 
thalami,  at  least  in  rodents.  Many  authors  however  state  that  dogs 
differ  from  rodents  inasmuch  as  in  dogs  lesions  of  the  corpora  striata 
always  cnt.iil  loss  of  coordination.  When  we  come  to  study  the 
functions  ot"  the  cerebral  hemispheres  in  particular  we  shall  have 
occasion  to  dwell  on  the  danger  of  drawing  con:lusions  from  the 
phenomen  I  exhibited  by  an  animal  immediately  after  a  grave  operation 
on  its  central  nervous  systenu  The  facts  described  above  in  reference 
to  mammals  refer  exclusively  to  the  period  immediately  following  the 
removal  of  the  hemispheres  ;  and  though  they  clearly  shew  that  com- 
plex coordinate  movements  may  then  be  carried  on,  they  cannot 
be  trusted  as  disclosing  to  us  the  exact  condition  of  a  mammal 
under  such  circumstances ;  we  have  yet  to  learn  the  details  of  the 
behaviour  of  a  mammal  deprived  of  the  whole  of  both  cerebral 
hemispheres  and  yet  enjoying  the  full  functional  activity  of  the  rest 
of  its  brain. 

With  the  removal  of  that  part  of  the  brain  which  lies  between 
the  hemispheres  and  the  medulla  a  large  number  of  these  co- 
ordinate movements  disappear.  The  animal  can  no  longer  balance 
itself,  it  lies  helpless  on  its  side,  and  though  various  movements 
of  a  complex  character,  including  cries,  may  be  produced  by 
appropriate  stimuli,  they  are  much  more  limited  than  when  these 
cerebral  structures  are  intact. 

We  may  therefore  state  that  in  the  higher  animals,  including 
mammals,  as  in  the  frog,  the  body,  after  the  removal  of  the 
cerebral  hemispheres,  is  capable  of  executing  all  the  ordinary 
movements  which  the  animal  in  its  natural  life  is  w-ont  to 
perform,  though  these  movements  necessitate  the  cooperation 
of  various  afferent  impulses ;  and  that  therefore  the  nervous 
machinery  for  the  execution  of  these  movements  lies  in  some 
part  of  the  brain  other  than  the  cerebral  hei^iispheres.  We  have 
reasons  for  thinking  that  it  is  situated  in  the  structures  forming 
the  middle  or  hind  brain. 


Sec    2      The  Mechanisms  of  Coordinated  Movements. 

When  in  a  pigeon  the  horizontal  membranous  circular  canal  of 
the  internal  ear  is  cut  through,  the  bird  is  observed  to  be  con- 
tinually moving  its  head  from  side  to  side.  If  one  of  the  vertical 
canals  be  cut  through,  the  movements  are  up  and  down.     The 

'  Syst.  Nerz\,  Lee.  xxiv 

40 — 2 


628  THE   SEMI-CIRCULAR   CANALS.  [BOOK  IIL 

peculiar  movements  are  not  witnessed  when  the  bird  is  perfectly- 
quiet,  but  they  make  their  appearence  whenever  it  is  disturbed, 
and  attempts  in  any  way  to  stir.  When  one  side  only  of  the  head 
is  operated  on,  the  condition  after  a  while  passes  away.  When  the 
canals  of  both  sides  have  been  divided,  it  becomes  much  ex- 
aggerated, and  remains  permanently.  And  it  is  then  found  that 
these  peculiar  movements  of  the  head  are  associated  with  what 
appears  to  be  a  complete  want  of  coordination  of  all  bodily  move- 
ments. If  the  bird  be  thrown  into  the  air,  it  flutters  and  falls 
down  in  a  helpless  and  confused  manner  ;  it  appears  to  have  totally 
lost  the  power  of  orderly  flight.  If  placed  in  a  balanced  position, 
it  may  remain  for  some  time  quiet,  generally  with  its  head  in  a 
peculiar  posture ;  but  directly  it  is  disturbed,  the  movements 
which  it  attempts  to  execute  are  irregular  and  fall  short  of  their 
purpose.  It  has  great  difficulty  in  picking  up  food  and  in  drink- 
ing ;  and  in  general  its  behaviour  very  much  resembles  that  of  a 
person  who  is  exceedingly  dizzy. 

It  can  hear  perfectly  well,  and  therefore  the  symptoms  cannot 
be  regarded  as  the  result  of  any  abnormal  auditory  sensations, 
such  as  'a  roaring'  in  the  ears.  Besides,  any  such  stimulation  of 
the  auditory  nerve  as  the  result  of  the  section,  would  speedily  die 
away,  whereas  these  phenomena  may  be  permanent. 

The  movements  are  not  occasioned  by  any  partial  paralysis, 
by  any  want  of  power  in  particular  muscles  or  group  of  muscles. 
Nor  on  the  other  hand  are  they  due  to  any  uncontrollable  impulse; 
a  very  gentle  pressure  of  the  hand  sufiiices  to  stop  the  movements 
of  the  head,  and  the  hand  in  doing  so  experiences  no  strain.  The 
assistance  of  a  very  slight  support  enables  movements  otherwise 
impossible  or  most  difficult  to  be  easily  executed.  Thus,  though 
when  left  alone  the  bird  has  great  difficulty  in  drinking  or  picking 
up  corn,  it  will  continue  to  drink  or  eat  with  ease  if  its  beak  be 
plunged  into  water,  or  into  a  heap  of  barley ;  the  slight  support 
of  the  water  or  of  the  grain  being  sufficient  to  steady  its  move- 
ments. In  the  same  way,  it  can,  even  without  assistance,  clean  its 
feathers  and  scratch  its  head,  its  beak  and  foot  being  in  these 
operations  guided  by  contact  with  its  own  body. 

After  the  operation  the  head  of  the  animal  frequently  assumes 
a  peculiar  position,  being  twisted  and  inclined  in  various  ways, 
sometimes  hanging  down  on  the  breast  with  the  neck  so  distorted 
that  the  right  eye  looks  to  the  left  and  vice  versa,  sometime'3 
turned  back  over  the  shoulder  so  that  one  eye  looks  directly 
upwards ;  the  exact  attitude  differing  apparently  according  as  this 
or  that  canal  has  been  injured.  And  Goltz'  has  called  attention 
'  Pfliiger's  Archiv,  iii.  (1870),  p.  172. 


CHAP.   VI.]  T1<E   BRAIN  G2y 

to  the  fiict  that  pigeons  whose  canals  have  been  left  intact  but 
whose  heads  Iiave  been  artificially  secured  in  similar  abnormal 
positions  are  incapable  of  orderly  flight,  and  in  their  general 
behaviour  closely  resemble  animals  whose  canals  have  been 
destroyed. 

Injury  to  the  bony  canals  alone  is  insufficient  to  produce  the 
symptoms ;  the  membranous  canals  themselves  must  be  divided 
or  destroyed. 

E.  Cyon'  thus  describes  the  effects  of  dividing  ihc  several  canals. 
When  the  horizontal  (exterior)  canal  is  cut,  the  movements  of  the 
head  are  from  side  to  side  round  an  axis  passing  vertically  through 
the  head.  When  the  posterior,  vertical,  canal  is  cut  the  head  is  moved 
up  and  down  round  an  a.xis  passing  from  ear  to  ear.  When  the 
anterior  (superior)  vertical  canal  is  cut  the  movement  of  the  head  is  in 
a  diagonal  direction,  a  combination  of  an  up-and-down  and  a  side-to- 
side  movement.  When  one  canal  on  one  side  only  is  divided  the 
effects  are  very  transient,  and  they  are  also  transient,  disappearing  on 
the  second  or  third  day,  even  when  all  three  canals  are  divided, 
provided  that  the  operation  is  confined  to  one  side  of  the  head.  When 
the  same  canal,  horizontal  or  vertical,  is  divided  on  both  sides  of  the 
head,  the  symptoms  are  more  lasting,  but  may  after  some  days  wholly 
or  almost  wholly  disappear.  When  different  canals  are  divided  on  the 
two  sides  of  the  head,  i.e.  when  the  operation  is  bilateral  and  unsym- 
metrical,  the  effects  become  permanent. 

In  mammals  (rabbits)  section  of  the  canals  produces  a  loss  of 
coordination  similar  to  that  witnessed  in  birds  ;  but  the  movements  of 
the  head  are  not  so  marked,  peculiar  oscillating  movements  of  the 
eye-balls  (nystagmus),  differing  in  direction  and  character  according  to 
the  canal  or  canals  operated  upon,  becoming  however  very  prominent. 
In  the  frog  no  deviations  of  the  head  are  seen,  but  there  is,  as  in  other 
animals,  a  loss  of  coordination  in  the  movements  of  the  body. 

Cyon  has  noticed  that  in  pigeons  after  section  of  the  canals  on 
both  sides  of  the  head,  the  leg  is  frequently  folded  up  under  the  body 
in  a  peculiar  way,  as  if  it  were  broken  ;  but  otherwise  there  are  no 
signs  of  any  paralysis. 

How  are  we  to  explain  these  remarkable  phenomena  ?  Let  us 
for  a  while  turn  aside  to  ourselves  and  examine  the  coordination 
of  the  movements  of  our  own  bodies.  When  we  appeal  to  our 
own  consciousness  we  fnid  that  our  movements  are  governed  and 
guided  by  what  we  may  call  a  sense  of  equilibrium,  by  an  appreci- 
ation of  the  position  of  our  body  and  its  relations  to  sj^ace.  When 
this  sense  of  equilibrium  is  disturbed  we  say  we  are  diz'y,  and  we 
then  stagger  and  reel,  being  no  longer  able  to  coordinate  the 
movements  of  our  bodies  or  to  adapt  them  to  the  position  of 
things  around  us.    What  is  the  origin  of  this  sense  of  equilibrium? 

'   Thise pour  le  Doctoral  >n  Midicine,  P.iris,  1S7S. 


630  THE   SEMI-CIRCULAR   CANALS.  [BOOK   HI. 

By  what  means  are  we  able  to  appreciate  the  position  of  our 
body  ?  There  can  be  no  doubt  that  this  appreciation  is  in  large 
measure  the  product  of  visual  and  tactile  sensations ;  we  recognise 
the  relations  of  our  body  to  the  things  around  us  in  great  measure 
by  sight  and  touch ;  we  also  learn  much  by  our  muscular  sense. 
But  there  is  something  besides  these.  Neither  sight  nor  touch  nor 
muscular  sense  would  help  us  when,  placed  perfectly  flat  and  at 
rest  on  a  horizontal  rotating  table,  with  the  eyes  shut  and  not  a 
muscle  stirring,  we  attempted  to  determine  whether  the  table  and 
we  with  it  were  moved  or  no,  or  to  ascertain  how  inuch  it  and  we 
were  turned  to  the  right  or  to  the  left.  Yet  under  such  circum- 
stances we  are  not  only  conscious  of  a  change  in  our  position  but 
according  to  Crum  Brown^  and  others  we  can  pass  a  tolerably 
successful  judgment  as  to  the  angle  through  which  we  have  been 
moved.  What  are  the  data  on  which  we  are  able  to  form  such  a 
judgment?  It  is  possible  that  the  mere  displacement  of  blood 
or  of  the  more  fluid  parts  of  the  tissues  in  various  regions  of 
the  body,  by  giving  rise  to  affections  of  general  sensibility,  may 
contribute  to  these  data  ;  but  the  peculiar  features  of  the  semi- 
circular canals  suggest  almost  irresistibly  that  they  are  special 
agents  in  this  matter.  The  three  canals  are,  as  we  know,  placed 
in  the  head  in  planes  nearly  at  right  angles  to  one  another.  Hence 
the  pressure  of  the  endolymph  on  the  walls  of  the  canal  (including 
the  maculae  of  the  ampullae)  in  any  given  position  of  the  head, 
and  variations  of  that  pressure  due  to  movements  of  the  head, 
would  be  different  in  the  three  canals;  a  sonorous  wave  on  the 
other  hand  would  affect  all  the  ampuUse  equally.  If  we  suppose 
that  the  pressure  of  the  endolymph  or  variations  in  that  pressure 
can  give  rise  to  afferent  impulses  which,  though  passing  up  to  the 
brain  along  the  auditory  nerve,  are  not  of  the  nature  of  auditory 
impulses,  we  have  found  the  data  for  which  we  are  seeking ;  for  it 
is  quite  possible  to  conceive  that  the  impulses  thus  generated  in 
the  ampullae  by  movements  of  the  head,  should  by  becoming 
transformed  into  sensations  enter  into  the  judgment  which  we  form 
of  the  movements  which  have  given  rise  to  them. 

When  a  person  under  the  circumstances  mentioned  above  is 
rotated  for  some  time,  the  sense  of  rotation  ceases  to  be  felt ;  but  on 
the  rotation  ceasing  a  sense  of  being  rotated  in  the  opposite  direction 
is  set  up  :  a  complementary  or  more  strictly  a  rebound  sensation  is 
caused.  Regarding  the  sensation  as  due  to  the  movement  of  the  fluid 
in  the  canals,  Crum  Brown  supposes  that  the  effect  is  different  ac- 
cording as  the  flow  is  from  the  ampulla  into  the  canal,  or  from  the 

'  yourn.  Anat.  Phys.  1874,  p.  327  ;  see  also  Mach,  Lehrev.  d.  BewegungS' 
Empfind,  1875  ;   Breuer,   Wien.  Med.  Jahrb.,  1874,  p.  72;   1875,  p.  87. 


CHAP.    VI.]  THE   BRAIN.  63 1 

canal  into  the  ampulla,  and  that  thus  we  are  able  to  recognise  the 
direction  of  the  rotation,  whether  positive  or  negative,  <:a-.  j/^r.  to  the 
riglu  or  to  the  left,  and  so  on.  llcncc  the  existence  of  six  ampulla*, 
two  for  each  of  the  three  axes  of  rotation  ;  and  Crum  Brown  asserts 
that  in  man  and  all  animals  which  he  has  examined  the  two  exterior 
canals  of  the  two  earj  are  very  nearly  in  the  same  plane,  and  the 
superior  c.mal  of  one  ear  very  nearly  in  the  same  plane  as  the  posterior 
canal  of  the  other. 

But  if  ampullar  sensations,  if  we  may  so  call  them,  thus  enter 
into  our  ap[)rociation  of  the  position  of  our  body  and  thus  form, 
in  part,  the  basis  of  our  sense  of  equilibrium,  it  is  obvious  that 
when  these  are  absent  or  deranged,  the  sense  of  equilibrium  will 
be  aftected  and  the  coordination  of  movements  interfered  with. 
And  this  seems  to  be  the  most  satisfactory  explanation  of  the 
plienomena  attendant  on  injury  to  the  semi-circular  canals.  We 
are  not  perhaps  yet  in  a  position  to  explain  the  whole  matter  in  a 
complete  manner ;  there  may  be  much  divergence  of  opinion  as 
to  the  exact  way  in  which  the  ampullar  impulses  are  generated, 
and  as  to  the  exact  manner  in  which  injury  to  the  canals  produces 
its  effects,  whether  by  causing  the  simple  absence  of  normal  im- 
pulses or  by  generating  abnormal  influences  ;  but  it  is  difficult  to 
withstand  the  general  conclusion  that  the  ampullae  have  in  some 
way  or  other  to  do  with  the  sense  of  equilibrium  and  with  the  co- 
ordination of  movements,  and  that  the  remarkable  effects  of 
injuring  them  are  connected  with  this  function. 

Some  authors'  have  adopted  the  former  view  that  the  phenomena 
are  due  to  the  mere  absence  of  the  normal  ampullar  sensations,  the 
usual  pressure  of  the  endolymjjh  failing  on  account  of  the  removal  of 
that  fluid.  A  difficulty  is  presented  to  this  view  by  the  fact  that  the 
canals  are  all  continuous  ;  and  hence  if  the  effects  of  section  are 
simply  due  to  loss  of  fluid,  and  consequent  absence  of  the  usual 
pressure  and  of  the  variations  in  that  pressure,  the  section  of  one 
canal  ought  to  produce  the  same  effect  as  that  of  all  of  them  ;  but  this 
is  not  the  case. 

On  the  other  hand  Cyon=  insists  very  strongly  that  mere  removal 
not  only  of  the  perilymph  but  also  of  the  endolymph  is  insufficient 
to  give  rise  to  the  symptoms.  He  states  that  he  has  removed  the 
endolymph  from  the  whole  labyrinth  by  very  careful  puncture  of 
the  vestibule  without  producing  any  effects,  but  that  section  of  the 
membranous  walls  of  the  emptied  canals  is  immediately  effective. 
He  regards  the  symptoms  as  due  to  irritation  caused  by  the  section. 

Tomaszewicz^  also  urges  that  the  effects  of  section  are  the  less  pro- 
nounced the  more  carefully  the  operation  is  performed.  He  indeed 
refuses  altogether  to  admit  the  existence  of  any  such  function  as  that 

'  Goltz,  op.  cit.  "  Op.  cit. 

•  Hofmann  u.  Schwalbe's  Bericht,  LUe>-atur,  iSj-j,  p.  203. 


632  VERTIGO.  [BOOK   III. 

we  are  discussing,  and  regards  the  permanent  want  of  coordination 
which  follows  upon  extensive  injury  to  the  canals  as  due  to  mischief 
set  up  as  a  secondary  result  in  the  cerebellum  or  other  regions  of  the 
brain.  Other  observers  insist  most  strongly  that  the  phenomena  of 
incoordination  may  be  most  fully  developed  without  the  slightest 
secondary  mischief  to  the  brain.  • 

The  injury  which  causes  the  loss  of  coordination  need  not  be  con- 
fined to  the  peripheral  organs  of  the  auditory  nerve.  Section  of  the 
auditory  trunk  produces  similar  effects. 

According  to  Cyon  however  the  loss  of  coordination  which  follows, 
in  the  rabbit,  upon  section  of  both  auditory  nerves  disappears  'almost 
wholly'  after  some  time.  If  this  is  really  the  case,  without  any  re- 
generation of  the  divided  nerves  taking  place,  it  is  clear  that  whatever 
normal  ampullar  impulses  may  be  generated  in  the  intact  canals, 
these  must  play  far  too  subordinate  a  part  in  maintaining  equilibrium 
to  permit  us  to  regard  their  mere  absence  as  the  cause  of  such  dis- 
order ;  for  we  can  hardly  imagine  that  an  animal  could  learn  to  do 
without  such  peculiar  and  important  normal  impulses,  as  on  that  view 
of  the  question  these  are  supposed  to  be  ;  and  consequently  are  driven 
to  look  upon  the  symptoms  arising  from  injury  to  the  canals  as  due  to 
irritation.  Tomaszewicz'  also  finds  that  animals  'in  successful  cases' 
exhibit  none  of  the  phenomena  of  incoordination  after  section  of  both 
auditory  nerves. 

We  compared  the  condition  of  a  pigeon  after  injury  to  the 
semicircular  canals  to  that  of  a  person  who  is  dizzy,  and  indeed 
one  great  characteristic  of  vertigo  or  dizziness  is  an  inability  on 
the  part  of  the  subject  to  maintain  a  due  equilibrium ;  he  cannot 
coordinate  his  movements  properly  or  adapt  them  to  the  circum- 
stances around  him,  and  in  consequence  staggers  and  reels. 
Vertigo  may  be  brought  about  in  various  ways.  It  may  be  the 
result  simply  of  unusual  and  powerful  visual  sensations,  such  as 
those  produced  by  water  falling  rapidly  from  a  great  height  or  by 
objects  moving  swifdy  across  the  field  of  vision.  It  may  arise 
from  changes  taking  place  in  the  brain  itself,  and  is  a  common 
symptom  of  many  maladies  and  of  the  action  of  many  poisons. 
As  is  well  known,  a  most  severe  vertigo  may  be  at  once  produced 
by  rapidly  rotating  the  body.  All  cases  of  vertigo,  however  pro- 
duced, have  this  common  subjective  feature,  that  one  or  rnore  of 
the  sets  of  sensations  which  form  the  basis  of  our  appreciation  of 
the  relation  of  our  body  to  external  things  disagree,  and  are  in 
conflict  with,  the  rest  of  the  sensations  which  go  to  make  up  the 
same  appreciation.  Thus  in  the  vertigo  after  rapid  rotation  of  the 
body,  while  we  seem  to  see  the  whole  world  whirling  round  us, 
this  conclusion  is  contradicted  by  other  sensations.  Correspond- 
ing to  this  subjective  feature  of  vertigo  is  the  objective  feature  of 

'  Op.  cit. 


CilAI'.    VI. J  Tlii:    liKAlN.  033 

the  failure  of  motor  coordination ;  and  there  can  be  no  doubt 
that  thj  two  arc  connected  together  as  cause  and  effect.  The 
exact  manner  in  which  the  vertigo  is  develoi)ed,  i.e.  tlie  sequence 
and  relation  of  the  various  factors  of  it,  will  naturally  vary  according 
to  the  nature  of  the  exciting  cause,  and  the  course  of  events  appears 
to  be  not  only  different  in  diliferent  forms,  but  in  many  cases  com- 
plex. Wlicn  vertigo  comes  on  from  rapidly  rotating  the  body  with 
the  eyes  open,  an  element  of  discord  is  introduced  by  the  eyeballs 
not  keeping  pace  with  the  movements  of  the  head  but  following 
irregularly,  executing  the  oscillatory  movements  known  as  nystag- 
mus, movements  which  continue  after  the  body  has  come  to  rest, 
and  then  give  rise  to  the  false  sensation  that  external  objects  are 
moving  ra|)idly.  But  in  this  vertigo  of  rotation  there  are  other 
factors  at  work,  for  the  di/.ziness  comes  on,  though  less  readily, 
when  the  eyes  are  kept  shut  all  the  time.  It  has  been  suggested 
that  false  ampullar  sensations  arise  from  the  rotation  of  the  body 
exciting  the  semi-circular  canals.  But,  even  admitting  this  as  a 
contribution  to  the  total  effect,  it  seems  probable,  as  Purkinje 
suggested,  that  changes  in  the  brain  due  to  the  displacement  of 
the  blood  or  even  of  the  brain-substance  itself  caused  by  the  too 
rapid  rotation  are  at  work.  It  is  difficult  otherwise  to  explain  the 
unconsciousness  which  may  ensue  if  the  rotation  be  rapid  and 
long  continued  ;  and  the  vertigo  resulting  from  various  poisons 
seems  to  be  distinctly  of  central  origin. 

Vertigo  as  in  the  so-called  Meniere's  malady  is  frequently  associated 
with  disease  of  the  scmi-circulir  canals  ;  but  it  must  be  remembered 
that  the  canals  are  frequently  diseased  without  any  vertigo  appearing. 
According  to  Cyon"  and  Tomaszewicz^  vertigo  by  rotation  may  be 
readily  induced  in  rabbits  after  section  of  both  auditory  nerves,  a  result 
which  indicates  that  the  semi-circular  canals  can  have  little  share  in 
this  form  of  vertigo. 

Whether  we  accept  the  viev/  of  ampullar  sen.sations  just  dis- 
cussed or  not,  and  whatever  be  the  exact  share  which  false 
sensations  take  in  the  causation  of  vertigo,  this  at  all  events  is 
clear,  that  afferent  impulses  of  various  kinds  so  far  contribute  to 
the  building  up  of  the  coordinating  mechanisms  that  changes  in 
these  impulses  go  far  to  throw  the  mechanisms  into  disorder,  or  at 
least  to  impair  their  proper  working.  It  is  not  necessary  that 
these  afferent  impulses  should  directly  affect  consciousness  (or  to 
speak  more  correctly,  should  affect  that  complete  consciousness 
which  is  associated  with  volition),  and  so  develop  into  distinct 
perceptions.     We  have  seen  that  a  bird  from  which  the  cerebral 

•  Op.  cit.  '  op.  cit. 


634  VERTIGO.  [BOOK   III. 

hemispheres  have  been  removed  is  perfectly  able  to  fly ;  and  that 
therefore  the  coordinating  nervous  mechanism  necessary  for  flight 
is  situated  in  the  parts  of  the  brain  lying  behind  the  cerebral 
hemispheres.  We  have  also  dwelt  on  the  fact  that  all  the  chief 
coordinating  mechanisms  of  the  frog  lie  in  the  hind  parts  of  the 
brain  ;  yet  in  the  frog,  as  in  the  bird,  and  we  may  add,  as  in  the 
mammal,  injury  to  the  hinder  parts  of  the  brain  produces  loss  of 
coordination  whether  the  hemispheres  be  present  or  not.  Now, 
we  have  no  satisfactory  reasons  for  either  asserting  or  denying  that 
what  we  call  consciousness,  i.e.  a  distinct  consciousness  similar  to 
our  own  consciousness,  exists  in  animals  deprived  of  their  cerebral 
hemispheres.  When  signs  of  volition  are  present,  we  may  safely 
take  these  signs  as  indications  of  consciousness  also;  but  we  are 
not  justified  in  saying  that  all  consciousness  is  absent  when  satis- 
factory signs  of  volition  are  wanting.  We  cannot  form  any  just 
judgment  on  the  matter  without  some  more  trustworthy  and 
objective  tokens  of  consciousness  than  we  at  present  possess. 
But  wliat  we  may  safely  assert  is,  that  the  coordinating  mechan- 
ism, the  retention  of  which  is  so  striking  a  feature  of  an  animal 
deprived  of  its  cerebral  hemispheres,  is  constructed  out  of  divers 
afferent  impulses  of  various  kinds  arriving  at  the  coordinating 
centre  from  various  p?.rts  of  the  body,  that  in  fact  the  coordination 
taking  place  at  the  centre  is  the  adjustment  of  efferent  to  affereat 
impulses.  Many,  if  not  all,  of  these  afferent  impulses  are  such 
that  in  the  presence  of  consciousnes's  they  would  give  rise  to 
perceptions  and  ideas  ;  but  we  have  no  reason  for  thinking  that 
the  complete  development  of  the  afferent  impulse  into  a  per- 
ception or  an  idea  is  always  necessary  to  the  carrying  out  of 
coordination.  We  may  say  that  we  have  a  sense  of  equilibrium 
by  means  of  the  semi-circular  canals,  and  vvhen  that  sense  is 
deranged,  we  feel  giddy  and  cannot  stand.  We  have  no  reason, 
however,  for  thinking  that  the  failure  to  keep  upright  is  due  to  the 
feeling  of  giddiness,  in  the  sense  of  being  a  direct  result  of  the 
condition  of  the  consciousness.  On  the  contrary,  since  the 
peculiar  movements  characteristic  of  vertigo  may  take  place  in 
the  absence  of  consciousness  without  the  vertigo  being  actually 
felt,  we  may  with  security  assert  that  the  failure  to  stand  upright 
and  the  feeling  of  giddiness  are  both  concomitant  effects  of  the 
sam.e  disarrangement  of  the  coordinating  mechanism. 

It  cannot  be  too  much  insisted  upon  that  for  every  bodily 
movement  of  any  complexity  afferent  impulses  are  as  essential 
as  the  executive  efferent  impulses.  Our  movements,  as  we  have 
already  urged,  are  guided  not  only  by  the  muscular  sense,  but 
also  by  contact  sensations,  auditory  sensations,  visual  sensations, 


CHAP.    VI.]  THE   T5RAIN.  63$ 

and  visual  perceptions  (for  the  remarks  marie  above  concerning 
llie  relations  of  tlic  coorclinaling  mechanism  to  consciousness  do 
not  exclude  the  pcssibilily  of  consciousness  affecting  the  meclian- 
ism,  indeed  not  only  may  percejjtions  enter  into  the  casuation  of 
vertigo,  but  even  an  imaginary  idea  may  be  the  sole  exciting  cause 
of  this  condition)  ;  and  when  we  say  'they  are  guided,'  we  mean 
that  without  the  sensations  the  movements  become  impossible. 
In  studying  vision  we  saw  repeatedly  that  the  movements  of  the 
eyes  were  directly  dependent  on  vision,  and  every  ball-room 
affords  abundant  evidence  of  the  ties  between  sensations  of  sound 
and  motions  of  the  limbs.  So  essential,  in  fact,  are  afferent  im- 
pulses to  the  development  of  complex  bodily  movements,  that  we 
are  almost  justified  in  considering  every  such  movement  in  the 
light  of  a  reflex  action  made  up  of  afferent  and  efferent  impulses 
and  central  actions,  and  set  going  by  the  influence  of  some  domi- 
nant afferent  impulse,  or  by  the  direct  action  of  those  nervous 
changes,  whose  psychical  correlative  is  what  we  call  the  will,  on 
the  centre  itself.  All  day  long  and  every  day  multitudinous 
afferent  impulses,  from  eye,  and  ear,  and  skin,  and  muscle,  and 
other  tissues  and  organs,  are  streaming  into  our  nervous  system  ; 
and  did  each  afferent  impulse  issue  as  its  correlative  efferent  motor 
impulse,  our  life  would  be  a  prolonged  convulsion.  As  it  is,  by 
the  checks  and  counterchecks  of  cerebral  and  spmal  activities,  all 
these  impulses  are  drilled  and  marshalled,  and  kept  in  hand  in 
orderly  array  till  a  movement  is  called  for ;  and  thus  we  are  able 
to  execute  at  will  the  most  complex  bodily  manoeuvres,  knowing 
only  7L>/iy,  and  unconscious  or  but  dimly  conscious  kow,  we  carry 
them  out. 

We  have  ventured  to  use  the  phrase  '  coordinating  centre,'  but 
it  must  be  understood  that  we  have  no  right  to  attach  more  than  a 
general  meaning  to  the  words,  ^^'e  cannot,  at  present  at  least, 
defme  such  a  centre  in  the  same  way  that  we  can  the  vaso-motor 
or  respiratory  centre.  When  the  optic  lobes  as  well  as  the  cere- 
bral hemispheres  are  removed  from  the  frog,  the  power  of  balan- 
cing itself  is  lost ;  when  such  a  frog  is  thrown  off  its  balance  by 
inclining  the  plane  on  which  it  is  placed,  it  falls  down.  The 
special  coordinating  mechanism  for-  balancing  must  therefore  in 
this  animal  be  situated  in  the  optic  lobes ;  but  after  removal  of  these 
organs,  the  animal  is  still  capable  of  a  great  variety  of  coordinate 
movements  :  unlike  a  frog  retaining  its  sjjinal  cord  only,  it  can 
swim  and  leap,  and  when  j^laced  on  its  back  immediately  regains 
the  normal  position.  The  cerebelhnn  of  the  frog  is  so  small,  and 
in  removing  it  injury  is  so  likely  to  be  done  to  the  underlying  parts, 
that  it  becomes  difficult  to  say  how  much  of  the  coordination 


636  FORCED   MOVEMENTS.  [BOOK   III. 

apparent  in  a  frog  possessing  cerebellum  and  medulla  is  to  be 
attributed  to  the  former  or  to  the  latter  ]  probably,  however,  the 
part  played  by  the  former  is  small.  In  the  mammal,  as  we  have 
stated,  removal  of  the  whole  middle  and  hind  brain  does  away 
with  the  most  marked  of  these  coordinating  mechanisms.  Re- 
moval of  the  pons  Varolii  alone  has  the  same  effect.  Injury 
to,  or  disease  of,  the  more  superficial  parts  of  the  corpora  quadri- 
gemina  or  of  the  cerebellum,  does  not  appear  to  influence  the 
movements  of  the  body  at  large  to  any  striking  extent ;  but  there 
are  many  pathological  cases,  as  well  as  experimental  observations, 
tending  to  associate  the  coordinating  mechanisms  of  wln'ch  we  are 
speaking  with  the  deeper  parts  of  the  cerebellum.  It  would  be 
hazardous,  in  the  present  state  of  our  knowledge,  to  make  any 
definite  statement  concerning  the  share  taken  by  these  several 
cerebral  structures  in  the  various  coordinations. 

The  results  of  experiments  are  in  many  ways  conflicting,  but  still 
more  conflicting  and  still  less  trustworthy  are  the  results  of  pathological 
observations.  In  this  and  in  so  many  other  parts  of  physiology  the 
so-called  '  experiments  of  nature '  as  seen  at  the  bed-side,  are  extremely 
useful  in  suggesting  and  correcting  experimental  inquiries  ;  but  they 
prove  broken  reeds  when  reliance  is  placed  on  them  alone.  There  is 
hardly  a  thesis  in  cerebral  physiology,  in  respect  of  which  a  long 
array  of  '  cases '  may  not  be  quoted  strikingly  supporting  the  views 
enunciated,  and  a  long  array  as  flatly  contradicting  them. 


Forced  Moveine?its. 

All  investigators  who  have  performed  experiments  on  the  brain, 
have  observed  as  the  result  of  injury  to  various  parts  of  it  remark- 
able compulsory  movements,  One  of  the  most  common  forms  is 
that  in  which  the  animal  rolls  incessantly  round  the  longitudinal 
axis  of  its  own  body.  This  is  especially  common  after  section  of 
one  of  the  crura  cerebri,  more  particularly  of  the  external  and 
superior  parts,  or  after  unilateral  section  of  the  pons  Varolii,  but 
has  also  been  witnessed  after  injury  to  the  medulla  oblongata  and 
corpora  quadrigemina.  Sometimes  the  animal  rotates  towards  and 
sometimes  away  from  the  side  operated  on.  Another  form  is  that 
in  which  the  animal  executes  '  circus  movements,'  i.e.  continually 
moves  round  and  round  in  a  circle,  sometimes  towards  and  some- 
times away  from  the  injured  side.  This  may  be  seen  after  several 
of  the  above-mentioned  operations,  but  is  perhaps  particularly 
common  after  injuries  to  the  corpora  striata  and  optic  thalami. 
There  is  a  variety  of  the  circus  movement  said  to  occur  frequently 
after  lesions  of  the  nates,  in  which  the  animal  moves  in  a  circle, 


CHAP.    VI.]  THE   BRAIN.  637 

with  the  longitudinal  axis  of  its  body  as  a  radius,  and  the  end  of 
its  tail  for  a  centre.  And  this  form  again  may  easily  pass  into  a 
simply  rolling  movement.  In  yet  another  form  the  animal  rotates 
over  the  transverse  axis  of  its  body,  tumbles  head  over  heels  in  a 
strics  of  somersaults  ;  or  it  may  run  incessantly  in  a  straight  line 
backwards  or  forwards  until  it  is  stopped  by  some  obstacle.  These 
litter  forms  of  forced  movements  are  frequently  seen  after  injury 
to  the  corpora  striata ;  and  Nothnagel  speaks  of  a  limited  portion 
of  the  grey  matter  of  the  corpus  striatum  as  the  nodus  cursorius, 
the  injection  of  chromic  acid  into  which  produces  in  the  rabbit 
the  straight-forward  running.  Lastly,  many,  if  not  all,  these 
various  forced  movements  may  result  from  injuries  which  appear 
to  be  limited  to  tlie  cerebral  hemispheres. 

Attemi)ts  have  been  made  to  explain  the  rotatory  movements 
by  reference  to  unilateral  paralysis  or  to  spasm  of  various  muscles 
of  the  body  caused  by  the  cerebral  injury  ;  and  in  the  case  of  the 
'  circus  '  movements  with  partial  hemiplegia,  which  follow  upon 
injury  to  the  corpora  striata  or  other  parts,  the  explanation  that 
the  animal  in  progressing  forward  naturally  bears  on  its  paralysed 
or  weak  side  seems  a  valid  one  ;  but  the  movements  may  fre- 
quently be  witnessed  in  the  complete  absence  of  either  paralysis 
or  spasm,  and  cannot  therefore  be  always  so  explained.  On  the 
other  hand,  if  the  views  urged  just  now  concerning  the  nature  of 
the  coordinating  mechanisms  of  the  brain  are  true,  it  is  evident 
that  they  afford  a  general  explanation  of  the  phenomena,  though 
our  present  knowledge  will  not  permit  us  to  explain  the  genesis  of 
each  particular  kind  of  movement.  Such  gross  injuries  as  are  in- 
volved in  dividing  cerebral  structures  or  in  injecting  corrosive 
substances  into  the  midst  of  cerebral  organs,  must  of  necessity, 
either  by  irritation  or  otherwise,  seriously  affect  the  transmission 
not  only  of  afferent  impulses  in  their  cerebral  course,  but  also  of 
central  impulses,  inhibitory  and  the  like,  passing  from  one  part  of 
the  brain  to  another  ;  and  must  therefore  seriously  affect  the  due 
working  of  the  general  coordinating  mechanisms.  The  fact  that 
an  animal  can,  at  any  moment,  by  an  effort  of  its  own  will,  rotate 
on  its  axis  or  run  straight  forwards,  shews  that  the  nervous  mechan- 
ism for  the  execution  of  those  movements  is  ready  at  hand  in  the 
brain,  waiting  only  to  be  discharged  ;  and  it  is  easy  to  conceive 
how  such  a  discharge  might  be  affected  either  by  the  substitution 
of  some  potent  intrinsic  afferent  impulse  for  the  will  or  by  some 
misdirection  of  the  volitional  impulses.  Persons  who  have  expe- 
rienced similar  forced  movements  as  the  result  of  disease  report 
that  they  are  frequently  accompanied,  and  seem  to  be  caused,  by 
disturbed  visual  or  other  sensations ;  they  say  they  fall  forward 


638  CEREBRAL   CONVOLUTIONS.  [BOOK  IIL 

because  the  ground  appears  to  sink  away  beneath  their  feet. 
Without  trusting  too  closely  to  the  interpretations  the  subjects  of 
the>e  disorders  give  of  their  own  feelings,  we  ni  y  at  least  con- 
clude that  the  disorderly  movements  ;  re  due  to  a  disorder  of  the 
coordinating  mechanism,  which  in  many  cases  is  itself  the  result 
of  disordered  sensory  impulses,  and  not  to  any  paralytic  or  othsr 
failing  of  the  simple  muscular  instruments  of  the  nervous  system. 
And  this  view  is  supported  by  the  fact  that  many  of  these  forced 
movements  are  accompanied  by  a  peculiar  and  wholly  abnormal 
position  of  the  eyes,  which  alone  might  perhaps  explain  many  of 
the  phenomena. 


Sec.  3.     The  Functions  of  the  Cerebral  Convolutions. 

All  the  older  observers,  Flourens  and  others,  agreed  that  Avhen 
the  cerebral  hemispheres  were  gradually  removed,  piece  by  piece 
or  slice  by  slice,  no  obvious  effects  manifested  themselves,  either 
in  the  intelligence  or  volition  of  the  animal,  when  the  first  portions 
only  were  taken  away  ;  but  that,  as  the  removal  was  continued, 
the  animal  became  more  and  more  dull  and  stupid,  until  at  last 
both  intelligence  and  volition  seemed  to  be  entirely  lost.  It  has 
been  frequently  observed  that  after  wounds  of  the  skull  large  por- 
tions of  the  brains  of  men  might  be  removed  without  any  marked 
effect  on  the  psychical  condition  of  the  patients.  The  brain  when 
exposed  was  found  not  to  be  sensitive  ;  and  ordinary  stimuli 
applied  to  the  surface  of  the  convolutions  of  animals  failed  in  the 
hands  of  most  experimenters  to  produce  any  clearly  recognizable 
effect.  Hence  it  became  very  common  to  deny  the  existence  of 
any  localization  of  functions  in  the  convolutions  of  the  hemisphere, 
and  to  speak  of  the  brain  as  '  acting  as  a  whole,'  whatever  that 
might  mean.  On  the  other  hand,  there  was  clear  evidence  that 
not  only  did  disease  of  the  superficial  grey  matter  of  the  hemi- 
spheres cause  delirium,  as  in  meningitis,  but  sometimes  convulsions 
either  of  an  epileptic  character  or  localized  to  particular  groups  of 
muscles'.  Hitzigand  Fritsch^  were  the  first  to  shew  that  the  local 
application  of  the  constant  galvanic  current  to  particular  convolu- 
tions and  to  particular  parts  of  convolutions  gave  rise  to  definite 
coordinate  movements  of  various  groups  of  muscles.  Thus  while 
the  stimulation  of  one  spot  (Fig.  68)  caused  movements  in  the 

^  Hughlings-Jackson,  London  IIosp.  Reports,  1S64  ;  Clinical  and  Physiol, 
Researches,  1873. 

^  Reichert  u.  du  Bois-Reymond'.s  Archiv,  1870,  p.  300.  See  also  Hitzig, 
Das  Gehirn,  Berlin,  1874. 


CHAP.    VI.]  THE   BRAIN.  639 

muscles  of  the  neck,  another  caused  extension  with  adduc- 
tion of  the  fore  leg,  a  third  movements  of  the  hind  leg,  a 
iburih  movements  of  the  eye  and  other  parts  of  the  face.  In 
fact,  they  and  Ferrier',  who  using  chiefly  the  interrupted  or 
faradaic  current,  repeated  and  extended  their  observations, 
were  able  to  map  out  the  convolutions  of  the  front  and  middle 
parts  of  the  hemisphere  of  the  dog  (Figs.  68,  69),  cat,  monkey 
(Figs.    70,   71),   and  other  animals,   into  a  number  of  precisely 


Fig.  63.    The  Areas  op  the  Cerebral   Convolutio.ns  of  the  Dog,  according   to 

HlTZlG   AND    FkITSCH. 

(i)  .i   The  Area  for  the  muscles  of  the  neck. 

(2)  +        ,,  ,,  extension  and  adduction  of  the  fore  limb. 

(3)  +         „  „  flexion  and  rotalion  of  the  fore  limb. 

(4)  tJ        ,,  ,,  hind  limb. 

Running  lran';vtrscly  towards   and   separating  (i)   and  (2)  from  (3)  and  (4)   is   seen    the 
cruciitl  siiicus. 

(5)  O  The  facial  Area. 

limited  areas,  the  stimulation  of  each  area  producing  a  distinct 
and  limited  movement,  while  stimulation  of  a  large  surface  pro- 
duced general  convulsions.  The  movements  were  so  precise  that 
they  answered  each  to  the  spot  stimulated  almost  as  completely 
as  a  note  answers  to  a  key  struck  on  the  piano. 

A  relationship  has  also  been  observed  between  the  brain  surface 
and  the  secretion  of  saliva,  the  beat  of  the  heart,  the  condition  of  the 
pupil,  the  action  of  vase  motor  nerves,  and  other  organic  functions. 

'   Wat  EiJittg  Ki-/>orls,'Vo\.  iii.  1S73.     Sec  aX^io  \\\^  Fufictwm  o/l/u  Brain, 
1  ondon,  1876. 


640 


CEREBRAL   CONVOLUTIONS.  [BOOK   IIL 


Fig.  69.     Thr   Areas   of  the  Cerebral   Convolutions  of  the  Dog,  according   to 

Ferrier. 
O.  The  Olfactory  Lobe.     A.  The  Fissure  of  Sylvius.     B.  The  Crucial  Sulcus. 
Faradaic  stimulations  of  the  areas  indicated  by  the  several  circles  produce  the  following 
results. 
(i)    The  hind  leg  is  advanced  as  in  walking. 
(3)''   Lateral  or  wagging  motion  of  the  tail. 

(4)  Retraction  and  adduction  of  the  opposite  fore  limb. 

(5)  Elevation  of  the  shoulder  of,  and  extension  forwards  of,  the  opposite  fore  limb. 

(7)  Closure  of  the  opposite  eye  caused  by  combined  action  of  the  orbicular  and  zygomatic 

muscles. 

(8)  Retraction  and  elevation  of  the  opposite  angle  of  the  mouth._ 

(gr  The  mouth  is  opened  and 'the  tongue  moved,  sometimes  barking  is  produced. 

(11)  Retraction  of  the  angle  of  the  mouth. 

(12)  Opening  of  the  eyes  and  dilation  of  the  pupils ;  the  eyes  and  then  the  head  turning 

to  the  opposite  side. 

(13)  The  eyeballs  move  to  the  opposite  side. 

(14)  Pricking  or  sudden  retraction  of  the  opposite  ear. 

iis)     Torsion  of  the  nostril  on  the  same  side. 
16)     Elevation  of  the  lip  and  dilation  of  the  nostril  (?) 

Eulenburg  and  Landois^  find  that  extirpation  of  the  motor  areas  for 
the  extremities  causes  a  rise  of  temperature  (lasting  in  some  cases  for 
months)  in  the  corresponding  limbs  ;  and  Hitzig  had  previously 
observed  the  same  thing!  Balogh^  describes  in  the  dog  and  rabbit 
areas  in  the  cerebral  surface  stimulation  of  which  causes  acceleration 
of  the  heart's  beat,  and  other  areas  stimulation  of  which  slows  the 
heart.  Bochefontaine^  observed  that  stimulation  of  the  cerebral 
surface  in  the  neighbourhood  of  the  crucial  sulcus  produced  a  rise 
of  arterial  pressure  with  alternating  acceleration  and  retardation  of 
the  heart's  beat.     Among  other  results  of  stimulating  the  same  and 

'  There  i=;  in  the  dog  no  movement  comparable  to  that  resulting  from  stimu- 
lating (2)  (Figs.  70,  71)  in  the  monkey.      (Ferrier.) 
^  Corresponding  to  (9)  and  (10)  in  the  monkey. 

3  Virchow's  Archiv,  6S  (1876),  p.  245. 

4  Cf.  however  Vulpian,  Archives  de  Fhysiol.  1876,  p.  814  ;  Kuessner,  Arch, 
f.  Psych.  VIII.  (1878)  p.  432. 

s  Hofmann  and  Schwalbe's  Bei-icht,  1876,  p.  38. 
*  Archives  de  Physiol.  III.  (1876)  p.  140. 


CHAP.  VI.] 


Tllli   BKAIN. 


641 


Fig.  70. 

Figs.  70  and  71.     Side  and    Uiter  Views   of   the  Brain  op  Man,  the  Areas  ok 
THE  Cerebral  Co.svolutio.vs,  according  to  Ferrier. 

TIte  Jtgures  are  constructed  by  marking  on  the  brain  0/  man.  in  their  respective  situa- 
tio'ts.  the  areas  of  the  brain  of  the  monkey  as  lietfrmined  by  experiment,  and  the  description 
0/  the  effects  of  stimulating  the  various  areas  refers  to  the  brain  <  f  the  monkey. 

(1)    (On  the  pcitero-pa-ictal   [superior  parietal]   Lbule).      Advance  of  the  opposite  hind 

limb  .li  in  walking. 
(2),  (3).  (4)    (Aroi:nd  the  upper  extremity  of  the  fissure  of  Rolando).     Complex  movements 

of  the  opposite  leg  and  arm,  and  of  the  trunk,  as  in  swimming. 
{a),  (i),  (c).  (tf)  (On  the  p  <stero-parieial  [posterior  central]  convolution).    Individual  and 

c  mbine  I  movements  tf   the  fingers  and  wrist  of  the  oppjsite  hand.      Prehensile 

m  ivcmcnts. 
(5)    (At  the  posteri  r  extremity  rf  the  superior  fr  ntal  coavoluli  n).     Extension  forward 

of  the  c  ppjsite  arm  and  hand. 

Other  regions  of  the  surface  he  witnessed  increased  flow  of  saliva, 
coiitra:tion  of  the  spleen,  bladder,  uterus,  &c.,  and  dilation  of  the 
pupil  ;  the  last  effect  might  follow  upon  stimulition  of  almost  any 
point  oi  the  cerebral  surface.  But  on  these  points  the  results  of 
various  observers  are  by  no  means  constant'.     Haemorrhage  into  the 

'  Ikown-Scquard,  Archives  de  P/tys.  II.  (1875^  p.  864.     Eckhard,  Bdlrdge, 
VII.  (1876)  199. 

F.  r.  .41 


CEREBRAL  CONVOLUTIONS.  [BOOK   III 


Fig.  71. 

(6)  (On  the  upper  part  of  the  antero-parietal  or  ascending  frontal  [anterior  central]  con- 

volution).    Supination  and  flexi  n  of  the  opposite  Lrearm. 

(7)  (On  the  median  portion  'f  the  same  convohition).     Retraction  and  elevation  of  the 

opposite  angle  cf  the  mouth  by  means  of  the  zvgomatic  muscles. 

(8)  (Lower  d  Avn  on  the  same  convohition).     Elevation  of  the  ala  nasi  and  upper  lip  with 

depress!,  n  of  the  lower  lip,  on  the  opposite  side. 
(9),  (10)    (At  the  inferior  e.xtremity  of  the  same  c  nvoliition,  Broca's  ccnvrluti:!n).     Opening 

of  the  m^uth  with  (9)  protrusion  and  (10)  retraction  of  the   tongue.     Region  of 

Aphasia.     Bilateral  action. 
(ii)    (Between  (10)  an  1  the  inferior  e.xtremity  of  the  p^stero-parietal  convolution).    Retrac:ion 

of  the  '  pposite  angle  of  the  mouth,  the  head  turned  slightly  to  one  side. 
(12)    (On  the  poiteri.r  ponions  of  the  superior  and  middle  fron;al  convolutions).     The  eyes 

open  widely,   the  pupils  dilate,  and  the  head  and  eyes  turn  towards  the  opijosite 

side. 
(13),  (13')    (On  the  supra-marginal  lobule  and  angular  gyrus).     The  eyes  move  towards  the 

oppoii  e  side  vith  an  ip:\ard  (13)  or  downward  (13")  deviation.     The  pupils  generally 

contracted.     (Genre  of  vision.) 
(14)    (On   the  infra-marginal  or  superior  [first]  tempcro-sphen-^idal  convolution).     Prxking 

of  the  opp  site  ear,  the  head  and  eyes  turn  to  the  opposite  side,  and  the  pupils  dilate 

largely.     (Centre  of  hearing  ) 
Ferrier  moreover  places  the  centres  of  taste  and  smell  at  the  extremity  of  the  tempore- 
sphenoidal  lobe,  and  that  of  touch  in  the  gyrus  uncinatus  and  hippocampus  major. 


CHAr.    VI.]  THE   BRAIN.  643 

lung  has  been  observed  in  th*e  rabbit  to  follow  upon  stimulation  of  the 
cerebral  surface'. 

These  experiments,  which  have  not  only  been  confirmed  by 
many  observers,  but  may,  with  due  care,  be  successfully  repeated, 
by  any  one,  clearly  shew,  in  spite  of  some  discordance  among- 
various  authors  as  to  the  exact  position  and  extent  of  the  several 
*  areas.'  that  there  is  a  connection  between  electric  stimulation  of 
certain  areas  of  the  brain-surface  and  certain  bodily  movements  ; 
but  the  exact  nature  of  this  connection  is  at  present  very  obscure. 
The  areas  in  question  have  been  spoken  of  by  some  authors  as 
'motor  centres.'  Such  a  term  is  however  misleading,  since  it 
suggests  that  the  brain-surface  in  a  given  area  is  largely  occupied 
in  giving  rise  to  the  coordinate  nervous  impulses  which  carry  out 
the  movement  resulting  from  stimulation  of  the  area,  just  as  the 
respiratory  centre  for  instance  is  occupied  in  giving  rise  to  the 
coordinate  respiratory  impulses  ;  but  it  is  absurd  to  suppose  that 
comparatively  large  areas  of  such  valuable  material  as  we  must 
needs  suppose  the  grey  matter  of  the  convolutions  to  be,  should 
be  taken  up  in,  so  to  speak,  menial  works,  such  for  instance  as 
that  of  discharging  the  nervous  impulses  required  for  bending  or 
for  straightening  the  arm.  Besides,  we  know  that  an  animal  can 
be  made  to  execute,  in  the  total  absence  of  the  cerebral  hemi- 
spheres, the  various  coordinate  movements  which  result  from  the 
stimulation  of  the  cerebral  areas  ;  coordination  in  fact  is,  as  we 
have  already  shewn,  effected  in  parts  of  the  brain  other  than  the 
surface  of  the  cerebral  hemispheres ;  and  all  that  the  areas  in 
question  do  is  to  make  use  in  some  way  or  other  of  these  lower 
coordinating  mechanisms.  If  on  the  other  hand  it  is  admitted 
that  the  movements  which  result  from  stimulation  of  an  area  form 
merely  a  small  and  insignificant  part  of  the  total  eflfects  of  stimu- 
lation, the  other  changes  brought  about  being  profound  but 
invisible  and  as  yet  unrecognizable,  the  use  of  the  term  '  motor 
centre  '  is  still  more  objectionable.  That  the  latter  view  is,  of  the 
two,  the  more  probable  seems  indicated  by  the  fact  that  over 
large  portions  of  the  brain-surface  electric  stimulation  produces  no 
movements  ;  these  portions  are  wholly  devoid  of  '  motor  centres.' 
The  real  interest  in  fact  in  the  results  of  electric  stimulation  of  the 
brain-surface  attaches  not  so  much  to  the  question  as  to  which  are 
the  exact  movements  resulting  from  the  stimulation  of  this  or  that 
area,  as  to  the  broad  fact  that  different  results  follow  upon  stimu- 
lation of  ditierent  regions,  thus  serving  to  indicate  that  there  is  af'.er 
all  a  'localization  of  functions'  in  the  brain-surfiice.     Experiments 

'  Nothnagel,  Cbl.  Med.  Wiss.  1874,  p.  209. 

41 — 2 


644  CEREBRAL   CONVOLUTIONS.  [BOOK   IIL 

have  been  made  with  the  view  of  attacking  the  problem  by 
another  method,  viz.  by  watching  the  results  following  upon  the 
removal  of  particular  parts  of  the  brain  ;  but  the  statements  of 
observers  are  in  this  respect  so  opposed  that  a  dogmatic  statement 
is  at  present  impossible. 

In  trying  to  appreciate  the  true  meaning  of  the  experiments  on 
electric  stimulation  of  the  brain-surface  the  following  facts  deserve 
attention.  Not  only  do  the  phenomena  continue  when  the  animal  is 
under  opium  and  chloroform,  provided  that  the  anaesthesia  is  not  too 
profound,  and  not  only  do  they  require  for  their  development  electric 
currents  of  a  considerable  strength,  mechanical  and  chemical  stimula- 
tion being  unable  to  produce  them,  but  the  results  of  stimulation  are 
the  same,  when  the  surface  of  the  convolution  operated  on  is  highly 
congested,  and  even  when  it  has  become  completely  dried  up,  or  after 
it  has  been  washed  with  strong  nitric  acid.  The  results,  moreover, 
remain  unchanged  when  the  area  experimented  upon  is  isolated  from 
the  surrounding  grey  matter,  by  plunging  a  cork-borer  for  some 
distance  into  the  brain  round  it  ;  and  even  when  the  brain-substance 
is  removed  to  some  depth  down  by  means  of  the  cork-borer,  and  the 
electrodes  plunged  into  the  blood  which  fills  up  the  cylindrical  hole 
thus  made'"  They  remain  the  same  when  the  surface  stimulated  is 
disconnected  physiologically  though  not  physically  from  the  deeper 
parts,  by  a  horizontal  incision  carried  some  little  distance  from  the 
surface-.  And  though  the  area,  stimulation  of  which  gives  rise  to  a 
definite  movement,  is  always  limited,  yet  it  is  not  constant  in  different 
individuals,  and  frequently  a  large  and  deep  sulcus  may  be  seen  run- 
ning through  its  very  midst  3.  All  these  facts  suggest  that  the  results 
are  due  to  the  escape  of  the  current  from  the  surface  to  which  the 
electrodes  are  applied  to  deeper  underlying  portions  of  the  brain,  the 
escape  taking  place  along  definite  lines  determined  by  the  electrical 
conductivity  of  the  brain-substance.  And  Burdon  Sanderson*  states 
that  local  stimulation  of  the  white  matter  immediately  surrounding  a 
corpus  striatum  produces  localized  movements  quite  similar  to  those 
caused  by  stimulation  of  the  coi'responding  cerebral  surface  ;  from 
which  it  may  be  inferred  that  when  the  surface  appears  to  be  stimu- 
lated, it  is  really  the  corpus  striatum  which  is  affected  physiologically 
by  the  stimulus.  Albertoni  and  Michielis  however  found  that  several 
weeks  after  the  removal  of  an  area  stimulation  of  the  scar  or  its 
immediate  neighbourhood  no  longer  produces  the  particular  move- 
ments characteristic  of  the  area.  Unless  it  can  be  shewn  that  the 
injury  in  such  cases  produces  marked  changes  in  the  electrical  con- 
ductivity of  the  brain-substance,  this  observation  may  be  taken  as 
indicating  that  the  fibres  passing  downwards  from  the  area  to  deeper 

'  Hermann,    P/luger's  Archiv,   X.    {1875)   77.     Braun,   Eckhard's  Beitrdge, 
VII.  (1874)  127. 

^  Burdon  Sanderson,  Proc.Roy.  Soc   xxii.  (1875)  368. 

3  Hermann,  op.  cit.  *  Qp.  cit. 

s  Hofmann  and  Schwalbe's  Bericht.  1876,  p.  30. 


CHAP.    Vl.J  IHt   BKAIN.  645 

parts  of  the  brain,  have  through  degeneration  become  incapable  of 
conveying  the  inipuisei  set  going  by  the  apphcation  of  the  current 
to  tlie  brain-surface  ;  that  the  connection  bL-tween  the  area  and  the 
deeper  puts  is  not  a  physijal  one,  depending  on  the  escape  of  the 
current,  but  a  physiologijal  one,  dependent  on  the  existence  of  fibres 
passing  from  the  area  to  some  more  central  mech mism  and  capable 
of  producing  their  speciil  effects  when  stimulated  in  any  part  of  their 
course '. 

At  all  events,  these  various  experiments  shew  that  the  fact  of 
certain  movements  following  upon  stimulation  of  certain  areas,  is 
m  itself  no  satisfactory  proof  that  those  areas  arc  to  be  considered 
as  'motor  centres.'  They  are  not  fundamentally  inconsistent  with 
the  hypothesis  that  su:h  centres  exi^t  ;  for  the  fibres  proceeding  from 
the  centres  to  the  corpus  striatum  or  to  other  organs,  might,  when 
artificially  stimulated,  produ:e  the  same  effect  as  when  they  were 
the  channels  of  impulses  originating  in  the  centres  in  a  normal 
manner,  just  as  cardiac  inhibition  may  be  brou.Ljht  about  by  artificial 
stimulation  of  the  vagus,  though  in  ordinary  life  it  occurs  through 
the  activity  of  the  meJuUary  cardio-inhibitory  centre.  They  are  not 
inconsistent  with  the  hypothesis,  but  they  afford  it  very  little  positive 
support. 

On  the  other  hand,  if  these  circumscribed  areas  of  superficial  grey 
matter  are,  as  they  have  by  some  been  suppose. 1  to  be,  motor  centres 
in  the  sense  of  being  necessary  for  the  volitional  or  psychical  initiation 
of  movements  corresponding  to  those  produced  by  artificial  stimulation, 
particular  sets  of  voluntary  movements  ought  to  disappear  when 
particular  areas  are  removed  or  otherwise  rendered  functionally 
incapable. 

Similarly  if  the  phenomena  attendant  on  stimulation  of  these 
'motor'  areas  are  to  be  interpreted  as  proving  a  localization  of 
function,  we  ought  to  expect  that  in  those  regions  of  the  cerebral 
surface  in  which  stimulation  produces  no  movements  and  which  have 
accordingly  been  called  'sensory'  (a  term  however  distinctly  open  to 
objection),  the  removal  of  particular  areas  would  give  rise  to  loss  or 
impairment  of  particular  cerebral  functions  even  though  no  derange- 
ment of  muscular  activity  was  manifested. 

In  respect  to  the  'motor'  areas  not  only  Hitzig  and  Ferrier,  but 
many  subsequent  inquirers,  have  observed  that  removal  or  destruction 
of  an  area  is  followed  by  an  inability  to  execute  the  movements  assigned 
to  the  area  or  at  least  by  a  difficulty  in  carrying  them  out.  Ferrier  at- 
tributes the  paralysis  thus  produced  to  an  absence  or  impairment  of 
volitional  or  psychical  initiation.  Hitzig-  on  the  other  hand  is  in- 
clined to  interpret  the  imperfection  of  the  movements  as  due  to  a  loss 
of  muscular  sense  or  'muscular  consciousness;'  and  NolhnageP,  who 
injected  minute  quantities  of  chromic  acid  into  limited  areas  of  the 
cerebral  surface,  observed  motorial  anomalies,  whch  he  also  was  in- 
clined to  regard  as  due  to  a  loss  or  impairment  of  the  muscular  sense. 

'  For  a  discussion  of  this  point  see  Report  by  Dobb^,  Journ.  Anat.   and 
Phys.,  Jan.  1878. 

'  Op.  lit.  3  Virchow'.-;  An/iiv,  lid,  57  (1S73),  P-  'S4. 


646  CEREBRAL   CONVOLUTIONS.  [BOOK   III. 

Nothnagel  however  made  the  important  observation  that  the  symptoms 
after  a  while  disappeared;  and  in  this  he  has  been  corroborated  by 
subsequent  observers.  Ferrier  appears  to  have  kept  his  animals  alive 
for  a  few  days  only  at  the  utmost,  and  to  have  ceased  his  observations 
before  adequate  recovery  had  taken  place.  Hermann^  removed  from 
dogs  cerebral  areas,  stimulation  of  which  gave  localized  movements, 
and  found  that  the  paralysis  which  immediately  followed  the  operation, 
after  some  days  wholly  disappeared.  Carville  and  Duret-  obtained  the 
same  results,  and  they  shewed  that  the  restitution  of  power  could  not 
be  due  to  a  vicarious  action  of  the  same  centre  of  the  other  hemisphere, 
since  after  recovery  from  a  left-sided  paralysis  due  to  an  operation  on 
the  right  hemisphere,  subsequent  operation  on  the  same  centre  of  the 
left  hemisphere  produced  the  usual  effect  on  the  right  side,  but  did  not 
cause  a  return  of  the  paralysis  on  the  left  side.  They  could  only  re- 
concile their  results  with  the  'motor  centre  '  theory  by  supposing  that 
when  a  centre  was  destroyed,  other  portions  of  the  same  hemisphere 
took  up  its  functions,  an  hypothesis  which  is  in  itself  opposed  to  the 
*  localisation  '  theory.  Moreover  paralysis  more  readily  makes  its  ap- 
pearance in  operations  on  the  areas  for  the  fore  leg  and  hind  leg  than  in 
those  on  other  areas  ;  thus  Albertoni  and  Michieli^  removed  the  centre 
for  the  movements  of  the  jaw  and  tongue  without  any  paralysis  in  those 
organs.  But  the  most  serious  objections  to  the  theory  of  'motor' 
centres  in  any  of  the  forms  in  which  it  has  yet  been  brought  forward, 
are  furnished  by  the  observations  by  Goitz-*  on  dogs.  He  removed 
parts  of  the  cerebral  surface  by  washing  the  nervous  substance  away 
with  a  stream  of  water,  a  method  which  has  the  advantage  of  causing 
comparatively  little  bleeding,  and  affording  considerable  localization  of 
the  injury  ;  and  he  found  that  the  operation  was  followed  at  first  by 
more  or  less  paralysis.  He  failed  however  to  find  any  exact  corre- 
spondence between  the  areas  destroyed  and  the  groups  of  muscles 
affected,  the  paralysis  manifesting  itself  most  readily  in  the  fore  and 
hind  limbs,  and  generally  to  a  certain  extent  in  both  together.  More- 
over, and  this  is  the  important  point,  the  paralysis  in  a  short  time 
wholly  disappeared  whatever  the  portions  of  brain  removed.  Both  the 
amount  of  mischief  done,  and  the  speed  and  completeness  with  which 
recovery  took  place,  depended  not  on  the  locality  operated  on,  but,  as 
older  observers  found,  on  the  quantity  of  brain-substance  removed. 
After  recovery  from  one  operation,  a  second  removal  of  brain-substance 
reproduced  the  same  phenomena  as  the  previous  one ;  and,  though  at 
first  sight  this  might  be  taken  as  supporting  Carville  and  Buret's  theory 
of  a  vicarious  action  of  other  parts  of  the  same  hemisphere,  the  impos- 
sibility of  such  a  view  is  proved  by  the  fact  that  Goltz  was  able  to  re- 
move the  greater  part  of  the  grey  matter  of  one  hemisphere,  and  yet 
recovery  of  muscular  power  eventually  took  place.  Goltz  argues 
that  all  the  temporary  phenomena  are  due  to  the  superficial  lesions 

^   Op.  cit.  ^  Archives  de Physiol.  11.  (1875)  p.  352. 

3  Op.  cil.  Cf.  also  Lussana  and  Lemoigne,  Archives  de  Fhysiologit  iv,  (i.Syy) 
p,  119  et  seq,  Luciani  and  Tamburini,  Sui  Cejitri  Psico-sensori  Corticali,  1879. 
Dupuy,  Researches  into  the  Physiology  of  the  Brain,  New  York,  1878. 

4  Ym.gQx\  Archiv,  xiii.  (1876)  p.  I,  xn.  (1877)  p.  412,  xx.  (1879)  p.i. 


CIJAl'.    VI.]  THE   BkAlN.  647 

excrcisinjT  inhibitory  influences  on  the  parts  of  the  brain  lyin;^  between 
the  cerebral  convolutions  and  the  sjjinal  cord.  He  very  aptly  compares 
the  paralysis  caused  by  operations  on  the  surface  of  the  cerebrum  to 
the  paralysis  of  the  lumbar  spinal  centres  which  results  froni  and  lasts 
some  time  after  division  of  the  spinal  cord  in  the  dorsal  region.  In  one 
case  in  which  he  removed  the  j^reater  part  of  both  hemispheres  the  dog 
lived  for  months,  and  shewed  eventually  no  sij:;ns  whatever  of  any 
muscular  weakness  ;  all  the  muscles  of  his  body  were  firm  and  well 
built,  and  the  only  permanent  failure  in  the  way  of  movement  was  a 
certain  dum-iness  ;  and  this  (lOltz  ar<^ues  to  be  merely  the  result  of  a 
d  li  ien.y  of  tactile  sensibility,  which  as  we  shall  see  presently  is  a 
stfi-ing  result  of  large  injuries  to  the  cerebral  hemispheres.  Goltz's 
experiments  are  in  fact  absolutely  oppose(J  to  the  hypothesis  of 
'motor'  areas  in  any  part  of  the  brain-surface. 

Turning  now  to  the  second  line  of  inquiry  indicated  above,  viz. 
whether  the  removal  of  particular  areas  of  the  brain-surface,  even  in 
those  regions  in  which  stimulation  evokes  no  vi-.ible  movements,  in- 
terferes with  the  production  or  development  of  particular  sensations  or 
otherwise  modifies  in  particular  ways  the  functions  of  the  brain,  we 
find  that  Fcrrier  and  others  contend  for  the  existence  of  definite  areas 
in  connection  with  the  various  senses,  areas  which  may  accordingly  ba 
spoken  of  as  *  sensory.'  Thus  Ferrier  describes  a  '  visual '  centre,  the 
destruction  of  which  entails  blindness  of  the  opposite  eye,  an 
'auditory'  centre,  a  'tactile'  centre,  centres  for  taste  and  smell,  and 
even  a  centre  fur  hunger.  Further  inquiries  have  brought  to  light  a 
number  of  facts  which  deserve  special  attention,  and  which  have  been 
most  fully  studied  in  reference  to  vision.  The  older  observers, 
Flourens  an:!  others,  had  remarked  that  injury  to,  or  removal  of  por- 
tions of,  the  cerebral  hemispheres  frequently  caused  blindness  ;  this 
however  appeared  to  be  of  a  temporary  character  only,  the  animal,  at  a 
later  period,  seeming  upon  a  superficial  examination  to  have  com- 
pletely regained  its  sight.  Goltz'  however  has  called  attention  to  a  re- 
markable imperfection  of  vision  which  is  more  or  less  permanent  after 
extensive  injuries  to  the  cerebral  hemispheres,  but  which  without  care 
might  escape  notice.  The  salient  character  of  this  imperfection  is 
that  though  the  animal  evidently  can  see,  and  uses  his  sight  success- 
fully in  avoiding  obstacles  and  guiding  his  movements,  yet  what  he 
sees  does  not  produce  its  usual  effect  on  him  ;  he  obviously  fails  to  re- 
cognise many  things,  and  has  become  indifferent  to  scenes  which  for- 
merly affected  him  strongly.  Thus  a  dog  from  which  portions  of  the 
cerebral  hemispheres  have  been  removed,  fails  to  recognise  his  food  by 
sight  ;  when  he  is  threatened  with  the  whip,  he  is  not  cowed  ;  when  the 
hand  is  held  out  for  his  paw  he  makes  no  response  ;  and  though  before 
the  operation  he  became  violently  excited  when  the  laboratory  servant 
dressed  in  a  fantastic  garb  was  presented  to  him,  he  remains  after  the 
operation  perfectly  indifl'erent  to  the  same  image.  .Another  striking 
character  of  this  imperfection  of  vision  is  that  recovery  from  it  to  a 
considerable  extent  is, under  certain  circumstances,  possible  by  means 
of  educational  exercise  ;  the  dog,  which  at  first  could  not  recognize  his 

'  Op.  cit. 


648  CEREBRAL   CONVOLUTIONS.  [BOOK   IIL 

food  by  sight,  and  was  indifferent  to  the  whip,  learns  after  a  while  to 
know  the  one  and  to  respect  the  other.  Now  it  is  obvious  that  two  in- 
terpretations may  be  given  of  this  peculiar  imperfection  of  vision. 
The  usual  psychical  effects  may  fail  simply  because  the  sensory  im- 
pulses are  unable  to  give  rise  to  sufficiently  well  defined  sensations  or 
perceptions  and  vision  consequently  remains  misty,  as  if  things  were 
seen  through  a  gauze,  and  possibly,  to  adopt  Goltz's  suggestion,  with  all 
their  colours  washed  out  ;  under  such  circumstances  the  dog  could  not 
readily  recognize  meat  as  meat  nor  appreciate  the  fantastic  dress  of 
the  laboratory  servant.  The  other  interpretation  supposes  that  the 
failure  is  due  to  the  absence  of  intellectual  factors,  that  the  sensations 
may  be  intact  but  from  the  break  in  the  cerebral  substance  cease  to 
give  rise  to  ideas  or  to  excite  the  memory  of  past  experience.  The 
beneficial  effects  of  exercise  are  obviously  explicable  on  both  hypo- 
theses. Under  the  first  view,  the  dog,  stid  possessing  intellectual 
powers,  simply  learns  to  make  use  of  his  imperfect  sensations,  just  as 
he  would  do  if  the  imperfect  vision  had  been  due  to  simple  injury  or 
disease  of  his  retina.  Under  the  second  view,  new  ideas,  new  ex- 
perience, and  a  new  memory  are  formed  afresh  ;  the  dog  learns  once 
more  to  interpret  his  visual  sensations  in  the  same  way  that  he 
did  in  his  early  days.  The  first  view  is  the  one  held  by  Goltz,  the 
second  view  is  maintained  by  Munk',  who  accordingly  speaks  of  the 
imperfection  of  vision  of  which  we  are  speaking  as  '  psychical ' 
blindness  in  contradistinction  to  a  blindness  in  which  sensory  im- 
pulses passing  along  the  optic  nerve  altogether  fail  to  excite  visual 
sensations  in  the  brain,  and  which  we  may  speak  of  as  '  absolute ' 
blindness. 

Similar  but  less  striking  imperfections  of  the  other  senses  were  ob- 
served by  Goltz  as  attendant  on  removal  of  portions  of  the  cerebral 
hemispheres,  and  Munk  in  accordance  with  the  view  just  stated 
describes  a  psychical  deafness  and  psychical  failures  of  the  other 
senses. 

Bearing  in  mind  the  distinctions  just  raised  we  may  return  to  the 
question  of  localization.  Munk^  insists  on  the  existence  of  a  'visual 
area,'  seated  on  the  posterior  lobes  but  differing  in  position  from  and  of 
much  wider  extent  than  that  of  Ferrier.  He  maintains  not  only  that 
removal  of  this  area  causes  blindness,  without  necessarily  producing 
any  other  change  in  the  animal,  but  also  that  parts  of  this  area  corre- 
spond to  parts  of  the  retina,  extirpation  of  small  portions  of  the  area 
giving  rise  to  blindness  in  particular  parts  of  the  retina,  the  retina 
being  as  it  were  projected  on  to  the  cerebral  surface  so  that  a  partial 
loss  of  the  'visual  area'  gives  rise  to  a  functional  blind  spot,  so  to 
speak,  in  the  retina.  Thus  rn  the  dog  the  retinal  area  of  distinct  vision 
he  regards  as  connected  with  the  central  parts  of  the  visual  area  of  the 
brain  of  the  opposite  side,  while  the  external  (temporal)  parts  of  the 
retina  are  connected  with  the  external  parts  of  the  area  of  the  brain  of 
the  same  side,  the  internal  (nasal)  parts  with  the  internal  (median)  parts, 

*  Verhandl.  d.  physiol.  Gesell.  z.  Berlin,  1876-77,  Nos.  16,  17,  35  ;  1877-78' 
Nos.  9,  10;  1878-79,  4,  5,  18.  Archivf.  Anat.  u.  Pays.  (Phys.  Abth.),  1878, 
pp.  162,  547,  599.  2  Op.  cit. 


CHAP.    VI.J  TlIK   BRAIN.  649 

the  upper  parts  with  the  front,  and  the  lower  parts  with  the  hind  parts 
vi  the  area  of  the  opposite  side.  These  results  of  circumscribed 
'absolute'  blindness,  he  states,  are  accompanied  by  psychical  blind- 
ness, from  which  the  anim  il  may  recover  by  due  practice  and  ex- 
perience, provided  that  tlic  whole  visual  area  be  not  removed.  The  re- 
covery from  psychical  blindness  Munk  interprets  as  being  carried  out 
by  what  may  be  crudely  spoken  of  as  the  deposition  of  new  visual  ex- 
periences in  the  rest  of  the  visual  area.  In  analogy  with  this  visual 
area  he  describes  an  auditory  area  differing  again  from  that  of  Ferrier, 
and  he  regards  the  whole  front  part  of  the  brain  as  forming  a  large 
'sensory'  area,  in  which  he  distinguishes  separate  sensory  areas  (areas 
of  tactile  sense,  of  muscular  sense  and  general  sensibility)  for  the  fore 
limb,  the  hind  limb,  the  eye,  the  head,  the  neck,  &c. 

.Vbsolutely  opposed  to  Munk  s  results  are  those  of  Goltz.  This 
author  in  his  latest,  as  in  his  earlier  researches,  insists  most  strongly 
that  he  can  no  more  obtain  distinct  evidence  of  localisation  in  reference 
to  sensation  than  in  reference  to  movements.  When  in  a  dog  the 
lesions  are  slight  the  recovery  from  imperfections  of  vision,  of  the 
other  senses,  and  of  general  sensibility  which  follow  immediately  on 
the  operation  may  be  complete.  When  a  larger  portion  of  brain  is  re- 
moved the  peculiar  imperfections  discussed  above  be:ome  striking,  and 
the  so-called  psychical  blindness,  together  with  the  corresponding  im- 
perfections of  tlie  other  senses,  may  become  permanent.  When  still 
larger  portions  are  removed,  as  in  the  case  of  the  dog  from  which  the 
greater  part  of  both  hemispheres  are  removed,  vision  becomes  so  im- 
perfect that  though  the  animal  can  see,  since  he  avoids  obstacles  in  his 
path,  and  his  movements  are  obviously  guided  by  vision,  still  to  a 
superficial  observer  he  see  r.s  completely  blind  ;  a  match  may  be  struck 
just  before  his  face  without  his  taking  any  notice  of  it  though  his 
pupils  contract,  so  little  able  are  visual  impulses  to  produce  any  cere- 
bral reactions.  Similar" phenomena  were  witnessed  by  Goltz  with 
regard  to  the  other  senses.  In  all  cases  the  characters  of  the  result 
depended  on  the  extent  of  the  injury,  on  the  quantity  of  brain-substance 
removed,  and  not  on  the  locality  operated  on  ;  the  amount  of  amelio- 
ration of  the  so-called  psychical  blindness  possible  by  practice  and  ex- 
perience being  determined  partly  by  the  amount  of  damage  done  to 
vision  itself  and  partly  by  the  degree  to  which  the  general  intellect  of 
the  animal  had  been  impaired  by  the  operation.  Goltz  thinks  that 
perhaps  destruction  of  the  parietal  lobes  has  the  greater  effect  on 
tactile,  and  destruction  of  the  posterior  lobes  the  greater  effect  on 
visual  sensations,  but  he  can  find  no  well-marked  localized  areas.  The 
dog,  according  to  him,  from  which  a  l.irge  portion  of  the  cerebral  hemi- 
spheres has  been  removed  is  a  dog  reduced  to  idiocy  by  a  cutting  oft"  of 
the  higher  elaborations  of  all  the  sensory  impulses  which  reach  him, 
and  by  a  curtailing  of  his  general  psychical  activity  ;  and  he  is  brought 
to  this  condition  step  by  step,  as  more  and  more  of  his  cerebral 
substance  is  removed. 

Besides  the  experimental  evidence  just  discussed  we  have  also 
pathological  indications  of  the  connection  of  certain  movements 


650  CEREBRAL  CONVOLUTIONS.  [BOOK  III. 

with  a  particular  convolution.  The  condition  known  as  aphasia, 
using  that  word  in  its  general  sense,  including  its  several  varieties, 
as  meanincj  the  loss  of  articulate  speech,  is  so  often  associated  with 
disease  of  the  posterior  portion  of  the  third  frontal  convolution 
Fig. -70,  71  (9)  (10),  that  it  becomes  impossible  not  to  admit  ihat 
there  must  be  some  causal  connection  between  this  part  of  the 
brain  and  speech.  In  the  vast  majority  of  cases  the  disease  is  on 
the  left  side  of  the  brain  and  occurs  in  company  with  right 
hemiplegia,  but  cases  have  been  recorded  where  the  right  side  of 
the  brain  was  affected. 

Seeing  that  articulate  speech  is  a  thing  learned  by  use,  it  has  been 
suggested  that  in  most  persons  one  side  of  the  brain  only  has  been 
educated  for  this  purpose,  and  hence  that  one  side  only  of  the  brain 
is  employed  ;  that  we  are  in  fact  left-brained  in  respect  to  speech  in 
the  same  way  that  we  are  right-handed  in  respect  to  many  bodily 
movements  ;  and  this  view  is  apparently  supported  by  the  fact  that 
the  left  side  of  the  brain  is  on  the  whole  larger  and  more  convoluted 
than  the  right  side' ;  but  the  question  of  the  dual  action  of  the  two 
cerebral  hemispheres  is  too  dark  a  subject  to  enter  into  here. 

It  is  obvious  that  loss  of  speech  may  arise  from  a  variety  of 
causes.  It  may  be  due  to  simple  paralysis  of  the  hypoglossal,  and 
other  nerves  concerned  in  speech.  It  may  be  occasioned  by  an  im- 
perfection in  the  coordinating  mechanism  by  which  the  efferent 
impulses  are  marshalled  just  previous  to  their  exit  from  the  centra] 
nervous  system.  Or  it  may  be  caused  by  a  break  in  the  nervous 
chain  connecting  the  idea  of  the  word  with  this  coordinated  motor 
mechanism  of  expression.  Lastly,  the  fault  may  lie  in  the  generation 
of  the  idea  itself.  It  is  the  two  latter  forms  of  aphasia  which  appear 
to  be  connected  with  the  cerebral  convolution  spoken  of  above.  The 
cases  are  strikingly  parallel  to  that  of  the  dog  just  mentioned. 

Sec.  4.     The  Functions  of  other  Parts  of  the  Brain. 

Although  much  has  been  written,  and  many  experiments  per- 
formed, in  reference  to  the  various  parts  of  the  brain,  the  views 
which  have  thereby  been  worked  out  are  for  the  most  part 
neither  satisfactory  nor  consistent :  indeed,  the  proper  method  to 
study  the  brain  is  probably  to  trace  out  a  cerebral  operation 
along  its  chain  of  events  rather  than  to  seek  to  attach  readily 
definable  functions  to  the  cerebral  anatomical  components. 

A  fundamental  difficulty  meets  us  at  the  threshold  of  every  inquiry 
into  the  particular  function  of  any  part  of  the  brain.  When  an  organ, 
such  for  instance  as  the  corpus  striatum,  is  removed  by  the  knife,  or 
placed  hors  de  combat,  or  thrown  into  an  abnormal  condition  by  the 

'  This  statement  by  Gratiolet  has  however  been  opposed  by  Ecker  and  others  j 
but  cf.  Boyd  {Phil.  Trans.  1861,  p.  261). 


CHAP.    VI.]  TIIF.    BRAIN.  6$  I 

injection  of  corrosive  fluids,  or  by  haemorrhage,  or  by  other  patho- 
logic il  chan;j;c-;,  \vc  have  no  ri^ht  to  inter  tliat  the  negative  phenomena, 
loss  of  volition,  of  sensation,  iS:c.,  wliich  miko  their  appearance,  prove 
th.it  in  its  normal  co.idiiion  the  organ  in  question  is  a  seat  or  a  main 
tract  of  volition,  loss  of  sensation,  &c.  This  may  be  the  explanation 
of  tne  experiment  or  malady  ;  but  it  may  not.  Whatever  may  prove 
in  t'le  end  to  be  the  nature  of  nervous-  inhibition,  it  is  clear  that 
inhibitory  actions  are  imjjortant  factors  in  the  production  of  nervous 
I)hcnomena.  In  almost  every  instance  in  whi  "h  we  have  treated  of  a 
nervous  mechanism  we  have  had  to  deal  with  inhibition,  i.e.,  with  a 
nervous  action  interfering  with  another  nervous  action.  Indeed  the 
nervous  phenomena  of  the  heart,  of  the  vaso-motor  system,  of  the 
respiratory  centre  and  of  the  spinal  cord  generally  become  a  confused 
medley  if  we  refuse  to  admit  that  certain  effects  are  due  to  the  action 
of  one  part  of  a  nervous  mechanism  inhibiting  (or  conversely  in- 
creasing) the  actions  of  another  part.  But  if  this  be  the  case  in  such 
compiratively  simple  nervous  mechanisms,  we  have  every  reason  to 
expect  that  inhibitory  actions  play  a  distinguishe  1  part  in  the  operations 
of  the  far  more  complex  nervous  machinery  of  the  brain.  This  being 
granted,  it  is  obvious  that  any  interference,  by  experiment  or  disease, 
with  the  normal  working  of  the  brain,  may  act,  as  far  as  inhibition  is 
concerned,  in  two  different  ways.  In  the  first  place  the  interference 
may  place  hors  de  combat  a  part  of  the  brain  which  previously  was 
exerting  an  inhibitory  influence  on  another  perhaps  quite  distant  part, 
just  as  section  of  the  vagi  in  the  dog  relieves  the  heart  from  the  cardio- 
inhibitory  influences  of  the  medulla  oblongata  ;  and  the  part  of  the 
brain  thus  freed  from  its  wonted  restraint  may  fall  into  disorderly 
action.  Obviously  in  such  a  case  the  real  seat  of  the  disorder  is  in 
this  part  and  not  in  the  (distant)  inhibitory  part  directly  operated  on. 
In  the  second  place  the  interference  itself,  the  injury  to  the  nervous 
elements  caused  by  the  knife,  or  the  cautery,  or  by  the  seqyent  in- 
flammatory processes,  or  by  the  irritation  of  disease,  may  act  as  a 
stimulus  discharging  impulses  which  exert  an  inhibitory  influence  on 
it  may  be  distant  organs.  And  when  we  consider  the  delicacy  and 
activity  of  the  elements  of  the  central  nervous  system,  it  is  not  sur- 
prising that  the  effects  of  even  a  simple  incision  should  be  profound 
and  should  last  some  considerable  time.  Goltz  has  called  attention,  in 
this  respect,  to  the  effects  of  dividing  in  the  dog  the  spinal  cord  in  the 
dorsal  region.  Immediately  after  the  operation,  reflex  movements  in 
the  hand,  legs,  and  other  parts  connected  with  the  lumbar  cord  are 
entirely  absent,  and  their  absence  continues  for  a  considerable  period, 
the  dog  in  this  respect  presenting  a  marked  contrast  to  the  frog.  In 
time  however,  as  the  wound  in  the  spinal  cord  heals  up,  reflex  move- 
ments make  their  appeirance,  and  as  we  have  already  seen  (p.  606) 
are  abundant  and  manifold.  In  sudi  a  case  we  must  either  suppose 
that  in  the  normal  dog  the  reflex  movements  of  the  hind  limbs,  (Sec, 
require  for  their  development  the  presence  and  activity,  not  only  of 
the  lumbir  cord  but  also  of  parts  of  the  cerebro-spinal  axis  lying 
higher  up,  and  that  such  reflex  movements  as  do  eventually  appear 
after  section  of  the  dorsal  corrl  are  new  achievements  gradually  forced, 
so  to  speak,  on  the  lumbar  cord  in  consequence  of  its  isolated  position  ; 


652  CORPORA   STRIATA.  [BOOK   III. 

or  we  must  admit  that  the  section  of  the  dorsal  cord  has  produced  for 
the  time  being  a  profound  inhibitory  action  on  the  lumbar  cord  below. 
The  latter  view  is  as  much  in  consonance  with,  as  the  former  view  is 
opposed  to,  all  other  physiological  experience.  But  if  we  admit  the 
latter  view,  then  we  may  fairly  ask,  why  should  not  section  of,  or 
injury  to,  or  disease  of  parts  of  the  still  more  highly  organized  brain 
produce  similar  inhibitory  effects  in  other  parts  of  the  cerebral 
machinery?  If  however  we  admit  this,  it  follows  that  great  caution 
is  necessary  in  explaining  the  results  of  any  operation  on  the  brain. 
Difficulties  such  as  these  are  more  likely  to  occur  in  cases  of  disease 
than  even  in  those  of  operative  interference  ;  and  it  is  this  which 
renders  caution  so  necessary  in  the  physiological  handling  of  clinical 
facts  ^ 

We  may  therefore  be  permitted  to  summarise  very  briefly  what  is 
actually  known. 

Corpora  Striata  and  Optic  Thalami. 

The  preceding  discussions  enable  us  to  lay  down  two  broad 
propositions:  (i)  The  functions  of  the  cerebral  convolutions  are 
eminently  psychical  in  nature  ;  these  parts  of  the  brain  intervene, 
and  as  far  as  we  can  judge,  intervene  only,  in  those  operations  of 
the  nervous  system  in  which  an  intelligent  consciousness  and 
volition  play  a  part.  (2)  The  hinder  parts  of  the  brain,  viz.  the 
corpora  quadrigemina,  crura  cerebri,  pons  Varolii,  cerebellum,  and 
medulla  oblongata,  are  capable  by  themselves  of  carrying  into 
execution  complex  movements,  the  coordination  of  which  implies 
very  cojisiderable  elaboration  of  afferent  impulses  ;  they  can  do 
this  even  in  the  case  of  such  mammals  as  the  rabbit  and  the  rat, 
in  the  total  absence  of  the  cerebral  hemispheres,  corpora  striata, 
and  optic  thalami.  These  two  latter  bodies,  often  spoken  of  as 
'  the  basal  ganglia,'  are  undoubtedly  the  great  means  of  communi- 
cation between  the  cerebral  hemispheres  on  the  one  hand  and  the 
crura  cerebri  on  the  other.  Though  some  fibres  ^  do  pass  from  the 
crura  by  or  through  the  ganglia  to  the  cerebral  convolutions  with- 
out being  connected  with  the  nerve-cells  of  those  ganglia,  the 
great  mass  of  the  peduncular  fibres  are  probably  connected  with 
the  superficial  grey  matter  of  the  hemispheres  in  an  indirect  man- 
ner only,  the  lower  or  anterior  fibres  (cricsta)  passing  first  into  the 
corpora  striata,  and  the  upper  or  posterior  fibres  (tegmentum)  into 
the  optic  thalami.  This  anatomical  disposition  would  lead  us  to 
suppose  that  these  bodies  have  important  functions  in  mediating 
between  the  psychical  operations  of  the  cerebral  convolutions  on 

'  Cf.  Brown-Sequard,  Archives  de  Physiol.  IV.  (1877)  p.  409  et  seq. 
'^  Quain's  Anatomy,  8th  ed.  II.  555. 


CHAT.    VI.]  THE    BRAIN.  653 

the  one  hand,  and  tlie  sensori-motor  machinery  of  the  middle  and 
hind  l)Vain  on  the  other;  and  the  separate  courses  taken  by  the 
])eduncuhir  fibres  would  further  lead  us  to  expect  tiuit  the  functions 
of  the  corpora  striata  differ  fundamentally  from  those  of  the  optic 
thalami. 

When  in  the  human  subject  a  lesion  occurs  involving  both  these 
bodies,  on  one  side  of  the  brain,  the  result  is  a  loss  of  sensation 
in,  and  voluntary  power  over,  the  o{)posile  side  of  the  body  and 
face,  a  so-called  hemiplegia,  which  may  be  absolutely  complete 
without  any  impairment  whatever  of  the  intellectual  faculties. 
The  will  and  the  power  to  receive  impressions  are  present  in  their 
entirety,  but  neither  efferent  nor  afferent  impulses  can  make  their 
way  to  or  from  the  peripheral  organs  and  the  cerebral  convolutions. 
The  injury  to  the  basil  ganglia  blocks  the  way.  In  the  great  ma- 
jority of  cases,  the  anaesthesia  (or  loss  of  sensation)  and  akinesia 
(or  loss  of  movement)  are  absolutely  confined  to  the  opposite  side 
of  the  body  ;  and  the  cases  in  which  a  lesion  of  the  basil  ganglia 
of  one  side  of  the  brain  aftects  the  same  side  of  the  body  or  both 
sides,  must  be  regarded  as  exceptional,  and  explicable  as  the  re- 
sults of  the  action  of  one  side  of  the  brain  on  the  other  side  either 
of  the  brain  or  of  some  region  of  the  cerebrospinal  axis.  The 
results  of  experiments  on  animals  agree  entirely  with  the  general 
experience  of  pathologists,  that  lesions  of  the  corpora  striata  and 
optic  thalami  produce  their  effect  on  the  opposite  side  of  the  body. 
Whatever  be  the  view  taken  concerning  the  decussations  of  sensory 
antl  motor  impulses  in  the  spinal  cord,  it  must  be  admitted  thai 
both  kinds  of  impulses  cross  over  completely  somewhere  during 
their  transmission  to  and  from  the  basil  ganglia  and  the  peripheral 
organs. 

When  howe\er  we  have  admitted  that  these  bodies  act,  as  it 
were,  the  part  of  middlemen  between  the  cerebral  convolutions 
and  the  rest  of  the  brain,  we  have  gone  almost  as  far  as  facts  will 
sup[)ort  us.  We  are  not  at  present  in  a  position  to  state  dog- 
matically what  is  the  nature  of  the  mediation  which  either  body 
resj^ectively  eflfects.  A  very  tempting  hypothesis  is  one  which 
suggests  that  the  corpora  striata  are  concerned  in  the  downward 
transmission  and  elaboration  of  eft'erent  volitional  impulses,  and 
the  optic  thalami  in  a  similar  ujiward  transmission  and  elaboration 
of  afferent  sensory  impulses ;  and  there  are  many  facts  which  may 
be  urged  in  favour  of  this  view,  which  was  first  developed  and  ex- 
pounded by  Carpenter  and  Todd.  So  much  acceptance  indeed 
has  it  founil,  that  many  pathologists  regard  it  as  established,  and 
speak  confidently  of  the  corpora  striata  as  motor  and  the  optic 
thalami  as  sensory  ganglia.     A  careful  review  however  of  all  the 


6S4  CORPORA   STRIATA.  [BOOK   III. 

facts  leads  to  the  conclusion  that  this  division  of  functions  has  not 
yet  been  clearly  proved. 

The  pathological  evidence  in  this  case,  were  it  sharply  defined  and 
accordant,  would  be  of  unusual  value  ;  but  it  is  neither  the  one  nor 
the  other.  A  number  of  cases  indeed  may  be  cited  to  shew  not  only 
that  lesions  of  a  corpus  striatum  may  be  accompanied  by  akinesia 
without  anaesthesia,  but  that  lesions  of  an  optic  thalamus  may  cause 
anesthesia  without  actual  akinesia,  that  is  without  any  further  inter- 
ference with  the  execution  of  voluntary  movements  than  is  occasioned 
by  the  loss  of  the  coordinating  sensations.  Of  these  two  classes  of 
cases,  the  latter  is  the  more  valuable,  since  all  clinical  experience  shews 
that  any  lesion  more  readily  interferes  with  volitional  movements  than 
with  the  reception  of  sensory  impressions.  Convulsions  are  not 
common  when  the  lesions  are  confined  to  these  bodies ;  but  when 
witnessed  they  can  generally  be  referred  to  the  corpora  striata  rather 
than  to  the  optic  thalami ;  like  the  paralysis,  the  convulsions  are 
generally  limited  to  the  opposite  side  of  the  body,  though  feeble 
movements  may  occasionally  be  seen  on  the  same  side  as  well.  On 
the  other  hand,  numerous  cases  have  been  recorded  where  an  injury 
apparently  confined  to  one  corpus  striatum  has  had  as  part  of  its 
results  ansesthesia  of  the  opposite  side  of  the  body  ;  and  others  where 
disease  apparently  confined  to  an  optic  thalamus  has  caused  loss  of 
movement  as  well  as  of  sensation. 

Experiments  on  animals,  though  very  valuable  as  regards  the 
investigation  of  movements,  are  imperfect  means  of  studying  the 
phenomena  of  conscious  sensations.  We  have  already  seen  that 
crude  unelaborated  sensations  may  originate  in  an  animal  deprived  of 
its  cerebral  hemispheres  ;  and  it  becomes  a  matter  of  great  difficulty 
to  disentangle  the  evidences  of  these  primitive  sensations  from  those 
of  the  higher  psychical  perceptions.  Moreover  we  do  not,  at  present, 
at  all  know  to  what  an  extent  the  larger  development  of  the  cerebral 
hemispheres  in  man  has  infiuenced  the  ordinary  functions  of  the  other 
parts  of  the  brain.  It  may  be  that  important  functions  which  in  the 
rabbit  belong  to  the  middle  and  hind  brain  have,  in  man,  almost  dis- 
appeared in  order  to  make  these  structures  more  useful  servants  of  the 
cerebral  hemispheres.  It  may  be,  however,  that  the  greater  activity 
of  the  convolutions  has  simply  increased  the  ordinary  labours  of  the 
middle  and  hind  brain.  We  cannot  at  present  say  which  effect  has 
resulted  ;  but  meanwhile  great  caution  ought  to  be  exercised  in  drawing 
inferences  from  experiments  on  a  rabbit,  or  on  a  dog,  as  to  what  are 
the  functions  of  the  corresponding  parts  of  the  human  brain. 

Ferrier '  observed  that  when  the  corpora  striata  were  stimulated 
with  an  interrupted  current,  convulsive  movements  of  the  opposite  side 
of  the  body  took  place  ;  the  animal,  when  the  stimulus  was  powerful, 
being  thrown  into  complete  pleurosthotonus,  the  side  of  the  body 
opposite  to  the  side  of  the  brain  stimulated  being  forcibly  drawn  into 
an  arch  ;  the  localized  movements  observed  by  Burdon-Sandei'son 
(p.  644)  were  lost  in  the  general  convulsions  caused  by  the  galvanic 

'  Op.  cit. 


CHAP.    VI.]  TlIK    MKAIN.  655 

current  affecting  a  large  portion  of  the  organ.  When,  on  the  other 
hanti,  the  optic  liialami  were  similarly  stimulated,  no  sucli  convulsions 
were  observed.  On  this  point  CarviUc  and  Durct's'  observations  are 
'\^^  accordance  witli  those  of  Ferrier  ;  and  the  results,  as  far  as  they 
go,  appear  at  lirst  sight  to  be  in  accordance  with  the  theory  of  the 
CNclusivcly  motor  functions  of  the  corpora  striati,  and  the  exclusively 
sensory  functions  of  the  optic  thalami.  But  it  would  obviously  be 
rash  to  draw  any  such  con:lusion  directly  from  them,  since,  if  the 
optic  thalamus  is  concerned  in  the  transmission  and  elaboration  of 
i~cnsory  impulses,  the  ap|)!ication  of  tiie  galvanic  current  to  it  ought, 
by  discharging  a  number  of  sensory  impulses,  to  give  rise  to  move- 
ments of  some  kind  or  other,  and  not  to  be  characterized  by  the 
absence  of  all  effects.  Moreover  any  such  inference  is  opposed  by 
the  results  of  Nothnagel's-  experiments.  This  observer  destroyed  by 
injection  of  chromic  acid  both  nuclei  lenticulares  (the  extra-ventricular 
portions  of  the  corpora  striata)  of  the  rabbit,  with  the  result  of  bringing 
the  animal  aln.ost  exactly  into  the  same  condition  as  if  both  its 
cerebral  hemispheres  had  been  removed.  When,  on  the  other  hand, 
by  the  help  of  a  special  instrument,  he  succeedci  in  destroying  both 
optic  thalami  without  any  other  injury  to  the  brain,  no  obvious  effects 
followed  ;  there  were  no  signs  of  either  loss  of  volition  or  of  sensa- 
tion, nothing  in  fact  could  be  noticed  except  a  rather  peculiar  dis- 
position of  the  limbs.  When  the  nuclei  lenticulares  were  destroyed 
there  was  no  apparent  loss  of  sensation,  that  is  to  say  the  animal 
readily  moved  when  stimulated  by  pinching  the  skin,  &;c.  :  but  it  was 
impossible  to  tell  whether  sensory  impulses  reached  the  cerebral 
convolutions,  since  no  manifestations  whatever  of  the  condition  of  the 
convolutions  were  possible.  The  animal  might  have  felt  acutely,  and 
yet  have  been  unable,  from  the  loss  of  the  appropriate  motor  tracts,  to 
express  itself ;  or  it  might  have  been  as  incapable  of  the  higher 
psychical  feeling  as  it  was  of  executing  spontaneous  movements.  The 
phenomena  resulting  from  destruction  of  the  nuclei  lenticulares  admit 
of  no  clear  proof  in  either  direction.  The  fact,  however,  that  voluntary 
movements  continued  as  usual  after  complete  destruction  of  the  optic 
thalami  goes  far  to  prove  that,  in  the  rabbit  at  least,  these  bodies  are 
not  the  only  means  by  which  sensory  impulses  pass  to  the  cerebral 
convolutions.  Even  admitting  (and  indeed  in  the  case  of  man  we 
know  that  the  general  anaesthesia  following  upon  lesions  of  the  optic 
thalami  is  not  necessarily  accompanied  by  biininess  or  loss  of  any 
other  special  sense;  that  visual  and  other  specilic  impulses  still  reached 
the  rabbit's  convolutions  and  that,  in  consequence  of  the  coordinating 
mechanisms  of  the  hinder  brain  being  still  intact,  the  coordination  of 
the  animal's  movements  might  still  have  been  carried  out,  yet  the 
initiation,  and  hence  the  general  character  of  those  movements,  must 
have  been  influenced  by  the  total  absence  of  all  psychical  tactile  sen- 
sations. Apparently  however  this  was  not  the  case  :  the  movements 
did  not  in  any  way  betray  the  loss  of  any  factors. 

'  0/>.  ci/.     Ibid.  Hd.   sS  (1873),  p.  420;  Iki.  60  (1S74),  p.   129;  Bd.  62 
(1875),  P-  -O'- 
»  op.  cit. 


656  CORPORA   STRIATA.  [BOOK  III. 

Lussana  and  Lemoigne ',  who  regard  the  optic  thalami  as  motor 
centres  for  the  lateral  movements  of  the  antetior  limbs  (a  lesion  of 
one  optic  thalamus  paralysing  the  adduction  of  the  forelimb  of  the 
corresponding  and  the  abduction  of  that  of  the  opposite  side),  saw  no 
evidence  of  any  loss  of  general  sensibility  or  any  signs  of  pain  to 
result  from  injuries  to  these  bodies,  and  no  movements  to  result  from 
stimulation  of  other  than  their  deep  parts.  After  a  lesion  however  of 
the  optic  thalamus  of  one  side  they  invariably  found  blindness  in  the 
opposite  eye. 

Carville  and  Duret^  found  that  in  the  dog  section  of  the  internal 
capsule,  or  expansion  of  fibres  passing  between  the  nucleus  lenti- 
cularis  and  optic  thalamus,  in  the  anterior  part  of  its  course  where 
it  passes  between  the  nucleus  lenticularis  and  the  nucleus  caudatus,  led 
to  hemiplegic  loss  of  voluntary  movement  on  the  opposite  side,  though 
stimulation  of  the  paralysed  limb  still  gave  rise  to  reflex  movements. 
When  the  section  was  carried  through  the  posterior  part  of  the  ex- 
pansion, between  the  nucleus  lenticularis  and  optic  thalamus,  the  loss 
of  voluntary  movement  on  the  opposite  side  of  the  body  was  accom- 
panied by  loss  of  sensation,  i.e.  when  the  paralysed  limbs  were 
pinched,  no  responsive  reflex  movements  followed.  It  is  hazardous, 
however,  to  draw  from  these  experiments  any  positive  conclusions. 

Nothnagel  3  observed  that  in  the  rabbit  voluntary  movements  still 
persisted  after  destruction  of  both  nuclei  caudati  ;  in  this  respect  these 
portions  of  the  corpora  striata  presented  a  marked  contrast  to  the 
nuclei  lenticulares.  Nevertheless  destruction  of  one  nucleus  caudatus 
frequently  induced  a  certain  amount  of  paralysis  of  the  opposite  side 
of  the  body,  which  disappeared  after  removal  of  the  nucleus  caudatus 
of  the  other  side  ;  and  as  we  have  already  stated,  destruction  or  injury 
to  a  particular  part  of  the  nucleus  caudatus,  viz.  the  so-called  nodus 
cursorius,  gave  rise  to  remarkable  forced  movements,  which  made 
their  appearance  even  after  the  previous  removal  of  the  nuclei  lenti- 
culares. The  injection  of  chromic  acid  into  other  parts  of  the  nucleus 
caudatus  also  frequently  caused  for  a  while  forced  movements,  either 
straight  forward,  or  of  the  circus  kind,  which  differed  from  those 
witnessed  by  older  observers  in  operations  on  the  corpora  striata  after 
removal  of  the  hemispheres,  inasmuch  as  they  were  executed  by  an 
animal  still  possessing  intelligence,  and  frequently  striving  to  avoid 
obstacles. 

It  is  impossible  at  present  to  give  a  satisfactory  explanation  of  all 
these  varied  and  frequently  inconstant  phenomena,  but  it  may  be  worth 
while  to  return  again  to  the  possibility  of  considering  some  at  least  of 
the  phenomena  as  inhibitory  effects.  The  fact  that  the  paralysis, 
curvature  of  the  body,  and  the  circus  movements  resulting  from  lesion 
of  one  nucleus  caudatus  or  nucleus  lenticularis,  disappear  when  the 
same  body  on  the  other  side  is  removed,  warns  us  against  too  hastily 
assuming  that  a  loss  or  diminution  of  voluntary  power  means  nothing 
more  than  a  break  in  the  transmission  of  volitional  impulses  ;  it  may 

'  Fistologia  del  centri  aervosi  encefalici,  1871,  and  Archives  de  Physiologies 
IV.  {1877)  p.  119  et  seq.  ^  Op.  cit, 

'  Op.  cit. 


CHAl'.    VI.]  THE   BKAIN.  C57 

mean  that,  but  it  may  mean  also  the  development  of  nervous  actions 
having  inhibitory  etTects.  In  the  experiment  of  Carville  and  Duret 
quoted  above,  pinching  the  left  hind  limb  after  section  of  the  right 
internal  capsule  produced  no  reflex  action  whatever.  Now  it  is  absurd 
to  suppose  that  in  this  case  the  reflex  centre  was  removed,  or  any  part 
of  a  veritable  reflex  chain  broken,  because,  as  we  know,  pinching  the 
hind  limb  will  produce  a  reflex  movement,  provided  only  a  portion  of 
the  lumbar  cord  be  left  intact  and  functional.  There  must  in  this  case 
have  been  inhibition  of  the  lumbar  reflex  centres  ;  and  if  of  these, 
why  not  of  other  centres,  reflex  or  automatic  ? 

Corpora  Quadrigemina. 

We  have  already  seen  that  the  centre  of  coordination  for  the 
movements  of  the  eyeballs  (p.  566)  and  that  for  the  contraction  of 
the  pupil  (p.  520),  lie  in  the  neighbourhood  of  the  nates  or  an- 
terior tubercles  of  the  corpora  quadrigemina.  These  two  centres 
are  associated  together  in  such  a  way  that  when  the  eyeballs  are 
voluntarily  directed  inwards  and  downwards,  as  for  near  vision,  the 
pupils  are  at  the  same  time  contracted  ;  and  when  the  eyeballs  are 
directed  upwards,  and  return  to  parallelism,  the  pupils  are  dilated 
to  a  corresponding  extent ;  when  both  eyeballs  are  moved  to- 
gether sideways  the  pupils  remain  unchanged.  We  have  seen 
(p.  566)  that  the  various  movements  of  the  eyeballs  may  be  brought 
about  by  direct  stimulation  of  particular  parts  of  the  nates,  and  are 
then  also  accompanied  by  the  appropriate  changes  in  the  pupils. 
The  association  therefore  of  the  movements  of  the  pupil  and  of 
the  ocular  muscles  is  not  simply  psychical  in  nature  but  is  depen- 
dent on  the  close  connection  of  their  respective  centres.  From 
the  fact  of  the  movements  of  the  eyeball  and  pupil  being  so 
readily  and  variously  excited  by  stimulation  of  the  nates,  it  has 
been  inferred  that  the  centres  for  these  movements  lie  in  those 
bodies ' ;  it  would  appear  however  that  what  may  be  called  the 
real  or  immediate  centres  of  these  movements  lie  beneath  the  cor- 
pora quadrigemina,  in  the  front  part  of  the  floor  of  the  aqueduct  of 
Sylvius,  and  therefore  are  affected  in  an  indirect  manner  only  when 
the  corpora  quadrigemina  are  stimulated. 

The  more  exact  determination  by  Hensen  and  Voelkers  of  the 
topography  of  the  centres  for  the  movements  of  the  eyeball  and  pupil 
(see  p.  524)  explains  the  results  of  Knoll  who  found,  in  opposition  to 
Flourens,  Budge,  and  others,  that  reflex  contraction  of  the  pupils 
remained  even  after  removal  of  the  corpora  quadrigemina,  and  helps 
to  clear  up  the  discrepancy  between  Adamuk*  and  Knoll  as  to  dilation 
of  pupil  being  produced  by  stimulation  of  the  testes  or  of  the  nates. 

'  Adamuk,  Cbt.  med.  Wiss.  1870,  p.  65.  '  Op.  cit. 

F.  P.  42 


658  CORPORA  QUADRIGEMINA.  [BOOK   III. 

Hensen  and  Voelkers  found  their  experiments  untrustworthy  so  long 
as  they  merely  stimulated  the  corpora  quadrigemina  ;  it  was  not  until 
they  divided  these  bodies  and  stimulated  the  underlying  parts  that 
their  results  became  uniform. 

Flourens  observed  that  unilateral  extirpation  of  the  corpora 
quadrigemina  in  mammals  or  of  the  optic  lobes  in  birds  produced 
blindness  in  the  opposite  eye  ;  and  the  same  result  has  been  gained 
by  many  subsequent  observers".  We  have  seen  moreover  that 
both  frogs,  birds,  and  mammals  continue  to  receive  and  within 
limits  to  react  upon  visual  impressions  after  the  total  removal  of 
the  cerebral  hemispheres.  From  these  facts  we  infer  that  visual 
sensory  impulses  become  transformed  into  visual  sensations  in  the 
corpora  quadrigemina  ;  or,  in  other  words,  that  these  nervous 
structures  are  centres  of  sight.  Bat  they  are  so  in  a  limited  sense 
only.  We  have  seen  that  destruction  or  injury  of  the  cerebral 
hemispheres  profoundly  affects  vision.  In  the  absence  of  the 
cerebral  convolutions,  a  crude  vision,  devoid  of  distinct  visual 
perceptions,  is  probably  all  that  is  possible.  The  processes  con- 
stituting distinct  and  perfect  vision,  in  fact,  begin  in  the  retina, 
and  are  partially  elaborated  in  the  corpora  quadrigemina,  possibly 
in  the  optic  thalamic,  but  do  not  become  completely  developed 
until  the  cerebral  convolutions  have  been  called  into  operation. 

In  those  animals  {ex.  gr.  rabbits)  in  which  unilateral  destruction  of 
the  corpora  quadrigemina  entails  blindness  of  the  opposite  eye,  and 
yet  does  not  affect  at  all  the  visual  sensory  impulses  originating  in  the 
eye  of  the  same  side,  it  is  obvious  that  a  complete  decussation  of  the 
sensory  impulses  must  take  place  before  the  centre  is  reached. 

The  question  however  whether  decussation  of  fibres  (and  con- 
sequently of  impulses)  in  the  optic  chiasma  is  complete  or  incomplete, 
whether  the  optic  tract  of  one  side  is  the  continuation  of  all  the  fibres 
in  the  optic  nerve  of  the  opposite  side  or  whether  it  is  composed  of 
representatives  of  the  optic  nerves  of  both  sides,  is  one  which  has 
been  much  debated,  both  from  an  anatomical  and  a  physiological 
standpoint.  As  regards  mammals,  the  results  of  experiment  and 
observation  differ  according  to  the  animal  employed  3.  In  the  rabbit, 
the  decussation  appears  to  be  complete ;  destruction  of  the  corpora 
quadrigemina  on  one  side  causes  degeneration  of  the  opposite  optic 
nerve  but  not  at  all  of  that  of  the  same  side,  and  removal  of  one  retina 
degeneration  of  the  opposite  optic  tract  but  not  at  all  of  that  of  the 
same  side,  while   longitudinal  section  of  the   chiasma  causes  total 

'  McKendrick,  Trans.  Roy.  Soc.  Ed.,  1873. 

*  Lussana  and  Lemoigne,  op.  cit. 

3  Biesiadecki,  Moleschott's  Untersiuh.  viii.  (1862)  156.  Mandelstamm,  Cbt. 
med.  Wiss.  i^T^,  p.  339;  and  Archiv  fiir  Opthalmol.  XIX.  (1873)  p.  39. 
Gudden,  Archiv  f.  Opthalmol.  XX.  (1874)  p.  249.  Michel,  ibid.  xix.  (1873) 
p.  29—37.5- 


ClIAI".    VI.J  THE   BRAIN,  659 

blindness.  In  the  dog,  destruction  of  one  retina  gives  rise  to  strands 
of  degeneration  in  both  optic  tracts',  and  Nicati'  has  in  the  cat 
suceedcd  in  dividing  the  chiasina  without  destroying  vision  ;  from 
which  it  is  interred  that  in  these  animals  the  decussation  is  incomplete. 
Munk's  experiments  (see  p.  648)  arc  aUo  in  favour  of  an  incomplete 
decussation  in  the  dog,  since  destruction  of  the  visual  area  on  one 
side  interferes  with  the  si;^'ht  of  both  eyes.  In  man  Mandelsiamm  ^ 
has  argued  from  the  various  forms  of  hemiopia  (in  which  portions 
only  of  the  retinae  are  insensible  to  light),  that  the  decussation  is  com- 
plete ;  but  the  concurrence  of  hemiopia  in  both  eyes  with  heinianthcsia, 
or  hemiplegia,  and  other  symptoms  indicating  disease  of  one  side  of 
the  brain  only,  has  generally,  though  not  periiaps  conclusively,  been 
held  to  prove  that  in  man  the  decussation  is  incomplete  ;  and  Gowers* 
quotes  a  case  where  hemiopia  of  both  sides  resulted  from  disease 
limited  to  one  optic  tract,  and  brings  other  evidence  in  favour  of  the 
view  that  the  decussation  is  incomplete. 

Flourens  and  subsequent  observers  noticed  that  injury  or 
removal  of  the  corpora  quadrigeminaon  one  side  frequently  caused 
forced  movements,  and  that  removal  of  the  whole  mass  led  to 
great  want  of  cordination.  These  results  are  quite  in  harmony 
with  the  f.xct  mentioned  above  (p.  635)  concerning  the  coordi- 
nating functions  of  the  optic  lobes  in  frogs.  But  at  present  we 
have  no  exact  knowledge  concerning  the  nature  of  the  coordina- 
tion, and  what  relations  are  borne  in  this  respect  by  the  corpora 
quadrigemina  to  the  cerebellum,  crura  cerebri,  and  pons  Varolii. 

Flourens  in  many  cases  entirely  removed  the  corpora  bigemina 
from  birds  without  any  incoordination  or  disturbance  of  movements 
resulting,  though  they  were  seen  by  McKendrick  in  pigeons  and  by 
Ferrier  in  rabbits  and  monkeys.  It  has  been  urged  however  by  many 
(Schiff)  th.it  when  such  phenomena  do  occur  after  removal  of  the 
corpora  quadrigemina,  they  are  the  result  of  coincident  injury  to  the 
underlying  crura  cerebri.  .Adamuk  ^  observed  in  rabbits  that  galvanic 
stimulation  of  the  posterior  tubercles,  in  contrast  to  the  anterior 
tubercles,  produced  movements  of  the  animal,  though  Knoll  observed 
no  such  efl'ect.  Ferrier '  saw  various  movements  follow  upon  stimu- 
lation of  the  surface  of  the  corpora  quadrigemina  with  the  interrupted 
current.  Flourens  found  that  while  mechanical  stimulation  of  the 
surface  of  these  bodies  produced  no  effe:t,  deep  puncture  caused 
various  movements,  which  he  attributed  to  stimulation  of  the  crura 
cerebri  beneath.  This  suggests  that  the  movements  caused  by  galvanic 
stimulation  are  due  to  escape  of  current,  and  we  here  meet  with  the 
same  difficulty  that  was  experienced  in  dealing  with  the  cerebral 
convolutions.  Ferrier  states  that  with  even  a  moderately  strong 
current  the  movements  may  be  so  violent  as  to  merge  into  a  gencr«il 

'  Gudden,  op.  cit.  ■♦  Archives  de  Physwloa;.  v.  1878,  p.  658. 

•  Op.  cU.  s  Cbt.f.  med.  VViss.  (187S)  p.  562. 

»  O/.  cU.  *  Op.  cit. 

42 — 2 


66o  CEREBELLUM.  [BOOK   III. 

opisthotonus.  He  also  observed  that  stimulation  of  the  posterior 
tubercles  was  followed  by  marked  and  distinct  cries,  affording  a  curious 
parallel  to  the  croaking  produced  by  reflex  stimulation  in  frogs,  the 
seat  of  which  is  in  the  optic  lobes.  Lussana  and  Lemoigne^  also 
observed  a  cry  invariably  to  follow  upon  section  of  the  corpora  quad- 
rigemina-  and  superior  peduncles  of  the  cerebellum  (processus  cerebelli 
ad  testes),  though  no  loss  of  sensibility  could  be  detected  as  resulting 
from  the  operation.  These  observers  assert  that  section  of  the 
superior  peduncles  paralyses  the  muscles  of  the  trunk  of  the  opposite 
side  and  thus  leads  to  the  vertebral  column  being  arched  towards  the 
same  side,  and  to  '  circus '  movements.  According  to  Valentin,  Budge, 
and  others,  stimulation  of  the  corpora  quadrigemina,  or  of  the  optic 
lobes,  produces  movements  in  the  oesophagus,  stomach,  and  other 
parts  of  the  alimentary  canal,  and  in  the  urinary  bladder.  In  such 
cases  the  stimulation  must  have  an  indirect  effect  on  the  centres  of  the 
above  movements,  which,  as  we  have  seen,  are  situate  in  the  medulla 
and  lumbar  cord  respectively.  Danilewsky,  junr.  ^  and  Ferrier  have 
observed  changes  in  the  blood-pressure  and  respiration  follow  upon 
stim.ulation  of  the  corpora  quadrigemina,  as  of  other  parts  of  the 
brain.  Martin  and  Booker  ^  find  in  the  frog  in  the  optic  lobes  and  in 
the  rabbit  beneath  the  posterior  corpora  quadrigemina,  close  to  the 
aqueduct  of  Sylvius,  a  respiration-regulating  centre,  stimulation  of 
which  accelerates  inspiration  and  diminishes  or  inhibits  expiration. 

Cerebellum. 

We  have  already  referred  to  the  cerebellum  as  being  probably 
concerned  in  the  coordination  of  movements.  Flourens  observed 
that  when  a  small  portion  of  the  cerebellum  was  removed  from 
a  pigeon,  the  animal's  gait  became  unsteady ;  when  larger  portions 
were  taken  away  its  movements  became  much  more  disorderly, 
and  when  the  whole  of  the  organ  was  removal  an  almost  total  loss 
of  coordination  supervened.  Other  observers  have  obtained  similar 
results  in  other  animals ;  and  it  has  in  general  been  found  that 
lateral  or  unsymmetrical  lesions  and  incisions  produce  a  greater 
effect  than  those  which  are  median  or  symmetrical.  Section  of  the 
middle  peduncle  on  one  side  almost  invariably  gives  rise  to  a 
forced  movement,  the  animal  rolling  rapidly  round  its  own  longi- 
tudinal axis ;  the  rotation  is  generally  though  not  always  towards 
the  side  operated  on  ;  and  is-  accompanied  by  nystagmus,  i.e.  by 
peculiar  rolling  movements  of  the  eyes  suggestive  of  vertigo ; 
frequently  one  eye  is  moved  in  one  direction,  ex.  gr.  inwards  and 
downwards,  and  the  other  in  a  different  or  opposite  direction, 
ex.  gr.  outwards  and  upwards.  The  clinical  evidence  is  discordant, 
for  though  unsteadiness  of  gait  has  been  frequently  witnessed  in 

'  Op.  cit.  ^  Pfluger's  Archiv  (1875),  p.  128. 

3  Journ,  Physiol.  I.  (1878)  p.  370. 


CHAP.    VI.]  THE  BRAIN.  66l 

cases  of  cerebellar  disease,  many  histories  have  been  recorded  in 
which  e.xtensive  disease,  amounting  at  times  to  almost  complete 
destruction,  of  the  cerebellum  has  existed  without  any  obvious 
disturbance  of  the  coorilination  of  movements.  Still  the  experi- 
mental evidence  is  so  strong,  that  we  must  consider  the  cerebellum 
as  an  important  organ  of  coordination,  though  we  are  unable  at 
present  to  define  its  functions  more  exactly.  It  is  probable,  but 
not  proved,  that  its  functions  are  especially  connected  with  the 
afferent  impulses  proceeding  from  the  semicircular  canals. 

Observers  are  not  agreed  as  to  how  far  the  loss  of  coordination 
which  follows  upon  lesion  or  removal  of  part  of  the  cerebellum  is  tem- 
porary or  permanent.  Flourcns  found  that,  when  the  portion  removed 
was  small,  the  disorderly  movements  which  at  first  appeared  eventu- 
ally vanished,  but  when  a  large  portion  was  removed  the  loss  of 
coordination  became  permanent.  These  results  are  capable  of  inter- 
pretation on  the  view  that  the  coordinating  mechanisms  are  situated 
in  the  deeper  stru  tares,  and  hence,  while  completely  removed  by  the 
deeper  incisions,  are  only  temporarily  paralysed  by  the  shock  of  the 
slighter  operations.  Hitzig  and  Ferrier  find  that  injury  to  or  removal 
of  the  lateral  lobe  produces  the  same  forced  movements  as  section  of 
the  middle  peduncle.  Flourens  and  others  have  observed  that,  while 
lateral  injury  gave  rise  to  lateral  movements,  injury  to  the  anterior  or 
posterior  median  portions  caused  the  animal  to  fall  forwards  and  back- 
wards respectively.  Nothnagel'  has  been  led  from  his  experiments  on 
rabbits  to  the  conclusion  that  the  lesions  which  determine  a  loss  of  co- 
ordination are  those  which  result  in  a  solution  of  continuity  in  the 
structures  uniting  the  two  sides  of  the  organ,  the  mere  loss  of  lateral 
parts,  even  amounting  to  an  entire  half,  having,  according  to  him,  no 
such  effect.  Ferrier  finds  that  stimulation  of  the  cerebellar  surface  by 
the  interrupted  current  causes  in  monkeys,  dogs,  and  cats,  movements 
of  both  eyes  with  associated  movements  of  the  head  and  limbs,  and  to 
a  certain  extent  of  the  pupils.  The  eyes  moved  horizontally  or  verti- 
cally or  obliquely,  symmetrically  or  unsymmetrically,  with  or  without 
rotation,  according  as  the  electrodes  were  applied  to  one  or  other 
portioa  of  the  surface.  In  fact  the  results  were  to  a  certain  extent 
similar  to  those  obtained  by  .Adamuk  on  stimulating  the  corpora  quad- 
rigemina,  but  they  cannot  be  wholly  explained  as  simply  due  to  escape 
of  current,  if,  as  Hitzig-  asserts,  very  similar  phenomena  may  be 
witnessed,  not  only  with  weaker  currents,  but  even  on  mechanical 
stimulation^. 

Nothnagel  ■•  also  finds  that  mechanical  stimulation  of  even  the  surface 
of  the  cerebellum  gives  rise,  without  signs  of  pain  being  felt,  to  move- 
ments chiefly  of  the  trunk  an  1  extremities  and  of  those  muscles  which 
are  govcrne  1  by  the  facial,  hypoglosvd,  and  fifth  nerves.  These  move- 
ments, which  are  developed  somewhat  slowly,  manifest  themselves  first 

'  Virchow's  Archiv,  Bel.  6S  {1876)  p.  33.  ="  Op.  cit. 

3  Cf.  however  Schwahn,  Eckhard's  Beitrligc,  viii.  (1878)  p.  149. 

«  Op.  cit. 


662  CEREBELLUM.  [BOOK    IIL 

on  the  side  operated  on,  and  then  ceasing  on  that  side  make  their 
ajjpearance  on  the  opposite  side. 

Lastly  we  may  observe  that  Flechsig  (see  p.  619)  on  anatomical 
grounds  connects  a  definite  portion  of  the  lateral  columns  of  the  spinal 
cord  with  the  cerebellum. 

Purkinje  observed  long  ago,  that  when  a  constant  current  of 
sufficient  strength  was  sent  through  the  head  from  ear  to  ear,  a  feeling 
of  giddiness  was  experienced  ;  external  objects  appearing  to  rotate  in 
the  direction  of  the  current,  from  right  to  left  for  instance  when  the 
anode  was  placed  at  the  right  ear,  while  at  the  same  time  the  subject 
himself  leant  towards  the  anode.  Hitzig'  has  more  fully  investigated 
and  described  the  phenomena.  When  the  current  is  sufficiently  strong, 
remarkable  movements  of  the  eyes  are  seen  to  take  place  on  the  cur- 
rent being  made  ;  these  are  varied,  and  partake  somewhat  of  the  nature 
of  nystagmus.  They  consist  of  a  rapid  snatching  movement  in  the 
direction  of  the  current,  and  a  slower  return  in  the  contrary  direction, 
the  eyes  oscillating  between  the  two.  Sometimes  the  two  eyes  move 
together,  sometimes  they  are  dissociated.  That  neither  the  feeling  of 
vertigo  nor  the  movements  of  the  body  are  dependent  on  abnormal 
visual  sensations  caused  by  the  ocular  movements,  is  shewn  by  the  fact 
that  they  occur  when  the  eyes  are  shut,  and  also  in  blind  people ;  and 
indeed  the  feeling  of  vertigo  may  be  induced  by  a  current  too  feeble  to 
cause  any  abnormal  movements  of  the  eyeballs.  The  application  of 
the  current  when  the  eyes  are  shut  gives  rise  to  a  sensation  similar  to 
that  of  sitting  or  standing  in  a  carriage  which  is  being  turned  over  in 
the  direction  of  the  current,  from  right  to  left  when  the  anode  is  placed 
at  the  right  ear.  When  the  current  is  broken,  there  is  rebound  of  the 
phenomena  in  an  opposite  direction.  The  person  now  leans  towards 
the  kathode,  and  external  objects  seem  to  revolve  from  the  kathode  to 
the  anode.  All  these  phenomena  are  best  explained  by  supposing  that 
the  current  interferes  with  the  cerebral  coordinating  mechanism,  from 
which  i-esult,  as  efferent  effects,  the  compensating  movements  of  the 
body  and  of  the  eyes,  the  change  in  the  mechanism  at  the  same  time 
so  affecting  consciousness  as  to  produce  a  feeling  of  vei'tigo.  Whether 
they  are  due  to  an  anelectrotonic  and  katelectrotonic  condition  of  the 
ampullar  fibres  of  the  respective  auditory  nerves,  or  are  caused  by  the 
action  of  the  current  on  cerebellar  or  other  structures,  must  be  left  for 
the  present  undecided. 

Attempts  have  been  made  to  connect  the  cerebellum  with  the 
sexual  functions  ;  but  there  is  no  satisfactory  evidence  of  any  such 
relation.  As  we  shall  see  later  on,  the  nervous  centres  connected 
with  the  sexual  and  generative  organs  are  seated,  in  the  case  of 
dogs  at  least  and  probably  of  all  animals,  in  the  lumbar  spinal 
cord ;  and  all  or  nearly  all  sexual  phenomena  may  be  witnessed  in 
animals,  the  lumbar  spinal  cords  of  which  have  been  isolated  by 
section  from  the  rest  of  the  cerebro-spinal  system.  Galvanic 
stimulation  of  the  cerebellum  produces  no  change  in  the  generative 
'  Op.  cit.  =  Op.  cit. 


CHAP.   VI  ]  THE  BRAIN.  663 

organs,  and  when  erection  of  the  penis  is  caused  by  emotions, 
the  tract  connecting  the  cerebral  convolutions  with  the  erectiqji- 
centre  in  the  spinal  cord  passes  straight  along  the  crura  cerebri 
and  medulla,  for  Eckhard  *  has  observed  that  stimulation  of  these 
parts  in  the  dog  will  produce  erection. 

Eckhard  has  brought  forward  facts  to  shew  that  lesions  of  certain 
parts  of  the  cerebellum,  li.>.e  those  of  certain  parts  of  the  medulla 
oblongata,  cause  either  diabetes  or  simple  hydruria. 

According  to  Budge,  stimulation  of  the  cerebellum  produces  peri- 
staltic movements  in  the  oesophagus  and  stomach  ;  and  Schiff  observed 
inflammation  of  the  intestine  with  haemorrhage  after  lesions  of  the 
peduncles  of  the  cerebellum. 

Crara  Cerebri  and  Pons   Varolii. 

Though  from  the  grey  matter  abundant  in  both  these  organs  we 
may  infer  that  they  possess  important  functions,  we  hardly  know 
more  concerning  them  than  that  the  former  ser\-e  as  the  great 
means  of  communication  between  the  spinal  cord  and  the  higher 
parts  of  the  brain,  and  that  both  are  intimately  connected  with 
the  coordination  of  movements,  since  either  forced  or  disorderly 
movements  are  the  frequent  results  of  section  of  eit-her  of  them ; 
and  as  we  have  seen,  the  possession  of  these  parts,  in  the  absence 
of  the  cerebral  hemispheres,  and  even  of  the  corpora  striata  and 
optic  thalami,  is  sufficient  to  carrj-  out  the  most  complex  bodily 
movements. 

Since  the  paralysis  of  the  face  seen  in  cases  of  hemiplegia  from 
disease  of  the  corpus  striatum  is  on  the  same  side  as  that  of  the 
body,  it  follows  that  the  impulses  proceeding  along  the  cranial 
nerves  cross  over  like  those  of  the  spinal  nerves.  Hence  when 
paralysis  of  the  face  occurs  on  the  opposite  side  to  that  of  the 
body,  it  may  be  inferred  that  the  injury  or  disease  has  affected  the 
cranial  nerve  (or  nerves)  in  a  part  of  its  course  before  decussation 
has  taken  place ;  and  pathological  observations  support  this  view, 
unilateral  disease  or  injury  of  the  pons  Varolii  not  unfrequently 
involving  the  facial  nerye  of  the  same  side  in  its  comparatively 
superficial  course,  and  so  causing  paralysis  of  the  muscles  of  the 
same  side  of  the  face  as  the  disease,  dnd  the  opposite  side  to  the 
paralysis  of  the  limbs.  It  is  probable  that  the  decussation  which 
we  have  seen  to  begin  in  the  spinal  cord,  is  gradually  completed 
as  the  impulses  pass  through  the  medulla  and  pons  Varolii*. 
Against  the  view  of  those  who  maintain  that  volitional  impulses 

'  Beitrd^e,  Vll.  (1S73)  p.  67. 

»  Cf.  Balighian.     Eckhard's  Beitrd^e,  viil.  (187S)  p.  193. 


664  MEDULLA   OBLONGATA.  [BOOK   III. 

cross  suddenly  and  completely  at  the  decussation  of  the  pyramids, 
may  be  urged  the  fact  that  a  longitudinal  section  through  the 
decussation  does  not  entail  loss  of  voluntary  movements  on  both 
sides  of  the  body,  as  it  ought  to  do  if  the  volitional  impulses 
crossed  completely  at  this  spot.  Moreover,  according  to  Vulpian, 
the  loss  of  voluntary  movement  which  follows  upon  a  unilateral 
section  of  the  medulla  is  not  confined  entirely  to  one  side  of  the 
body. 

Medulla  Oblongata. 

We  have  so  often  spoken  of  this  link  between  the  brain  and 
the  spinal  cord,  that  it  is  hardly  necessary  here  to  do  more  than 
recall  the  fact,  that  the  majority  of  the  'centres'  for  various 
organic  functions  are  situated  in  it. 

These  we  may  briefly  recapitulate  as  follows  :  i.  The  respira- 
tory centre  (p.  369),  with  its  neighbouring  convulsive  centre  (p. 
388).  2.  The  vaso-motor  centre  (p.  219).  3.  The  cardio-inhibi- 
tory  centre  (p.  193).  4.  The  diabetic  centre,  or  centre  for  the 
production  of  artificial  diabetes  (p.  433).  5.  The  centre  for  deglu- 
tition (p.  294).  6.  The  centre  for  the  movements  of  the  oesopha- 
gus and  stomach  (p.  299)  with  its  allied  vomiting  centre  (p.  306). 
7.  The  centre  for  reflex  excitation  of  the  secretion  of  the  saliva 
(p.  266),  with  which  may  be  associated  the  centre  through  which 
the  vagus  influences  the  secretion  of  pancreatic  juice  (p.  279),  and 
possibly  of  the  other  digestive  juices. 

In  the  frog,  as  we  have  urged,  p.  624,  the  medulla  is  undoubt- 
edly largely  concerned  in  the  coordination  of  movements,  and  it 
is  exceedingly  probable  that  in  the  mammal  also  a  considerable 
portion  of  work  of  this  kind  falls  to  its  lot. 

In  conclusion,  we  may  call  attention  to  the  fact,  that  of  the 
whole  brain  certain  parts  respond  easily,  by  various  movements  in 
different  parts  of  the  body,  to  mechanical  or  other  stimuli  applied 
directly  to  them,  while  others  will  not.  The  former  are  conse- 
quently spoken  of  as  sensitive,  and  together  form  what  has  been 
called  an  excito-motor  centre;  they  are. the  (deep  parts  of)  the 
corpora  quadrigemina,  the  crura  cerebri,  the  pons  Varolii,  the  (deep 
parts  of)  the  cerebellum,  and  the  medulla.  The  latter  are  spoken 
of  as  insensitive  ;  they  are  the  cerebral  hemispheres  together  with 
the  corpora  striata  and  optic  thalami  (and  the  superficial  portions 
of  the  cerebellum  and  corpora  quadrigemina).  In  view  of  the 
results  obtained  by  electrical  stimulation  of  the  cerebral  convolu- 
tions and  other  parts,  this  distinction  cannot  however  be  regarded 
as  important 


CHAP.    VI.l  THE    BRAIN.  66^ 


Sec.  5.    On  the  R.apidity  of  Cerebral  Operations. 

Wc  have  already  seen  (p.  608)  that  a  considerable  time  is  taken  up 
in  a  purely  rctlcx  act,  such  as  that  of  winking,  though  this  is  perhaps 
the  most  rapid  form  of  rcllcx  movement.  When  the  movement  which  is 
executed  in  response  to  a  stimulus  involves  mental  operations  a  still 
longer  time  is  needed  ;  and  the  interval  between  the  application  of  the 
stimulus  and  the  commencement  of  the  muscular  contraction  varies 
according  to  the  nature  of  the  mental  labour  involved. 

The  simplest  case  is  that  in  which  a  person  makes  a  signal  imme- 
diately that  he  perceives  a  stimulus,  tx.  t^r.  closes  or  opens  a  galvanic 
circuit  the;  moment  that  he  feels  an  induction  shock  applied  to  the 
skin,  or  sees  a  flash  of  light,  or  hears  a  sound.  By  arrangements 
similar  to  those  employed  in  mea^,uring  the  velocity  of  nervous  im- 
pulses, the  moment  of  the  application  of  the  stimulus  and  the  moment 
of  the  making  of  the  signal  are  both  recorded  on  the  same  travelling 
surface,  and  the  interval  between  them  is  carefully  measured.  This 
interval,  which  has  been  called  by  Exner  '  the  reaction  period,'  con- 
sists of  three  portions  ;  (i)  the  passage  of  afferent  impulses  from 
the  peripheral  sensory  organ  to  the  central  nervous  system,  includ- 
ing the  possible  latent  period  of  the  generation  of  the  impulses  in  the 
sensory  organ,  (2)  the  transformation,  by  the  operations  of  the  central 
nervous  system,  of  the  afferent  into  efferent  impulses,  and  (3)  the 
pass.age  of  the  efferent  impulses  to  the  muscles,  including  the  latent 
period  of  the  muscular  contractions.  If  the  time  required  for  the  first 
and  third  of  these  events  be  deducted  from  the  whole,  the  'reduced 
reaction  period,'  as  it  may  be  called,  gives  the  time  taken  up  exclusively 
by  the  operations  going  on  in  the  central  nervous  system. 

The  reaction  period,  both  reduced  and  unreduced,  varies  according 
to  the  nature  and  disposition  of  the  peripheral  organs  stimulated.  The 
reaction  period  of  vision  has  long  been  known  to  astronomers.  It  was 
early  found  that  when  two  observers  were  watching  the  appearance  of 
the  same  star,  a  considerable  discrepancy  existed  between  their  respec- 
tive reaction  periods  ;  and  that  the  difference,  forming  the  basis  of  the 
so-called  '  personal  equation,'  varied  from  time  to  time  according  to  the 
personal  conditions  of  the  observers.  Thus  the  difference  between  the 
celebrated  astronomers  Struve  and  Bessel  varied  between  the  years 
1 8 14  and  1834.  from  "04  to  ro2  sec.,  the  reaction  period  of  Struve  being 
so  much  longer  than  that  of  Bessel.  These  figures,  however,  are  not 
to  be  compared  with  those  which  will  be  given  immediately,  inas- 
much as  several  complications  were  introduced  by  the  method  of 
observation. 

Lxner'  has  carefully  determined  the  reaction  period  of  himself  and 
others  with  different  stimuli,  and  under  various  circumstances.  When 
the  stimulus  was  an  induction  shock  thrown  into  the  skin  of  the  left 
hand,  the  signal  being  made  with  the  right  hand,  the  reaction  period 
varied  from  '1337  sec.  in  Exner  himself  to  '3576,  or  even  to  '9952,  in  an 
obtuse  individual.     When  the  stimulus  was  applied  in  dificrcnt  ways, 

'  Pfliigei-'s  Archiv,  vil.  (1873)  P-  ^oi. 


666        RAPIDITY   OF   CEREBRAL   OPERATIONS.      [BOOK    III. 

the  signal  always  being  made  with  the  right  hand,  the  results  in  Exner's 
own  case  were  as  follows  : 

Direct  electrical  stimulation  of  the  retina 'ii39 

Electric  shock  on  the  left  hand "1283 

Sudden  noise '1360 

Electric  shock  on  the  forehead "1374 

„  „      on  the  right  hand "1390 

Visual  impression  from  an  electric  spark •1506 

Electric  shock  on  the  toe  of  the  left  foot '1749 

Hence  tactile  sensations,  produced  by  the  stimulus  of  an  electric 
shock  applied  to  the  skin,  are  followed  by  a  shorter  reaction  period 
than  are  auditory  sensations  ;  but  the  period  of  these  is  in  turn  shorter 
than  that  of  visual  sensations  produced  by  luminous  objects,  though 
the  shortest  period  is  that  of  visual  sensations  produced  by  direct  elec- 
trical stimulation  of  the  retina.  Hirsch  had  previously  arrived  at 
similar  results,  and  Bonders  i  had  similarly  determined  the  reaction 
period  or  physiological  time,  as  he  termed  it,  to  be,  roughly  speaking, 
for  feeling  }th,  for  hearing  ^th,  and  for  sight  ^th  of  a  second.  With 
Dietl  and  Vintschgau  ^  the  reaction  period  for  tactile  sensations  from 
the  middle  finger  of  the  right  hand  was  respectively  '1371  sec.  and  '1532 
sec.  Von  Wittich^  found  the  reaction  period  to  be  '167  sec,  when  the 
application  of  a  constant  current  to  the  tongue  produced  a  gustatory 
sensation.  Vintschgau  and  Honigschmied'*  determined  the  reaction 
period  of  taste  to  be  for  salines  '1598  sec,  for  sugar  '1639,  acids  "1676, 
and  quinine  '2351.  Even  with  the  same  stimulus,  the  reaction  period 
will  vary  according  to  circumstances,  such  as  the  time  of  year,  weather, 
&c.,  and  according  to  the  condition  of  the  individual.  Exner  found 
that  while  strong  tea  had  no  obvious  effect,  two  bottles  of  Rhine  wine 
lengthened  the  period  from  '1904  to  '2969.  Dietl  and  Vintschgau^,  as 
the  result  of  an  elaborate  inquir}',  came  to  the  conclusion  that  while 
opium  had  a  temporary  lengthening  effect,  coffee  produced  a  much 
more  striking  and  lasting  shortening  of  the  period,  while  the  effect  of 
wine  (champagne)  varied  according  to  the  quantity  drunk  and  the 
rapidity  with  which  it  was  taken  ;  a  small  quantity  shortened,  but  a 
large  quantity  (a  bottle  drunk  rapidly)  lengthened  the  period. 

The  calculations  involved  in  'reducing'  the  reaction  period  are 
obviously  open  to  much  error  ;  Exner's  own  reduced  period  was  "0828, 
that*  of  the  obtuse  individual  quoted  above  '3050  and  '9426  ;  that  is  to 
say,  an  intelligent  person  takes  less  than  -^  of  a  second  to  perceive 
and  to  will.  If  the  whole  reaction  period  of  the  case  when  the  retina 
was  directly  stimulated  be  deducted  from  the  period  of  the  case  when 
a  luminous  object  was  used  to  create  visual  impressions,  the  difference 
(•0367  sec.)  would  indicate  the  latent  period  of  the  luminous  stimula- 
tion of  the  retina  ;  but  it  is  doubtful  whether  any  great  dependence  can 
be  placed  on  such  a  calculation. 

'  Reichert  and  du  Bois-Reymond's  Archiv,  1868,  p.  657. 
^  Pfliiger's  ^riT/^zV,  XVI.  (1878)  p.  316. 

3  Zt.  rat.  Med.  (3)  xxxi.  p.  113. 

4  Pfliiger's  yi;r/i2'z',  X.  (1875)  p.  I. 

5  Op.  cit. 


CHAF.    VI.J  THK    HRAIN.  66/ 

In  all  the  above  instances  a  single  stimulus  was  used,  and  all  that 
the  person  experimented  on  had  to  do  was  to  perceive  the  stimulus, 
and  to  make  an  effort  in  accordance.  If,  however,  the  stimulus,  instead 
of  bein},'  apjjlied  to  a  part  of  the  body  dcteriiiined  by  previous  arrange- 
ment, as  for  instance  to  tiie  left  foot,  were  applied  citlier  to  the  left  or 
the  right  foot,  without  the  ].)crson  being  told  which  it  was  to  be,  and  it 
was  arranged  that  he  should  make  a  signal  when  tlic  left  foot,  but  not 
when  the  right  foot  was  stimulated,  additional  mental  exertions  would 
be  necessary  ;  and  Dondcrs'  found  that  in  such  a  case  the  reaction 
period  was  considerably  prolonged.  The  following  table  gives  the 
difference  between  a  simple  reaction  period,  and  one  in  which  a  mental 
decision  has  to  be  carried  out  before  the  voluntary  effort  to  make  the 
signal  is  initiated,  i.e.  gives  the  time  rccjuired  for  the  person  to  '  make 
up  his  mind'  in  accordance  with  the  nature  of  the  sensation  which  he 
receives ;  this  it  will  be  seen  is,  roughly  speaking  from  \  to  7,^(jth  of  a 
second. 

Dilemma  between  two  spots   of    the  skin,  right  and   left   foot 

stimulated  by  an  induction  shock  "066 

Dilemma  of  visual  sensations   between   two   colours,   suddenly 

presented  to  the  view  :  signal  to  be  made  on  seeing  one  but 

not  on  seeing  the  other 184 

Dilemma  between  two  letters  :  signal  to  be  made  on  seeing  one 

only '166 

Dilemma  between  five  letters  :  signal  to  be  made  on  seeing  one 

only '170 

Dilemma  of  auditory  sensations  :    two  vowels  suddenly  sung  : 

signal  to  be  made  on  hearing  one  only "056 

Dilemma  between  five  vowels :  signal  to  be  made  on  hearing  one 

only -088 

Sec.  6.     The  Cranial  Nerves. 

Though  we  have  incidentally  dwelt  on  the  functions  of  all 
these  nerves,  it  may  be  as  well  to  recapitulate  them  in  a  tabular 
form. 

1.  Olfactory.     Nerve  of  smell. 

2.  Optic.     Nerve  of  sight. 

3.  Oculo-vwtor.  Motor  nerve  to  the  levator  palpebrae  superi- 
oris  and  all  the  muscles  of  the  eye,  except  the  obliquus  superior 
and  the  rectus  externus.  Efferent  nerve  for  the  coruraciion  of  the 
pupil  and  for  the  muscles  of  accommodation.  Hence  when  the 
nerve  is  divided  or  otherwise  paralysed  the  ujiper  eyelid  falls 
(ptosis) ;  the  eye,  which  is  turned  outwards,  is  capable  of  partial 
movements  only,  vi/.  such  as  can  be  produced  by  the  rectus 
externus  and  obliquus  superior  ;  when  the  head  is  moved,  the  eye 

'  Op.  cit. 


668  CRANIAL   NERVES.  [BOOK   III. 

moves  with  it,  the  inferior  oblique  not  being  able  to  execute  the 
usual  compensating  movements  of  the  eyeball ;  the  pupil  is  dilated, 
and  the  eye  cannot  accommodate  for  near  distances. 

The  root  of  the  nerve  shews  recurrent  sensibility,  due  to  fibres 
from  the  fifth,  but  is  otherwise  a  purely  motor  nerve'. 

4.  Troc/i/ear  or  Pathetic.  Motor  nerve  to  the  obliquus 
superior.  When  the  nerve  is  paralysed,  no  marked  difference  is 
observed  in  the  position  of  the  eye,  but  the  patient  sees  double 
when  he  attempts  to  look  straight  forward  or  towards  the  paralysed 
side ;  the  images  however  coalesce  when  he  turns  his  head  to  the 
sound  side.  When  the  head  is  moved  from  side  to  side  the  eye 
moves  with  it,  the  usual  compensating  movement  of  the  eye  which 
accompanies  the  movements  of  the  head  failing  in  consequence 
of  the  superior  oblique  not  acting. 

It  is  a  purely  motor  nerve,  but  receives  recurrent  fibres  from  the 
fifth. 

5.  Trigeminus.  A  mixed  efferent  and  afferent  nerve  with 
distinct  motor  and  sensory  roots,  the  latter  bearing  the  ganglion  of 
Gasser. 

Efferent  Fibres.  Motor  fibres  to  the  muscles  of  mastication, 
temporal,  masseter,  two  pterygoids  (mylo-hyoid,  anterior  belly  of 
digastric),  to  the  tensor  palati,  and  tensor  tympani ;  vaso-motor 
fibres  to  various  parts  of  the  head  and  face  ;  secretory  fibres  to 
the  lachrymal  gland,  and  according  to  some  authors  to  the  parotid 
and  submaxillary  glands  by  fibres  joining  the  facial.  Trophic  (?) 
fibres  to  eye,  nose,  and  other  parts  of  face,  see  p.  489.  Efferent 
fibres  for  the  dilation  of  the  pupil,  see  p.  524. 

Afferent  Fibres.  General  nerve  of  sensation  of  the  skin  of 
head  and  face,  and  of  the  mucous  membrane  of  the  mouth,  except 
the  back  part  of  the  tongue,  the  posterior  pillars  of  the  fauces, 
and  a  large  part  of  the  pharynx,  these  parts  being  supplied  by  the 
glosso-pharyngeal  and  vagus  ;  the  back  of  the  head  is  chiefly 
supplied  by  branches  from  the  cranial  nerves,  and  the  external 
meatus  and  concha  are  supplied  chiefly  by  the  auricular  branch  of 
the  vagus.  Nerve  of  special  sense  of  taste  for  the  front  part  of 
the  tongue,  see  p.  587. 

6.  Abducens.  Motor  nerve  to  the  rectus  externus.  When 
the  nerve  is  divided  or  otherwise  paralysed,  the  eye  is  turned 
inwards. 

'  Schiff,  Lehrb,  p.  376. 


CHAP.    VI.]  THE   BRAIN.  '  669 

The  abducens  is  joined,  by  fibres  coming  from  the  cervical  sym- 
pathetic ;  wlicn  this  nerve  is  divided  in  the  neck,  the  action  of  the 
muscle  is  weakened. 

It  probably  also  receives  recurrent  sensory  fibres  from  the  fifth. 

7.  Facial.  Motor  nerve  to  the  muscles  of  the  face  ;  hence 
nerve  of  expression.  Sup[<lies  also  stylohyoid,  jjosterior  belly  of 
the  digastric,  buccinator,  stapedius,  muscles  of  the  external  ear, 
platysma,  some  muscles  of  the  palate,  viz.  the  levator  palati  and 
])robably  others.  Secretory  nerve  of  submaxillary  and  parotid 
gland.  Receives  aflerent  possibly  efferent  fibres  from  trigeminus 
and  also  from  vagus.  According  to  Vulpian  contains  vaso-motor 
fibres  for  the  tongue  and  side  of  the  face.  1  he  effects  of  paraly- 
sis of  the  facial,  from  the  inability  of  the  orbicularis  to  close  the 
eye,  the  drawing  of  the  face  to  the  sound  side,  and  the  smooth- 
ness of  ihe  paralysed  side,  are  very  striking. 

8.  Auditory  Ncn'e.  Special  nerve  of  hearing ;  afferent  nerve 
for  impulses  other  than  auditory  proceeding  from  the  semicircular 
canals. 

9.  Glossopharyngeal.  Motor  nerve  for  levator  palati,  azygos 
yvulae,  stylo-pharyngeus,  constrictor  faucium  medius  ;  the  motor 
functions  of  this  nerve  have  been  disputed.  Special  nerve  of 
taste  for  the  back  of  the  tongue.  General  nerve  of  sensation  for 
the  root  of  the  tongue,  the  soft  palate,  the  pharynx  (being  here 
associated  with  the  vagus),  the  Eustachian  tube  and  the 
tympanum. 

10.  Pneumogaslric.      Vagus. 

Efferent  Fibres.  Motor  nerve  for  the  muscles  of  the  pharynx, 
for  the  movements  of  the  oesophagus  (sec  p.  299),  of  the  stomach 
(see  p.  301),  of  the  intestines  (see  p.  297),  for  the  muscles  of  the 
larynx,  possibly  for  the  plain  muscular  fibres  of  the  trachea  and 
bronchial  divisions.  Vaso-motor  fibres  for  lungs'.  Inhibitory 
nerve  of  the  heart.  Trophic  fibres  for  lungs  and  heart  (see 
p.  490). 

Afferent  Fibres.  Sensory  nerve  of  the  respiratory  passages,  and 
of  the  pharynx,  oesophagus  and  stomach.  Afferent  nerve,  aug- 
menting and  inhibiting,  of  the  respiratory  centre  (see  p.  372), 
afferent  inhibitory  nerve  (depressor  branch)  of  the  medullary 
vaso  motor  centre  (see  p.  209),  afferent  nerve  producing  salivary 
secretion  (see  p.  270),  inhibiting  pancreatic  secretion  (see  p.  279). 

*  Michaelbon,  Mitth.  a.  d.  Konigsberger physiol.  Lab.  (iSjS)  p.  85. 


6^0  CRANIAL   NERVES.  [BOOK   III. 

According  to  Steiner',  the  vagus  in  the  rabbit  may  be  easily 
dissected  into  two  strands,  an  outer  one  containing  the  afferent,  and 
an  inner  one  containing  the  efferent  fibres. 

II.  Spinal  accessory.  Motor  nerve  to  the  sterno-mastoid  and 
trapezius  muscles."  It  receives  recurrent  sensory  fibres  from  the 
cervical  nerves.  Part  of  the  spinal  accessory  blends  with  the 
pneumogastric,  and  the  efferent  effects  (such  as  the  movements  of 
the  larynx,  pharynx,  &c.,  and  cardiac  inhibition)  of  the  united 
trunk  seem  to  be  largely  due  to  the  spinal  accessory  fibres  con- 
tained in  them.  It  is  stated  however  that  division  of  the  spinal 
accessory  before  it  joins  the  pneumogastric,  does  not  entirely  do 
away  with  either  swallowing  or  the  movements  of  the  larynx.  In 
the  movements  of  the  oesophagus  and  stomach,  brought  about  by 
the  vagus  acting  as  an  efferent  nerve,  the  accessory  fibres  seem  to 
have  no  share.  The  cardiac  inhibitory  fibres  seem  to  be  distinctly 
of  accessory  origin. 

12.  Hypoglossal.  Motor  nerve  for  the  muscles  of  the  tongue, 
and  for  all  the  muscles  connected  with  the  hyoid  bone  except  the 
digastric,  stylo-hyoid,  mylo-hyoid,  and  middle  constrictor  of  the 
pharynx ;  it  also  supplies  the  sterno-thyroid.  It  receives  sensory 
fibres  from  the  fifth  and  vagus,  and .  is  also  connected  with  the 
three  upper  cervical  nerves  as  well  as  with  the  sympathetic. 

To  Charles  Bell  is  due  the  merit  of  having  made  the  fundamental 
discovery  of  the  distinction  between  motor  and  sensory  fibres.  Led 
to  this  view  by  reflecting  on  the  distribution  of  the  nerves,  he  experi- 
mentally, verified  his  conclusions  by  observing  that  while  mechanical 
irritation  of  a  posterior  root  gave  rise  to  no  movements  in  the  muscles 
to  which  the  nerve  was  distributed,  these  were  very  evident  when  the 
anterior  root  was  pricked  or  pinched.  He  printed  his  views  for 
private  circulation  in  1811,  under  the  title  of  '  Idea  of  a  New  Anatomy 
of  the  Brain,'  and  communicated  them  to  the  Royal  Society  in  July, 
1821,  in  a  paper  'On  the  Arrangement  of  the  Nerves.'  In  1822 
Majendie^  shewed  that  section  of  the  posterior  root  caused  loss  of 
sensation  and  section  of  the  anterior  root  loss  of  motion  :  an  observa- 
tion no  less  epoch-making  than  that  of  Bell.  Majendie  was  however 
led  by  the  phenomena,  which  we  can  now  explain  as  due  to  recurrent 
sensibility  or  reflex  action,  to  believe  that  the  distinction  between  the 
two  roots  was  partial  only  ;  and  it  was  not  till  Johannes  Miiller^  some 
years  afterwards  conducted  experiments  on  frogs  and  made  use  of 
galvanic  stimulation,  that  the  doctrine  of  motor  and  sensory  nerves 
became  thoroughly  established.  The  next  great  step  was  the  esta- 
blishment of  the  theory  of  Reflex  Action.     Although  this  important 

'  Arch.f.  Anai.  u.  Phys.  (Pfiys.  Abth.)  1878,  p.  2i6. 
=  Journal  de  Physiol.  II.  p.  276. 
3  Physiology,  Engl.  ed.  I.  691. 


CHAP.   VI.]  THK   BRAIN.  67 1 

function  of  nervous  centres  was  recognized  dimly  by  older  observers 
such  as  Whytt",  more  closely  defined  by  Prochaska",  an'l  clearly 
graspe'l  by  Johannes  Miillcr  in  1833',  it  was  independently  discovered 
in  1832  by  Marshall  IlalM  ;  anrl  it  was  owing  to  the  enthusiastic 
labours  of  the  latter  observer  that  the  new  doctrine  was  rapidly 
accepted  and  developed.  Among  the  more  important  labours  since 
that  time  may  be  mentioned  the  remarkable  book  of  Flourens',  the 
work  of  Longet'',  and  the  rosear:hcs  of  SchifF',  Brown-Sdquard^,  and 
others.  The  work  of  Goltz'  on  the  frog,  though  small,  contains  many 
valuable  facts  and  suggestions  ;  and  an  admirable  summary  of  the 
whole  physiology  of  the  nervous  system  is  given  by  Vulpian"",  to 
whom  also  we  are  indebted  for  many  valuable  observations.  The 
chief  of  the  more  recent  inquiries  have  been  mentioned  in  the 
text. 

'  On  the  Vital  and  other  Involuntary  McrL'cments  of  A nitnals,  1 75 1. 

'  Lehr,(itz   aiis  (Lr  Physiol.  1797. 

3  In  the  first  edition  of  his  Physiology. 

*  More  fully  in  Phil.  J'rans.  1833. 

s  Rcch.  Exf>.  sitr  Irs  Proprietes  d  Us  Fonctions  an  Systime  N^eri'eux,  1st  ed. 
in  1824,  2nd  nuich  enlarged  and  containing  many  new  facts,  in  1842. 

'  Anat.  et  Phys.  clit  Svstime  Nei~vciix,  1841, 

^  Lehrb.  d.  Phy.iol.  1858. 

®  AVc//.  et  Exp.  siir  la  Phys.  dela  moelle  ipin.  1846,  and  numerous  subsequent 
papers. 

9  Beitrdge  z.  Lehrev.  d.  Ftinctioncn  de*- Nervencentren  des  Frosches,  1869. 

^^  Lemons  sttr  la  Phys.  generak  et  comparie  du  Systime  Nervetix,  1866. 


CHAPTER  VII. 
SPECIAL   MUSCULAR   MECHANISMS. 

Sec.  I.     The  Voice. 

A  BLAST  of  air,  driven  by  a  more  or  less  prolonged  expiratory- 
movement,  throws  into  vibrations  two  elastic  membranes — the 
chordce  vocales.  These  impart  their  vibrations  to  the  column  of  air 
above  them,  and  so  give  rise  to  the  sound  which  M^e  call  the  voice. 
Since  the  sound  is  generated  in  the  vocal  cords,  we  may  speak  of 
them  and  of  those  parts  of  the  larynx  which  decidedly  affect  their 
condition  as  constituting  the  essential  vocal  apparatus ;  while 
the  chamber  above  the  vocal  cords,  comprising  the  ventricles  of 
the  larynx  with  the  false  vocal  cords,  the  pharynx  and  the  cavity 
of  the  mouth,  the  latter  varying  much  in  form,  constitute  a  sub- 
sidiary apparatus  of  the  nature  of  a  resonance-tube,  modifying  the 
sound  originating  in  the  vocal  cords.  In  the  voice,  as  in  other 
sounds,  we  distinguish :  (i)  Loudness.  This  depends  on  the 
strength  of  the  expiratory  blast.  (2)  Pitch.  This  depends  on  the 
length  and  tension  of  the  vocal  cords.  Their  length  may  be  re- 
garded as  constant,  or  varying  only  with  age.  It  consequently 
determines  the  range  only  of  the  voice,  and  not  the  particular  note 
given  out  at  any  one  time.  The  shrill  voice  of  the  child  is  deter- 
mined by  the  shortness  of  the  cords  in  infancy,  and  the  voices  of 
a  soprano,  tenor  and  baritone  are  all  dependent  on  the  respective 
lengths  of  their  vocal  cords.  Their  tension  is  on  the  contrary  vari- 
able ;  and  the  chief  problems  connected  with  the  voice  refer  to 
variations  in  the  tension  of  the  vocal  cords.  (3)  Quality.  This 
depends  on  the  number  and  character  of  the  overtones  accom- 
panying any  fundamental  note  sounded,  and  is  determined  by  a 
variety  of  circumstances,  chief  among  which  is  the  physical  quality 
of  the  cords. 

The  vocal  cords,  attached  m  front  to  the  thyroid  cartilage,  end 
behind   in    the   processus    vocales    of  the    arytenoid  cartilages. 


CHAF.    VII.]      SrECIAL   MUSCULAR   MECHANISMS. 


^73 


Hence  a  distinction  has  been  drawn  between  the  rima  vocalis,  i.e. 
the  opening  bounded  laterally  by  the  vocal  cords,  and  the  rima 
respiratoria,  or  space  between  the  arytenoid  cartilages  behind  the 
processus  vocales ;  these  names  however  are  not  free  from  objec- 


Fig.  ^7.    Thb  Larynx  as  seen  by  means  of  the  Laryngoscope  in  different  con- 
ditions OF  THE  Glottis.    (From  Quain's  Anatomy  after  Czermak.) 
A  while  singing  a  high  note  ;  B  in  quiet  breathing  ;  C  during  a  deep  inspiration.     The 
Cirresponding  diagrammatic  figures  A',  B',  C,  ilhistrate  the  changes  in  position  of  the 
arytenoid  cariilajies;  and  the  form  of  the  rima  vocalis  and  rima  respiratoria  in  the 
above  three  conditions. 
/  the   base  of  the  tongue  ;  e  the  upper  free  part  of  the  epiglottis  ;   e'  the   tubercle  or 
cushion  of  the   epiglottis  ;    //*.  pari  of  the  anterior  wall  of   the   phar^'nx  behind   the 
larynx  ;  w  swelling  in  the  aryteno-epigloltidcan  fold  caused  by  the  cartilage  cf  Wris- 
berg;  s  swelling  caused  by  the  cartilage  of  Santorini ;  a  the  summit  of  the  arytenoid 
cartilage  ;  ci'  the  true  v.)cal   cords  :  cz>s  the  false  vocal  cords  ;  tr  the  trachea  with  its 
rings  ;  b  the  two  bronchi  at  their  commencement. 

tions.  In  quiet  breathing  (Fig.  72  j9)  the  two  form  together  a  V- 
shaped  space,  which,  as  we  have  seen  (p.  340),  in  deep  inspiration 
is  widened  into  a  rhomboidal  opening  by  the  divergence  of  the 
processus  vocales  (Fig.  72  C).  When  a  note  is  about  to  be  uttered, 
the  vocal  cords  are  by  the  approximation  of  the  processus  vocales 
F.  P.  43 


674  THE   VOICE.  [book   III. 

brought  into  a  position  parallel  to  each  other,  and  the  whole  rima 
is  narrowed  (Fig.  72  A).  By  their  parallelism  and  by  the  narrow- 
ness of  the  interval  between  them  the  cords  are  rendered  more 
susceptible  of  being  thrown  into  vibration  by  a  moderate  blast  of 
air.  The  problems  we  have  to  consider  are,  first,  by  what  means 
are  the  cords  brought  near  to  each  other  or  drawn  asunder  as 
occasion  demands ;  and  secondly,  by  what  means  is  the  tension  of 
the  cords  made  to  vary.  We  may  speak  of  these  two  actions  as 
narrowing  or  widening  of  the  glottis,  and  tightening  or  relaxation 
of  the  vocal  cords. 

Narrowing  of  the  Glottis.  The  change  of  form  of  the 
glottis  is  best  understood  when  it  is  borne  in  mind  that  each 
arytenoid  cartilage  is,  when  seen  in  horizontal  section  (Fig.  72), 
somewhat  of  the  form  of  a  triangle,  with  an  internal  or  median, 
an  external,  and  a  posterior  side,  the  processus  vocalis  being  placed 
in  the  anterior  angle  at  the  junction  of  the  median  and  external 
sides.  When  the  cartilages  are  so  placed  that  the  processus  vocales 
are  approximated  to  each  other,  and  the  internal  surfaces  of  the 
cartilages  nearly  parallel,  the  glottis  is  narrowed.  When  on  the 
contrary  the  cartilages  are  whetled  round  on  the  pivots  of  their 
articulations,  so  that  the  processus  vocales  diverge,  and  the 
internal  surfaces  of  the  cartilages  form  an  angle  with  each  other, 
the  glottis  is  widened. 

There  are  several  muscles  forming  together  a  group,  which  has 
been  called  by  Henle  the  sphincter  of  the  larynx.  These  are  (i) 
the  thyro-a7-y-epiglotticus ^  proceeding  from  the  inner  surface  of  the 
thyroid  cartilage  and  from  the  arytenoid  epiglottidean  ligament, 
and  sweeping  round  the  outer  ridge  of  the  arytenoid  cartilage  of  its 
own  side  to  be  inserted  into  the  processus  muscularis  of  the  ary- 
tenoid cartilage  of  the  other  side  :  (2)  the  thyro-arytenoideus 
exterjius,  passing  from  the  reentrant  angle  of  the  thyroid  cartilage  to 
be  inserted  into  the  outer  edge  of  the  arytenoid  cartilage  of  the 
same  side  :  (3)  the  thyro-ary  tenoideus  inte7-mis,  passing  from  the 
angle  of  the  thyroid  cartilage  to  the  processus  vocalis  and  outer 
side  of  the  arytenoid  cartilage  :  (4)  the  arytowideus  (posticus),  pass- 
ing transversely  from  one  arytenoid  cartilage  to  another.  All  these 
muscles,  when  they  act  together,  grasp  round  the  glottis  and  tend 
to  close  it  up  :  and  each  of  them,  acting  alone,  has,  with  the 
exception  of  the  last-named  (arytenoideus),  the  same  effect.  In 
addition  to  these,  the  crico-aryienoideus  latej'alis,  which  passes  from 
the  lateral  border  of  the  cricoid  cartilage  upwards  and  backwards 
to  the  outer  angle  of  the  arytenoid,  by  pulling  this  outer  angle 
forwards  throws  the  processus  vocalis  inwards,  and  so  also  narrows 
the  glottis. 


CH\P.   VIl]      SPECIAL   MUSCULAR   MECHANISMS.  675 

Widening  of  the  Glottis.  The  crico-ary-Unoideus posticus 
passing  tVom  the  posterior  surface  of  the  cricoid  cartilage  to  the 
outer  angle  of  the  arytenoid  cartilage  behind  the  attachment  of  the 
lateral  crico-arytenoideus.  pulls  back  this  outer  angle,  and  so 
causing  the  processus  vocalis  to  move  outwards,  widens  the  glottis. 
The  arytirtoideus  postiats,  acting  alone,  has  a  similar  effect 

Tightening  of  the  Vocal  Cords.  The  crico-thyrouieus  pulls 
the  thyroid  downwards  and  torwards,  and  so  increases  the  distance 
between  that  cartilage  and  the  arjtenoids  when  the  latter  are  fixed. 
Supposing  then  the  antenoideus  and  crico-arytenoideus  posticus 
to  fix  the  arytenoids,  the  effect  of  the  contraction  of  the  crico- 
th\Toiceus  would  be  to  tighten  the  vocal  cords. 


Slackening  of  the  Vocal  Cords.  This  is  effected  by  the 
whole  sphincter  group  just  mentioned,  but  more  especially  by 
the  thyroarytenoidei  exUmus  and  inUmus ;  these  acting  alone, 
supposing  the  artenoid  cartilages  to  be  fixed,  would  pull  the 
thyroid  cartilage  upwards  and  backwards,  and  so  shorten  the 
distance  between  the  processus  vocales  and  that  body. 

Thus  almost  every  movement  of  the  lar}nx  is  effected  not  by 
one  muscle  only  but  by  several,  or  at  least  by  more  than  one, 
acting  in  concert.  The  movements  which  give  rise  to  the  voice 
are  pre-eminently  combined  and  coordinate  movements.  When 
we  remember  how  very  slight  a  variation  in  the  tension  of  the 
vocal  cords  must  give  rise  to  a  marked  difference  in  the  pitch  of 
the  note  uttered,  and  yet  what  a  multitude  of  fine  differences  of 
pitch  are  at  the  command  of  a  singer  of  even  moderate  ability,  it 
appears  exceedingly  probable  that  the  various  muscular  combina- 
tions required  to  produce  the  possible  variations  in  pitch  are  of 
such  a  kind  that  frequently  a  part  only,  possibly  a  few  fibres  only, 
of  a  particular  muscle,  may  be  thrown  into  contraction,  while  *ill 
the  rest  of  the  muscle  remains  quiet.  Taking  into  \iew  moreover 
the  great  range  of  pitch  possessed  by  even  common  voices,  as 
compared  with  the  possible  variations  of  tension  of  which  the 
vocal  cords  in  their  natural  length  are  capable,  it  has  been 
suggested  that  some  of  the  fibres  of  the  thyro-ar)tenoideus 
internus,  which  passing  either  from  the  thyroid  or  from  the  ary- 
tenoid, appear  to  end  in  the  vocal  cords  themselves,  may,  by 
fixing  particular  points  of  the  cords,  so  to  speak,  'stop'  them; 
and  by  thus  artificially  shortening  the  length  actually  thrown  into 
vibration,  produce  higher  notes  than  the  cords  in  their  natural 
length  are  capable  of  producing.     It  has  been  also  suggested  that 

43—2 


6^6  ,         THE   VOICE.  [BOOK   III 

the  processus  vocales  may  overlap  each  other,  and  thereby  shorten 
the  length  of  cord  available  for  vibration  ^ 

These  various  muscles  are  supplied  by  the  vagus  nerve,  or 
rather  by  spinal  accessory  fibres  running  in  the  vagus  trunk.  The 
superior  laryngeal  is  the  afferent  nerve  supplying  the  mucous 
membrane,  but  it  also  contains  the  motor  fibres  distributed  to  the 
crico-thyroid  muscle  ;  hence  when  this  nerve  is  divided  on  one 
side  the  corresponding  vocal  cord  is  relaxed  and  high  notes 
become  impossible.  It  is  vi^orthy  of  notice  that  this,  the  chief 
tensor,  and  therefore  the  most  important,  muscle  of  the  larynx, 
has  a  separate  and  distinct  nervous  supply. 

According  to  some  authors  the  arj'tenoideus  posticus  also  receives 
its  nervous  supply  from  this  nerve  ;  but  this  is  denied  by  Schech*. 

The  inferior  laryngeal  or  recurrent  branch  supplies  all  the  other 
muscles.  When  this  nerve  is  divided  the  voice  is  lost,  since  the 
approximation  and  parallelism  of  the  vocal  cords  can  no  longer  be 
effected.  When  in  a  living  animal  both  recurrent  nerves  are  divided, 
the  glottis  is  seen  to  become  immobile  and  partially  dilated,  the  vocal 
cords  assuming  the  position  in  which  they  are  found  in  the  body  after 
death,  and  which  may  be  considered  as  the  condition  of  equili- 
brium between  the  dilating  and  constricting  muscles.  During 
forcible  inspiration  the  glottis  passes  from  this  condition  in  the 
direction  of  m.ore  complete  dilation ;  during  forcible  expiration, 
the  change  is  one  of  constriction.  When  the  peripheral  portion 
of  one  recurrent  nerve  is  stimulated,  the  vocal  cord  of  the  same 
side  is  approximated  to  the  middle  line ;  when  both  nerves  are 
stimulated,  the  vocal  cords  are  brought  together  and  the  glottis  is 
narrowed.  Though  the  nerve  is  distributed  to  both  dilating  and 
constricting  muscles,  the  latter  overcome  the  former  when  the 
nerve  is  artificially  stimulated.  In  the  complete  closure  of  the 
glottis,  which  is  so  important  a  part  of  the  act  of  coughing  (p.  396), 
the  group  of  muscles  which  we  have  spoken  of  as  constituting  a 
sphincter  is  thrown  into  forcible  contractions  by  the  recurrent 
laryngeal  nerve. 

Though  fundamentally  a  voluntary  act,  the  utterance  of  a  given 
note  is  not  affected  by  the  direct  passage  of  simple  volitional  im- 
pulses down  to  the  laryngeal  muscles.  So  complex  and  coordinate 
a  movement  as  that  of  sounding  even  a  simple  and  natural  note, 
requires  a  coordinating  nervous  mechanism  in  which,  as  in  other 

'  Cf.  Riihlmann,  Witn.  Siizungibericht,  LXix.  (1874)  p.  257. 
^  Zt.f.  Biol.  IX.  p.  258. 


CI  [AT.   Vll.]      SPIXIAl-    MUSCULAR    MECHANISMS.  677 

complex  muscular  actions,  afferent  impulses  play  an  important 
part.  Auditory  sensations,  if  not  as  important  for  an  accurate 
manai^emont  of  the  voice  as  are  visual  sensations  for  the  move- 
ments of  the  eye,  are  yet  of  prime  importance.  This  is  recognized 
when  we  say  that  such  and  such  a  one  whose  power  over  his 
laryngeal  muscles  is  imperfect,   *  has  no  ear.' 

The  '  falsetto '  voice  is  one  not  at  present  clearly  understood. 
According  to  some  authors  the  vocal  cords  are  seen  to  be  wide  apart 
when  falsetto  notes  are  uttered,  and  not  close  and  parallel  as  in  the 
ordinary  voice.  Hence  for  the  development  of  these  notes,  a  stronger 
blast  of  air  and  a  greater  effort  are  rct|uircd.  When,  as  in  ;m  ordinary 
full  voice,  the  glottis  is  very  narrow,  the  trachea  and  bronchi  serve  the 
purpose  of  a  resonance  chamber  ;  hence  such  a  voice  is  spoken  of  as 
a  '  chest '  voice.  In  the  falsetto  voice,  where  the  vocal  cords  are  wide 
apart,  this  function  of  the  air-tubes  is  in  abeyance.  This  view  is 
combated  by  V'achcr",  who,  from  observations  on  himself,  has  come  to 
the  conclusion  that  the  glottis  is  narrowed  in  both  kinds  of  notes,  the 
cords  vibrating  along  their  whole  length  in  the  chest  notes,  and  along 
their  anterior  portions  only  in  the  high  falsetto  notes.  According  to 
him,  therefore,  the  high  notes  ^re  the  result  of  a  '  stopping '  of  the 
vocal  cords,  but  whether  this  is  eftccted  by  the  action  of  the  thyro- 
arytenoidcus  intcrnus  spoken  of  above,  must  be  left  at  present  un- 
certain. Johannes  Miiller  was  of  opinion  that  in  the  falsetto  notes 
the  edges  only  of  the  vocal  cord  vibrate,  while  in  the  chest  notes  the 
whole  width  of  each  cord  is  involved.  It  is  exceedingly  probable  that 
the  falsetto  notes  are  produced  by  some  muscular  manoeuvre,  since 
they  may  by  exercise  be  uttered  with  comparative  ease.  The  change 
from  the  chest  to  the  falsetto  range  is  an  abrupt  one,  and  the  com- 
bined range  may  be  very  extensive,  as  in  the  case  of  persons  who  can 
carry  on  a  duet,  singing  alternately,  for  instance,  in  a  tenor  (chest) 
and  a  soprano  (falsetto;  voice.  According  to  Vacher  the  rima  respira- 
toria  is  always  completely  closed  during  singing,  whether  chest  or 
falsetto  notes,  and  not  as  Mandl  thought  in  the  latter  only. 

The  ventricles  of  Morgagni  are  apparently  of  use  in  giving  the 
vocal  cords  sufficient  room  for  their  vibrations.  The  purpose  of  the 
false  vocal  cords  is  not  exactly  known.  Some  authors  think  that  in 
the  falsetto  voice  they  are  brought  down  into  contact  with,  and  thus 
serve  to  stop,  the  true  vocal  cords. 

At  the  age  of  puberty  a  rapid  development  of  the  larynx  takes 
place,  leading  to  a  change  in  the  range  of  the  voice.  The  peculiar 
harshness  of  the  voice  when  it  is  thus  'breaking'  seems  to  be  due  to 
a  temporary  congested  and  swollen  condition  of  the  mucous  mem- 
brane of  the  vocal  cords  accompanying  the  active  growth  of  the 
whole  larynx.  The  change  in  the  mucous  membrane  may  come  on 
quite  suddenly,  the  voice  'breaking'  for  instance  in  the  course  of  a 
night. 

'  De  la  Voijc,  Paris,  1877. 


678  SPEECH.  [BOOK   III. 

Sec.  2.    Speech.  • 

Vowels. 

Every  sound,  or  every  note  {for  all  vocal  sounds  when  con- 
sidered by  themselves  are  musical  sounds),  caused  by  the  vibrations 
of  the  vocal  cords,  besides  its  loudness  due  to  the  force  of  the  ex- 
piratory blast,  and  its  pitch  due  to  the  tension  of  the  cords,  has  a 
quality  of  its  own,  due  to  the  number  and  relative  prominence  of 
the  overtones  which  accompany  the  fundamental  tone.  Some  of 
these  features  which  make  up  the  quality  are  imposed  on  the 
note  by  the  nature  of  the  vocal  cords,  but  still  more  arise  from 
various  modifications  which  the  relative  intensities  of  the  overtones 
undergo  through  the  resonance  of  the  cavity  of  the  mouth  and 
throat.  Whenever  we  hear  a  note  sounded  by  the  larynx  we  are 
able  to  recognize  in  it  features  which  enable  us  to  state  that  one 
or  other  of  the  '  vowels '  is  being  uttered.  Vowel  sounds  are  in 
fact  only  extreme  cases  of  quality,  extreme  prominence  of  certain 
overtones  brought  about  by  the  shape  assumed  by  the  buccal  and 
pharyngeal  passages  and  orifices,  as  the  vibrations  pass  through 
them.  Each  vowel  has  its  appropriate  and  causative  disposition 
of  these  parts.  When  i  (cit  in  feet)  is  sounded,  the  sounding-tube 
of  the  upper  air  passages  is  made  as  short  as  possible,  the  larynx 
is  raised  and  the  lips  are  retracted,  the  whole  cavity  of  the  mouth 
taking  on  the  form  of  a  broad  flask  with  a  narrow  neck.  During 
the  giving  out  of  e  {a.  in  fat)  the  shape  of  the  mouth  is  similar,  but 
somewhat  longer.  For  the  production  of  a  (as  in  father)  the 
mouth  is  widely  open,  so  that  the  buccal  cavity  is  of  the  shape  of 
a  funnel  with  the  apex  at  the  pharynx.  With  0,  the  buccal  cavity 
is  agam  flask-shaped,  with  the  mouth  more  closed  than  in  a,  but 
the  lips,  instead  of  being  retracted  as  in  z  and  e,  are  somewhat  pro- 
truded, so  that  the  sounding  tube  is  prolonged.  The  greatest 
length  of  the  tube  is  reached  in  u  (00),  in  which  the  larynx  is 
depressed  and  the  lips  protruded  as  much  as  possible.  While  the 
two  latter  vowels  are  being  uttered,  the  general  form  of  the  buccal 
cavity  is  that  of  a  flask  with  a  short  neck  and  a  small  opening,  the 
orifice  being  smaller  for  u  than  for  0. 

Each  of  these  various  '  vowel '  forms  of  the  mouth  possesses  a 
note  of  its  own,  one  towards  which  it  acts  as  a  resonance  chamber. 
Thus  if  several  tuning-forks  of  various  pitch  be  held  while  sounding 
before  a  mouth  which  has  assumed  the  particular  form  necessary  for 
sounding  U,  it  will  be  found  that  the  resonance  will  be  particularly 
great  with  the  fork  having  the  pitch  of  the  bass  d-Mt.  Similarly  the 
pitch  of  the  treble  l>  will  be  more  intensified  by  the  mouth  moulded  to 


CHAP.    VII.J      SPECIAL   MUSCULAR    MLCHANLSMS.  679 

sound  (),  the  octave  b  above  the  treble  will  correspond  to  A,  another 
octave  hiijhcr  to  M,  and  still  an  octave  hi^jhcr  to  \.  And  it  is  the 
experience  of  singers  that  each  vowel  is  sung  with  peculiar  case  on  a 
note  having  a  prominent  overtone  corresponding  to  the  tone  proper  to 
the  mouth  when  moulded  to  utter  the  vowel.  The  precise  nature  of 
the  vowel  sounds  however  requires  further  investigation'. 

As  the  vibrations  are  travelling  through  the  pharyngeal  and 
buccal  cavities,  the  posterior  nares  are  closed  by  the  soft  palate ; 
and  it  may  be  shewn,  by  holding  a  flame  before  the  nostril,  that 
no  current  oY  air  issues  from  the  nose  when  a  vowel  is  properly 
said  or  sung.  When  the  posterior  nares  are  not  effectually  closed 
the  sound  acquires  a  nasal  character.  The  same  happens  when 
the  anterior  nares  are  closed,  as  when  the  nose  is  held  between 
the  fingers,  the  nasal  chamber  then  forming  a  cavity  of  resonance. 

Consonants. 

Vowels  are,  as  their  name  implies,  the  only  real  vocal  sounds. 
It  is  only  on  a  vowel  that  a  note  can  be  said  or  sung.  Our 
speech  however  is  made  up  not  only  of  vowels  but  also  of  con- 
sonants, i.e.  of  sounds  which  are  produced  not  by  the  vibrations 
of  the  vocal  cords  but  by  the  expiratory  blast  being  in  various 
ways  interrupted  or  otherwise  modified  in  its  course  through  the 
throat  and  mouth. 

The  distinction  between  the  two  is  however  not  an  absolute 
one,  since,  as  we  have  seen, -the  characters  of  the  several  vowels 
depend  on  the  form  of  the  mouth,  ahd  in  the  production  of  some 
consonants  (B,  D,  M,  N,  &c.)  vibrations  of  the  vocal  cords  form  a 
necessary  though  adjuvant  factor. 

Consonants  have  been  classified  according  to  the  place  at 
which  the  characteristic  interruption  or  modification  takes  place. 
Thus  it  may  occur. 

1.  At  the  lips,  by  the  movement  or  position  of  the  lips  in 
reference  to  each  other  or  to  the  teeth,  giving  rise  to  labial 
consonants. 

2.  At  the  teeth,  by  the  movement  or  position  of  the  front 
part  of  the  tongue  in  reference  to  the  teeth  or  the  hard  palate, 
giving  rise  to  dental  consonants. 

3.  In  the  throat,  by  the  movement  or  position  of  the  root  of 
the  tongue  in  reference  to  the  soft  palate  or  pharynx,  giving  rise  tc 
guttural  consonants. 

'  Cf.  Jenkin  and  Ewing,  Nature,  1878,  pp.   167  et  seq. 


68o  CONSONANTS.  [BOOK   III. 

Among  the  dentals  again  may  be  distinguished  the  dentals 
commonly  so  called,  such  as  T,  the  sibilants  such  as  S,  and  the 
lingual  L,  all  differing  in  the  relative  position  of  the  tongue, 
teeth,  and  palate. 

Consonants  may  also  be  classified  according  to  the  character 
of  the  movements  which  give  rise  to  them.  Thus  they  may  be 
either  explosive  or  continuous. 

1.  Explosives.  In  these  the  characters  are  given  to  the 
sound  by  the  sudden  establishment  or  removal  of  the  appropriate 
interruption.  Thus,  in  uttering  the  labial  P,  the  lips  are  first 
closed,  then  an  expiratory  current  of  air  is  driven  against  them, 
and  upon  their  being  suddenly  opened,  the  sound  is  generated. 
Similarly,  the  dental  T  is  generated  by  the  sudden  removal  of 
the  interruption  caused  by  the  approximation  of  the  tip  of  the 
tongue  to  the  front  of  the  hard  palate,  and  the  guttural  K  by 
the  sudden  removal  of  the  interruption  caused  by  the  approxima- 
tion of  the  root  of  the  tongue  to  the  soft  palate. 

The  labial  B  differs  from  P,  inasmuch  as  it  is  accompanied  by 
vibrations  of  the  vocal  cords  (that  is,  a  vowel  sound  is  uttered  at 
the  same  time),  and  these  vibrations  continue  after  the  removal  of 
the  interruption.  Hence  B  is  often  spoken  of  as  being  uttered 
with  voice  and  P  without  voice  ;  and  D  and  G  (hard)  with  voice 
bear  the  same  relation  to  T  and  K  without  voice. 

The  continuous  consonants  may  further  be  divided  into 

2.  Aspirates.  In  these  the  sound  is  generated  by  a  rush  of 
air  through  a  constriction  formed  by  the  partial  closure  of  the 
lips,  or  by  the  raising  of  the  tongue  against  the  hard  or  soft 
palate,  &c.  Thus  F  is  sounded  when  the  lips  are  brought  into 
partial,  and  not  as  in  P  and  B  into  complete  approximation,  and 
a  current  of  air  is  driven  through  the  narrowed  opening.  F  is 
uttered  without  any  accompanying  vibration  of  the  vocal  cords, 
i.e.  without  voice.     With  voice  it  becomes  V. 

The  sibilant  S  is  formed  by  a  rush  of  air  past  an  obstruction 
caused  by  the  partial  closure  of  the  teeth,  the  front  of  the  tongue 
being  depressed  at  the  same  time;  and  S  accompanied  with 
vibrations  of  the  vocal  cords  becomes  Z. 

In  Sh  the  dorsal  surface  of  the  tongue  is  raised  so  as  to 
narrow  the  passage  between  that  organ  and  the  palate  for  a 
considerable  portion  of  its  length. 

Th  is  formed  by  placing  the  tongue  between  the  two  partially 
open  rows  of  teeth  ;  and  the  hard  and  soft  Th  bear  to  each  other 
the  same  relation  as  do  P  and  B. 


CHAP.    VII.]      SPECIAL   MU.SCULAR    MECHANISMS.  68l 

L  is  produced  when  the  passage  is  cIose(i  in  the  middle  by 
pressing  the  tip  of  the  tongue  against  the  hard  palate  and  the 
air  is  allowed  to  escape  at  the  sides  of  the  tongue. 

When  the  constriction  in  an  aspirate  is  formed  by  the  approxi- 
mation of  the  root  of  the  tongue  to  the  soft  palate,  we  have  the 
guttural  CH  (as  in  loch)  without  voice  and  GH  (as  in  lough)  with 
voice. 

3.  Rcsonatits.  In  these,  all  of  which  must  have  vibrations  of 
the  vocal  cords  as  a  basis,  the  usual  passage  through  the  mouth  is 
closed  either  in  a  labial,  dental,  or  guttural  fashion,  and  the 
peculiar  character  is  given  to  the  sound  by  the  nasal  chambers 
acting  as  a  resonance  cavity.  Thus  in  M,  the  passage  is  closed 
by  the  approximation  of  the  lips,  in  N,  by  the  approximation  of 
the  tongue  to  the  hard  palate,  and  in  NG  by  the  approximation 
of  the  root  of  the  tongue  to  the  soft  palate. 

4.  The  various  forms  of  R  are  often  spoken  of  as  vibratory, 
the  characteristic  sounds  being  caused  by  the  vibration  of  some 
or  other  of  the  parts  forming  a  constriction  in  the  vocal  passage. 
Thus  the  ordinary  R  is  produced  by  vibrations  of  the  point  of  the 
tongue  elevated  against  the  hard  palate,  the  guttural  R  by  the 
vibrations  of  the  uvula  or  other  parts  of  the  walls  of  the  pharynx; 
and  in  some  languages  there  seems  to  be  an  R  produced  by  the 
vibrations  of  the  lips. 

H  is  caused  by  the  rush  of  air  through  the  widely  open  glottis. 
When,  in  sounding  a  vowel,  the  sound  coincides  with  a  sudden 
change  in  the  position  of  the  vocal  cords  from  one  of  divergence 
to  one  of  approximation,  the  vowel  is  pronounced  with  the  spiritus 
asper.  When  the  vocal  cords  are  brought  together  before  the  blast 
of  air  begins,  the  vowel  is  pronounced  with  the  spiritus  lenis. 
The  Arabic  H  is  produced  by  closing  the  rima  vocalis,  the  epiglot- 
tis and  false  vocal  cords  bemg  depressed,  and  sending  a  blast  of 
air  through  the  rima  respiratoria. 

On  many  of  the  above  points,  however,  there  are  great  dif- 
ferences of  opinion,  the  discussion  of  which  as  well  as  of  other 
more  rare  consonantal  sounds  would  lead  us  too  far  away  from  the 
purpose  of  this  book.  The  following  tabular  statement  must 
therefore  be  regarded  as  introduced  for  convenience  only. 

Explosives.     Labials,  without  voice,  P. 

,,  with  voice,     B. 

J  entals,  without  voice,   T. 

„  with  voice,     D. 

Gutturals,  without  voice,   K . 

,,  with  voice,     G  (hard). 


682  LOCOMOTOR   MECHANISMS.  [BOOK   III. 

Aspirates.     Labials,  without  voice,   F. 

„  with  voice,     V. 

Dentals,  without  voice,  S,  L,  Sh,  Th  (hard). 

.,  with  voice,     Z,  Zh,  (in  azure,  the 

French  j),  Th  (soft). 

Aspirates.     Gutturals,  without  voice,    CH  (asin/(?/r/i). 

, ,  with  voice,    GH  (as  in  lough), 

Resonants.   Labial,  M. 

Dental,  N. 

Guttural,  NG. 

Vibratory.    Labial,  not  known  in  European  speech. 

Dental,  R  (common). 

Guttural,  R  (guttural). 

Whispering  is  speech  without  any  employment  of  the  vocal 
cords,  and  is  effected  chiefly  by  the  lips  and  tongue.  Hence 
in  whispering  the  distinction  between  consonants  needing  and 
those  not  needing  voice,  such  as  B  and  P,  becomes  for  the 
most  part  lost. 

Sec.  3.     Locomotor  Mechanisms. 


The  skeletal  muscles  are  for  the  most  part  arranged  to  act 
on  the  bones  and  cartilages  as  on  levers,  examples  of  the  first  kind 
of  lever  being  rare,  and  those  of  the  third  kind,  where  the  power 
is  applied  nearer  to  the  fulcrum  than  is  the  weight,  being  more 
common  than  the  second.  This  arises  from  the  fact  that  the 
movements  of  the  body  are  chiefly  directed^  to  moving  compara- 
tively light  weights  through  a  great  distance,  or  through  a  certain 
distance  with  great  precision,  rather  than  to  moving  heavy  weights 
through  a  short  distance.  The  fulcrum  is  generally  supplied  by  a 
(perfect  or  imperfect)  joint,  and  one  end  of  the  acting  muscle  is 
made  fast  by  being  attached  either  to  a  fixed  point,  or  to  some 
point  rendered  fixed  for  the  time  being  by  the  contraction  of  other 
muscles.  There  are  few  movements  of  the  body  in  Avhich  one 
muscle  only  is  concerned  3  in  the  majority  of  cases  several  mus- 
cles act  together  in  concert;  nearly  all  our  movements  are 
coordinate  movements.  When  gravity  or  the  elastic  reaction  of 
the  parts  acted  on  does  not  afford  a  sufficient  antagonism  to  the 
contraction  of  a  muscle  or  group  of  muscles,  the  return  to  the 
condition  of  equilibrium  is  provided  for  by  the  action  either  elastic 
or  contractile  of  a  set  of  antagonistic  muscles  ;  this  is  seen  in  the 
case  of  the  face. 


rilAP.   VII.J      SPFXIAL   MUSCULAR    MECHANISMS.  683 

The  erect  posture,  in  which  the  weiglit  of  the  body  is 
borne  by  the  plantar  arches,  is  the  result  of  a  series  of  contrac- 
tions of  the  muscles  of  the  trunk  and  legs,  having  for  tlicir  object 
the  keeping  the  body  in  such  a  position  that  the  line  of  gravity 
falls  within  the  area  of  the  feet.  That  this  does  require  muscular 
exertion  is  shewn  by  the  facts,  that  a  person  when  standing  per- 
fectly at  rest  in  a  completely  balanced  position  falls  when  he 
becomes  unconscious,  and  that  a  dead  body  cannot  be  set  on  its 
feet.  The  line  of  gravity  of  the  head  falls  in  front  of  the 
occipital  articulation,  as  is  shewn  by  the  nodding  of  the  head  in 
sleep.  The  centre  of  gravity  of  the  combined  head  and  trunk 
lies  at  about  the  level  of  the  ensiform  cartilage,  in  front  of  the 
tenth  dorsal  vertebra,  and  the  line  of  gravity  drawn  from  it 
passes  behind  a  line  joining  the  centres  of  the  two  hip-joints,  so 
that  the  erect  body  would  fall  backward  were  it  not  for  the  action 
of  the  muscles  passing  from  the  thighs  to  the  pelvis  assisted  by 
the  anterior  ligaments  of  the  hip-joints.  The  line  of  gravity  of 
the  combined  head,  trunk  and  thighs  falls  moreover  a  little  behind 
the  knee-joints,  so  that  some,  though  little,  muscular  exertion  is 
required  to  prevent  the  knees  from  being  bent.  Lastly,  the  line  of 
gravity  of  the  whole  body  passes  in  front  of  the  line  drawn  be- 
tween the  two  ankle-joints,  the  centre  of  gravity  of  the  whole  body 
being  placed  at  the  end  of  the  sacrum  ;  hence  some  exertion  of 
the  muscles  of  the  calves  is  required  to  prevent  the  body  falling 
forwards. 

In  walking,  there  is  in  each  step  a  moment  at  which  the 
body  rests  vertically  on  the  foot  of  one,  say  the  right  leg,  while  the 
other,  the  left  leg,  is  inclined  obliquely  behind  with  the  heel  raised 
and  the  toe  resting  on  the  ground.  The  left  leg,  slightly  flexed  to 
avoid  contact  with  the  ground,  is  then  swung  forward  like  a  pen- 
dulum, the  length  of  the  swing  or  step  being  determined  by  the 
length  of  the  leg  ;  and  the  left  toe  i  is  brought  to  the  ground.  On 
this  left  toe  as  a  fulcrum,  the  body  is  moved  forward,  the  centre  of 
gravity  of  the  body  describing  a  curve  the  convexity  of  which  is 
upward,  and  the  left  leg  necessarily  bocomitig  straight  and  rigid. 
As  the  body  moves  forward,  a  point  will  be  reached  similar  to  that 
with  which  we  suppose  the  step  to  be  started,  the  body  resting 
vertically  on  the  left  foot,  and  the  right  leg  being  directed  behind 
in  an  oblique  position.  The  movement  on  the  left  foot  however 
carries  the  body  beyond  this  point,  and  in   doing  so  swings  the 

'  This  indicates  perhaps  what  should  be  done  rather  than  the  actual  prac- 
tice ;  most  people  put  the  heel  to  the  ground  first,  the  contact  with  the  toe 
coming  later. 


684  LOCOMOTOR   MECHANISMS.  [BOOK   III. 

right  leg  forward  until  it  is  the  length  of  a  step  in  advance  of 
its  previous  position,  and  its  toe  in  turn  forms  a  fulcrum  on 
which  the  body,  and  with  it  the  left  leg,  is  again  swung  for- 
ward. Hence  in  successive  steps  the  centre  of  gravity,  and  with 
it  the  top  of  the  head,  describes  a  series  of  consecutive  curves, 
with  their  convexities  upwards,  very  similar  to  the  line  of  flight 
of  many  birds. 

Since  in  standing  on  both  feet  the  line  of  gravity  falls  between 
the  two  feet,  a  lateral  displacement  of  the  centre  of  gravity  is 
necessary  in  order  to  balance  the  body  on  one  foot.  Hence  in 
walking  the  centre  of  gravity  describes  not  only  a  series  of 
vertical,  but  also  a  series  of  horizontal  curves,  inasmuch  as  at 
each  step  the  line  of  gravity  is  made  to  fall  alternately  on  each 
standing  foot.  While  the  left  leg  is  swinging,  the  line  of  gravity 
fails  within  the  area  of  the  right  foot,  and  the  centre  of  gravity  is 
on  the  right  side  of  the  pelvis.  As  the  left  foot  becomes  the 
standing  foot,  the  centre  of  gravity  is  shifted  to  the  left  side  of  the 
pelvis.  The  actual  curve  described  by  the  centre  of  gravity  is 
therefore  a  somewhat  complicated  one,  being  composed  of  vertical 
and  horizontal  factors.  The  natural  step  is  the  one  which  is  deter- 
mined by  the  length  of  the  swinging  leg,  since  this  acts  as  a 
pendulum  ;  and  hence  the  step  of  a  long-legged  person  is  naturally 
longer  than  that  of  a  person  with  short  legs.  The  length  of  the 
step  however  may  be  diminished  or  increased  by  a  direct  mus- 
cular effort,  as  when  a  line  of  soldiers  keep  step  in  spite  of  their 
having  legs  of  different  lengths.  Such  a  mode  of  marching  must 
obviously  be  fatiguing,  inasmuch  as  it  involves  an  unnecessary 
.expenditure  of  energy. 

In  slow  walking  there  is  an  appreciable  time  during  which, 
while  one  foot  is  already  in  position  to  serve  as  a  fulcrum,  the 
other,  swinging,  foot  has  not  left  the  ground.  In  fast  walking  this 
period  is  so  much  reduced,  that  one  foot  leaves  the  ground  the 
moment  the  other  touches  it ;  hence  there  is  practically  no  period 
during  which  both  feet  are  on  the  ground  together. 

When  the  body  is  swung  forward  on  the  one  foot  acting 
as  a  fulcrum  with  such  energy  that  this  foot  leaves  the  ground 
before  the  other,  swinging,  foot  has  reached  the  ground,  there 
being  an  interval  during  which  neither  foot  is  on  the  ground,  the 
person  is  said  to  be  running,  not  walking. 

In  jumping  this  propulsion  of  the  body  takes  place  on  both 
feet  at  the  same  time ;  in  hopping  it  is  effected  on  one  foot  only. 

The  locomotion  of  four-footed  animals  is  necessarily  more 
complicated  than  that  of  man.  The  simple  walk,  such  as  that  of 
the  horse,  is  executed  in  four  times,  with  a  diagonal  succession : 


CHAP.   VH.]      SPECIAL   MUSCULAR   MECHANISMS.  685 

thus,  riglit  fore  log,  left  hind  leg,  left  fore  leg,  right  hind  leg.  In 
the  amble,  such  as  that  of  the  camel,  the  two  feet  of  the  same  side 
are  put  down  at  one  and  the  same  time,  this  movement  being  fol- 
lowed 1)}'  a  similar  movement  of  the  other  two  legs  ;  it  corresponds 
therefore  very  closely  to  human  walking.  In  the  trot,  which 
corresponds  to  human  running,  the  two  diagonally  opposite  feet 
are  brought  to  the  ground  at  the  same  time,  and  the  body  is  pro- 
pelled forwards  on  them.  Of  the  gallop  and  canter  there  are 
many  varieties,  and  the  movements  become  very  complicated'. 

The  other  problems  connected  with  the  action  of  the  various 
skeletal  muscles  of  the  body  are  too  special  to  be  considered 
here. 

'  See  Marey,  Im  Machine  Animale  (1876). 


BOOK    IV. 


THE    TISSUES    AND    MECHANISMS    OF 
REPRODUCTION. 


THE   TISSUES   AND    MECHANISMS   OF   REPRO- 
DUCTION. 

Many  of  the  individual  constituent  parts  of  the  body  are  capable 

of  reproduction,  i.e.  they  can  give  rise  to  parts  like  themselves ;  or 

they  are  capable  of  regeneration,  i.e.  their  places  can  be  taken 

by  new   parts  more  or  less  closely  resembUng  themselves.     The 

elementary  tissues   undergo   during  life  a  very  large  amount  of 

regeneration.      Thus  the  old  epithelium  scales  which  fall   away 

from  the  surface  of  the  body  are  succeeded  by  new  scales  from  the 

underlying  layers  of   the  epidermis  ;    old  blood-corpuscles  give 

place  to  new  ones  ;  worn-out  muscles,  or  those  which  have  failed 

from  disease,  are  renewed  by  the  accession  of  fresh  fibres  ;  divided 

nerves  grow  again  ;  broken  bones  are  united  ;  connective  tissue 

seems  to  disappear  and  appear  almost  without  limit ;  new  secreting 

cells  take  the  place  of  the  old  ones  which  are  cast  off;  in  fact, 

with  the  exception  of  some  cases,    such  as  cartilage,  and  these 

doubtful  exceptions,  all   those  fundamental  tissues  of  the  body, 

which  do  not  form  part  of  highly  differentiated  organs,  are,  within 

limits  fixed  more  by  bulk  than  by  anything  else,  capable  of  re- 

creneration.      That    regeneration    by   substitution   of  molecules, 

which  is  the  basis  of  all  life,  is  accompanied  by  a  regeneration 

by  substitution  of  mass. 

In  the  higher  animals  regeneration  of  whole  organs  and 
members,  eveii  of  those  w|;iose  continued  functional  activity  is 
not  essential  to  the  well-being  of  the  body,  is  never  witnessed, 
though  it  may  be  seen  in  the  lower  animals  ;  the  digits  of  a  newt 
may  be  restored  by  growth,  but  not  those  of  a  man.  And  the 
repair  which  follows  even  partial  destruction  of  highly  differen- 
tiated  organs,  such  as  the  retina,  is  in  the  higher  animals  very 

imperfect.  •   j-  -j 

In  the  higher  animals  the  reproduction  of  the  whole  individual 
can  be  effected  in  po  other  way  than  by  the  process  of  sexual 
generation,  through  which  the  female  representative  element  or 
F.P.  '*4 


690  MECHANISMS   OF   REPRODUCTION.      [BOOK  IV. 

ovum  is,  under  the  influence  of  the  male  representative  or  sperma- 
tozoon, developed  into  an  adult  individual. 

We  do  not  purpose  to  enter  here  into  any  of  the  morphological 
problems  connected  with  the  series  of  changes  through  which  the 
ovum  becomes  the  adult  being;  or  into  the  obscure  biological 
inquiry  as  to  how  the  simple  all  but  structureless  ovum  contains 
within  itself,  in  potentiality,  all  its  future  developments,  and  as  to 
what  is  the  essential  nature  of  the  male  action.  These  problems 
and  questions  are  fully  discussed  elsewhere  ;  they  do  not  properly 
enter  into  a  work  on  physiology,  except  under  the  view  that  all 
biological  problems  are,  when  pushed  far  enough,  physiological 
problems.  We  shall  limit  ourselves  to  a  brief  survey  of  the  more 
important  physiological  phenomena  attendant  on  the  impregnation 
of  the  ovum,  and  on  the  nutrition  and  birth  of  the  embryo. 


CHAPTER  I. 

MENSTRUATION. 

From  puberty,  which  occurs  at  from  13  to  17  years  of  age,  to  the 
climacteric,  which  arrives  at  from  45  to  50  years  of  age,  the  human 
female  is  subject  to  a  monthly  discharge  of  ova  from  the  ovaries, 
accompanied  by  special  changes,  not  only  in  those  organs  but  also 
in  the  Fallopian  tubes  and  uterus,  as  well  as  by  general  changes 
in  the  body  at  large,  the  whole  constituting  'menstruation.'  The 
essential  event  in  menstruation  is  the  escape  of  an  ovum  from 
its  Graafifian  follicle.  The  whole  ovary  at  this  time  becomes 
congested,  and  the  ripe  follicle  bulging  from  the  surface  of  the 
ovary,  is  grasped  by  the  trumpet-shaped  fringed  opening  of  the 
Fallopian  tube,  itself  turgid  and  congested  ;  by  what  mechanism 
this  is  eftected  is  not  exactly  known.  The  most  projecting 
portion  of  the  wall  of  the  follicle,  which  has  previously  become 
excessively  thin,  is  now  ruptured,  and  the  ovum,  which  having 
left  its  earlier  position,  is  lying  close  under  the  projecting  surface 
of  the  follicle,  escapes,  together  with  the  cells  of  the  discus  pro- 
lii^^erus,  into  the  Fallopian  tube.  Thence  it  travels  downwards, 
very  slowly,  by  the  action  probably  of  the  cilia  lining  the  tube, 
though  possibly  its  progress  may  occasionally  be  assisted  by  the 
peristaltic  contractions  of  the  muscular  walls.  The  stay  of  the 
ovum  in  the  Fallopian  tube  may  extend  to  several  days.  There 
is  an  eftusion  of  blood  into  the  ruptured  follicle,  which  is  subse- 
quently followed  by  histological  changes  in  the  coats  of  the  follicle 
resulting  in  a  corpus  lutcum.  The  discharge  of  the  ovum  is  ac- 
companied not  only  by  a  congestion  or  erection  of  the  ovary 
and  Fallopian  tube,  but  also  by  marked  changes  in  the  uterus, 
especially  in  the  uterine  mucous  membrane.  While  the  whole 
organ  becomes  congested  and  enlarged,  the  mucous  membrane, 
and  especially  the  uterine  glands,  are  distinctly  hypertrophied. 
The  swollen  internal  surface  is  thrown  into  folds  which  almost  ob- 
literate the  cavity  ;  and  a  hsemorrhagic  discharge,  often  considerable 

44—2 


692  '  MENSTRUATION.  [BOOK   IV. 

in  extent,  constituting  the  menstrual  or  catamenial  flow,  takes 
place  from  the  greater  part  of  its  surface.  The  blood  as  it  passes 
through  the  vagina  becomes  somewhat  altered  by  the  acid  secre- 
tions of  that  passage,  and  when  scanty  coagulates  but  slightly ; 
when  the  flow  however  is  considerable,  distinct  clots  may  make 
their  appearance.  It  is  not  certain  that  menstruation,  in  the 
human  subject  at  all  events,  is  always  accompanied  by  a  discharge 
of  an  ovum ;  indeed  cases  have  been  recorded  in  which  menstrua- 
tion continued  after  what  appeared  to  be  complete  removal  of 
both  ovaries.  And  it  seems  probable  also  that  under  certain 
circumstances,  ex.  gr.  coitus,  a  discharge  of  an  ovum  may  take 
place  at  other  times  than  at  the  menstrual  period.  Since  however 
the  time  during  which  both  the  ovum  and  the  spermatozoon  may 
remain  in  the  female  passages  alive  and  functionally  capable  is 
considerable,  probably  extending  to  some  days,  coitus  effected 
either  some  time  after  or  some  time  before  the  menstrual  escape 
of  an  ovum  might  lead  to  impregnation  and  subsequent  develop- 
ment of  an  embryo  ;  hence  the  fact  that  impregnation  may  follow 
upon  coitus  at  some  time  after  or  before  menstruation  is  no  very 
cogent  argument  in  favour  of  the  view  that  such  a  coitus  has 
caused  an  independent  escape  of  an  ovum.  The  escape  of  the 
ovum  is  said  to  precede,  rather  than  coincide  with  or  follow,  the 
catamenial  flow  ^.  If  no  spermatozoa  come  in  contact  with  the 
ovum  it  dies,  the  uterine  membrane  returns  to  its  normal  condi- 
tion, and  no  trace  of  the  discharge  of  an  ovum  is  left,  except  the 
corpus  luteum  in  the  ovary. 

According  to  many  authors  the  uterine  mucous  membrane  is 
actually  shed  during  menstruation,  and  subsequently  entirely  regene- 
rated. According  to  their  view  the  hasmorrhagic  discharge  is  due  to  a 
positive  '  solution  of  continuity.'  In  animals  no  discharge  of  blood, 
or  a  very  scanty  one,  takes  place  at  '  heat '  or  '  rut ' ;  hence  this  point 
cannot  be  settled  by  comparative  studies  ;  and  in  the  human  subject 
the  interval  which  must  necessarily  elapse  between  death  and  examina- 
tion, is  sufficiently  long  to  render  investigation  very  difficult.  Williams" 
has  brought  forward  strong  evidence  in  favour  of  an  actual  loss  of 
substance  taking  place.  According  to  him,  menstruation  is  accom- 
panied by  a  rapid  growth  and  subsequent  rapid  degeneration  of  the 
mucous  membrane,  for  a  depth  reaching  down  to  that  layer  of  muscular 
fibres  which  passes  among  the  deeper  parts  of  the  uterine  glands. 
The  growth  and  degeneration  begin  at  an  abrupt  line  near  the  cervix, 
and  spread  towards  the  fundus.  The  decay  lays  bare  small  blood- 
vessels, from  which  the  haemorrhage  takes  place. 

'  Williams,  Proc.  Roy.  Soc.  xxill.  439. 

^  Proc.  Roy.  Soc.  xxil.  297.  See  also  his  Slruc.  Muc.  Memb.  0/  Uterus, 
1875. 


CHAP.   I.]  MENSTRUATION.  693 

It  is  obvious  that  in  these  phenomena  of  menstruation  we 
have  to  deal  with  comphcated  reflex  actions  affecting  not  only 
the  vascular  supply,  but,  apparently  in  a  direct  manner,  the  nutri- 
tive changes  of  the  organs  concerned.  Our  studies  on  the  nervous 
action  of  secretion  render  it  easy  for  us  to  conceive  in  a  general 
way  how  the  several  events  are  brought  about.  It  is  no  more 
difficult  to  suppose  that  the  stimulus  of  the  enlargement  of  a 
(iraaftian  folhcle  causes  nutritive  as  well  as  vascular  changes  in 
the  uterine  mucous  membrane,  than  it  is  to  suppose  that  the 
stimulus  of  food  in  the  alimentary  canal  causes  those  nutritive 
changes  in  the  salivary  glands  or  pancreas  which  constitute  secre- 
tion. In  the  latter  case  we  can  to  some  extent  trace  out  the  chain 
of  events ;  in  the  former  case  we  hardly  know  more  than  that  the 
maintenance  of  the  lumbar  cord  is  sufficient,  as  far  as  the  central 
nervous  system  is  concerned,  for  the  carrying  on  of  the  work.  In 
the  case  of  a  dog  observed  by  Goltz',  '  heat '  or  menstruation 
took  place  as  usual,  though  the  spinal  cord  had  been  completely 
divided  in  the  dorsal  region  while  the  animal  was  as  yet  a  mere 
puppy. 

The  operation  was  performed  in  Dec.  1873.  ^^  the  following  May 
the  animal  was  in  excellent  health,  and  there  was  not  the  slightest 
indication  that  any  functional  connection  between  the  dorsal  and 
lumbar  portions  of  the  spinal  cord  had  been  re-established.  At  the 
end  of  that  month  'heat'  came  on,  attended  by  all  the  ordinary 
phenomena  psychical  as  well  as  physical.  Impregnation  was  etitected 
and  the  animal  became  gravid.  The  pregnancy,  like  the  heat,  was 
marked  by  all  the  usual  signs  ;  the  mammary  glands  enlarged,  and  the 
usual  mental  accompaniments  of  the  condition  were  present.  Finally, 
one  living  and  two  dead  puppies  were  born,  the  first  without  and  the 
latter  two  with  assistance  ;  the  mother  however  sank  soon  afterwards 
from  puerperal  peritonitis.  The  post-mortem  examination  shewed 
that  there  had  been  no  regeneration  of  the  divided  spinal  cord  ;  the 
two  portions  were  separated  by  more  than  a  centimetre. 

In  this  case  the  connection  between  the  ovary  on  the  one  hand  and 
the  mammary  gland,  brain,  &c.,  on  the  other,  must,  if  a  nervous  one, 
have  been  furnished  by  the  abdominal  sympathetic.  We  may  however 
suppose  that  the  nexus  was  a  chemical  one  ;  that  the  condition  of  the 
ovary  and  uterus  effected  a  change  in  the  blood,  which  in  turn  excited 
the  mammary  gland  to  increased  action  and  produced  special  changes 
in  the  brain. 

'  Pfliiger's  Archiv,  ix.  (1874)  p.  552. 


CHAPTER  II. 

IMPREGNATION. 

In  coitus  the  discharge  of  the  semen  containing  the  spermatozoa 
is  most  probably  effected  by  means  of  the  peristaltic  contractions  of 
the  vesicula;  seminales  and  vasa  deferentia,  assisted  by  rhythmical 
contractions  of  the  bulbo-cavernosus  muscle,  the  whole  being  a 
reflex  act,  the  centre  of  which  appears  to  be  in  the  lumbar  spinal 
cord.  Goltz''  has  shewn  that  in  the  dog,  emission  of  semen  can  be 
brought  about  by  stimulation  of  the  glans  penis  after  complete 
division  of  the  spinal  cord  in  the  dorsal  region.  The  emission 
of  semen  is  preceded  by  an  erection  of  the  penis.  This  we  have 
already  seen,  p.  215,  is  in  part  at  least  due  to  an  increased  vascular 
supply  brought  about  by  means  of  the  nervi  erigentes ;  it  is 
probable,  however,  that  the  condition  is  further  secured  by  a 
compression  of  the  efferent  veins  of  the  corpora  cavernosa  by 
means  of  smooth  muscular  fibres  present  in  those  bodies.  The 
semen  being  received  into  the  female  organs,  which  are  at  the 
time  in  a  state  of  turgescence  resembling  the  erection  of  the.  penis, 
but  less  marked,  the  spermatozoa  find  their  way  into  the  Fallopian 
tubes,  and  here  (probably  in  its  upper  part)  come  in  contact  with 
the  ovum.  In  the  case  of  some  animals  impregnation  may  take 
place  at  the  ovary  itself.  The  passage  of  the  spermatozoa  is  most 
probably  effected  mainly  by  their  own  vibratile  activity ;  but  in 
some  animals  a  retrograde  peristaltic  movement  travelling  from 
the  uterus  along  the  Fallopian  tubes  has  been  observed  ;  this 
might  assist  in  bringing  the  semen  to  the  ovum,  but  inasmuch 
as  these  movements  are  probably  parts  of  the  act  of  coitus  and 
impregnation  may  be  deferred  till  some  time  after  that  event,  no 
great  stress  can  be  laid  upon  them. 

The  ascent  of  the  spermatozoa  is  certainly  puzzling  if  the  cilia  of 
the  Fallopian  tubes,  which  act  from  above  downwards,  continue  their 
activity  after  the  escape  of  the  ovum.     The  spermatozoa  directly  they 

'  Pfluger's  Archiv,  viii.  (1874)  p.  460. 


CHAP.   II.]  IMPREGNATION.  695 

come  in  contact  with   tlic  ovum  become  motionless;    this  suggests 
that  the  final  cause  of  their  activity  is  to  enable  them  to  reach  the 

ovum. 

As  the  result  of  the  action  of  the  spermatozoa  on  the  ovum,  the 
latter,  instead  of  dying  as  when  impregnation  fails,  awakes  to 
great  nutritive  activity  accompanied  by  remarkable  morphological 
changes ;  it  enlarges  and  developes  into  an  embryo.  No  sooner, 
however,  have  these  changes  begun  in  the  ovum  than  correlative 
changes,  brought  about  probably  by  reflex  action,  but  at  present 
most  obscure  in  their  causation,  take  place  in  the  uterus.  The 
mucous  membrane  of  this  organ,  whether  the  coitus  resulting  in 
impregnation  be'  coincident  with  a  menstrual  period  or  not, 
becomes  congested,  and  a  rapid  growth  takes  place,  characterized 
by  a  rapid  proliferation  of  the  e|)ithelial  and  subepithelial  tissues. 
Unlike  the  case  of  menstruation,  however,  this  new  growth  does 
not  give  way  lo  immediate  decay  and  haemorrhage,  but  remains  ; 
and  may  be  distinguished  as  a  new  temporary  lining  to  the  uterus, 
the  so-called  decidua.  Into  this  decidua  the  ovum,  on  its  descent 
from  the  Fallopian  tube,  in  which  it  has  undergone  developmental 
changes,  extending  most  probably  as  far  at  least  as  the  formation 
of  the  blastoderm  if  not  farther,  is  received ;  and  in  this  it 
becomes  embedded,  the  new  growth  closing  in  over  it.  Mean- 
while the  rest  of  the  uterine  structures,  especially  the  muscular 
tissue,  become  also  much  enlarged  ;  as  pregnancy  advances  a 
large  number  of  new  muscular  fibres  are  formed.  As  the  ovum 
continues  to  increase  in  size,  it  bulges  into  the  cavity  of  the 
uterus,  carrying  with  it  the  portion  of  the  decidua  which  has 
closed  over  it.  Henceforward,  accordingly,  a  distinction  is  made 
in  the  now  well-developed  decidua  between  the  decidua  rc/lcxa,  or 
that  part  of  the  membrane  which  covers  the  projecting  ovum,  and 
the  decidua  vera,  or  the  rest  of  the  membrane  lining  the  cavity  of 
the  uterus,  the  two  being  continuous  round  the  base  of  the  pro- 
jecting ovum.  That  part  of  the  decidua  which  intervenes  between 
the  ovum  and  the  nearest  uterine  wall  is  frequently  spoken  of  as 
the  duidua  serotina.  As  the  ovum  develops  into  the  foetus  with 
its  membranes,  the  decidua  reflexa  becomes  pushed  against  the 
decidua  vera ;  about  the  end  of  the  third  month,  in  the  human 
subject,  the  two  come  into  complete  contact  all  over,  and 
ultimately  the  distinction  between  them  is  lost.  In  the  region 
of  the  decidua  seratina  the  allantoic  vessels  of  the  foetus  develop 
a  placenta.  For  an  account  of  the  various  changes  by  which 
these  events  are  brought  about,  as  well  as  of  the  history  of  the 
embryo  itself,  we  must  refer  the  reader  to  anatomical  treatises. 


CHAPTER  III. 

THE  NUTRITION  OF  THE  EMBRYO. 

During  the  development  of  the  chick  within  the  hen's  egg  the 
nutritive  material  needed  for  the  growth  first  of  the  blastoderm, 
and  subsequently  of  the  embryo,  is  suppHed  by  the  yolk,  while  the 
oxygen  of  the  air  passing  freely  through  the  porous  shell,  gains 
access  to  all  the  tissues  both  of  the  embryo  and  yolk,  either 
directly  or  by  the  intervention  of  the  allantoic  vessels.  The 
mammalian  embryo,  during  the  period  which  precedes  the  ex- 
tension of  the  allantoic  vessels  into  the  cavities  of  the  uterine 
walls  to  form  the  placenta,  must  be  nourished  by  direct  diffusion, 
first  from  the  contents  of  the  Fallopian  tube,  and  subsequently 
from  the  decidua ;  and  its  supply  of  oxygen  must  come  from  the 
same  sources.  All  analogy  would  lead  us  to  suppose  that,  from 
the  very  first,  oxidation  is  going  on  in  the  blastodermic  and  em- 
bryonic structures  ;  but  the  amount  of  oxygen  actually  withdrawn 
from  without  is  probably  exceedingly  small  in  the  early  stages, 
seeing  that  nearly  the  whole  energy  of  the  metabolism  going  on 
is  directed  to  the  building  up  of  structures,,  the  expenditure  of 
energy  in  the  form  of  either  heat  or  external  work  being  extremely 
small.  The  marked  increase  of  bulk  which  takes  place  during 
the  conversion  of  the  mulberry  mass  into  the  blastodermic  vesicle, 
shews  that  at  this  epoch  a  relatively  speaking  large  quantity  of 
water  at  least,  and  probably  of  nutritive  matter,  must  pass  from 
without  into  the  ovum  ;  and  subsequently,  though  the  blastoderm 
and  embryo  may  for  some  time  draw  the  material  for  their  con- 
tinued construction  at  first  hand  from  the  yolk-sac  or  umbilical 
vesicle,  both  this  and  they  continue  probably  until  the  allantois  is 
formed  to  receive  fresh  material  from  the  mother  by  direct 
diff'usion. 

As  the  thin-walled  allantoic  vessels  come  into  closer  and 
fuller  connection  with  the  material  uterine  sinuses,  until  at  last 
in  the  fully  formed  placenta  the  former  are  freely  bathed  in  the 


CHAP.    III.  I      rilE    NUTRITION    OF   THE   EMBRYO.  697 

blood  streaming  throu^'h  the  latter,  the  nutrition  of  the  embryo 
bcconics  more  and  more  confined  to  this  special  channel.  The 
blood  of  the  foetus  flowing  along  the  umbilical  arteries  effects 
exchanges  with  the  venous  blood  of  the  mother,  and  leaves  the 
placenta  by  the  umbilical  vein  richer  in  oxygen  and  nutritive 
material  and  poorer  in  carbonic  acid  and  excretory  products  than 
when  it  issued  from  the  foetus. 

As  far  as  the  gain  of  oxygen  and  the  loss  of  carbonic  acid  are 
concerned  these  are  the  results  of  simple  diffusion.  Venous 
blood,  as  we  have  already  seen,  always  contains  a  quantity  of 
oxyha^moglobin,  and  the  quantity  of  this  substance  present  in  the 
blood  of  the  uterine  veins  is  sufficient  to  supply  all  the  oxygen 
that  the  embryo  needs ;  the  blood  of  the  foetus,  containing  less 
oxygen  than  even  the  venous  blood  of  the  mother,  will  take  up  a 
certain  though  small  quantity.  The  fcetal  blood  travelling  in  the 
umbilical  artery  must,  in  proportion  to  the  extent  of  the  nutritive 
changes  going  on  in  the  embryo,  possess  a  higher  carbonic 
tension  than  that  in  the  umbilical  vein  or  uterine  sinus  ;  and  by 
di'ffusion  gets  rid  of  this  surplus  during  its  stnv  in  the  placenta. 
The  blood  in  the  umbilical  arteries  and  veins  is  therefore,  rela- 
tively speaking,  venous  and  arterial  respectively,  though  the  small 
excess  of  oxyhemoglobin  in  the  blood  of  the  umbilical  vein  '  is 
insufficient  to  give  it  a  distinctly  arterial  colour,  or  to  distinguish 
it  as  sharply  from  the  more  venous  blood  of  the  umbilical  artery, 
as  is  ordinary  arterial  from  ordinary  venous  blood.  Thus  the 
foetus  breathes  by  means  of  the  maternal  blood,  in  the  same  way 
that  a  fish  breathes  by  means  of  the  water  in  which  it  dwells. 

The  blood  of  the  foetus,  according  to  Zuntz-,  is  very  poor  in  haemo- 
globin corresponding  to  its  low  oxygen  consumption.  When  the 
mother  is  asphyxiated,  the  foetus  is  asphyxiated  too,  the  oxygen  of  the 
latter  passing  back  again  in  the  blood  of  the  former  ;  and  the  asphyxia 
thus  produced  in  the  fcetus  is  much  more  rapid  than  that  which  results 
when  the  oxygen  is  used  up  by  the  tissues  of  the  foetus  alone,  as  when 
the  umbilicus  is  ligatured  and  the  foetus  not  allowed  to  breathe. 

If  oxygen  and  carbonic  acid  thus  pass  by  diffusion  to  and 
from  the  mother  and  the  fcetus,  one  might  fairly  expect  that 
diffusible  salts,  proteids,  and  carbohydrates  would  be  conveyed  to 
the  latter,  and  difl'usible  excretions  carried  away  to  the  former,  in 
the  same  way  ;  and  if  fats  can  pass  directly  into  the  portal  blood 
during  ordinary  digestion,  there  can  be  no  reason  for  doubting 
that  this  class  of  food-stuffs  also  would  find  its  way  to  the  fcetus 

'  Zwcifel,  Arch,  fiir  Gynakologie,  IX.  lift.  2. 
'•'  rfliJijcr's  Archiv,  X'v.  (1877)  p.  605. 


698  FCETAL   RESPIRATION.  [BOOK   IV. 

through  the  placental  structures.  We  do  know  from  experiment 
that  diffusible  substances  will  pass  both  from  the  mother  to 
the  foetus,  and  from  the  foetus  to  the  mother ;  but  we  have  no 
definite  knowledge  as  to  the  exact  form  and  manner  in  which, 
during  normal  intra-uterine  life,  nutritive  materials  are  conveyed 
to  or  excretions  conveyed  from  the  growing  young.  The  placenta 
is  remarkable  for  the  great  development  of  cellular  structures, 
apparently  of  an  epithelial  nature,  on  the  border-land  between 
the  maternal  and  foetal  elements  ;  and  it  has  been  suggested  that 
these  form  a  temporary  digestive  and  secretory  (excretory)  organ. 
But  we  have  no  exact  knowledge  of  what  actually  does  take  place 
in  these  structures.  From  the  cotyledons  of  ruminants  may  be 
obtained  a  white  creamy-looking  fluid,  which  from  many  features 
of  its  chemical  composition  might  be  almost  spoken  of  as  a 
'  uterine  milk.' 

Speaking  broadly,  the  foetus  lives  on  the  blood  of  its  mother, 
very  much  in  the  sam.e  way  as  all  the  tissues  of  any  animal  live 
on  the  blood  of  the  body  of  which  they  are  the  parts. 

For  a  long  time  all  the  embryonic  tissues  are  '  protoplasmic  ' 
in  character ;  that  is,  the  gradually  differentiating  elements  of  the 
several  tissues  remain  still  embedded,  so  to  speak,  in  undifferen- 
tiated protoplasm  ;  and  during  this  period  there  must  be  a  general 
similarity  in  the  metabolism  going  on  in  various  parts  of  the  body. 
As  differentiation  becomes  more  and  more  marked,  it  obviously 
would  be  an  economical  advantage  for  partially  elaborated  material 
to  be  stored  up  in  various  foetal  tissues,  so  as  to  be  ready  for 
immediate  use  when  a  demand  arose  for  it,  rather  than  for  a 
special  call  to  be  made  at  each  occasion  upon  the  mother  for  com- 
paratively raw  material  needing  subsequent  preparatory  changes. 
Accordingly,  we  find  the  tissues  of  the  foetus  at  a  very  early 
period  loaded  with  glycogen.  The  muscles  are  especially  rich 
in  this  substance,  but  it  occurs  in  other  tissues  as  well.  The 
abundance  of  it  in  the  former  may  be  explained  partly  by  the  fact 
that  they  form  a  very  large  proportion  of  the  total  mass  of  the 
foetal  body,  and  partly  by  the  fact  that,  while  during  the  presence 
of  the  glycogen  they  contain  much  undifferentiated  protoplasm, 
they  are  exactly  the  organs  which  will  ultimately  undergo  a  large 
amount  of  differentiation,  and  therefore  need  a  large  amount  of 
material  for  the  metabolism  which  the  differentiation  entails.  It 
is  not  until  the  later  stages  of  intra-uterine  life,  at  about  the  fifth 
month,  when  it  is  largely  disappearing  from  the  muscles,  that  the 
glycogen  begins  to  be  deposited  in  the  liver.  By  this  time  histo- 
logical differentiation  has  advanced  largely,  and  the  use  of  the 
glycogen  to  the  economy  has  become  that  to  which  it  is  put  in 


CHAP.   III.]     THE   NUTRITION    OF   TllK   EMBRYO.  699 

the  ordinary  life  of  the  animal ;  hence  we  find  it  deposited  in  the 
usual  place.  Besides  being  present  in  the  foetal,  glycogen  is  found 
also  in  the  placental  structures ;  but  here  probably  it  is  of  use,  not 
for  the  ftetus,  but  for  the  nutrition  and  growth  of  the  placental 
structures  themselves.  We  do  not  know  how  much  carbohydrate 
material  finds  its  way  into  the  umbilical  vein  ;  and  we  cannot 
therefore  state  what  is  the  source  of  the  foetal  glycogen ;  but  it 
is  at  least  possible,  not  to  say  probable,  that  it  arises,  as  we 
have  reason  (p.  436)  to  think  it  may,  from  a  splitting  up  of 
proteid  material. 

Concerning  the  rise  and  development  of  the  functional  activi- 
ties of  the  embryo,  our  knowledge  is  almost  a  blank.  We  know 
scarcely  anything  about  the  various  steps  by  which  the  primary 
fundamental  qualities  of  the  protoplasm  of  the  ovum  are  differen- 
tiated into  the  complex  phenomena  which  we  have  attempted  in 
this  book  to  expound.  We  can  hardly  state  more  than  that  while 
muscular  contractility  becomes  early  developed,  and  the  heart 
probably,  as  in  the  chick,  boats  even  before  the  blood-corpuscles 
are  formed,  movements  of  the  foetus  do  not,  in  the  human  subject, 
become  pronounced  until  after  the  fifth  month  ;  from  that  time 
forward  they  increase  and  subsequently  become  very  marked. 
They  are  often  spoken  of  as  reflex  in  character ;  but  only  a  pre- 
conceived bias  w^ould  prevent  them  from  being  regarded  as  largely 
automatic  The  digestive  functions  are  naturally,  in  the  absence 
of  all  food  from  the  alimentary  canal,  in  abeyance.  Though 
pepsin  may  be  found  in  the  gastric  membrane  at  about  the  fourth 
month,  it  is  doubtful  whether  a  truly  peptic  gastric  juice  is  secreted 
during  intra-uterine  life ;  trypsin  appears  in  the  pancreas  some- 
what later,  but  an  amylolytic  erment  cannot  be  obtained  from 
that  organ  till  after  birth'.  Tne  excretory  functions  of  the  liver 
are  developed  early,  and  about  the  third  month  bile-pigment  and 
bile-salts  find  their  way  into  the  intestine.  The  quantity  of  bile 
secreted  during  intrauterine  life,  accumulates  in  the  intestine  and 
especially  in  the  rectum,  forming,  together  with  the  smaller  secre- 
tion of  the  rest  of  the  canal,  and  some  desquamated  epithelium, 
the  so-called  meconium.  Bile  salts,  both  unaltered  and  variously 
changed,  the  usual  bile  pigments,  and  cholesterin,  are  all  present 
in  the  meconium.  The  distinct  formation  of  bile  is  an  indication 
that  the  products  of  fcetal  metabolism  are  no  longer  wholly  carried 
off  by  the  maternal  circulation  ;  and  to  the  excretory  function 
of  the  liver  there  are  now  added  those  of  the  skin  and  kidney. 
The  substances  escaping  by  these  organs  find  their  way  into  the 

'  I.angendorff,  Arch  f.  Anal.  u.  Phys.  (Phys.  Abth.)  1879,  p.  90.  Cf 
Moriggia,  Moleschott's  Untersuch.  xi.  (1875)  P-  455- 


700  FCETAL   CIRCULATION.  [BOOK  IV. 

allantois  or  into  the  amnion,  according  to  the  arrangement  of  the 
foetal  membranes  in  different  classes  of  animals  ;  m  both  these 
fluids  m-ea  representatives  have  been  found  as  well  as  the  ordmary 
saline  constituents  ;  the  latter  may  or  may  not  have  been  actually 
secreted.  From  the  allantoic  fluid  of  rummants  the  body  allantom 
has  been  obtained,  and  human  and  other  amniotic  fluids  have 
been  found  to  contain  urea. 

Zuntz^  however  argues  that  since  sodium  sulphindigolate  injected 
into  the  veins  of  the  mother  (rabbits)  is  readily  found  in  the  fluid  of 
the  amnion  but  not  in  any  part  of  the  body  of  the  foetus  (save  a  small 
quantity  in  the  stomach,  probably  derived  from  amniotic  fluid  which 
had  been  swallowed),  the  fluid  must  be  discharged  from  the  maternal 
structures,  and  cannot,  at  all  events,  be  regarded  as  wholly  a  secretion 
from  the  foetus.  The  sulphindigolate  also  made  its  way  into  the 
amnion  when  the  fcetus  had  been  previously  killed.  The  urea  of  the 
amniotic  fluid  may  accordingly,  in  part  at  least,  have  escaped  by 
diffusion  from  the  blood  of  the  mother^ 

The  date  at  which  pepsin  and  other  ferments  make  their  appearance 
in  the  embryo  appears  to  differ  in  different  animals 3. 

About  the  middle  of  intra-uterine  life,  when  the  foetal  circula- 
tion is  in  full  development,  the  blood  flowing  along  the  umbdical 
vein  is  carried  chiefly  by  the  ductus  venosus  into  the  inferior  vena 
cava  and  so  into  the  right  auricle.     Thence  it  is  directed  by  the 
valve  of  Eustachius  through  the  foramen  ovale  into  the  left  auricle, 
passing  from  which  into  the  left  ventricle  it  is  driven  into  the  aorta. 
Part  of  the  umbilical  blood,  however,  instead  of  passing  directly 
to  the  interior  cava,  enters  by  the  portal  vein  into  the  hepatic 
circulation,  from  which  it  returns  to  the  inferior   cava   by   the 
hepatic  veins.     The  inferior  cava  also  contains  blood  coming  from 
the  lower  limbs  and  lower  trunk.     Hence  the  blood  which  passing 
from  the  right  auricle  into  the  left  auricle  through  the  foramen 
ovale  is  distributed  by  the  left  ventricle  through  the  aortic  arch, 
though  chiefly  blood  coming  direct   from  the  placenta,  is   also  • 
blood  which  on  its  way  from  the  placenta  has  passed  through  the 
liver  and  blood  derived  from  the  dssues  of  the  lower  part  of  the 
body  to  the  foetus.     The  blood  descending  as  foetal  venous  blood 
from  the  head  and  limbs  by  the  superior  vena  cava  does  not 
mingle  with  that  of  the  inferior  vena  cava,  but  falls  into  the  right 
ventricle,  from  which  it  is  discharged  through  the  ductus  arteriosus 
(Botalli)  into  the  aorta,  below  the  arch,  whence  it  flows  partly  to 
the  lower  trunk  and  limbs,  but  chiefly  by  the  umbihcal  arteries  to 

'■  Pfliiger's  Archiv,  XVI.  (1878)  p.  S48. 

=  Cf.  Fehling,  Arch.  f.  Gyndk.  XIV.  (1879)  p.  221. 

3  Langendorff,  oj>.  cii.     Sewall,  Journal  of  Physiol,  r.  (1878)  p.  32I. 


CHAP.    III.]     THE   NUTRITION   OF   THE   EMBRYO.  70I 

the  placenta.  A  small  quantity  only  of  the  contents  of  the  right 
ventricle  finds  its  way  into  the  lungs.  Now  tlie  blood  which 
comes  from  the  placenta  by  the  umbilical  vein  direct  into  the 
right  auricle  is,  as  far  as  the  foetus  is  concerned,  arterial  blood ; 
and  the  portion  of  umbilical  blood  which  traverses  the  liver 
probably  loses  at  this  epoch  very  little  oxygen  during  its  transit 
through  that  gland,  the  liver  being  at  this  period  a  simple  excretory 
rather  than  an  actively  metabolic  organ.  Hence  the  blood  of  the 
inferior  vena  cava,  though  mixed,  is  on  the  whole  arterial  blood ; 
and  it  is  this  blood  which  is  sent  by  the  left  ventricle  through  the 
arch  of  the  aorta  into  the  carotid  and  subclavian  arteries.  Thus 
the  head  of  the  foetus  is  provided  with  blood  comparatively  rich 
in  oxygen.  The  blood  descending  from  the  head  and  upper  limbs 
by  the. superior  vena  cava  is  distinctly  venous  ;  and  this  passing 
from  the  right  ventricle  by  the  ductus  arteriosus  is  driven  along  the 
descending  aorta,  and  together  with  some  of  the  blood  passing 
from  the  left  ventricle  round  the  aortic  arch  falls  into  the  umbilical 
arteries  and  so  reaches  the"  placenta.  The  foetal  circulation  then 
is  so  arranged,  that  while  the  most  distinctly  venous  blood  is 
driven  by  the  right  ventricle  back  to  the  placenta  to  be  oxygenated, 
the  most  distinctly  arterial  (but  still  mixed)  blood  is  driven  by  the 
left  ventricle  to  the  cerebral  structures,  which  have  more  need  of 
oxygen  than  the  other  tissues.  In  the  later  stages  of  ])regnancy 
the  mixture  of  the  various  kinds  of  blood  in  the  right  auricle 
increases  preparatory  to  the  changes  taking  place  at  birth.  But 
during  the  whole  time  of  intra-uterine  life  the  amount  of  oxygen 
in  the  blood  passing  from  the  aortic  arch  to  the  medulla  oblongata 
is  sufficient  to  prevent  any  inspiratory  impulses  being  originated 
in  the  medullary  respiratory  centre.  This  during  the  whole  period 
elapsing  between  the  date  of  its  structual  establishment,  or  rather 
the  consequent  full  development  of  its  irritability,  and  the  epoch 
of  l)irth,  remains  dormant;  the  oxygen-supply  to  the  protoplasm 
of  its  nerve-cells  is  never  brought  so  low  as  to  set  going  the 
respiratory  molecular  explosions.  As  soon  however  as  the  inter- 
course between  the  maternal  and  umbilical  blood  is  interrupted 
by  separation  of  the  placenta  or  by  ligature  of  the  umbilical  cord, 
or  when  in  any  other  way  blood  of  sufficiently  arterial  quality 
ceases  to  find  its  way  by  the  left  ventricle  to  the  medulla  oblongata, 
the  supply  of  oxygen  in  the  respiratory  centre  sinks,  and  when 
the  fall  has  reached  a  certain  point  an  impulse  of  inspiration  is 
generated  and  the  foetus  for  the  first  time  breathes.  Through 
this  first  inspiratory  movement  the  thorax,  by  an  upward  movement 
of  the  ribs,  is  permanently  enlarged,  and  the  lungs  assume  that 
condition   of  partial    distension  which  we   studied    (p.   330)   in 


^"02  FCETAL   CIRCULATION.  [BOOK   IV. 

treatmg  of  respiration'.  When  the  first  breath  is  taken,  as  under 
normal  circumstances  it  is,  with  free  access  to  the  atmosphere,  the 
lungs  become  filled  with  air,  and  the  scanty  supply  of  blood  which 
at  the  moment  was  passing  from  the  light  ventricle  along  the 
pulmonary-  arter}*  returns  to  the  left  auricle  brighter  and  richer  in 
oxygen  than  ever  was  the  fcetal  blood  betore.  With  the  diminution 
of  resistance  in  the  pulmonary-  circulation  caused  by  the  expansion 
of  th«  thorax,  a  larger  supply  of  blood  passes  into  the  pulmonary 
artex}-  instead  of  into  the  ductus  arteriosus,  and  this  derivation  of 
the  contents  of  the  right  ventricle  increasing  with  the  continued 
respirator^-  movements,  the  current  through  the  latter  canal  at 
last  ceases  altogether,  and  its  channel  shortly  after  birth  becomes 
obliterated.  Corresponding  to  the  greater  flow  into  the  pulmonar)- 
arter>-.  a  larger  and  larger  quantity  of  blood  returns  from  the 
pulmonan.-  veins  into  the  left  auricle.  At  the  same  time  the 
current  through  the  ductus  venosus  from  the  umbilical  vein  having 
ceased,  the  flow  from  the  inferior  cava  has  diminished  ;  and  the 
blood  of  the  right  auricle  finding  little  resistance  in  the  direction 
of  the  Ventricle,  which  now  readily  discharges  its  contents  into 
the  pulmonary  anen*-  (where  as  we  have  seen  (p.  i6i)  the  mean 
pressure  and  the  peripheral  resistance  are  ver)-  low),  but  finding  in 
the  left  auricle,  which  is  continually  being  filled  from  the  lungs, 
an  obstacle  to  its  passage  through  the  foramen  ovale,  ceases  to 
take  that  course,  and  the  foramen  speedily  becomes  closed.  Thus 
the  foetal  circulation,  in  consequence  of  the  respirator)-  movements 
to  which  its  interruption  gives  rise,  changes  its  course  into  that 
characteristic  of  the  adult 

■  Benstdn,  Pfliige's  ArcAhr,  mi.  (1S78)  p.  617. 


CHAPTEF.    IV. 

PARTUEXnOX- 

Ls  spite  of  the  irxreasing  distensioii  of  it5  czrrhj.  the  vloaa 
remains  quiescent,  as  far  as  anj  marked,  rnnscular  coBiractioBS 
are  coacemed,  Tintil  a  certain  time  has  been  nrnu  In  the  TmniaM 
subject  the  period  of  gestation  generally  lasts  from  275  to  280 
days,  r>.  about  forty  weeks,  the  general  custom  being  to  expect 
partmition  at  abont  280  days  from  the  la^t  menstmatioru  Seang 
tiiat,  in  many  cases,  it  is  micatarn  whether  the  ovimi  wriich  de- 
velopes  iato  the  embryo  lefi:  the  ovary  at  the  menstruation  preced- 
tug  or  suceeedrng  coitus,  or,  as  some  have  urged,  indecendertt  of 
menstraatiQn,  by  reason  of  the  coitus  itself,  an  exact  detamiinatioQ 
of  the  duration  of  pregnancy  is  impossible. 

In  tiie  cow  the  period  of  gestatfon  is  25o  02.7-,  in.  ihe  ~^re  abont 
55a,  sheep  about  150  days,  dog  about  60  days,  rabbit  abour  30  days. 

The  extrusion  of  tie  foetus  is  brought  aboot,  partly  by  rhyth- 
mical contractions  of  the  uterus  itsd^  and  partly  by  a  pressure 
exerted,  by  the  contraction  of  the  abdominal  muscles,  ?;ryr:TT;n-  to 
that  described  in  defecadon.  The  contractions  of  the  uterus  are 
the  frrst  to  appear,  and  thefr  first  ^ect  is  to  bring  about  a  dilation 
of  the  OS  uteri ;  it  is  not  till  the  later  stages  of  labour,  wtiile  the 
foetus  is  passing  into  the  vagina,  that  the  abdominal  muscles  axe 
brought  into  play. 

The  whole  process  of  parturition  may  be  broadly  consid^ed  as 
a  reflex  act,  the  nervoTis  centre  being  placed  rn  the  lumbar  cord. 
In  a  dog,  whose  dorsal  cord  had  been  completely  sevoed  (see 
p.  619),  parturition  took  place  as  usual;  and  the  &ct  that,  in  the 
human  subject,  labour  will  progress  quite  naturally  while  tie 
patient  is  unconscious  fix^m  the  administration  of  chloroform, 
shews  that  in  woman  also  the  whole  matter  is  an  involuntary 
action,  however  much  it  may  be  assisted  by  direct  Tolittonal 
efforts.  That  the  uterus  is  capable  of  being  thrown  into  am- 
tractkms   through  renex   action,   excited  by  srimnli   applied  to 


704  UTERINE   CONTRACTIONS.  [BOOK.   IV. 

various  afferent  nerves,  is  well  known.  The  contraction  of  the 
uterus,  which  is  so  necessary  for  the  prevention  of  haemorrhage 
after  delivery,  may  frequently  be  brought  about  by  pressure  on  the 
abdomen,  by  the  introduction  of  foreign  bodies  into  the  vagina, 
and  especially  by  the  application  of  the  child  to  the  nipple.  But 
we  are  not  thereby  justified  in  considering  the  rhythmical  con- 
tractions of  the  uterus  during  parturition  as  simple  reflex  acts 
excited  by  the  presence  of  the  foetus.  We  are  utterly  in  the 
dark  as  to  why  the  uterus,  after  remaining  apparently  perfectly 
quiescent  (or  with  contractions  so  slight  as  to  be  with  difficulty 
appreciated)  for  months,  is  suddenly  thrown  into  action,  and 
within  it  may  be  a  few  hours  gets  rid  of  the  burden  it  has  borne 
with  such  tolerance  for  so  long  a  time ;  none  of  the  various  hypo- 
theses which  have  been  put  forward  can  be  considered  as  satis- 
factory. And  until  we  know  what  starts  the  active  phase,  we  shall 
remain  in  ignorance  of  the  exact  manner  in  which  the  activity  is 
brought  about.  The  peculiar  rhythmic  character  of  the  contrac- 
tions, each  '  pain '  beginning  feebly,  rising  to  a  maximum,  then 
declining,  and  finally  dying  away  altogether,  to  be  succeeded  after 
a  pause  by  a  similar  pain  just  like  itself,  pain  following  pain  like 
the  tardy  long-drawn  beats  of  a  slowly  beating  heart,  suggests  that 
the  cause  of  the  rhythmic  contraction  is  seated,  like  that  of  the 
rhythmic  beat  of  the  heart,  in  the  organ  itself.  And  this  view  is 
supported  by  the  fact  that  contractions  of  the  uterus,  similar  to 
those  of  parturition,  have  been  observed  in  animals  even  after 
complete  destruction  of  the  spinal  cord.  Nevertheless  general 
evidence  supports  the  conclusion  that,  in  a  normal  state  of  things 
at  all  events,  the  contractions  of  the  uterus  like  those  of  the  lymph^ 
hearts,  are  largely  dependent  on  the  spinal  cord. 

The  action  of  the  abdominal  muscles,  on  the  other  hand,  is 
obviously  a  reflex  act  carried  out  by  means  of  the  spinal  cord,  the 
necessary  stimulus  being  supplied  by  the  pressure  of  the  foetus  in 
the  vagina,  or  by  the  contractions  of  the  uterus.  Hence  the 
whole  act  of  parturition  may  with  reason  be  considered  as  a  reflex 
one. 

.  Whether  it  be  wholly  a  reflex  or  partly  an  automatic  one,  the 
act  can  readily  be  inhibited  by  the  action  of  the  central  nervous 
system.  Thus  emotions  are  a  very  frequent  cause  of  the  pro- 
gress of  parturition  being  suddenly  stopped ;  as  is  well  known, 
the  entrance  into  the  bed-room  of  a  stranger  often  causes  for  a 
time  the  sudden  and  absolute  cessation  of  '  labour '  pains,  which 
previously  may  have  been  even  violent.  Judging  from  the  analogy 
of  micturition,  between  which  and  parturition  there  are  many 
points  of  resemblance,  we  may  suppose  that   this  inhibition  of 


CHAP.   IV,]  PARTURITION.  705 

uterine  contractions  is  brought   about   by  an   inhibition   of  the 
centre  in  the  lumbar  cord. 

Experimental  investigations  into  the  movements  of  the  uterus  have 
been  carried  out  chiefly  on  rabbits  and  dogs.  In  these  animals,  rhyth- 
mical contracHons  may  occur  spontaneously  or  be  induced  by  direct 
stimul  ition  .ifccr  the  connections  of  the  uterus  with  the  general  nervous 
^ystem  hive  been  entirely  severed.  The  application  of  the  interrupted 
current  produces  a  local  contraction  frequently  accompanied  or  fol- 
lowed by  a  general  movement  of  the  whole  organ.  This  general 
movement  may  fail  to  make  its  appearance  especially  in  an  unim- 
pregnated  uterus  (and  indeed  the  results  of  stimulating  the  uterus 
whether  directly  or  indirectly  are  for  some  reason  or  other  remarkably 
inconstant)  ;  where  it  does  occur,  it  possesses,  like  an  artificially  pro- 
duced heart-beat  (p.  1S6),  characters  resembling  those  of  a  reflex  act. 

Rhythmical  contractions  of  the  uterus  may  be  induced  by  directly 
stimulating  the  spinal  cord  along  any  part  of  its  course  from  the 
medulla  oblongata  to  the  lumbar  region,  as  well  as  in  a  reflex  manner 
by  stimulation  of  the  central  ends  of  various  spinal  nerves'.  Stimula- 
tion of  the  cerebellum,  crura  cerebri,  and  other  parts  of  the  brain  as 
high  up  as  the  corpora  striata  and  optic  thalami,  will  also  give  rise  to 
uterine  contractions*. 

The  movements  brought  about  by  direct  electric  stimulation  of  the 
central  nervous  system  are  niore  enct'getic  when  the  electrodes  are 
applied  low  down,  near  the  lumbar  region  of  the  cord,  than  when  they 
are  applied  high  up,  and  such  contractions  as  are  caused  by  direct 
stimulation  of  various  parts  of  the  brain  are  comparatively  feeble. 
When  the  cord  is  divided  at  the  level  of  the  tenth  dorsal  vertebra, 
stimulation  of  the  cord  above  the  section  gives  rise  to  no  movements 
These  facts  support  the  conclusion  that  the  uterine  centre  is  placed  in 
the  lumbar  spinal  cord,  and  that  the  movements  witnessed  when  parts 
higher  up  are  stimulated  are  due  to  the  lumbar  centre  being  thus  in- 
directly stimulated.  Rohrig  finds  that  reflex  movements  are  more 
easily  induced  by  central  stimulation  of  the  sciatic  or  crural  than  of 
the  brachial  or  other  nerves  of  the  anterior  part  of  the  body ;  and 
especially  energetic  movements  are  witnessed  when  the  central  ends 
of  the  ovarian  nerves  are  stimulated.  The  same  observer  states 
that  the  contractions  of  the  uterus  which  (in  urarized  unimpregnated 
rabbits)  are  brought  about  by  an  asphyxiated  condition  of  the  blood, 
by  compression  of  the  aorta,  by  strychnia,  picrotoxin  and  ergotin,  fail 
to  appear  if  the  lumbar  cord  be  previously  destroyed.  These  agents 
therefore  he  considers  produce  their  elfect  by  acting  not  directly  on 
the  uterus  but  on  the  lumbar  centre.  The  injection  of  ammonia,  or 
ammonia  salts,  into  the  blood  gives  rise  to  energetic  movements  even 
after  complete  destruction   of  the  central   nervous   system.       Other 

'  Schlesinger,  IVUn.  Med.  Jahrb.  i.  (1873)  Hft.  4.  Cyon,  V^\\'y^x%  Archiv, 
VIII.  (1S74.)  349.  Basch  and  Hofmann,  Wien.  MM  Jahrb.  1S77,  Hft.  4. 
Rohrig,  Virchow's  Archiv,  Bd.  76  (1879),  P-  •• 

'  Korner,  Studien  Phys.  Inst.  Breslau,  ill.  34. 

'  Kohrig,  op.  cU. 

F.  P.  45 


706  PARTURITION.  [BOOK   IV. 

observers  have  seen  contractions  result  from  asphyxia  after  removal 
of  the  spinal  centre. 

Basch  and  Hofmann^  distinguish,  in  the  dog,  two  paths  along 
which  efferent  impulses  may  pass  from  the  central  nervous  system  to 
the  uterus;  one,  a  sympathetic  tract,  consisting  of  nerves  passing  from 
^  inferior  mesenteric  ganglion  (lying  in  the  dog  at  the  extreme  end 
xji  the  aorta)  to  the  hypogastric  plexus,  and  the  other,  a  spinal  tract, 
consisting  of  branches  passing  from  the  sacral  nerves  across  the  pelvis 
to  the  same  plexus,  and  being  the  representatives  in  the  female  of 
Eckhard's  nervi  erigentis  in  the  male  (see  p.  215).  Stimulation  of  the 
former  produces  contractions  of  the  uterus  chiefly  circular  in  nature, 
with  descent  of  the  cervix,  and  dilation  of  the  os  ;  when  the  latter  are 
stimulated,  the  uterus  is  shortened,  as  if  by  longitudinal  contractions, 
the  cervix  ascends,  and  the  os  is  closed.  Both  nerves  apparently  may 
take  part  in  a  contraction  brought  about  in  a  reflex  manner.  When 
one  tract  is  divided,  the  results  of  reflex  stimulation  resemble  those  of 
direct  stimulation  of  the  other  tract.  When  both  tracts  are  divided, 
stimulation  of  the  central  end  of  a  spinal  nerve,  such  as  the  sciatic,  is 
without  effect.  The  sacral  nerves  sharing  in  this  spinal  tract  are 
branches  from  the  first,,  second,  and  occasionally  the  third.  Rohrig^ 
also  finds  (in  the  rabbit)  two  efferent  paths  from  the  spinal  cord  to  the 
uterus,  viz.  the  uterine  (sympathetic)  and  the  sacral  (spinal)  nerves  ; 
but  he  makes  no  marked  distinction  of  character  between  them  ;  he 
regards  both  sets  of  nerves  as  containing  also  afferent  fibres.  Basch 
and  Hofmann  further  assert  that  the  sympathetic  tract  contains  vaso- 
constrictor and  the  spinal  tract  vaso-dilator  nerves,  both  of  which  may 
be  thrown  into  action  in  a  reflex  manner,  the  former,  however,  more 
readily  than  the  latter.  The  occurrence  of  contractions  in  conse- 
quence of  an  asphyxiated  condition  of  the  blood,  explains  why  when 
pregnant  animals  are  asphyxiated,  an  extrusion  of  the  foetus  frequently 
takes  place.  There  is  no  evidence,  however,  that  the  onset  of  labour 
is  caused  by  a  gradual  diminution  of  oxygen  in  the  blood,  reaching  at 
last  to  a  climax.  Nor  are  there  sufficient  facts  to  connect  parturition 
with  any  condition  of  the  ovary  resembling  that  of  menstruation. 

After  the  expulsion  of  the  foetus,  the  foetal  placenta  separates 
from  the  uterine  walls,  and  is,  together  with  the  remnants  of  the 
membi:anes,  expelled  after  it.  The  uterus  then  falls  into  a  firm 
tonic  contraction,  similar  to  that  of  the  emptied  bladder,  by  which 
means  haemorrhage  from  the  vessels  torn  by  the  separation  of 
the  placenta  is  avoided.  The  lining  membrane  of  the  uterus  is 
gradually  restored,  the  muscular  elements  are  reduced  by  a  rapid 
fatty  degeneration,  and  in  a  short  time  the  whole  organ  has 
returned  to  its  normal  condition. 

'  Op.  cit.  '  Op.  cii. 


CHAPTER  V. 

THE  PHASES  OF  LIFE. 

The  child  has  at  birth,  on  an  average,  rather  less  than  one-third 
tlie  jiiaximum  length,  and  about  one-twentieth  the  maxinmrn 
weight,  to  which  in  future  years  it  will  attain. 

'I  he  composition  of  the  body  of  the  new-born  babe,  as  com- 
pared with  that  of  the  adult,  will  be  seen  from  the  following 
table,'  in  which  the  details  are  more  full  than  those  given 
on  p.  455  : 


Weight  of 

■  organ 

in  percentage 

Weight  of  organ  in 

of 

Body-wcighl 

.-idiill.   as  comp:ired 

w.th  that  of  new-bom 
babe  taken  as  i. 

New-born  babe. 

Adult. 

Eye 

•28 

.028 

17 

Brain 

I4'34 

2-37 

3-7 

Kidneys 

•88 

•48 

12 

Skin 

ii-3 

6-3 

12 

l,iver 

4-39 

277 

136 

Heart 

•89 

■52 

15 

Stomach 

and     ) 

Intestine 

1 

2-53 

234 

20 

Lungs 

2- 1  6. 

2"OI 

20 

Skeleton 

167 

15-35 

26 

Muscles, 

&c. 

23.4 

43-i 

28 

Testicle 

•037 

•8 

60 

It  will  be  observed  that  the  brain  and  eyes  are,  relatively  to 
the  whole  body-weight,  very  much  larger  in  the  babe  than  in  the 
adult,  as  is  also,  though  to  a  less  extent,  the  liver.  This  dispro- 
portion is  a  very  marked  embryonic  feature,  and  as  far  as  the 
brain  and  eye  are  concerned  at  least,  has  a  morphological  or 
phylogenic,  as  well  as  a  physiological  or  tcleological,  sigmticance. 
Inasmuch  as  the  smaller  body  has  relatively  the  larger  surface,  the 

'  Vierordt,  Grundriss  der  Physioloi^u;  5th  ed.  p.  605. 

45—2 


7o8 


CHILDHOOD.  [BOOK   IV. 


skin  is  naturally  proportionately  greater  m  the  babe.  It  is  chiefly 
bv  the  accumulation  of  muscle  or  flesh,  properly  so  called,  that 
the  child  acquires  the  bulk  and  weight  of  the  man, _  the  skeletal 
framework,  in  spite  of  its  being  specifically  lighter  in  its  earlier 
cartilaginous  condition,  maintaining  throughout  life  about  the 
same  relative  weight. 

The  increase  in  stature  is  very  rapid  in  early  mfancy,  proceed- 
ing however  by  decreasing  increments.  Accordmg  to  Quetelet% 
there  is  a  gain  in  height  of  about  20  centimetres  during  the  first 
year  the  co  cm.  babe  enlarging  to  the  70  cm.  infant  of  pne  year 
old  •  of  about  9  during  the  second,  of  about  7  during  the  third, 
of  about  6 1  for  the  fourth,  and  so  on,  decreasmg  to  rather  below 
6  for  the  succeeding  ten  or  twelve  years.  During  or  shortly 
before  puberty,  there  is  again  a  somewhat  sudden  rise,  with  a 
subsequent  more  steady  but  diminishing  increase  up  to  about  the 
twenty-fifth  year.  From  thence  to  about  fifty  years  of  age  the 
height  remains  stationary,  after  which  there  may  be  a  decrease, 
especially  in  extreme  old  age.  . ,       .  ■,  a 

The  increase  in  weight  is  also  very  rapid  at  first,  and  proceea- 
ing  hke  the  height,  with  diminishing  increments,  may  contmue 
tni  about  the  fortieth  year.  After  the  sixtieth  year  a  dechne  ot 
variable  extent  is  generally  witnessed.  It  is  a  remarkable  fact, 
however,  that  in  the  first  few  days  of  life,  so  far  from  there  being 
an  increase,  there  is  an  actual  decrease  of  weight,  so  that  according 
to  Quetelet,  even  on  the  seventh  day  the  weight  still  continues  to 
be  less  than  at  birth. 

The  saliva  of  the  babe  is  active  on  starch,  and  its  gastric 
juice  has  good  peptic  powers,  from  which  we  may  infer  that  its 
digestive  processes  in  general  are  identical  with  that  of  the  adult ; 
but  the  faeces  of  the  infant  contain,  besides  a  considerable  quantity 
of  undigested  food  (fat,  casein,  &c.),  unaltered  bfle-pigment,  and 
undecomposed  bile  salts. 

■  According  to  Hammarsten^  the  gastric  juice  of  new-born  puppies, 
though  sufficiently  acid  to  curdle  milk,  does  not  contam  pepsin,  or  the 
lactiS  acid  ferment  ;  it  is  not  till  the  third  week  that  peptic  digestion 
is  setup,  the  casein  previously  taken  being  digested  by  the  pancreatic 
juice  ;  in  young  rabbits  it  appears  a  week  earlier.  Like  Zweitei , 
Hammarsten  however  found  pepsin  in  the  stomach  of  the  new-born 
babe  Zweifel  states  that  the  pancreatic  juice  in  children,  while 
active  on  fat  and  proteids  from  the  first,  is  inert  towards  starch  tor 

'  Physique  Sociale  (1869)  II.  p.  13. 
»  Ludwig's^^j<?-«'^^(i874)P-  "6. 
3  Untersuch.  u.  d.  Verdauungsapparat  d^  Neugehorenen,  i»74. 


CHAK    v.]  THE   PHASES   OF    LIFE.  709 

tlic  first  two  months  ;  and  that  the  amylolytic  ferment  is  for  the  same 
period  absent  from  the  submaxillary,  though  present  in  the  parotid 
saliva. 

Tiie  heart  of  the  babe  (see  Table,  p.  707)  is,  relatively  to  its 
body-weight,  larger  than  the  adult,  and  the  frecjuency  of  the 
heart-beat  much  greater,  viz.  about  130  or  140  per  minute,  falling 
to  about  no  in  the  second  year,  and  about  90  in  the  tenth  year. 
Corresponding  to  the  smaller  bulk  of  the  body,  the  whole  circuit 
of  the  blood  system  is  traversed  in  a  shorter  time  than  in  the 
adult  (12  seconds  as  against  22)'  ;  and  consequently  the  renewal 
of  the  blood  in  the  tissues  is  exceedingly  rapid.  The  respiration  of 
the  babe  is  quicker  than  that  of  the  adult,  being  at  first  about  35 
per  minute,  falling  to  28  in  the  second  year,  to  26  in  the  fifth 
year,  and  so  onwards.  The  respiratory  work,  while  it  increases 
absolutely  as  the  body  grows,  is,  relatively  to  the  body-weight, 
greatest  in  the  earlier  years.  It  is  worthy  of  notice,  that  the  ab- 
sorption of  oxygen  is  said  to  be  relatively  more  active  than  the 
production  of  carbonic  acid  ;  that  is  to  say,  there  is  a  continued 
accumulation  of  capital  in  the  form  of  a  store  of  oxygen-holding 
explosive  compounds  (see  p.  367).  This,  indeed,  is  the  striking 
feature  of  infant  metabolism.  It  is  a  metabolism  directed  largely 
to  constructive  ends.  The  food  taken  represents,  undoubtedly, 
so  much  potential  energy;  but  before  that  energy  can  assume  a 
vital  mode,  the  food  must  be  converted  into  tissue ;  and,  in  such 
a  conversion,  morphological  and  molecular,  a  large  amount  of 
energy  must  be  expended.  The  metabolic  activities  of  the  infant 
are  more  pronounced  than  those  of  the  adult,  for  the  sake,  not  so 
much  of  energies  which  are  spent  on  the  world  without,  as  of 
energies  which  are  for  a  while  buried  in  the  rapidly  increasing 
mass  of  flesh.  Thus  the  infant  requires  over  and  above  the  wants 
of  man,  not  only  an  income  of  energy  corresponding  to  the  energy 
of  the  flesh  actually  laid  on,  but  also  an  income  corresponding 
to  the  energy  used  up  in  making  that  living  sculptured  flesh  out 
of  the  dead  amorphous  proteids,  flits,  carbohydrates  and  salts, 
which  serve  as  food.  Over  and  above  this,  the  infant  needs  a 
more  rapid  metabolism  to  keep  up  the  normal  bodily  tempera- 
ture. This,  which  is  no  less,  indeed  slightly  (•3")  higher,  than 
that  of  the  adult,  requires  a  greater  expenditure,  inasnmch  as  the 
infant  with  its  relatively  far  larger  surface,  and  its  extremely  vas- 
cular skin,  loses  heat  to  a  proportionately  much  greater  degree  than 
docs  tlie  grown-up  man.  It  is  a  matter  of  common  experience 
that  children  are  more  aftected  by  cold  than  are  adults. 

'  Vierordt,  op.  cit. 


7 TO  CHILDHOOD.  [BOOK   IV. 

This  rapid  metabolism  is  however  manifest  immediately  upon 
birth.  During  the  first  few  days,  corresponding  to  tie  loss  of  weight 
mentioned  above,  the  respiratory  activities  of  the  tissues  are  feeble  ; 
the  embryonic  habits  seem  as  yet  not  to  have  been  completely  thrown 
off,  and,  as  was  stated  on  p.  390,  new-born  animals  bear  -with 
impunity  a  deprivation  of  oxygen  which  would  be  fatal  to  them  later 
on  in  life. 

The  quantity  of  urine  passed,  though  scanty  in  the  first  two 
days,  rises  rapidly  at  the  end  of  the  first  week,  and  in  youth  the 
quantity  of  urine  passed  is,  relatively  to  the  body-weight,  larger 
than  in  adult  life.  This  may  be,  at  least  in  quite  early  life, 
partly  due  to  the  more  liquid  nature  of  the  food,  but  is  also  in 
part  the  result  of  the  more  active  metabolism.  For  not  only  is 
the  quantity  of  urine  passed,  but  also  the  amount  of  urea  and 
some  other  urinary  constituents  excreted,  relatively  to  the  body- 
weight,  greater  in  the  child  than  in  the  adult.  The  presence  of 
uric,  of  oxalic,  and,  according  to  some,  of  hippuric  acids  in  un- 
usual quantities  is  a  frequent  characteristic  of  the  urine  of  children. 
It  is  stated  that  calcic  phosphates,  and  indeed  the  phosphates 
generally,  are  deficient,  being  retained  in  the  body  for  the  building 
up  of  the  osseous  skeleton. 

Associated  probably  with  these  constructive  labours  of  the 
growing  frame  is  the  prominence  of  the  lymphatic  system.  Not 
only  are  the  lymphatic  glands  largely  developed  and  more  active 
(as  is  probably  shewn  by  their  tendency  to  disease  in  youth),  but 
the  quantity  of  lymph  circulation  is  greater  than  in  later  years. 
Characteristic  of  youth  is  the  size  of  the  thymus  body,  which 
increases  up  to  the  second  year,  and  may  then  remain  for  a  while 
stationary ;  but  generally  before  puberty,  has  suffered  a  retro- 
gressive metamorphosis,  and  frequently  hardly  a  vestige  of  it 
remains  behind.  The  thyroid  body  is  also  relatively  greater  in 
the  babe  than  in  the  adult ;  the  spleen,  on  the  other  hand,  which 
grows  rapidly  in  early  infancy,  is  not  only  absolutely,  but  also 
relatively,  greater  in  the  adult.  It  need  hardly  be  said  that  the 
recuperative  power  of  infancy  and  early  youth  is  very  marked. 

It  would  be  beyond  the  scope  of  this  work  to  enter  into  the 
psychical  condition  of  the  babe  or  the  child,  and  our  knowledge 
of  the  details  of  the  working  of  the  nervous  system  in  infancy 
is  too  meagre  to  permit  of  any  profitable  discussion.  It  is  hardly 
of  use  to  say  that  in  the  young  the  whole  nervous  system  is  more 
irritable  or  more  excitable  than  in  later  years  ;  by  which  we  pro- 
bably to  a' great  extent  mean  that  it  is  less  rigid,  less  marked  out 
into  what,  in  preceding  portions  of  this  work,  we  have  spoken 
of  as  nervous  mechanisms.     It  may  be  mentioned  that,  according 


CHAP,   v.]  THE    THASES   OF   LIFE.  7II 

to  Soltmann',  stimulation  of  Hitzig's  cerebral  areas,  in  new-born 
animals,  docs  not  give  rise  to  the  usual  localised  movements. 
The  sense  of  touch,  both  as  regards  pressure  and  temperature, 
appears  well  developed  in  the  infant,  as  does  also  the  sense  of 
taste,  and  possibly,  tiiough  this  is  disputed,  that  .of  smell.  The 
pupil  (larger  in  the  infant  than  in  the  man)  acts  fully,  and  Donders' 
observed  normal  binocular  movements  of  the  eyes  in  an  infant 
less  than  an  hour  old.  The  eye  is  (in  man)  from  the  outset  fully 
sensitive  to  light,  though  of  course  visual  perceptions  are  imper- 
fect. As  regards  hearing,  on  the  other  hand,  very  little  reaction 
follows  upon  sounds,  i.e.  auditory  sensations  seem  to  be  dull 
during  the  first  few  daj's  of  life  ;  this  may  be  partly  at  least  due 
to  absence  of  air  from  the  tympanum  and  a  tumid  condition  of 
the  tympanic  mucous  membrane.  As  the  child  grows  up  his  senses 
rapidly  culminate,  and  in  his  early  years  he  possesses  a  general 
acuteness  of  sight,  hearing,  and  touch,  which  frequently  becomes 
blunted  as  his  psychical  life  becomes  fuller.  Children  however 
are  said  to  be  less  apt  at  distinguishing  colours  than  in  sighting 
objects  ;  but  it  docs  not  appear  whether  this  arises  from  a  want 
of  perceptive  discrimination  or  from  their  being  actually  less 
sensitive  to  variations  in  hue.  A  characteristic  of  the  nervous 
system  in  childhood,  the  result  probably  of  the  more  active 
metabolism  of  the  body,  is  the  necessity  for  long  or  frequent 
and  deep  slumber. 

Dentition  marks  the  first  epoch  of  the  new  life.  At  about 
seven  months  the  two  central  incisors  of  the  lower  jaw  make  their 
way  through  the  gum,  followed  immediately  by  the  corresponding 
teeth  in  the  upper  jaw.  The  lateral  incisors,  first  of  the  lower 
and  then  of  the  upper  jaw,  appear  at  about  the  ninth  month,  the 
first  molars  at  about  the  twelfth  month,  the  canines  at  about  a 
year  and  a  half,  and  the  temporary  dentition  is  completed  by  the 
appearance  of  the  second  molars  usually  before  the  end  of  the 
second  year. 

About  the  sixth  year  the  permanent  de-ntition  commences  by 
the  appearance  of  the  first  permanent  molar  beyond  the  second 
temporary  molar;  in  the  seventh  year  the  central  permanent 
incisors  replace  their  temporary  representatives,  followed  in  the 
next  year  by  the  lateral  incisors.  In  the  ninth  year  the  temporary 
first  mola.s  are  replaced  by  the  first  bicuspids,  and  in  the  tenth 
year  the  second  temporary  molars  are  similarly  replaced  by  the 
second  bicuspids.     The  canines  are  exchanged  about  the  eleventh 

'  Centrblt.  Med.  IViss.  1875,  p.  209.    Jahrb.f.  A'inderheilkundc  l\.(i?>']S) 
106. 

"  Pfliiger's  Arcliiv,  xiii.  (1876)  p.  384. 


712  PUBERTY.  [book.   IV. 

or  twelfth  year  and  the  second  pernianent  molars  are  cut  about  the 
twelfth  or  thirteenth  year.  There  is  then  a  long  pause,  the  third 
or  wisdom  tooth  not  making  its  appearance  till  the  seventeenth, 
or  even  twenty-fifth  year,  or  in  some  cases  not  appearing  at  all. 

Shortly  after  the  conclusion  of  the  permanent  dentition  (the 
wisdom  teeth  excepted)  the  occurrence  of  puberty  marks  the 
beginning  of  a  new  phase  of  life ;  and  the  difference  between  the 
sexes,  hitherto  merely  potential,  now  becomes  functional.  In 
both  sexes  the  maturation  of  the  generative  organs  is  accompanied 
by  the  well-known  changes  in  the  body  at  large ;  but  the  events 
are  much  more  characteristic  in  the  typical  female  than  in  the 
aberrant  male.  Though  in  the  boy,  the  breaking  of  the  voice  and 
the  rapid  growth  of  the  b^ard  which  accompany  the  appearance 
of  active  spermatozoa,  are  striking  features,  yet  they  are  after  all 
superficial.  The  curves  of  his  increasing  weight  and  height,  and 
of  the  other  events  of  his  economy,  pursue  for  a  while  longer  an 
unchanged  course ;  the  boy  does  not  become  a  man  till  some 
years  after  puberty  ;  and  the  decline  of  his  functional  manhood  is 
so  gradual  that  frequently  it  ceases  only  when  disease  puts  an  end 
to  a  ripe  old  age.  With  the  occurrence  of  menstruation,  on  the 
other  hand,  at  from  thirteen  to  seventeen  years  of  age,  the  girl 
almost  at  once  becomes  a  woman,  and  her  functional  woman- 
hood ceases  suddenly  at  the  climacteric  in  the  fifth  decennium. 
During  the  whole  of  the  child-bearing  period  her  organism  is  in 
a  comparatively  stationary  condition.  While  before  the  age  of 
puberty  up  to  about  the  eleventh  or  twelfth  year,  the  girl  is  lighter 
and  shorter  than  the  boy  of  the  same  age,  in  the  next  few  years 
her  rate  of  growth  exceeds  his^ ;  but  she  has  then  nearly  reached 
her  maximum,  while  he  continues  to  grow.  Her  curve  of  weight 
from  the  nineteenth  year  onward  to  the  climacteric,  remains 
stationary,  being  followed  subsequently  by  a  late  increase,  so  that 
while  the  man  reaches  his  maximum  of  weight  at  about  forty,  the 
woman  is  at  her  greatest  weight  about  fifty ^. 

Of  the  statical  difterences  of  sex,  some,  such  as  the  formation 
of  the  pelvis,  and  the  costal  mechanism  of  respiration,  are  directly 
connected  with  the  act  of  child-bearing,  while  others  have  only  an 
indirect  relation  to  that  duty ;  and  indications  at  least  of  nearly 
all  the  characteristic  differences  are  seen  at  birth.  The  baby  boy 
is  heavier  and  taller  than  the  baby  girl,  and  the  maiden  of  five 
breathes  with  her  ribs  in  the  same  way  as  does  the  matron  of 
forty.     The  woman  is  lighter  and  shorter  than  the  man,  the  hmits 

'  Bowditch,  "The  growth  of  children,"  Annual  Report  of  the  State  Board 
of  Health  of  Massachusetts,  1877.  Cf.  also  Pagliani,  Moleschott's  Untersuch. 
XII.  (1878)  p.  89.  =  Quetelft,  op.  cit. 


CHAP,    v.]  TIIK    MLVSliS   OK    LIFE.  713 

in  the  case  of  the  former  being  from  1*444  to  1740  metres  of 
heii^lit  and  from  39-8  and  93-8  kihjs  of  weight,  in  the  latter  from 
I  "467  to  I  890  ol  height,  and  from  49' i  to  98 '5  kilos  of  weight'. 
The  muscular  system  and  skeleton  are  both  absolutely  and  rela- 
tively less  in  woman,  and  her  brain  is  lighter  and  smaller  than  that 
of  man,  being  about  1272  grammes  to  1424.  Her  metabolism,  as 
measured  by  the  respiratory  and  urinary  excreta,  is  also  not  only 
absolutely  but  relatively  to  the  body-weight  less,  and  her  blood  is 
not  only  less  in  quantity  but  also  of  lighter  specific  gravity  and 
contains  a  smaller  proportion  of  red  corpuscles.  Her  strength  is 
to  that  of  man  as  about  5  to  9,  and  the  relative  length  of  her  step 
as  1000  to  1157. 

From  birth  onward  (and  indeed  from  early  intra-uterine  life) 
the  increment  of  growth  progressively  diminishes.  At  last  a 
point  is  reached  at  which  the  curve  cuts  the  abscissa  line,  and 
the  increment  becomes  a  decrement.  After  the  culmination  of 
manhood  at  forty  and  of  womanhood  at  the  climacteric,  the  prime 
of  life  declines  into  old  age.  The  metabolic  activity  of  the  body, 
which  at  first  was  sufficient  not  only  to  cover  the  daily  waste,  but 
to  add  new  material,  later  on  is  able  only  to  meet  the  daily  wants, 
and  at  last  is  too  imperfect  even  to  sustain  in  its  entirety  the 
existing  frame.  Neither  as  regards  vigour  and  functional  capacity, 
nor  as  regards  weight  and  bulk,  do  the  turning-points  of  the 
several  tissues  and  organs  coincide  either  with  each  other  or  with 
that  of  the  body  at  large.  We  have  already  seen  that  the  life  of 
such  an  organ  as  the  thymus  is  far  shorter  than  that  of  its  pos- 
sessor. The  eye  is  in  its  dioptric  prime  in  childhood,  when  its 
media  are  clearest  and  its  muscular  mechanisms  most  mobile,  and 
then  it  for  the  most  part  serves  as  a  toy  ;  in  later  years,  when  it 
could  be  of  the  greatest  service  to  a  still  active  brain,  it  has 
already  fallen  into  a  clouded  and  rigid  old  age.  The  skeleton 
readies  its  limit  very  nearly  at  the  same  time  as  the  whole  frame 
reaches  its  maximum  of  height,  the  coalescence  of  the  various 
epiphyses  being  pretty  well  completed  by  about  the  twenty-fifth 
year.  Similarly  the  muscular  system  in  its  increase  tallies  with 
the  weight  of  the  whole  body.  The  brain,  in  spite  of  the  in- 
creasing complexity  of  structure  and  function  to  which  it  continues 
to  attain  even  in  middle  life,  early  reaches  its  limit  of  bulk  and 
weight.  At  about  seven  years  of  age  it  attains  what  may  be  con- 
sidered as  its  first  limit,  for  though  it  may  increase  somewhat  up 
to  twenty,  thirty,  or  even  later  years,  its  progress  is  much  more 
slow  after  than  before  seven.  The  vascular  and  digestive  organs 
as  a  whole  may  continue  to  increase  even  to  a  very  late  period. 
'  Quetelet,  op.  cit.  11.  p.  S9. 


714  OLD   AGE.  [book   IV. 

From  these  facts  it  is  obvious  that  though  the  phenomena  of  old 
age  are,  at  bottom,  the  result  of  the  individual  decline  of  the 
several  tissues,  they  owe  many  of  their  features  to  the  disarrange- 
ment of  the  whole  organism  produced  by  the  premature  decay  or 
disappearance  of  one  or  other  of  the  constituent  bodily  factors. 
Thus,  for  instance,  it  is  clear  that  were  there  no  natural  intrinsic 
limit  to  the  life  of  the  muscular  and  nervous  systems,  they  would 
nevertheless  come  to  an  end  in  consequence  of  the  nutritive  dis- 
turbances caused  by  the  loss  of  the  teeth.  And  what  is  true  of  the 
teeth  is  probably  true  of  many  other  organs,  with  the  addition 
that  these  cannot,  like  the  teeth,  be  rejDlaced  by  mechanical  con- 
trivances. Thus  the  term  of  life  which  is  allotted  to  a  muscle  by 
virtue  of  its  molecular  constitution,  and  which  it  could  not  exceed 
were  it  always  placed  under  the  most  favourable  nutritive  con- 
ditions, is,  in  the  organism,  determined  by  the  similar  life-terras 
of  other  tissues  ;  the  future  decline  of  the  brain  is  probably 
involved  in  the  early  decay  of  the  thymus. 

Two  changes  characteristic  of  old  age  are  the  so-called  cal- 
careous and  fatty  degenerations.  These  are  seen  in  a  completely 
typical  form  in  cartilage,  as,  for  instance,  in  the  ribs  ;  here  the 
protoplasm  of  the  cartilage-corpuscle  becomes  hardly  more  than 
an  envelope  of  fat  globules,  and  the  supple  matrix  is  rendered 
rigid  Avith  amorphous  deposits  of  calcic  phosphates  and  car- 
bonates, which  are  at  the  same  time  the  signs  of  past  and  the 
cause  of  future  nutritive  decHne.  And  what  is  obvious  in  the, 
case  of  cartilage  is  more  or  less  evident  in  other  tissues.  Every- 
where we  see  a  disposition  on  the  part  of  protoplasm  to  fall  back 
upon  the  easier  task  of  forming  fat  rather  than  to  carry  on  the 
more  arduous  duty  of  manufacturing  new  material  like  itself; 
everywhere  almost  we  see  a  tendency  to  the  replacement  of  a 
structured  matrix  by  a  deposit  of  amorphous  material.  In  no 
part  of  the  system  is  this  more  evident  than  in  the  arteries  ; 
one  common  feature  of  old  age  is  the  conversion  by  such  a 
change  of  the  supple  elastic  tubes  into  rigid  channels,  whereby 
the  supply  to  the  various  tissues  of  nutritive  material  is  rendered 
increasingly  more  difficult,  and  their  intrinsic  decay  proportionately 
hurried. 

Of  the  various  tissues  of  the  body  the  muscular  and  nervous 
are  however  those  in  which  functional  decline,  if  not  structural 
decay,  becomes  soonest  apparent.  The  dynamic  coefficient 
of  the  skeletal  muscles  diminishes  rapidly  after  thirty  or  forty 
years  of  life,  and  a  similar  want  of  power  comes  over  the  plain 
muscular  fibres  also ;  the  heart,  though  it  may  not  diminish,  or 
even  may  still  increase  in  weight,  possesses  less  and  less  force, 


CHAl'.    v.]  THE   PHASES  OF   LHK.  /IS 

.and  the  movements  of  the  intestine,  bladder,  and  other  organs, 
diminish  in  vigour.  In  the  nervous  system,  the  h'nes  of  resist- 
ance, which,  as  we  have  seen,  help  to  map  out  the  central  ofgans 
into  mechanisms,  and  so  to  produce  its  multiflirious  actions, 
become  at  last  hindrances  to  the  passage  of  nervous  impulses 
in  any  direction,  while  at  the  same  time  the  molecular  energy  of 
the  impulses  themselves  becomes  less.  The  eye  becomes  feeble, 
not  only  from  cloudiness  of  the  media  and  presbyopic  muscular 
inability,  but  also  from  the  very  bluntness  of  the  retina ;  tl>e 
sensory  and  motor  impulses  pass  with  increasing  slowness  to  and 
from  the  central  nervous  system,  and  the  brain  becomes  a  more 
and  more  rigid  mass  of  protoplasm,  the  molecular  lines  of  which 
rather  mark  the  history  of  past  actions  than  serve  as  indications 
of  present  potency.  The  epithelial  glandular  elements  seem  to 
be  those  whose  powers  are  the  longest  preserved  ;  and  hence  the 
man  who  in  the  prime  of  his  manhood  was  a  '  martyr  to  dys- 
pepsia '  by  reason  of  the  sensitiveness  of  his  gastric  nerves  and 
the  reflex  inhibitory  and  other  results  of  their  irritation,  in  his 
later  years,  when  his  nerves  are  blunted,  and  when  therefore  his 
peptic  cells  are  able  to  pursue  their  chemical  work  undisturbed  by 
extrinsic  nervous  worries,  eats  and  drinks  with  the  courage  and 
success  of  a  boy. 

Within  the  range  of  a  lifetime  are  comprised  many  periods  of 
a  more  or  less  frequent  recurrence.  In  spite  of  the  aids  of  a  com- 
plex civilisation,  all  tending  to  render  the  conditions  of  his  life 
more  and  more  equable,  man  still  shews  in  his  economy  the  effects 
of  the  seasons.  Some  of  these  are  the  direct  results  of  varying 
temperature,  but  some  probably,  such  as  the  gain  of  weight  in 
wii.ter  and  the  loss  in  summer,  are  habits  acquired  by  descent. 
Within  the  year,  an  approximately  monthly  period  is  manifested 
in  the  female  by  menstruation,  though  there  is  no  exact  evidence 
of  even  a  latent  similar  cycle  in  the  male.  The  phenomena  of 
recurrent  diseases,  and  the  marked  critical  days  of  many  other 
maladies,  may  be  regarded  as  pointing  to  C)cles  of  smaller  dura- 
tion than  that  of  the  moon's  revolution,  unless  we  admit  the  view 
urged  by  some  authors  that  in  these  cases  the  recurrence  is  to  be 
attributed  rather  to  periodical  phases  in  the  disease-producing 
germ  itself,  than  to  variations  in  the  medium  of  the  disease. 

Prominent  among  all  other  cyclical  events  is  the  fact  that  all 
animals  possessing  a  well-developed  nervous  system,  must,  night 
after  night,  or  day  after  day,  or  at  least  time  after  time,  lay  them 
down  to  sleep.  The  salient  feature  of  sleep  is  the  cessation  of 
the  automatic  activity  of  the  brain  ;  it  is  the  diastole  of  the 
cerebral   beat.     But  the  condition  is  not  confined  to  the  cerebral 


7l6  SLEEP.  [BOOK   IV. 

hemispheres ;  all  parts  of  the  body  either  directly  or  indirectly  , 
take  share  in  it.  The  phenomena  of  sleep  are  perhaps  seen  in 
their  .simplest  form  in  the  winter-sleep  of  hybernation,  to  which 
especially  cold-blooded  animals,  but  also  to  some  extent  warm- 
blooded animals,  are  subject.  In  these  cases  the  cold  of  winter 
slackens  the  vibrations  and  lessens  the  explosions  of  the  proto- 
plasm, not  only  of  nervous  but  also  of  muscular  and  glandular 
structures  ;  indeed  the  activity  of  the  whole  body  is  lowered,  in 
some  respects  almost  to  actual  arrest.  At  the  same  time  that 
the  labour  of  the  cerebral  molecules  becomes  insufficient  to 
develope  consciousness,  the  respiratory  centre  is  either  wholly 
quiescent  or  discharges  feeble  impulses  at  rare  intervals,  and  the 
heart  beats  with  a  slow  infrequent  stroke,  not  by  reason  of  any 
inhibitory  restraint,  but  because  its  very  substance  in  its  slow 
molecular  travail  can  gather  head  for  explosions  only  after  long 
pauses  of  rest.  And  such  few  and  distant  beats  as  do  occur  are 
amply  sufficient  to  meet  the  needs  of  the  feeble  metabolism  of 
the  several  tissues.  The  sleep  of  every  day  differs  from  the 
sleep  of  winter-cold  chiefly  because  the  slackening  of  molecular 
activities  is  due  in  the  former  not  to  extrinsic  but  to  intrinsic 
causes,  not  to  changes  in  the  medium,  but  to  exhaustion  of  the 
subject,  and  because  the  phenomena  are  largely  confined  to  the 
cerebral  hemispheres.  It  is  true  that  the  whole  body  shares  in 
the  condition  ;  the  pulse  and  breathing  are  slower,  the  intestine 
and  other  internal  muscular  mechanisms  are  more  or  less  at  rest, . 
the  secreting  organs  are  less  active,  and  the  whole  metabolism 
and  the  dependent  temperature  of  the  body  are  lowered ;  but  we 
cannot  say  at  present  how  far  these  are  the  indirect  results  of  t-he 
condition  of  the  nervous  system,  or  how  far  they  indicate  a 
partial  slumbering  of  the  several  tissues. 

According  to  Mosso^  thoracic  respiration  becomes  more  prominent 
than  diaphragmatic  respiration  during  sleep,  and  the  Cheyne-Stokes 
rhythm  of  respiration  (see  p.  378)  is  frequently  observed.  During 
sleep  the  pupil  is  contracted,  during  deep  sleep  exceedingly  so  ;  and 
dilation,  often  unaccompanied  by  any  visible  movements  of  the 
limbs  or  body,  takes  place  when  any  sensitive  surface  is  stimulated^ ; 
on  awaking  also  the  pupils  dilate.  The  eyeballs  have  .been  gene - 
ally  described  as  being  during  sleep  directed  upwards  and  converging, 
or  according  to  some  authors,  diverging  ;  but  Sander  3  states  that  in 
true  sleep  the  visual  axes  are  parallel  and  directed  to  the  far  dis- 
tance.    Rahlmann  and  Witkowski'*  describe  the  eyes  of  children  as 

'  Arch.f.  Anat.  u.  Phys.  (Phys.  Abth.),  1878,  p.  441. 
^  Rahlmann  and  Witkovvski,  Arch.f.  Atiat.  u.  Fkys.  (Phys.  Abth.),  1878, 
p.  109.     Sander,  Arch.f.  Psych,  ix.  (1879)  p.  129.     Siemens,  ibid.  p.  72. 
3  Op.  cit.  t  Op.  dt. 


ciiAi*.  v.j  nil:  riiASKS  of  i-u-e.  717 

continually  executing  during  sleep  movements,  often    irregular  and 
unsymnicirical  an  1  unaccoini)anicU  by  chiUo'CS  in  the  pupils. 

We  art;  not  at  present  in  a  position  to  trace  out  the  events 
which  culminate  in  this  inactivity  of  tiie  cerebral  structures.  It 
has  been  urged'  that  dining  sleep  the  brain  isanicuiic  ;  but  even  if 
this  an;cmia  is  a  constant  accompanin\ent  of  sleep,  it  must,  like 
the  vascular  condition  of  a  gland  or  any  other  active  organ, 
bvi  regarded  as  an  effect,  or  at  least  as  a  subsidiary  event  rather 
than  as  a  primary  cause.  The  explanation  of  the  condition  is 
rather  to  be  sought  in  purely  molecular  changes  ;  and  the  analogy 
between  the  systole  and  diastole  of  the  heart,  and  the  waking  and 
slee[)ing  of  the  brain,  may  be  profitably  pushed  to  a  very  consider- 
able e.Ktent.  The  sleeping  brain  in  many  respects  closely  resembles 
a  quiescent  but  still  living  ventricle.  Both  are  as  far  as  outward 
manifestations  are  concerned  at  rest,  but  both  may  be  awakened 
to  activity  by  an  adequately  powerful  stimulus.  Both,  though 
quiescent,  are  irritable:  in  both  the  quiescence  will  ultimately  give 
place  to  activity,  and  in  both  an  appropriate  stimulus  applied  at 
the  right  time  will  determine  the  change  from  rest  to  action. 
Just  as  a  single  prick  will  under  certain  circumstances  awake  a 
ventricle,  which  for  some  seconds  has  beon  motionltiss,  into  a 
rhythmic  activity  of  many  beats,  so  a  loud  noise  will  start  a  man 
from  sleep  into  a  long  day's  wakefulness.  And  jubt  as  in  the 
heart  the  cardiac  irritability  is  lowest  at  the  beginning  of  the 
diastole  and  increases  onwards  till  a  beat  bursts  out,  so  is  sleep 
deepest  at  its  commencement  after  the  day's  labour ;  thence 
onward  slighter  and  slighter  stimuli  are  needed  to  wake  the 
sleeper. 

Kohlschiitter-,  judging  of  the  depth  of  ordinary  nocturnal  sleep  by 
the  intensity  of  the  noise  required  to  wake  the  sleeper,  concludes  that, 
increasing  very  rapidly  at  first,  it  reaches  its  niaxinaim  within  the 
first  hour  ;  from  then'  e  it  diminishes,  at  first  rapidly,  but  afterwards 
more  slow  ly.  At  the  end  of  an  hour  and  a  hnlf  it  falls  tox)nc-fourth,  at 
the  end  of  two  hours  to  one-eighth  of  its  maximal  intensity,  and  thence 
onward  diminishes  with  gradually  diminishing  decrements. 

We  cannot  at  present  make  any  definite  statements  concerning 
the  nature  of  the  n»olecular  changes  which  determine  this  rhyth- 
mic rise  and  fall  of  cerebral  irritability.  Preyer^,  leaning  towards 
the  view  that  the  accumulation  of  the  products  of  protoplasmic 

'   Durh.-im,  Guy's  Hospital  Reports,  Vol.  VI.  i860. 
"  /.eitschr.  f.  rat.  Med.  XVil.  (1862)  p.  209,  XXXIV.  (1869)  p.  42. 
3  Centralb'latt  f.  Med.   Wiss.  1S75,  p.  577.    Uebcr  die  Unache  des  Schlafes, 
1S77. 


7l8  SLEEP.  [book   IV. 

activity  may  become  in  the  end  an  obstruction  to  that  activity,  has 
been  led  to  think  that  the  presence  of  lactic  acid,  one  of  the  pro- 
ducts certainly  of  muscular  and  probably  of  nervous  metabolism, 
tends  to  produce  sleep  ;  but  this  is  doubtful.  The  suggestion 
of  Pfluger"^,  that  the  diminution  of  irritability,  and  consequent 
suspension  of  automatism,  is  dependent  on  the  exhaustion  of 
the  store  of  intramolecular  oxygen  (p.  364,  is  more  worthy  of 
attention. 

As  was  previously  stated  (p.  473),  there  is  at  present  at  least  no 
satisfactory  evidence  that  the  assumption  of  oxygen  is  directly  depen- 
dent on  the  time  of  day,  the  striking  result  obtained  by  Pettenkofer  and 
Voit  there  quoted  not  being  corroborated  by  subsequent  trials^.  The 
hypothesis  of  Pfliiger,  therefore,  unless  subsequent  researches  rein- 
state pettenkofer  and  Voit's  first  view,  needs  an  addition  to  explain 
how  it  is  that  the  store  of  intramolecular  oxygen  becomes  exhausted  in 
the  nervous  system.  Henke^  had  previously  put  forward  a  not  wholly 
unlike  hypothesis,  as  had  also  Sommer''. 

The  phenomena  of  sleep  shew  very  clearly  to  how  large  an 
extent  an  apparent  automatism  is  the  ultimate  outcome  of  the 
effects  of  antecedent  stimulations.  When  we  wish  to  go  to  sleep 
we  withdraw  our  automatic  brain  as  much  as  possible  from  the 
influence  of  all  extrinsic  stimuli ;  and  an  interesting  case  is  re- 
corded^ of  a  lad  whose  connection  with  the  external  world  was, 
from  a  complicated  anaesthesia,  limited  to  that  afforded  by  a  single 
eye  and  a  single  ear,  and  who  could  be  sent  to  sleep  at  will,  by 
closing  the  eye  and  stopping  the  ear. 

The  cycle  of  the  day  is  however  manifested  in  many  other  ways 
than  by  the  alternation  of  sleeping  and  waking,  with  all  the  indirect 
effects  of  these  two  conditions.  There  is  a  diurnal  curve  of  tem- 
perature (see  p.  487),  apparently  independent  of  all  immediate 
circumstances,  the  hereditary  impress  of  a  long  and  ancient  se- 
quence of  days  and  nights.  Even  the  pulse,  so  sensitive  to  all 
bodily  changes,  shews,  running  through  all  the  immediate  effects 
of  the  changes  of  the  minute  and  the  hour,  the  working  of  a 
diurnal  influence  which  cannot  be  accounted  for  by  waking  and 
sleeping,  by  working  and  resting,  by  meals  and  abstinence  be- 
tween meals.  And  the  same  may  be  said  concerning  the  rhythm 
of  respiration,   and  the  products   of  pulmonary,   cutaneous  and 

'  Pfliiger's  Archiv,  x.  (1875)  p.  468. 

^  Siizungsbencht.  Acad.  Wiss.  Milnchen,  1866 — 67. 

3  Zeilschr.f.  rat.  Med.  xiv.  (1861)  p.  363. 

4  Zeitschr.  f.  rat.  Med.  xxxill.  (1 868). 

5  Cf.  Heubel,  Pfliiger's  Archiv,  xiv.  (1877)  p.  158. 
^  Pfliiger's  Archiv,  xv.  (1877)  p.  573. 


CIIA1\   v.]  THE   PHASES   OF    LIFE.  719 

iirinnry  excretion.  There  seems  to  be  a  daily  curve  of  bodily 
metabolism,  which  is  not  the  product  of  the  day's  events.  ^Vilhin 
the  day  we  have  the  narrower  rhythm  of  the  respiratory  centre 
witli  the  accompanying  rise  and  fall  of  activity  in  the  vaso-motor 
centres.  And  lastly,  as  the  fundamental  fact  of  all,  bodily  perio- 
dicity is  that  alternation  of  the  heart's  systole  and  diastole  which 
ceases  only  at  death.  Though,  as  we  have  seen,  the  intermittent 
flow  in  the  arteries  is  toned  down  in  the  capillaries  to  an  appar- 
ently continuous  flow,  still  the  constantly  repeated  cycle  of  the 
cardiac  shuttle  must  leaves  its  mark  throughout  the  whole  web  of 
the  body's  life.  Our  means  of  investigation  are,  however,  still  too 
gross  to  permit  us  to  track  out  its  influence.  Still  less  are  we  at 
present  in  a  position  to  say  how  far  the  fundamental  rhythm  of 
the  heart  itself,  that  rhythm  which  is  influenced,  but  not  created, 
by  the  changes  of  the  body  of  which  it  is  the  centre,  is  the  result 
of  cosmical  changes,  the  reflection  as  it  were  in  little  of  the  cycles 
of  the  universe,  or  how  far  it  is  the  outcome  of  the  inherent 
vibrations  of  the  molecules  which  make  up  its  substance. 


CHAPTER   VI. 

DEATH. 

When  the  animal  kingdom  is  surveyed  from  a  broad  stand -point 
it  becomes  obvious  that  the  ovum,  or  its  correlative  the  sperma- 
tozoon, is  the  goal  of  an  individual  existence  :  that  life  is  a  cycle 
beginning  in  an  ovum  and  coming  round  to  an  ovum  again.  The 
greater  part  of  the  actions  which,  looking  from  a  near  point  of 
view  at  the  higher  animals  alone,  we  are  apt  to  consider  as 
eminently  the  purposes  for  which  animals  come  into  existence, 
when  viewed  from  the  distant  outlook  whence  the  whole  living 
world  is  surveyed,  fade  away  into  the  likeness  of  the  mere  byplay 
of  ovum-bearing  organisms.  The  animal  body  is  in  reality  a 
vehicle  for  ova;  and  after  the  life  of  the  parent  has  become 
potentially  renewed  in  the  offspring,  the  body  remains  as  a  cast- 
off  envelope  whose  future  is  but  to  die. 

Were  the  animal  frame  not  the  complicated  machine  we  have 
seen  it  to  be,  death  might  come  as  a  simple  and  gradual  disso- 
lution, the  '  sans  everything '  being  the  last  stage  of  the  successive 
loss  of  fundamental  powers.  As  it  is,  however,  death  is  always 
more  or  less  violent ;  the  machine  comes  to  an  end  by  reason  of 
the  disorder  caused  by  the  breaking  down  of  one  of  its  parts. 
Life  ceases  not  because  the  molecular  powers  of  the  whole  body 
slacken  and  are  lost,  but  because  a  weakness  in  one  or  other  part 
of  the  machinery  throws  its  whole  working  out  of  gear. 

We  have  seen  that  tlie  central  factor  of  life  is  the  circulation 
of  the  blood,  but  we  have  also  seen  that  blood  is  not  only  useless, 
but  injurious,  unless  it  be  duly  oxygenated ;  and  we  have  further 
seen  that  in  the  higher  animals  the  oxygenation  of  the  blood  can 
only  be  duly  effected  by  means  of  the  respiratory  muscular  mechan- 
ism, presided  over  by  the  medulla  oblongata.     Thus  the  life  of  a 


CIIAi^    VI.]  DEATH.  721 

complex  animal  is,  when  reduced  to  a  simple  form,  composed  of 
tliree  factors  :  the  maintenance  of  the  circulation,  the  access  of 
air  to  die  haemoglobin  of  tlie  blood,  and  tiie  functional  activity  of 
the  respiratory  centre  ;  and  death  may  come  from  the  arrest  of 
cither  of  these.  As  Bichat  put  it,  death  takes  i)lace  by  the  heart 
or  by  the  lungs  or  by  the  brain.  In  reality,  however,  when  we 
.l)usli  the  analysis  furtlier,  the  central  fact  of  death  is  the  stoppage 
of  the  heart,  and  the  consequent  arrest  of  the  circulation ;  the 
tissues  then  all  die,  because  they  lose  their  internal  medium.  The 
failure  of  the  heart  may  arise  in  itself,  on  account  of  some  failure 
in  its  nervous  or  muscular  element^',  or  by  reason  of  some  mis- 
chief affecting  its  mechanical  working.  Or  it  may  be  due  to 
some  fault  in  its  internal  medium,  such  for  instance  as  a  want  of 
oxygenation  of  the  blood,  which  in  turn  may  be  caused  by  either 
a  change  in  the  blood  itself,  as  in  carbonic  oxide  poisoning,  or  by 
a  failure  in  the  mechanical  conditions  of  respiration,  or  by  a  ces- 
sation of  the  action  of  the  respiratory  centre.  The  failure  of  this 
centre,  and  indeed  that  of  the  heart  itself,  may  be  caused  by 
nervous  influences  proceeding  from  the  brain,  or  brought  into 
operation  by  means  of  the  central  nervous  system  ;  it  may,  on  the 
other  hand,  be  due  to  an  imperfect  state  of  blood,  and  this  in 
turn  may  arise  from  the  imperfect  or  perverse  action  of  various 
secretory  or  other  tissues.  The  modes  of  death  are  in  reality  as 
numerous  as  are  the  possible  modifications  of  the  various  factors 
of  life ;  but  they  all  end  in  a  stoppage  of  the  circulation,  and  the 
withdrawal  from  the  tissues  of  their  internal  medium.  Hence  we 
come  to  consider  the  death  of  the  body  as  marked  by  the  ces- 
sation of  the  heart's  beat,  a  cessation  from  which  no  recovery 
is  possible  ;  and  by  this  we  are  enabled  to  fix  an  exact  time 
at  which  we  say  the  body  is  dead.  We  can,  however,  fix  no 
such  exact  time  to  the  death  of  the  individual  tissues.  They 
are  not  mechanisms,  and  their  death  is  a  gradual  loss  of  power. 
In  the  case  of  the  contractile  tissues,  we  have  apparently 
in  rigor  mortis  a  fixed  term,  by  which  we  can  mark  the  exact 
time  of  their  death.  If  we  admit  that  after  the  onset  of  rigor 
mortis  recovery  of  irritability  is  impossible,  then  a  rigid  muscle 
is  one  permanently  dead.  In  the  case  of  the  other  tissues, 
we  have  no  such  objective  sign,  since  the  rigor  mortis  of 
simple  protoplasm  manifests  itself  chiefly  by  obscure  chemical 
signs.  And  in  all  cases  it  is  obvious  that  the  possibility  of  re- 
covery, depending  as  it  does  on  the  skill  and  knowletlge  of  the 
experimenter,  is  a  wholly  artificial  sign  of  death.  Yet  we  can 
draw  no  other  sharp  line  between  the  seemingly  dead  tissue 
whose  life  has  flickered  down  into  a  smouldering  ember  which 
F.  P.  46 


722  DEATH.  [book  IV. 

can  still  be  fanned  back  again  into  flame,  and  the  aggregate 
of  chemical  substances  into  which  the  decomposing  tissue  finally 
crumbles. 

Moreover,  the  failure  of  the  heart  itself  is  at  bottom  loss  of 
irritability,  and  the  possibility  of  recovery  here  also,  rests,  as  far 
as  is  known  at  present,  on  the  skill  and  knowledge  of  those  who 
attempt  to  recover.  So  that  after  all  the  signs  of  the  death  of  the 
whole  body  are  as  artificial  as  those  of  the  death  of  the  constituent 
tissues. 


APPENDIX. 


46-: 


APPENDIX, 


ON  THE  CHEMICAL   BASIS  OF   THE  ANIMAL  BODY. 

Native  protoplasm,  whenever  it  can  be  obtained  in  sufficient  quantity 
for  chemical  analysis,  is  found  to  contain  representatives  of  three 
large  classes  of  chemical  substances,  viz.,  proteids,  carbohydrates 
and  fats,  in  association  with  smaller  quantities  of  various  saline  and 
other  crystalline  bodies.  By  prot-eids  are  meant  bodies  containing 
carbon,  oxygen,  hydrogen  and  nitrogen  in  a  certain  proportion, 
varying  within  narrow  limits,  and  having  certain  general  features  ; 
they  are  frequently  spoken  of  as  albuminoids.  By  carbohydrates  are 
meant  starches  and  sugars  and  their  allies.  Of  these  three  classes  of 
bodies,  the  proteids  form  the  chief  mass  of  ordinary  protoplasm,  but 
fats  and  carbohydrates  are  never  wholly  absent.  To  obtain  evidence 
of  the  presence  of  any  one  of  them  in  living  protoplasm  we  are  obliged 
to  submit  the  protoplasm  to  destructive  analysis.  We  do  not  at  present 
know  anything  definite  about  the  molecular  composition  of  active 
living  protoplasm  ;  but  it  is  more  than  probable  that  its  molecule  is  a 
large  complex  one  in  which  a  protcid  substance  is  peculiarly  asso- 
ciated with  a  complex  fat  and  with  some  representative  of  the  carbo- 
hydrate group,  i.e.,  that  each  molecule  of  protoplasm  contains  residues 
of  each  of  these  three  great  classes. 

The  whole  animal  body  is  modified  protoplasm.  Consequently 
when  we  examine  the  various  tissues  and  fluids  from  a  chemical  point 
of  view,  we  find  present  in  different  places,  or  at  different  times, 
several  varieties  and  derivatives  of  the  three  chief  classes ;  we  find 
many  forms  of  proteids  and  cfcrivatives  of  proteids  in  the  forms  of 
gelatine,  chondrin,  &c.  ;  many  varieties  of  fats;  and  several  kinds  of 
carbohydrates. 

We  find  moreover  many  other  bodies  which  w*e  may  regard  as 
stages  in  the  constructive  or  destructive  metabolism  of  both  native 
and  differentiated  protoplasm,  and  which  are  important  not  so  much 


726  PROTEIDS.  [APP. 

from  the  quantity  in  which  they  occur  in  the  animal  body  at  any  one 
time  as  from  their  throwing  light  on  the  nature  of  animal  metabolism ; 
these  are  such  bodies  as  urea,  lactic  acid,  and  the  extractives  in 
general. 

In  the  following  pages  the  chemical  features  of  the  more  important 
of  these  various  substances  which  are  known  to  occur  in  the  animal 
body  will  be  briefly  considered,  such  characters  only  being  described 
as  possess  or  promise  to  possess  physiological  interest.  The  physio- 
logical function  of  any  substance  must  depend  ultimately  on  its 
molecular  (including  its  chemical)  nature  ;  and  though  at  present  our 
chemical  knowledge  of  the  constituents  of  an  animal  body  gives  us 
but  little  insight  into  their  physiological  properties,  it  cannot  be 
doubted  that  such  chemical  information  as  is  attainable  is  a  necessaiy 
preliminary  to  all  physiological  study. 


PROTEIDS. 

These  form  the  principal  solids  of  the  muscular,  nervous,  and 
glandular  tissues  of  the  serum  of  blood,  of  serous  fluids,  and  of 
lymph.  In  a  healthy  condition,  sweat,  tears,  bile  and  urine  contain 
mere  traces,  if  any,  of  proteids.  Their  general  percentage  com- 
position may  be  taken  as 

C.  S. 

51-5  0-3 

to   54-5  to   2'0 

(Hoppe-Seyler '.) 

These  figures  are  obtained  from  a  consideration  of  numerous  analyses, 
slight  differences  in  the  various  results  being  immaterial,  where  the  purity  of 
the  substance  operated  upon  cannot  be  definitely  determined. 

In  addition  to  the  above  constituents,  proteids  leave  on  ignition  a  variable 
quantity  of  ash.  In  the  case  of  egg-albumin  the  principal  constituents  of  the 
ash  are  chlorides  of  sodium  and  potassium,  the  latter  greatly  exceeding  the 
former  in  amount.  The  remainder  consists  of  sodium  and  potassium,  in  com- 
bination with  phosphoric,  sulphuric,  and  carbonic  acids,  and  very  small 
quantities  of  calcium,  magnesium  and  iron,  in  union  with  the  same  acids. 
There  is  also  a  trace  of  silica  ^  The  ash  of  Ferum-albumin  contains  an  excess 
of  sodium  chloride,  but  the  a«h  of  the  proteids  of  muscle  contains  an  excess 
of  potash  salts  and  phosphates.  The  nature  of  the  connection  of  the  ash  with 
the  proteid  is  still  a  matter  of  obscurity.  Globin  fi-om  haemoglobin  is  free 
from  ash.  • 


0. 

H. 

N. 

From     20 '9 

6-9 

15-2 

to  23-5 

to  7-3 

to  17-0 

Hdb.  Phys.  Path.  Chem.  Anal,  Ed.  iv.  (1875)  S.  223. 
See  Gmelin,  Hdb.  Org.  Chnn.,  Bd.  viii.  S.  285. 


APr.]        CHEMICAL   BASIS   Oi''   THE   ANIMAL    liODV.  727 

Protcids  arc  all  amorphous  ;  some  are  soluble,  some  insoluble  in 
water,  and  all  arc  lor  the  most  part  insoluble  in  alcohol  and  a-thcr  ;  they 
are  all  soluble  in  stron<;  acids  and  alkalis,  but  in  bcconiing  dissolved 
mostly  undergo  composition.  Their  solutions  possess  a  left-handed 
rotatory  action  on  the  plane  of  polarisation,  the  amount  depending  on 
various  circumstances,  and  being,  with  one  exception,  viz.,  peptones, 
changed  by  heating. 

Cry.stals  into  whose  composition  cert.-xin  protcicl  (globulin)  elements  enter 
were  long  since  observed  in  the  seeds  of  many  plants  ;  as  yet  I  hey  have  not 
been  obtained  sufficiently  isolated  or  in  quantities  large  enough  to  permit  of 
any  accurate  analy.sis  to  be  made.  Quite  recently  however  '  a  method  of 
isolating  in  quantity  and  recry.stallizing  these  substances  has  been  indicated, 
and  it  seems  probalile  that  analysis  of  the^e  may  lead  to  interesting  informa- 
tion on  the  subject  of  the  constitution  and  combinations  of  proteids. 

Their  presence  piay  be  detected  by  the  following  tests. 

1.  Heated  with  strong  nitric  acid,  they  or  their  solutions  turn 
yellow,  and  this  colour  is,  on  the  addition  of  ammonia,  changed  to  a 
deep  orange  hue.     (Xanthoproteic  reaction.) 

2.  With  Millon's  reagent  they  give,  when  present  in  sufficient 
quantity,  a  precipitate,  which,  with  the  supernatant  fluid,  turns  red  on 
heating.  If  they  are  only  present  in  traces,  no  precipitate  is  obtained, 
but  merely  the  red  colouration. 

3.  With  caustic  soda  solution,  and  one  or  two  drops  of  a  solution 
of  cupr  c  sulphate,  a  violet  colour  is  obtained,  which  deepens  on 
boiling. 

The  above  serve  to  detect  the  smallest  traces  of  all  proteids.  The 
two  following  tests  may  be  used  when  there  is  more  than  a  trace 
present,  but  do  not  hold  for  every  kind  of  proteid. 

4.  Render  the  fluid  strongly  acid  with  acetic  acid,  and  add  a  few 
drops  of  a  solution  of  ferrocyanide  of  potassium  ;  a  precipitate  shews 
the  presence  of  proteids. 

5.  Render  the  fluid,  as  before,  strongly  acid  with  acetic  acid,  add 
an  equal  volume  of  a  concentrated  solution  of  sodium  sulphate,  and 
boil.     A  precipitate  is  formed  if  proteids  are  present. 

This  last  reaction  is  useful,  not  only  on  account  of  its  exactness,  but  also 
because  the  reagents  u.sed  produce  no  decomposition  of  other  bodies  which 

•  T>Kchx\,  /oum.  f,  prakt.  Chem.,  N.  F.  Bd.  xix.  (1S79)  S.  331. 


728  PROTEIDS.  [APP. 

may  be  present ;  and  hence  after  filtration  the  same  fluid  may  be  further 
analysed  for  other  substances.  Additional  methods  of  freeing  a  solution  from 
proteids  are  :  acidulating  with  acetic  acid  and  boiling,  avoiding  any  excess 
of  the  acid  ;  precipitation  by  excess  of  alcohol  ;  in  the  latter  case  the  solution 
must  be  neutral  or  faintly  acid.  Hoppe-Seyler  ^  recommends  the  employment 
of  a  saturated  solution  of  freshly  precipitated  ferric  oxide,  in  acetic  acid. 
Briicke's  method  of  removing  the  last  traces  of  proteids  from  glycogen 
solutions  is  also  of  use  (see  p.  757).  Precipitation  of  the  last  traces  of  pro- 
teids by  means  of  hydrated  oxide  of  lead  at  a  boiling  temperature  ^  may  be 
also  employed. 

Proteids  may  be  very  conveniently  divided  into  Classes. 

Class  I.     Native  Albumins. 

Members  of  this  class,  as  their  name  implies,  occur  in  a  natural 
condition  in  animal  tissues  and  fluids.  They  are  soluble  in  water, 
are  not  precipitated  by  very  dilute  acids,  by  carbonates  of  the  alkalis, 
or  by  sodium  chloride.  They  are  coagulated  by  heating  to  a  tempera- 
ture of  about  70°.  If  dried  at  40°,  the  resulting  mass  is  of  a  pale 
yellow  colour,  easily  friable,  tasteless,  and  inodorous, 

I.     Egg-albumin. 

Forms  in  aqueous  solution  a  neutral,  transparent,  yellowish  fluid. 
From  this  it  is  precipitated  by  excess  of  strong  alcohol.  If  the  alcohol 
be  rapidly  removed  the  precipitate  may  be  readily  redissolved  in  water  ; 
if  subjected  to  lengthier  action  a  coagulation  occurs,  and  the  albumin 
is  then  no  longer  thus  soluble.  Strong  acids,  especially  nitric  acid, 
cause  a  coagulation  similar  to  that  produced  by  heat  or  by  the  pro- 
longed action  of  alcohol  ;  the  albumin  becomes  profoundly  changed 
by  the  action  of  the  acid  and  does  not  dissolve  upon  removal  of  the 
acid.>  Mercuric  chloride,  silver  nitrate,  and  lead  acetate,  preci)- itate 
the  albumin  without  coagulation  ;  on  removal  of  the  precipitant  the 
precipitate  may  be  redissolved. 

Strong  acetic  acid  in  excess  gives  no  precipitate,  but  when  the 
solution  is  concentrated  the  albumin  is  transforricd  into  a  transparent 
jelly.  A  similar  jelly  is  produced  when  strong  caustic  potash  is  added 
to  a  concentrated  solution  of  egg-albumin.  In  both  these  cases  the 
substance  is  profoundly  altered. 

The  specific  rotatory  power  of  egg-albumin  in  aqueous  solution  is, 
for  yellow  light,  — 35 "5°.  Hydrochloric  acid,  added  until  the  reaction 
is  sti^ongly  acid,  increases  this  rotation  to  — 377''.  The  formation  of 
the  gelatinous  compound  with  caustic  potash  is  at  first  accompanied 
with  an  increase,  but  this  is  followed  by  a  decrease  of  rotation, 

'  Op.  cit.  S.  227. 

"  Hofmeister,  Zeitsch.  f.  physiol.  Chem.,  Bd.  il.  (1878)  S.  288. 


APP.]       CHEMICAL   BASIS   OF   THE   ANIMAL    BODY.  729 

Preparation.  White  of  hen's  egg  is  broken  up  with  scissors  into 
small  pieces,  diluted  with  an  cciual  bulk  of  water,  and  the  mixture 
sh  iken  strongly  in  a  tlask  till  quite  frothy  ;  on  standing  the  foam  rises 
to  the  top,  and  carries  all  the  fibres  in  whose  meshwork  the  albumin 
was  contained.  The  tkiid,  from  which  the  foam  has  been  removed, 
is  strained,  and  treated  carefully  with  dilute  acetic  acid  as  long  as 
any  precipitate  is  formed  ;  the  precipitate  is  then  filtered  off,  and 
the  filtrate  after  neutralisation  concentrated  at  40'^  to  its  original 
bulk, 

2.     Senini-albumin. 

This  form  of  albumin  resembles,  to  a  great  extent,  the  one 
previously  described.  The  following  may  suffice  as  distinguishing 
features. 

1.  The  specific  rotation  of  serum-albumin  is  —56°;  that  of  egg- 
albumin  is -35*5°,  both  measured  for  yellow  light. 

2.  Serum-albumin  is  not  coagulated  by  aether,  egg-albumin  is. 

3.  Serum-albumin  is  not  very  readily  precipitated  by  strong 
hydrochloric  acid,  and  such  precipitate  as  does  occur  is  readily  re- 
dissolved  on  further  addition  of  the  acid  ;  the  exact  reverse  of  these 
two  features  holds  good  for  egg-albumin. 

• 

4.  Precipitated  or  coagulated  serum-albumin  is  readily  soluble, 
egg-albumin  is  with  difficulty  soluble,  in  strong  nitric  acid. 

Serum-albumin  is  found  not  only  in  blood-serum,  but  also  in  lymph, 
both  that  contained  in  the  proper  lymphatic  channels  and  that  diffused 
in  the  tissues  ;  in  chyle,  milk,  transudations  and  many  pathological 
fluids. 

It  is  this  form  in  which  albumin  generally  appears  in  the  urine. 

In  addition  to  the  above,  Scherer '  has  described  two  closely  related  bodies, 
to  which  he  gives  the  names  Paralbumin  and  Metalbumin.  The  first  he 
obtained  from  ovarian  cysts  ;  its  alkaline  solutions  are  remarkable  for  being 
very  ropy.  It  seems  doubtful  whether  this  body  is  a  proteid  ;  it  differs  sensibly 
in  composition  from  these.  Ilaerlin  ^  gives  as  its  composition,  O.  26'8i 
H.  69,  N.  i2'8,  C.  Si'8,  S.  i'7  p.c.  It  seems  to  be  associated  with  some 
body  like  glycogen,  capable  of  being  converted  into  a  substance  giving  the 
reactions  of  dextrose.  Metalbumin,  found  in  a  dropsical  fluid,  resembles  the 
preceding,  but  is  not  precipitated  by  hydrochloric  acid,  or  by  acetic  acid  and 

'  Ann.  der  Ghent,  und  Pharm.,  Bd.  82,  S.  135. 
■  Chenu  Centralblatt,  1862.     No.  56. 


730  PROTEIDS.  [aPP. 

ferrocyanide  of  potassium  ;  it  is  precipitated,  but  not  coagulated,  by  alcohol ; 
its  solution  is  scarcely  coagulated  on  boiling. 

Albumins  are  generally  found  associated  with  small  but  definite 
amounts  of  saline  matter.  A.  Schmidt^  says  that  they  maybe  freed 
from  these  by  dialysis,  and  that  they  are  then  not  coagulated  on  boiling. 
From  this  it  might  be  inferred  that  the  albumin  and  the  saline  matters 
were  pecuharly  related,  and  that  the  latter  pla3pd  some  special  part 
during  the  coagulation  of  the  former  by  heat.  Schmidt's  observa- 
tions however  have  not  been  conclusively  corroborated  by  subsequent 
observers. 

Class  1 1 .     Derived  A  lbii7nins  {Albuminates). 
I .     A  cid-albumin. 

When  a  native  albumin  in  solution,  such  as  serum-albumin,  is 
treated  for  some  little  time  with  a  dilute  acid  such  as  hydrochloric,  its 
properties  become  entirely  changed.  The  most  marked  changes  are 
(i)  that  the  solution  is  no  longer  coagulated  by  heat ;  (2)  that  when 
the  solution  is  carefully  neutralized  the  whole  of  the  proteid  is  thrown 
down  as  a  precipitate  ;  in  other  words,  the  serum-albumin  which  was 
soluble  in  water,  or  at  least  in  a  neutral  fluid  containing  only  a  small 
quantity  of  neutral  salts,  has  become  converted  into  a  substance  in- 
soluble in  water  or  in  similar  neutral  fluids.  The  body  into  which 
serum-albumin  thus  becomes  converted  by  the  action  of  an  acid  is 
spoken  of  as  acid-albumin.  Its  characteristic  features  are  that  it  is 
insoluble  in  distilled  water,  and  in  neutral  saline  solutions,  such  as 
those  of  sodium  chloride,  that  it  is  readily  soluble  in  dilute  acids  or 
dilute  alkalis,  and  that  its  solutions  in  acids  or  alkalis  are  not  coagu- 
lated by  boihng.  When  suspended,  in  the  undissolved  state,  in  water, 
and  heated  to  70^,  it  becomes  coagulated,  and  is  then  undistinguishable 
from  coagulated  serum-albumin,  or  indeed  from  any  other  form  of 
coagulated  proteid.  It  is  evident  that  the  substance  when  in  solution 
in  a  dilute  acid  is  in  a  different  condition  from  that  in  which  it  is  when 
precipitated  by  neutralisation.  If  a  quantity  of  serum-  or  egg-albumin 
be  treated  with  dilute  hydrochloric  acid,  it  will  be  found  that  the  con- 
version of  the  native  albumin  into  acid-albumin  is  gradual ;  a  speci- 
men heated  to  70°  immediately  after  the  addition  of  the  dilute  acid, 
will  coagulate  almost  as  usual;  and  another  specimen  taken  at  the 
same  time  will  give  hardly  any  precipitate  on  neutralisation.  Some 
time  later,  the  interval  depending  on  the  proportion  of  the  acid  to  the 
albumin,  on  temperature,  and  on  other  circumstances,  the  coagulation 
will  be  less,  and  the  neutralisation  precipitate  will  be  considerable. 
Still  later  the  coagulation  will  be  absent,  and  the  whole  of  the  proteid 
will  be  thrown  down  on  neutralisation. 

'  Pfliiger's  Archiv,  xi.  (1875)  S.  I. 


API'.]        CHEMICAL   LASIS   OF   THE   ANIMAL    BODY.  73I 

If  finely-chopped  muscle,  from  which  the  sokible  albumins  have 
been  rcnu)vc(.l  by  repeated  uasliin};,  be  treated  for  some  time  with 
dilute  ("2  per  cent.)  hydrochloric  acid,  the  greater  part  of  the  muscle 
is  dissolved.  The  transparent  acid  filtrate  contains  a  lar^e  quantity 
of  proteid  material  in  a  form  which,  in  its  general  characters  at  least, 
agrees  with  acid-albumin.  The  acid  solution  of  the  proteid  is  not 
coagulated  by  boiling,  but  the  whole  of  the  proteid  is  precipitated  on 
neutralisation  ;  and  the  precipitate,  insoluble  in  neutral  sodic  chloride 
solutions,  is  readily  dissolved  by  even  dilute  acids  or  alkalis.  •  The 
proteid  thus  obtained  from  muscle  has  been  called  syntonin,  but  we 
have  at  present  no  satisfactory  test  to  distinguish  the  acid-albumin 
(or  syntonin)  prepared  from  muscle  from  that  prepared  from  egg-  or 
serum-albumin.  When  coagulated  albumin  or  other  coagulated  pro- 
teid or  librin  is  dissolved  in  strong  acids,  acid-albumin  is  formed  ;  and 
when  fibrin  or  any  other  proteid  is  acted  upon  by  gastric  juice,  acid- 
albumin  is  one  of  the  first  products  ;  and  these  acid-albumins  cannot 
be  distinguished  from  acid-albumin  prepared  froni  muscle  or  native 
albumin.  Though  hydrochloric  acid  is  i)erhaps  the  most  convenient 
acid  for  forming  acid-albumin,  other  acids  may  also  be  used  fur  the 
purpose  of  preparing  it.  Acid-albumin  is  soluble  not  only  in  dilute 
alkalis,  but  also  in  dilute  solutions  of  alkaline  carbonates  ;  its  solutions 
in  these  are  not  coagulated  by  boiling. 

•  If  sodic  chloride  in  excess  is  added  to  an  acid  solution  of  acid- 
albumin,  the  acid-albumin  is  precipitated  :  this  also  occurs  on  adding 
sodium  acetate  or  phosphate. 

As  special  tests  of  acid-albumin  may  be  given  :  i.  Partial  coagula- 
tion of  its  solution  in  lime-water  on  boiling.  2.  Further  precipitation 
of  the  same  solution  after  boiling,  on  the  addition  of  calcic  chloride, 
magnesic  sulphate,  or  sodic  chloride. 

Dissolved  in  very  dilute  hydrochloric  acid,  acid-albumin  (syntonin) 
prepared  from  muscle  possesses  a  specific  la;vo-rotatory  power  of  —72° 
for  yellow  light,  this  being  independent  of  the  concentration'.  On 
heating  the  solution  in  a  closed  vessel  in  a  water-bath,  the  rotatory 
power  rises  to  -84*8^. 

2.     Alkali-albumin. 

If  serum-  or  egg-albumin  or  washed  muscle  be  treated  with  dilute 
alkali  instead  of  with  dilute  acid,  the  proteid  undergoes  a  change  quite 
similar  to  that  which  was  brought  about  by  the  acid.  The  alkaline 
solution,  when  the  change  has  become  complete,  is  no  longer  coagu- 
lated by  heat,  the  proteid  is  wholly  precipitated  on  neutralisation, 
and  the  precipitate,  insoluble  in  water  and  in  neutral  sodic  chloride 

•  Hoppe-Seyler,  Hdb.  Phys.  Path.  Oum.  Anal.,  Ed.  iv.  (1875)  S.  246. 


732  PROTEIDS.  [APP. 

solutions,  is  readily  soluble  in  dilute  acids  or  alkalis.  Indeed  in  a  general 
way  it  may  be  said  that  acid-albumin  and  alkali-albumin  are  nothing 
more  than  solutions  of  the  same  substance  in  dilute  acids  and  alkalis 
respectively.  When  the  precipitate  obtained  by  the  neutralisation  of  a 
solution  of  acid-albumin  in  dilute  acid  is  dissolved  in  a  dilute  alkali, 
it  may  be  considered  to  become  alkali-albumin  ;  and  conversely  when 
the  precipitate  obtained  from  an  alkali-albumin  solution  is  dissolved  in 
dilute  acid,  it  may  be  regarded  as  acid-albumin. 

It  is  stated  as  a  characteristic  reaction  of  this  modified  or  derived 
albumin  that  it  is  not  precipitated  when  its  alkaline  solutions  are 
neutralised  in  the  presence  of  alkaline  phosphates  ;  solutions  of  acid- 
albumin  on  the  contrary  are  said  to  be  precipitated  on  neutralisation 
in  the  presence  of  alkaline  phosphates,  and  this  difference  is  considered 
to  be  a  distinguishing  feature  of  the  two  proteids. 

Alkali-albumin  may  be  prepared  by  the  action  not  only  of  dilute 
alkalis  but  also  of  strong  caustic  alkalis  on  native  albumins  as  well  as 
on  coagulated  albumin  and  other  proteids.  The  jelly  produced  by  the 
action  of  caustic  potash  on  white  of  egg,  spoken  of  in  Class  I.  i,  is 
alkali-albumin  ;  the  similar  jelly  produced  by  strong  acetic  acid  is 
acid-albumin.  One  of  the  most  productive  methods  of  obtaining 
alkali-albumin  is  that  produced  by  Lieberkiihn',  and  consists  in  adding 
strong  solution  of  caustic  potash  to  white  of  egg  until  the  above- 
mentioned  jelly  is  obtained.  This  is  then  cut  into  small  pieces,  arfli 
dialysed  until  quite  white.  The  lumps  are  then  dissolved  in  the  water- 
bath,  and  the  alkali-albumin  precipitated  by  the  careful  addition  of 
acetic  acid. 

Both  alkali-  and  acid-albumin  are  with  difficulty  precipitated  by 
alcohol  from  their  alkaline  or  acid  solutions.  The  neutralisation  pre- 
cipitate however  becomes  coagulated  under  the  prolonged  action  of 
alcohol. 

The  body  '  protein, '  for  whose  existence  Mulder  has  so  much  contended, 
appears,  if  it  exists  at  all,  to  be  closely  connected  with  this  body.  All  subse- 
quent observers  have  however  failed  to  confirm  his  views. 

The  rotatory  power  of  alkali-albumin  varies  according  to  its 
source  ;  thus  when  prepared  by  strong  caustic  potash  from  serum- 
albumin,  the  rotation  rises  from  — 56°  (that  of  serum-albumin)  to  — 86°, 
for  yellow  light.     Similarly  prepared  from  egg-albumin,  it  rises  from 

—  38*5°   to— 47°,    and    if  from  coagulated    white   of  egg,    it   rises   to 

—  58'8°.  Hence  the  existence  of  various  forms  of  alkali-albumin  is 
probable. 

In  addition  to  the  methods  given  above,  alkali-albumin  may  be  also  readily 
obtained  by  shal<ing  milk  with  strong  caustic  soda  solution  and  sether,  removing, 

'  Poggendorff's  Annalen,  Bd.  LXXXVI.  S.  118. 


Arr.]         CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  733 

the  aclherii'il  solution,  ])rccipitating  the  remaining  fluid  with  acetic  acid  and 
washing  tiic  precipitate  with  water,  cold  alcohol  and  athcr. 

The  most  satisfactory  method  of  regarding  acid-  and  alkali-albumin 
is  to  consider  them  as  respectively  acid  and  alkali  compounds  of  the 
neutralisation  precipitate.  We  have  reason  to  think  that  when  the 
precipitate  is  dissolved  in  either  an  acid  or  an  alkali,  it  does  enter  into 
combination  with  them.  The  neutralisation  precipitate  is  in  itself 
neither  acid-  nor  alkali-albumin,  but  may  become  either,  upon  solution 
in  the  respective  reagent. 

It  is  probable  that  several  derived  albumins  exist,  difTering  according  to  the 
proteid  from  which  they  are  formed  or  possibly  according  to  the  mode  of  their 
preparation,  and  that  each  of  these  may  exist  in  its  correlative  forms  of  acid- 
and  alkali-albumin  ;  but  the  whole  subject  requires  further  invetigation. 

Acid-albumin,  prepared  by  the  direct  action  of  dilute  acids  on 
native  albumins  or  on  muscle-substance,  contains  sulphur,  as  shewn 
by  the  brown  colouration  which  appears  when  the  precipitate  is  heated 
with  caustic  potash  in  the  presence  of  basic  lead  acetate.  Alkali- 
albumin,  at  all  events  as  prepared  by  the  action  of  strong  caustic 
potash  or  soda,  does  not  contain  any  sulphur ;  and  the  acid-albumin, 
prepared  by  the  solution  in  an  acid  of  the  neutralisation  precipitate 
from  such  an  alkali-albumin  solution,  is  similarly  free  from  sulphur. 

3.     Casern. 

This  is  the  well-known  proteid  existing  in  milk.  When  freed  from 
fat,  and  in  the  moist  condition,  it  is  a  white  friable,  opaque  body.  In 
most  of  its  reactions  it  corresponds  closely  with  alkali-albumin  ;  thus 
it  is  readily  soluble  in  dilute  acids  and  alkalis,  and  is  re-precipitated 
on  neutralisation  ;  if,  however,  potassium  phosphate  is  present,  as  is 
the  case  in  milk,  the  solution  must  be  strongly  acid  before  any 
precipitate  is  obtained. 

Various  reactions  have  at  different  times  been  assigned  to  casein  as  charac- 
terising it  from  the  clo-ely  allied  body  alkali-albumin.  Later  researches  have 
however  in  most  cases  cast  so  much  doubt  on  these  differences  that  the  identity 
or  non-identity  of  casein  and  alkali-albumin  must  still  be  left  an  ojftn 
question. 

Casein,  as  occurring  in  milk,  has  had  several  reactions  ascribed  to  it,  as 
characteristic;  but  these  lose  their  importance  on  considering  that  milk  con- 
tains, in  addition  to  casein,  other  su'istances  such  as  potassium  phosphate,  and 
a  number  of  bodies  which  yield  acids  by  fermentation.  The  .jjresence  of 
potassium  phosphate  has  an  e.'pecial  influence  on  the  reaction  of  casein.  In 
the  entire  absence  of  this  salt,  acetic  acid  in  the  smallest  quantities,  as  also 
carbonic  acid,  gives  a  precipitate  ;    but  if  this  salt  is  present,  carbonic  acid 


734  PROTEIDS.  [app. 

gives  no  precipitate,  and  acetic  acid  one  only  when  the  solution  is  acid  from 
the  presence  of  free  acid,  and  not  from  that  of  acid  potassium  phosphate'. 

When  prepared  from  milk  by  magnesium  sulphate  (see  below), 
freed  by  aether  from  fats,  and  dissolved  in  water,  casein  possesses  a 
specific  rotatory  power  of  —80°  for  yellow  light  ;  in  dilute  alkaline 
solutions,  of-76°;  in  strong  alkaline  solutions,  of— 91°  ;  in  dilute 
hydrochloric  acid,  of-S/^ 

Casein  has  been  asserted  to  occur  in  muscle,  in  serous  fluids,  and 
in  blood-serum  (Serum-casein).  In  many  cases  it  has  probably  been 
confounded  with  globulin  (see  Class  III.)  ;  but  blood-serum  and 
muscle-plasma  undoubtedly  contain  an  alkali-albumin  in  addition  to 
whatever  globulin  may  be  present,  but  the  usual  doubt  exists  as  to 
the  identity  of  this  with  true  casein.  Its  presence  may  be  shewn  by 
adding  dilute  acetic  acid  to  blood-serum  which  has  been  freed  from 
globulin  by  a  current  of  carbonic  acid  gas  ;  a  distinct  precipitate  is 
thrown  down.  A  substance  similar  to  casein  has  also  been  described 
as  existing  in  unstriated  muscle  and  in  the  protoplasm  of  nerve-cells. 

P7'eparation.  Dilute  milk  with  several  times  its  bulk  of  water,  add 
dilute  acetic  acid  till  a  precipitate  begins  to  appear,  then  pass  a  current 
of  carbonic  acid  gas,  filter,  and  wash  the  precipitate  with  water,  alcohol 
and  aether  :  the  complete  removal  of  the  fat  carried  down  with  the 
casein  presents  some  difficulties.  Magnesium  sulphate  added  to 
saturation  also  precipitates  casein  from  milk  ;  the  precipitate  thus 
formed  is  readily  soluble  on  the  addition  of  water. 

Class  III.     Globulins. 

Besides  the  native  albumins  there  are  a  number  of  native  proteids 
which  differ  from  the  albumins  in  not  being  soluble  in  distilled  water  ; 
they  need  for  their  solution  the  presence  of  an  appreciable,  though  it 
may  be  a  small,  quantity  of  a  neutral  saline  body  such  as  sodium 
chloride.  Thus  they  resemble  the  albuminates  in  not  being  soluble 
in  distilled  water,  but  differ  from  them  in  being  soluble  in  dilute  sodium 
chloride  or  other  neutral  saline  solutions.  Their  general  characters 
may  be  stated  as  follows. 

They  are  insoluble  in  water,  soluble  in  dilute  (i  p.c.)  solutions  of 
sodium  chloride  ;  they  are  also  soluble  in  dilute  acids  and  alkalis,  being 
cnanged  on  solution  into  acid-  and  alkali-albumin  respectively.  The 
saturation  with  solid  sodium  chloride  of  their  solutions  in  dilute 
sodium  chloride,  precipitates  most  members  of  this  class. 

I.     Glohdin  {Crystalliii). 

If  the  crystalline  lens  be  rubbed  up  with  fine  sand,  extracted  with 
water  and  filtered,  the  filtrate  will  be  found  to  contain  at  least  three 

'  See  Kiihne,  Lehrb.  d.  Fhysiol.  Chem.,  1868,  S.  565. 


AW.]         CHEMICAL    BASIS    Ol      1  HE    ANIMAL    KODV.  735 

proteifls.      On   passing   a   current    of  carbonic    acid   j,'as   a   copious 
precipitate  occurs  ;  this  is  globulin. 

The  addition  of  dilute  acetic  acid  to  the  fdtratc  from  the  globulin,  gives  a 
precipitate  of  alkali-albumin  ;  and  the  fdtrate  from  this  if  heated  gives  a 
further  precipitate,  due  to  serum-albumin. 

In  its  general  reactions  globulin  corresponds  almost  exactly  with 
the  next  members  of  this  class  (paraglobulin  and  fibrinogen),  but  has  no 
power  to  form  or  promote  the  formation  of  fibrin  in  fluids  containing 
the  above-mentioned  bodies,  and  possesses  the  following  special 
features,  i.  According  to  Lehmann,  its  oxygenated,  neutral  solutions 
become  cloudy  on  heating  to  73°,  and  arc  coagulated  at  93°.  2.  It  is 
readily  precipitated  on  the  addition  of  alcohol.  According  to  Hoppe- 
Seyler,  it  is  not  precipitated  on  saturation  with  sodium  chloride, 
resembling  vitcllin  in  this  respect. 

According  to  Kuhne '  and  Eichwald  ^  a  globulin  with  properties  identical 
with  those  just  given  may  be  precipitated  from  dilute  serum  by  the  cautious 
addition  of  acetic  acid.  This  body  is  stated  by  Weyl^to  be  the  same  as 
paraglobulin  (fibrinoplastin),  the  latter  differing  from  it  only  by  a  small 
admixture  of  fibrin-ferment. 

2.     Paraglobulm  {Fibrinoplastin). 

Preparation.  Blood-scrum  is  diluted  tenfold  with  water,  and  a 
brisk  current  of  carbonic  acid  gas  is  passed  through  it.  The  first- 
formed  cloudiness  soon  becomes  a  flocculent  precipitate,  which  is 
finally  quite  granular,  and  may  easily  be  separated'  by  decantatiorv 
and  filtration  :  it  should  be  washed  on  the  filter  with  water  containing 
carbonic  acid. 

It  has  usually  been  stated  that  paraglobulin  may  be  separated  from 
serum  by  saturation  with  sodic  chloride.  According  to  Hammarsten* 
however  this  is  only  in  part  true,  a  considerable  portion  of  the  globulin 
remaining  unprccipitated.  The  separation  may  however  be  completely 
effected  by  saturation  with  magnesic  sulphate.  When  determined  by 
this  method  the  amount  of  paraglobulin  in  serum  is  very  considerable, 
amounting  according  to  Hammarsten,  to  as  much  as  4'565  p.  c 
(reckoned  on  100  cc.  of  serum).  The  cpiantity  seems  to  vary  in 
different  animals,  the  precipitation  being  much  more  complete  in  serum 
Irom  ox-blood  than  in  that  from  the  blood  of  horses. 

'  Op.  cit.  S.  175. 

"  Beitrai^e  zur  Chan.  d.  geuuhebilJ.  Subst.     Berlin,  1873.     Hf.  I. 

3  Zettschr.  f.  Physiol.  Chcvt.,  lid.  1.  (187S),  S.  79. 

*  rfliiger's  Archiv,  Bd.  xvii.  (1878),  S.  446. 


736  PROTEIDS.  ^  [app. 

From  its  solution  in  dilute  sodic  chloride,  paraglobulin  may  be  pre- 
cipitated by  a  current  of  carbonic  acid  gas,  or  the  addition  of 
exceedingly  dilute  (less  than  i  pro  miile)  acetic  acid.  If  the  acid  is 
strong  enough  to  dissolve  the  precipitated  proteid,  this  becomes 
immediately  changed  into  acid-albumin  (Class  II.).  In  pure  water, 
free  from  oxygen,  paraglobulin  is  insoluble,  but  on  shaking  with  air  or 
passing  a  current  of  oxygen,  solution  readily  takes  place  ;  from  this  it 
may  be  re-precipitated  by  a  current  of  carbonic  acid  gas.  Very  dihite 
alkalis  dissolve  this  body  without  change  ;  if,  however,  the  strength 
of  the  alkali  be  raised  even  to  i  p.  c.  the  paraglobulin  is  changed  into 
alkali -albumin  (Class  II.). 

According  to  Kiihne  and  A.  Schmidt  the  solutions  of  this  body  in 
water  containing  oxygen  or  in  very  dilute  alkalis  are  not  coagulated  on 
heating.  The  sodic  chloride  solutions  do  however  coagulate  when  heated 
to  68° — 70°  C,  and  if  the  substance  itself  be  suspended  in  water  and 
heated  to  70°  it  is  coagulated.  Although  insoluble  in  alcohol,  its 
solutions  are  wi^h  difficulty  precipitated  by  this  reagent. 

A  characteristic  test  for  this  body  is  that  it  gives  rise  to  fibrin  when 
added  to  many  transudations,  e.g.  hydrocele,  pericardial,  peritoneal, 
and  pleural  fluids. 

Paraglobulin  occurs  not  only  (and  chiefly)  in  blood-serum,  but  it  is 
also  found  in  white  corpuscles,  in  the  stroma  of  red  corpuscles  (to 
some  extent  at  least),  in  connective  tissue,  cornea,  aqueous  humour, 
lymph,  chyle,  and  serous  fluids. 

For  the  occurrence  of  globulin  in  urine,  see  Edlefsen^  and  Senator.  3 

3.  Fibrinogen. 

•  The  general  reactions  of  this  body  are  identical  with  those  of  para- 
globulin. The  most  marked  difference  between  the  two  is  the  point  at 
which  coagulation  of  their  solutions  takes  place.  Hammarsten  *  has 
shewn  that  fibrinogejj  in  a  i — 5  per  cent,  solution  of  sodic  chloride 
coagulates  at  from  52° — 55°  C,  whereas,  as  stated  above,  paraglobulin 
(fibrinoplastin)  coagulates  first  at  from  68° — 70°  C.  The  character- 
istic test  for  its  presence  is  the  formation  of  fibrin  when  its  solution  is 
added  to  a  solution  known  to  contain  paraglobulin  and  fibrin-ferment. 
Minor  diiferences  between  the  two  may  be  thus  enumerated  : — In  the 
prepaisation  of  fibrinogen,  the  containing  fluid  must  be  much  more 
strongly  diluted,  and  the  current  of  carbonic  acid  gas  must  pass  for  a 
much  longer  time.     The  precipitate  thus  obtained  differs  from  that  of 

'  Hammarsten,  op.  cit. 

=  Centralblatt  f.  d.  med.  Wiss.  1870,  S.  367.  Also  Arch.  f.  /din.  Med. 
Bd.  7,  S.  69. 

3  Virchow's  Archiv,  Bd.  60,  S.  476. 

*  Upsala  Ldkareforenings  forhandlingar,  Bd.  Xi.  1876. 


APP.]        CHEMICAL   BASIS   UK   THE   ANIMAL   h(JbY.  "jn 

paraglobulin  in  that  it  forms  a  viscous  deposit,  adhering  more  closely 
to  the  sides  and  bottom  of  the  containing  vessel ;  there  is  also  no 
llocculent  stage  previous  to  the  viscous  precipitate.  The  two  also 
exhibit  slight  microscopical  differences.  Alcohol  and  aether  both  pre- 
cipitate this  body  from  its  solution,  but  the  mixture  of  the  two  (3 
parts  alcohol,  i  part  aether)  is  most  effectual. 

Fibrinogen  occurs  in  blood,  chyle,  serous  fluids,  and  in  various 
transudations. 

Preparation.  This  is  the  same  as  for  paraglobulia,  regard  being 
had  to  the  peculiarities  mentioned  above'. 

There  is  no  proof  that  the  whole  of  the  substance  thrown  down  by 
carbonic  acid  from  diluted  blood-serum  is  fibrinoplastic,  indeed  we 
know  that  a  true  globulin  devoid  of  fibrinoplastic  properties  may  be 
prepared  from  serum"".  VVeyl  ^  considers  that  there  is  only  one  globulin 
in  serum,  which  he  characterises  by  the  name  of  'scrum-globulin,'  and 
regards  fibrinoplastin  as  a  mixture  of  this  body  with  a  portion  of 
fibrin-ferment.  We  know  for  certain  (see  p.  22)  that  the  whole  of  the 
fibrinoplastic  precipitate,  used  to  cause  the  coagulation  of  a  fibri- 
nogenous  fluid,  does  not  enter  into  the  composition  of  the  fibrin 
produced  ;  we  also  know  that  such  a  precipitate  may  lose  its  fibrino- 
plastic powers  without  any  marked  change  in  its  general  reactions. 
It  would  seem  advisable  therefore  to  speak  of  the  deposit  produced 
by  carbonic  acid  in  dilute  serum,  or  by  saturation  with  sodium 
chloride  in  undiluted  serum,  as  globulin,  and  to  distinguish  it  as 
fibrinoplastic  globulin  when  it  is  able  to  give  rise  to  fibrin.  Fibrinogen 
similarly  might  be  spoken  of  as  fibrinogenous  globulin.  The  name 
crystallin  rather  than  globulin  might  then  be  given  to  the  substance 
obtained  from  the  crystalline  lens. 

4.  Myosin. 

This  is  the  substance  which  forms  the  chief  proteid  constituent  of 
dead,  rigid  muscle ;  its  general  properties  and  mode  of  preparation 
have  been  already  described  at  p.  69.  In  the  moist  condition,  it 
forms  a  gelatinous,  elastic,  clotted  mass  ;  dried,  it  is  very  brittle, 
slightly  transparent  and  elastic.  From  its  solution  in  a  sodium 
chloride  solution  it  is  precipitated,  either  by  extreme  dilution,  or  by 
saturation  with  the  solid  salt.  When  precipitate!  by  dilution  and 
submitted  to  the  prolonged  action  of  water,  myosin  loses  its  property 
of  being  soluble  in  solutions  of  sodic  chloride*.     The  sodic  chloride 

'  See  Hanimarsten,  Pflugcr's  Archiv,  Bd.  XIX.  S.  563- 
'  Kiihnc  and  Eichwald,  loc.  cit. 
3  Loc.  cit. 

*'  Weyl,  Zcitichr.  f.  fhysiol   Chem.  Bd.  i.  (1S78)  S.  77. 
F.   P.  47 


738  PROTEIDS.  [APP. 

solution,  if  exposed  to  a  rising  temperature,  becomes  milky  at  55°, 
and  gives  a  flocculent  precipitate  at  60°,  This  precipitate  is  however 
no  longer  myosin,  for  it  is  insoluble  m  a  10  p.  c.  sodium  chloride 
solution,  and  does  not,  until  after  many  days'  digestion,  yield  syntonin 
on  treatment  with  hydrochloric  acid  ('i  p.  c. ).  It  is  in  fact  coagulated 
proteid  (see  Class  V.). 

Myosin  is  excessively  soluble  in  dilute  acids  and  alkalis,  but  under- 
goes in  the  act  of  solution  a  radical  change,  becoming  in  the  one  case 
acid-albumin  or  syntonin,  in  the  other  alkali-albumin  (Class  II.). 

Like  fibrin,  it  can  in  some  cases  decompose  hydrogen  dioxide,  and  oxidise 
guaiacum  with  formation  of  a  blue  colour. 

5 .    Vitellin. 

As  obtained  from  yolk  of  ^%g,  of  which  it  is  the  chief  proteid  con- 
stituent, vitellin  is  a  white  granular  body,  insoluble  in  water,  but 
very  soluble  in  dilute  sodium  chloride  solutions  ;  it  surpasses  myosin 
in  this  respect,  for  the  solution  may  be  easily  filtered.  Its  coagulation 
point  is  higher  than  that  of  myosin,  lying  according  to  WeyP,  between 
70°  C.  and  80°  C.  Saturation  with  sohd  sodium  chloride  gives  no  pre- 
cipitate ;  in  this  respect  it  differs  from  most  other  members  of  this 
class.  In  yolk  of  tgg  vitellin  is  always  associated  with,  and  probably 
exists  in  combination  with,  the  peculiar  complex  body  lecithin  (see 
p.  768.) 

Denis,  and  after  him,  Hoppe-Seyler,  have  shewn  that  vitellin  before  the 
treatment  requisite  to  free  it  from  lecithin,  possesses  properties  quite  different 
from  other  proteids. 

A  theory  has  been  advanced  that  vitellin  is  really  a  complex  body 
like  haemoglobin,  and  on  treatment  with  alcohol  splits  up  into  coagu- 
lated proteid  and  lecithin.  When  well  purified  it  contains  "75  p.  c. 
sulphur,  but  no  phosphorus.  Dilute  acids  or  alkalis  readily  convert  it 
in  its  uncoagulated  form  into  a  member  of  Class  II. 

Fremy  and  Valenciennes  ^  have  described  a  series  of  proteids,  viz,  ichthin, 
ichthidin,  &c.,  derived  from  fish  and  amphibia.  They  appear  to  be  either 
identical  with,  or  closely  related  to,  vitellin. 

Preparation.  Yolk  of  &gg  is  treated  with  successive  quantities  of 
eether,  as  long  as  this  extracts  any  yellow  colouring  matter  ;  the 
residue  is  dissolved  in  moderately  strong  (10  p.  c.)  sodium  chloride 
solution,  and  filtered.  The  filtrate  on  falling  into  a  large  excess  of 
water  is  precipitated.  In  this  state  it  is  mixed  with  lecithin  and 
nuclein,  and  in  order  to  free  it  from  these  it  was  usually  treated  with 

'  Op.  cit.  '  Compt.  Rend.,  T.  38,  pp.  469  and  525. 


AFl'.]        CHEMICAL   BASIS   OF   THE   ANIMAL    BODY.  739 

alcohol.  This,  as  above  stated,  entirely  changes  the  vitellin  into  a 
coagulated  form.  It  seems  probable  that  the  separation  of  vitellin 
from  the  other  bodies  with  which  it  is  mixed  in  the  yolk  of  egg  may 
be  effected  by  precipitating  the  sodic  choride  solution  by  the  addition 
of  CKCCss  of  water  ;  the  precipitate  is  then  re-dissolved  in  10  p.  c. 
solution  of  sodic  chloride  and  the  process  repeated  as  rapidly  as 
possible'. 

6.    Glabiii. 

Globin,  stated  by  Preyer'  to  be  the  proteid  residue  of  the  complex  body 
haemoglobin  (see  p.  356),  ought  probably  to  l)e  con^idercd  as  an  outlying 
member  of  this  cla-is.  It  is  however  not  readily  soluble  either  in  dilute  acids 
or  sodium  chloride  solutions.  It  is  remarkable  for  being  absolutely  free  from 
ash. 

Class  IV.     Fibrin. 

Insoluble  in  water  and  dilute  sodium  chloride  solutions  ;  soluble 
with  difficulty  in  dilute  acids  and  alkalis,  and  more  concentrated 
neutral  saline  solutions. 

Fibri^,  as  ordinarily  obtained,  exhibits  a  filamentous  structure,  the 
component  threads  possessing  an  elasticity  much  greater  than  that  of 
any  other  known  solid  proteid. 

If  allowed  to  form  gradually  in  large  masses,  the  filamentous  structure  is 
not  so  noticeable,  and  it  resembles  in  this  form  pure  india-rubber.  Such 
lumps  of  fibrin  are  capable  of  being  split  in  any  direction,  and  no  definite 
arrangement  of  parallel  bundles  of  fibres  can  be  made  out. 

At  ordinary  temperatures  fibrin  is  insoluble  in  water,  being  dissolved 
only  at  very  high  temperatures,  and  then  undergoing  a  complete 
change  in  its  ch.iracters  In  hydrochloric  acid  solutions  of  i — 5  p.  c. 
fibrin  swells  up  and  becomes  transparent,  but  is  not  dissolved 3.  In 
this  condition  the  mere  removal  of  the  acid  by  an  excess  of  water, 
neutralisation,  or  the  addition  of  some  salt,  causes  a  return  to  the 
original  state.  If,  however,  the  acid  be  allowed  to  act  for  many  days 
at  ordinary  temperatures  or  for  a  few  hours  at  40°— 60",  solution  takes 
place,  and  the  resulting  proteid  is  syntonin.  In  dilute  alkalis  and 
ammonia,  fibrin  is  much  more  readily  soluble,  though  in  this  case  also 
the  solution  is  greatly  aided  by  warming  ;  the  resulting  fluid  contains 
no  longer  fibrin,  but  alkali-albumin.  This  property  is  not  distinctly 
characteristic  of  fibrin,  although  it  dissolves  perhaps  more  readily  in 
both  dilute  acids  and  alkalis  than  do  coagulated  proteids.  None  of  these 
solutions  can  be  coagulated  on  heating,  which  is  intelligible  when  it  is 

'  Weyl,  op.cit.  S.  74,  '  Die  BlutkiyslalU  {\%1\),  S.  166. 

3  Complete  solution  may  however  take  place  if  the  fibrin  contain  pepsin. 
See  note,  p.  284. 

47—2 


740  PROTEIDS.  [APP. 

remembered  that  they  no  longer  contain  fibrin,  but  either  acid-  or 
alkali-albumin.  In  addition  to  the  above,  fibrin  is  soluble,  though 
with  difficulty  and  only  after  a  considerable  time,  in  lo  p.  c.  solutions 
of  sodium  chloride,  potassium  nitrate  or  sodium  sulphate.  These 
solutions  may  be  coagulated  by  a  temperature  of  60°  ;  in  fact,  by  the 
action  of  the  neutral  saline  solutions  the  fibrin  has  become  converted 
into  a  body  exceedingly  like  myosin  or  globulin. 

■  On  ignition  of  fibrin  a  residue  of  inorganic  matter  is  always 
obtained  ;  it  is,  however,  considered  that  sulphur  is  the  only  one  of 
these  elements  which  enters  essentially  into  its  composition.  In  other 
respects  fibrin  corresponds  entirely  in  general  composition  with  other 
proteids. 

Suspended  in  water  and  heated  to  70°,  it  loses  its  elasticity,  and 
becomes  opaque  ;  it  is  then  indistinguishable  from  other  coagulated 
proteids. 

A  peculiar  property  of  this  body  remains  yet  to  be  mentioned,  viz.  its 
power  of  decomposing  hydrogen  dioxide.  Pieces  of  fibrin  placed  in  this  fluid, 
though  themselves  undergoing  no  change,  soon  become  covered  with  bubbles 
of  oxygen  ;  and  guaiacum  is  turned  blue  by  fibrin  in  presence  of  hydrogen 
dioxide  or  ozonised  turpentine.  In  the  language  of  Schonbein's  tlfeory  fibrin 
is  an  ozone-bearer. 

Preparation.  Either  by  washing  blood-clots,  or  whipping  blood 
with  a  bundle  of  twigs  and  then  washing.  If  required  quite  colourless 
it  should  be  prepared  from  plasma  free  from  corpuscles.  If  the  blood, 
before  whipping,  be  diluted  with  an  equal  bulk  of  water,  the  subsequent 
washing  of  the  fibrin  is  much  facilitated,  and  it  may  readily  be 
obtained  quite  white. 

When  globulin,  myosin,  and  fibrin  are  compared  with  each  other, 
it  will  be  seen  that  they  form  a  series  in  which  myosin  is  intermediate 
between  globulin  and  fibrin.  Globulin  is  excessively  soluble  in  even 
the  most  dilute  acids  and  alkalis  ;  fibrin  is  almost  insoluble  in  these  ; 
while  myosin,  though  more  soluble  than  fibrin,  is  less  soluble  than 
globulin.  Globulin  again  dissolves  with  the  greatest  ease  in  a  very 
dilute  solution  of  sodium  chloride.  Myosin,  on  the  other  hand,  dis- 
solves with  difficulty  ;  it  is  much  more  soluble  in  a  10  per  cent,  than  in 
a  one  per  cent,  solution  of  sodium  chloride  ;  and  even  in  a  10  per 
cent,  solution  the  myosin  can  hardly  be  said  to  be  dissolved,  so  viscid 
is  the  resulting  fluid  and  with  such  difficulty  does  it  filter.  Fibrin 
again  dissolves  with  great  difficulty  and  very  slowly  in  even  a  10  per 
cent,  solution  of  sodium  chloride,  and  in  a  one  per  cent,  solution  it  is 
practically  insoluble.  When  it  is  remembered  that  fibrin  and  myosin 
are,  both  of  them,  the  results  of  coagulation,  their  similarity  is 
intelligible.  Myosin  is  in  fact  a  somewhat  more  soluble  form  of  fibrin, 
deposited  not  in  threads  or  filaments  but  in  clumps  and  masses. 


APP.]       CHEMICAL   BASIS   OF   THE   ANI.MM.   15UDY.  74I 

Class  V.     Coagulated  P  rote  ids. 

These  are  insoluble  in  water,  dilute  acids  and  alkalis,  and  neutral 
saline  solutions  oi  all  strengths.  In  fact  they  are  really  soluble  only 
in  strong  acids  and  strong  alkalis,  though  prolonged  action  of  even 
dilute  acids  and  alkalis  will  effect  some  solution,  especially  at  high 
temperatures.  During  solution  in  strong  acids  and  alkalis  a  destructive 
de-'omposition  takes  place,  but  some  amount  of  acid-  or  alkali-albumin 
is  always  produced. 

Very  little  is  known  of  the  chemical  characteristics  of  this  class- 
"i'hey  are  produced  by  heating  to  70',  solutions  of  egg-  or  serum- 
albumin,  globulins  suspended  in  u'ater  or  dissolved  in  saline  solutions, 
fibrin  suspended  in  water  or  dissolved  in  saline  solutions,  or  precipitated 
a?id-  and  alkili-albumin  suspended  in  water.  They  are  readily  con- 
verted at  the  temperature  of  the  body  into  peptones,  by  the  action  of 
gastric  juice  in  an  acid,  or  of  pancreatic  juice  in  an  alkaline  medium. 

Class  VI.    Peptones. 

Very  soluble  in  water,  and  not  precipitated  from  their  aqueous 
solutions  by  the  addition  of  acids  or  alkalis,  or  by  boiling.  Insoluble 
in  ahohol,  they  are  precipitated  with  difficulty  by  this  reagent,  and  are 
unchanged  in  the  process  ;  they  differ  from  all  other  proteidr  in  not 
being  coagulated  by  exposure  to  alcohol.  They  are  not  precipitated 
by  cupric  sulphate,  ferric  chloride,  or  except  in  the  instances  to  be 
mentioned  presently,  by  potassium  ferrocyanide,  and  acetic  acid.  In 
these  points  they  differ  from  most  Oti^er  proteids.  On  the  other  hand, 
precipitation  is  caused  by  chlorine,  iodine,  tannin,  mercuric  chloride, 
nitrates  of  mercury  and  silver,  and  both  acetates  of  lead  ;  also  by 
bile-acids  in  an  acid  solution.  In  common  with  all  proteids,  these 
bodies  possess  a  specific  Isevo-rotatory  power  over  polarised  light ;  but 
they  dift'er  from  all  other  proteids  in  the  fact  that  boiling  produces  no 
change  in  the  amount  of  rotation. 

A  solution  of  peptones,  mixed  with  a  strong  solution  of  caustic 
potash  gives,  on  the  addition  of  a  viere  trace  of  cupric  sulphate,  a  red 
colour.  An  excess  of  the  cupric  salt  gives  a  violet  colour,  which 
deepens  in  tint  on  boiling,  in  fact  the  ordinary  proteid  reaction.  Other 
proteids  simply  give  the  violet  colour.  But  the  most  characteristic 
feature  of  peptones  is  their  extreme  diffusibility,  a  property  which  they 
alone,  of  all  the  proteids,  may  be  said  to  possess,  since  all  other  forms 
of  proteids  pass  through  membranes  with  the  greatest  difficulty, 
if  at  all. 

Notwithstanding  their  probable  formation  in  large  quantities  in  the 
stomach  and  intestine,  to  judge  from  the  result  of  artificial  digestion, 
a  very  small  quantity  only  can  be  found  in  the  contents  of  these 
organs,    or  in  the  chyle.     They  are    probably  absorbed  as  soon  as 


742  PROTEIDS.  [APP. 

formed.  Another  point  of  interest  is  their  reconversion  into  other 
forms  of  proteids,  since  this  must  occur  to  a  great  extent  in  the  body. 
We  are  however  as  yet  ignorant  of  the  manner  in  which  this  reverse 
change  is  effected. 

Production  All  proteids,  with  the  exception  of  lardacein,  yield 
peptones  (and  other  products)  on  treatment  with  acid  gastric  or  alkaline 
pancreatic  juice,  most  readily  at  the  temperature  of  the  human  body. 
Peptones  are  likewise  produced,  in  the  absence  of  pepsin  and  trypsin, 
by  the  action  of  dilute  and  moderately  strong  acids  at  medium  tempera- 
tures, also  by  the  action  of  distilled  water  at  very  high  temperatures 
and  great  pressure.  For  various  methods  of  preparing  peptones,  see 
Adamkiewicz  ^  and  Henninger  =. 

No  exact  difference  in  percentage  composition  between  peptones 
and  the  proteids  from  which  they  are  formed  has,  at  present,  been 
established. 

We  have  used  the  phrase  '  peptones '  in  the  plural  number  because 
we  have  reason  to  think  that  more  than  one  kind  of  peptone  exists. 
Meissner  3  described  three  peptones,  naming  them  respectively  A-  B- 
and  C-peptone.  He  distinguished  them  as  follows.  A-peptone  is 
precipitated  from  its  aqueous  solutions  by  concentrated  nitric  acid,  and 
also  by  potassium  ferrocyanide  in  the  presence  of  even  weak  acetic 
acid.  B-peptone  is  not  precipitated  by  concentrated  nitric  acid,  no 
will  potassium  ferrocyanide  give  a  precipitate  unless  a  considerable 
quantity  of  strong  acetic  acid  be  added  at  the  same  time.  C-peptone 
is  precipitated  neither  by  nitric  acid  nor  by  potassium  ferrocyanide 
and  acetic  acid,  whatever  be  the  strength  of  the  acetic  acid.  In  place 
however  of  speaking  of  all  these  as  peptones,  it  is  better  to  consider 
C-peptone  as  the  only  real  peptone,  and  the  A-  and  B-peptones  as  not 
peptones  at  all.  Nevertheless  we  have  reason,  from  the  researches  of 
Kiihne,  to  speak  of  more  than  one  peptone,  viz.  of  a  hemipeptone 
which  is  capable  under  the  action  of  trypsin  of  being  converted  into 
leucin  and  tyrosin,  and  of  an  antipeptone  which  resists  such  a  de- 
composition. The  name  antipeptone  is  given  to  the  latter  on  account 
of  this  resistance  which  it  offers  towards  trypsin  ;  the  name  hemi- 
peptone, given  to  the  former,  signifies  that  this  peptone  is  the  twin  or 
correlative  half  of  antipeptone. 

We  have  seen  (p.  248)  that  when  any  proteid  is  digested  with 
pepsin,  what  we  may  preliminarily  call  a  bye-product  inakes  its 
appearance.  This  bye-product,  which  has  many  resemblances  to  acid- 
albumin  or  syntonin,  appearing  as  a  neutralisation  precipitate  soluble 
in  dilute  acids  and  alkalis  but  insoluble  in  distilled  water,  is  generally 

'     Die  Nafur  u.  Ndhrwerth  d.  Peptons  (1877),  S.  33. 

^     De  la  Nature  et  du  Rdle  pJiysiotogique  des  P,ptons,  Paris,  18.78. 

3     Z.eitschr.f.  rat.  Med.,  Bde.  vii.,  viii.,  x.,  xii.  undxiv. 


APP.]        CHEMICAL    HASIS   UK    THE    ANIMAL    BODY.  743 

spoken  cf  as  parnpcptone.  According  to  Finklcr'  thfs  neutralisation 
precipitate  is  especially  abundant  if  the  pci)sin  be  previou-.ly  modified 
by  exposure  to  a  temperature  of  40°  to  60°,  C.  The  pepsin  thus 
modified  is  spoken  of  by  Finkler  as  '  isopepsin.'  Many  authors  regard 
puapeptone,  syntonin,  and  acid-albumin  as  being  the  same  thing. 
Meissncr  however  gave  the  name  parapeptonc  to  a  body,  which  need 
not  and  probably  does  not  make  its  appearance  during  normal  natural 
digestion  or  during  artificial  digestion  with  a  thoroughly  active  pepsin, 
but  which  is  formed  when  protcids  are  subjected  to  the  action  of  weak 
hydrochloric  acid,  either  alone  or  in  company  with  an  imperfectly- 
acting  pepsin,  and  which  in  certain  characters  is  quite  distinct  from 
ordinary  syntonin  or  acid-albumin.  Its  distinguishing  feature  is  that 
it  cannot  be  changed  into  peptone  by  the  action  of  even  the  most 
energetic  pepsin,  though  it  is  readily  so  converted  under  the  influence 
of  trypsin  ;  otherwise  it  very  closely  resembles  syntonin.  We  have 
here  an  indication  that  the  simple  characters  by  which  we  have 
described  acid-albumin  may  be  bonie  by  bodies  having  marked 
diftcrenccs  from  each  other.  The  researches  of  Kiihne,  to  which  we 
have  briefly  referred  in  the  text  (p.  262),  have  thrown  an  important 
light  on  these  differences.  The  fundamental  notion  of  Kiihne's  view 
is  that  an  ordinary  native  albumin  of  fibrin  contains  within  itself  two 
residues,  which  he  calls  respectively  an  anti-residue  and  a  hcmi-residue. 
The  result  of  either  peptic  or  tryptic  digestion  is  to  split  up  the 
albumin  or  fibrin,  and  to  produce  on  the  part  of  the  anti-residue  anti- 
peptone,  and  on  the  part  of  the  hcmi-residue  hemipeptone,  the  latter 
being  distinguished  from  the  former  by  its  being  susceptible  of  further 
change  by  tryptic  digestion  into  leucin,  tyrosin,  &c.  Antipeptone  re- 
mains as  antipeptone  even  when  placed  under  the  action  of  the  most 
powerful  trypsin,  provided  putrefractive  changes  do  not  intervene. 

Before  the  stage  of  peptone  (whether  anti-  or  hemi-)  is  reached, 
there  is  an  intermediate  stage  corresponding  to  the  formation  of 
syntonin.  In  both  normal  peptic  and  tryptic  digestion  antipeptone  is 
preceded  by  an  anti-albumose,  and  hemipeptone  by  a  hemi-albumose. 
Of  these  the  anti-albumose  is  closely  related  to  syntonin,  and  has 
hitherto  been  regarded  as  syntonin.  The  hemi-albumose  has  not  been 
so  frequently  observed  ;  it  was  however  isolated  by  Meissner  ;  it  is 
apparently  the  body  called  by  him  A-pcptone.  It  possesses  a  peculiar 
feature  in  being  soluble  at  about  70'  C,  and  being  re-precipitated  on 
cooling  ;  in  this  respect  it  closely  resembles  a  protcid  body  observed 
by  Bencc-Joncs  in  the  urine  of  osteomalacia.  It  approaches  myosin 
in  being  readily  soluble  in  a  10  per  cent,  solution  of  sodium  chloride. 

If  however  albumin  be  digested  with  insufficient  or  with  imperfectly 
acting  pepsin,   or  simply  with  dilute  hydrochloric  acid  at  40^,  anti- 

'  Pfluger's  Archiv,  xiv.  (1877)  S.  128. 


744  PROTEIDS.  [APP. 

albumose  is  not  formedj  but  in  its  place  a  body  makes  its  appearance 
which  Kiihne  calls  anti-albumate*.  Its  characteristic  property  is  that 
it  cannot  be  converted  by  peptic  digestion  into  peptone,  though  it  can 
be  so  changed  by  tryptic  digestion.  It  is  in  fact  the  parapeptone  of 
Meissncr. 

It  may  perhaps  be  advisable,  now  that  Meissner's  parapeptone  is 
cleared  up,  to  reserve  the  name  parapeptone  for  the  initial  products  of 
both  peptic  and  trj'ptic  digestion,  to  speak  of  anti-albumose  and  hemi- 
albumose  as  being  both  parapeptones.  But  in  this  sense  parapeptone 
will  be  an  intermediate  and  not  a  collateral  product  of  digestion. 

Meissner  also  described  a  particularly  insoluble  form  of  his  para- 
peptone as  dyspeptone,  and  another  intermediate  product  as  meta- 
peptone  ;  but  further  investigation  of  both  these  bodies,  as  well  as  of 
his  B-peptone,  is  necessary.  Under  the  influence  of  dilute  hydro- 
chloric acid,  anti-albumate  becomes  changed  into  a  body  which  Kiihne 
calls  anti-albumid  and  which  seems  identical  with  the  very  insoluble 
proteid  described  by  Schiitzenbsrger  as  '  hemiprotein,'  and  probably 
with  Meissner's  dyspeptone.  The  same  body  is  produced  at  once  in 
company  with  products  belonging  to  the  henii-group  by  the  action  of 
3  to  5  per  cent,  sulphuric  acid  on  native  albumin  or  fibrin.  The  fol- 
lowing table  shews  the  relations  and  genesis  of  the  bodies  we  have 
just  described.  The  several  products  (antipeptone,  &c.)  are  given  in 
duplicate,  on  the  hypothesis  (which  though  not  proved  is  probable) 
that  the  changes  of  digestion  are  essentially  hydrolytic  changes, 
accompanied  by  deduplication.  That  just  as  a  molecule  of  starch 
splits  up  into  at  least  two  molecules  of  dextrose,  or  as  a  molecule  of 
cane-sugar  splits  up  into  a  molecule  of  dex^trose  and  a  molecule  of 
levulose,  so  a  molecule  of  antialbumose,  for  instance,  splits  up  into 
two  molecules  of  antipeptone,  and  so  on.  But  the  whole  scheme  is  of 
course  only  provisional. 

Decomposition  of  Proteids  by  Digestion. 

Albumin.  s 

■ ' I 


Antialbumose.  Hemialbumose 


.' 1  f 1 

Antipeptone.         Antipeptone.       Hemipeptone.    Hemipeptone. 


.1 '  '  ' 

Leucin.  Tyrosin.  Leucin.  Tyrosin. 

etc.  etc. 

'  An  albumate  must  not  be  confounded  with  an  albuminate. 


APP.]        CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  745 


Decomposition  of  Acids. 

I.  • 

By  -25  p.  c.  HCl  at  40°  C. 

Albumin. 


( 
Antialbumate.  Hemialbumose. 


I  I 1 

Antialbumid.  Hemipeptone.  Hemipeptone. 


By  3—5  p.  c.  H.SO4  at  100°  C. 
Albumin. 


I 
Antialbumid. 


Hemialbumose. 

I 

I n 

Hemipeptone.     Hemipeptone. 

I  i 

Leucin.  Tyrosin.  etc.    Leucin.  Tyrosin.  etc. 

Class  VII.     Lardacein,  or  the  so-called  amyloid  substance. 

The  substance  to  which  the  above  name  is  applied,  is  found  as  a 
deposit  in  the  spleen  and  liver,  also  in  numerous  other  organs,  such  as 
the  blood-vessels,  kidneys,  lungs,  &.Z. 

It  is  insoluble  in  water,  dilute  acids  and  alkalis,  and  neutral  saline 
solutions. 

In  centesimal  composition  it  is  almost  identical  with  other  proteids ', 
viz.  : — 

O.  and  S.  H.  N.  C. 

24-4  7.0  15-0  536 

The  sulphur  in  this  body  exists  in  the  oxidised  stite,  for  boiling 
with  caustic  potash  gives  no  sulphide  of  the  alkali.  The  above  results 
of  analysis  would  lead  at  once  to  the  ranking  of  lardacein  as  a  pro- 
teid,  and  this  is  borne  out  by  other  facts.  Strong  hydrochloric  acid 
converts  it  into  acid  albumin,  and  caustic  alkali i  into  alkali-albumin. 
On  the  other  hand,  it  exhibits  t'.ie  following  marked  ditTercn::es  from 

'  C.Schmidt,  Ann.  d.  Client  u.  Pliarin.,  Bd.  no,  S.  250,  and  Friedreich 
and  Kckule,  Virchow's  Arcliiv,  Bd.  16,  S.  50. 


746  PROTELDS.  [APP. 

other  proteids  : — It  wholly  resists  the  action  of  ordinary  digestive 
fluids  ;  it  is  coloured  red,  not  yellow,  by  iodine,  and  violet  or  pure  blue 
by  the  joint  action  of  iodine  and  sulphuric  acid.  From  these  last 
reactions  it  has  derived  one  of  its  names,  'amyloid,'  though  this  is 
evidently  badly  chosen.  Not  only  does  it  differ  from  the  starch  group 
in  composition,  but  by  no  means  can  it  be  converted  into  sugar  :  this 
latter  is  one  of  the  crucial  tests  for  a  true  member  of  the  amyloid 
group.  According  to  Heschl  ^  and  Cornil ""  anilin-violet  (methyl- 
anilin)  colours  lardaceous  tissue  rosy  red,  but  sound  tissue  blue. 

The  colours  mentioned  above,  as  being  produced  by  iodine  and  sulphuric 
acid,  are  much  clearer  and  brighter  when  the  reagents  are  applied  to  the 
purified  lardacein.  Wiien  the  i-eagents  are  applied  to  the  crude  substance  in 
its  normal  position  in  the  tissues,  the  colours  obtained  are  always  dark  and 
dirty-looking. 

Purified  lardacein  is  readily  soluble  in  moderately  dilute  ammonia, 
and  can,  by  evaporation,  be  obtained  from  this  solution  in  the  form  of 
tough  gelatinou-s  flakes  and  lumps  ;  in  this  form  it  gives  feeble  reactions 
only  with  iodine.  If  the  excess  of  ammonia  is  expelled,  the  solution 
becomes  neutral,  and  is  precipitated  by  dilute  acids. 

Preparation.  The  gland  or  other  tissue  containing  this  body  is 
cut  up  into  small  pieces,  and  as  much  as  possible  of  the  surrounding 
tissue  removed.  The  pieces  are  then  extracted  several  times  with 
water  and  dilute  alcohol,  and  if  not  thus  rendered  colourless,  are 
repeatedly  boiled  with  alcohol  containing  hydrochloric  acid.  The 
residue  after  this  operation  is  digested  at  40°,  with  good  artificial 
gastric  juice  in  excess.  Everything  except  lardacein,  and  small 
quantities  of  mucin,  nuclein,  keratin,  together  with  some  portion  of 
the  elastic  tissue*,  will  thus  be  dissolved  and  removed^.  From  the 
latter  impurities  it  may  be  separated  by  decantation  of  the  finely- 
powdered  substance. 


The  chief  products  of  the  decomposition  of  proteids  are  ammonia, 
carbonic  acid,  leucin,  and  tyrosin.  Several  other  bodies,  for  the  most 
part,  like  leucin,  amidated  acids,  such  as  aspartic  acid,  glutamic  acid, 
&c.,  have  also  been  obtained.  But  urea  has  never  yet  been  derived 
by  direct  decomposition  from  proteid  material,  the  statements  to  this 
effect  having  been  based  on  errors.  In  spite  of  numerous  researches, 
we  cannot  at  present  state  definitely  what  is  the  real  constitution  of  a 

^    Wien.  fried.  Wochenschr.  No.  32.  S.  714- 
=   Conipt.  Rend.  May  24,  1875. 
3  Kiihne,  Virchow's  Arch.  Bd.  33. 


APP.]         CHEMICAL    BASIS   OF   THE    ANIMAL    IHJDW  747 

proteid,  or  in  what  manner  these  several  residues  are  contained  in  the 
iiiidcconiposcd  substance.  It  is  unnecessary  to  give  here  any  of  the 
formula?,  nearly  all  empirical,  which  have  been  made  to  represent 
these  bodies  ;  they  all  give  with  equal  exactitude  the  percentage  com- 
position, but  beyond  this  they  are  untrustworthy.  Of  the  various 
attempts  wiiich  have  been  made  to  assign  to  proteids  some  definite 
molecular  structure,  none  appear,  at  the  present  stage  of  information, 
sufficiently  reliable  for  general  acceptance. 

Among  the  mcst  elaborate  labours  in  this  direction  may  be  mentioned  tho-e 
of  Hlasiwetz  and  Haberman.  In  their  first  publication',  starting  from  the 
general  similarity  of  the  products  of  decomposition  of  the  proteids  and  carbo- 
hydrates, they  tried  to  establish  a  definite  relation  between  the  two  clashes  of 
bodies.  In  this  they  were  not  successful,  and  from  their  second  research*  they 
come  to  the  conclusion  that  the  carbohydrates  take  no  part  in  the  formation  of 
the  proteids. 

Other  experiments  in  the  same  direction  arc  due  to  Schiitzenberger^.  He 
shews  that  albumin  can  be  decomposed  into  carbonic  anhydride  and  ammonia, 
and  thai:  the  ratio  of  these  two  is  the  same  as  though  urea  had  been  the  body 
on  which  he  operated.  From  this  he  concludes  that  "  the  molecule  of  albumin 
contains  the  grouping  of  urea  and  represents  a  complex  ureide."  In  his 
second  pubiicatitm  *  he  confirms  his  previous  results,  stating  that  the  ammonia, 
carbonic  anhydride  and  oxalic  acid,  produced  by  the  decomposition  of  pioteids, 
are  so  connected  quantitatively  as  to  be  capable  of  derivation  from  varying 
proportions  of  urea  and  oxamide.  He  abo  obtained  from  the  decomposition 
of  proteids  a  nitrogenous  residue  which  could  be  formulated  as  giving  rise  to 
all  the  amidated  acids  and  other  bodies  spoken  of  above.  Thus  according  to 
him,  albumin,  built  up  as  a  complex  ure'.de,  decomposes  into  ammonia, 
carbonic,  oxalic,  and  acetic  acids,  and  this  nitrogenous  body  :  this  last  then 
gives  ri.-e  to  the  other  products  of  de^\,mpositionS. 

It  will  be  noticed  that  in  the  general  description  of  the  various 
proteids,  distinctive  reactions  for  each  could  not  be  given,  but  that 
varying  solubilities  were  the  chief  ^leans  at  our  disposal  for  distin- 
guishing them.  They  may  be  arranged  according  to  their  solubilities 
in  the  following  tabular  form  : — 

Soluble  in  distilled  water; 

Aqueous  solution  not  coagulated  on  boiling  .  Peptones. 
Aqueous  solution  coagulated  on  boiling Albiimitis, 

'  Ann.  d.  Chun.  11.  P!:ann.  15^.  159,  S.  304. 
"  Ibid.  \\A   169,  S.  150. 
3  Couples  Rend  lis,  T.  So,  p.  232. 
*  Ibid.  81,  p.  1 108. 

s  See  also  Schiitzenberger,  Ann.  de  Client,  et  de  Phys.  T.  xvi.  (1S79), 
p.  280. 


748  PROTEIDS.  [APP. 

Insohtble  in  distilled  water: 

Soluble  in  NaCl  solution  i  per  cent Globulins, 

Insoluble      „  „  ,, 

Soluble  in  HCl  "i  percent,  in  the  cold/  ^'''^'  ^'^^   ^Z-^^/^- 
^  (^  albumin. 

Insoluble   in    HCl  "i    per   cent,  in  thel         ,    . 

cold,  but  soluble  at  60°    /   i'^^rtn. 

Insoluble  in  HCl  "i  per  cent,  at  60°  ;  soluble  in  strong  acids. 

Soluble  in  gastric  juice   Coagulated  albumin. 

Insoluble       „         ,,        Lai'dacein. 

Such  a  classification  is,  however,  obviously  a-wholly  artificial  one, 
useful  for  temporary  purposes,  but  in  no  way  illustrating  the  natural 
relations  of  the  several  members.  Nor  is  a  division  into  '  native '  and 
'derived'  proteids  much  more  satisfactory.  It  is  true  that  we  may 
thus  put  together  serum-  and  egg-albumin,  with  vitellin,  myosin,  and 
fibrin,  on  the  one  hand  ;  and  peptones,  coagulated  proteids,  and 
acid-  with  alkali-albumin,  on  the  other.  But  in  what  light  are  we  to 
consider  casein,  seeing  that  though  a  natural  product,  it  has  so  many 
resemblances  to  alkali-albumin .''  Moreover  the  system  of  classification 
must  be  useless  which  would  place  fibrinoplastic  globulin  and  fibri. 
nogen  in  the  same  class  as  fibrin,  and  yet  we  can  hai-dly  speak  of 
either  of  the  two  former  bodies  as  derived  proteids.  If  the  view  be 
true  that  when  fibrin  is  converted  into  peptone  the  large  molecule  of  the 
former  is  split  up,  with  assumption  of  water,  into  two  smaller  molecules 
of  the  latter,  one  belonging  to  the  '  anti '  and  the  other  to  the  '  hemi ' 
group,  we  might  speculate  on  a  possible  classification  of  all  proteids 
into  hemi-proteids,  anti-proteids,  and  holo-proteids.  Thus  serum- and 
egg-albumin,  myosin,  and  fibrin  would  be  undoubtedly  holo-proteids, 
peptones  either  anti-  or  hemi-proteids,  and  M'e  should  have  to  distin- 
guish probably  in  the  heterogeneous  group  of  derived  albumins  both 
anti-,  hemi-,  and  holo-proteid  members.  It  is  possible,  moreover, 
that  fibrinoplastic  and  fibrinogenous  globulin  and  casein  may  be 
natural  hemi-  or  anti-proteids  and  not  holo-proteids.  But  we  have  at 
present  no  positive  knowledge  on  these  points. 


Nitrogenous  Non-Crystalline  Bodies  allied  to  Proteids. 

These  resemble  the  proteids  in  many  general  points,  but  exhibit 
among  themselves  much  greater  differences  than  the  proteids  do.  As 
regards  their  molecular  structure  nothing  satisfactory  is  known.  Their 
percentage  composition  approaches  that  of  the  proteids,  and  like  these 


APP.]        CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  749 

they  yield,  under  hydrolytic  treatment,  large  quantities  of  leucin  and 
in  some  cases  tyrosin.     They  are  all  amorphous. 

Mucin     (0,3375.     H,6Si.     N,  8-50.     C,  48-94.') 

The  characteristic  component  of  mucus.  Its  exact  composition  is 
not  yet  known,  the  figures  given  above  being  merely  an  approximation. 

As  occurring  in  the  normal  condition  it  gives  to  the  fluids  which 
contain  it  the  well-known  ropy  consistency,  and  can  be  precipitated 
from  these  by  acetic  acid,  alcohol,  alum  and  mineral  acids  ;  the  latter, 
if  in  excess,  redissolve  the  precipitate,  but  this  is  not  the  case  with 
aoetic  acid.  In  its  precipitated  form  it  is  insoluble  in  water,  but  swells 
up  strongly  in  it,  and  this  etTcct  is  increased  by  the  presence  of  many 
alkali  salts.  Alkalis  and  alkaline  earths  dissolve  it  readily.  Its  solu- 
tions do  not  dialyse  ;  they  give  the  proteid  reactions  with  Millon's 
reagent  and  nitric  acid,  but  not  that  with  sulphate  of  copper,  and  are 
precipitated  by  basic  lead  acetate  only  when  neutral  or  faintly  alkaline. 
According  to  Eichwald^  when  heated  with  dilute  mineral  acids,  mucin 
yields  acid-albumin,  and  another  body  which  in  many  of  its  properties 
closely  resembles  a  sugar ;  it  reduces  solutions  of  cupric  sulphate.  Pro- 
longed boiling  with  sulphuric  acid  gives  leucin  and  about  7  p.  c.  of 
tyrosin. 

Preparation.  From  ox-gall,  by  precipitation  with  alcohol,  redis- 
solving  in  water  and  precipitating  with  acetic  acid.  It  may  also  be 
advantageously  obtained  from  snails  ^  or  the  submaxillary  gland  of 
the  ox  •♦. 

Chotidrin.    (0,31  •04.    K,  676.    N.  13-87.    €,4774.    S,  •6op.c.)s. 

This  is  usually  regarded  as  forming  the  essential  part  of  the  matrix 
of  hyaline  cartilage,  and  is  contained  in  the  interstices  of  the  fibres  in 
elastic  cartilage.  A  similar  substance  can  be  prepared  from  the  cornea. 
Boiled  with  water,  it  dissolves  slowly,  forming  an  opalescent  solution, 
which  is  precipitated  by  acetic  acid,  lead  acetate,  dilute  mineral  acids, 
alum,  and  salts  of  silver  and  copper ;  an  excess  of  the  last  four  reagents 
redissolves  the  precipitate.  Solutions  of  this  body  gelatinise  on  standing, 
even  if  very  dilute  ;  the  solid  mass  is  insoluble  in  cold  water,  readily 
soluble  in  hot  water,  alkalis  and  ammonia. 

The  aqueous  and  alkaline  solutions  of  chondrin  possess  a  left- 
handed  rotatory  power  on  polarised  light  of — 2i3"5°;  in  presence  of 

*  Eichwald,  Ann.  d.  Chem.  u.  Phartu.,  Bd.  134,  S.  193. 
«  Of>.  at. 

3  Eichwald,  of.  cil.  and  Client.  Centralb.,  1S66,  No,  14. 
<  .Stacdcier,  Anti.  d.  C/unt.  u.  Fhartn.,  Dd.  Ill,  S.  14. 
S  I.  V.  Mering,  Beitrag  zur  Chemie  des  Knorpels,  1873. 


75  O  PROTEIDS.  [APP. 

excess  of  alkali  this  becomes  — 552'o°,  both  measured  from  yellow 
light. 

It  seems,  according  to  the  observations  of  many,  that  chondrin  can, 
by  heating  with  hydrochloric  acid,  be  converted  into  a  body  whose 
reactions  resemble  those  of  syntonin,  and  another  substance,  which 
like  the  similar  product  from  mucin,  so  far  resembles  grape-sugar  that 
it  reduce  cupric  salts  in  alkaline  solution'  :  it  appears  however  to 
contain  nitrogen.  A  recent  observer^  has  denied  the  existence  of 
chondrin  as  a  distinct  substance  and  regards  it  as  in  all  cases  a  mere 
mixture  of  other  bodies.  He  states  that  a  substance  having  all  the 
reactions  of  the  so-called  chondrin,  may  at  any  time  be  produced  by 
a  mixture  of  mucin,  glutin  and  inorganic  salts.  The  extreme  simi- 
larity in  the  reactions  of  chondrin  and  mucin  point  to  a  close  relation- 
ship between  the  two.  The  whole  subject,  however,  requires  more 
complete  investigation.  With  alkalis  or  dilute  sulphuric  acid  f;hon- 
drin  gives  leucin,  but  no  tyrosin  or  glycocoll.  Whether  chondrin 
exists  as  such  in  cartilage  is  uncertain  ;  it  seems  probable  that  it  does 
not,  since  its  extractfon  from  cartilage  requires  an  amount  of  boiling 
with  water  much  greater  than  that  requisite  to  dissolve  dried  chondrin. 

Preparation.     From  cartilage  by  extracting  with  water,  and  preci- 
pitating with  acetic  acid. 

G  hi  tin  or  Gelatin.  (0,23-21.  H,  7'i5.  N,  18-32.  0,5076.  S, 
•56  pj;.) 

This  is  the  substance  which  is  yielded  when  connective  tissue  fibres 
are  heated  for  several  days  with  very  dilute  acetic  acid,  at  a  tempera- 
ture of  about  15°  C,  or  when  they  are  treated  with  water  in  a  digester. 
The  elastic  elements  of  connective  tissue  are  unaffected  by  the  above 
treatment. 

As  obtained  in  this  way  glutin  is  when  heated  a  thin  fluid,  solidi- 
fying on  cooling  to  the  well-known  gelatinous  form.  When  dried  it  is 
a  colourless,  transparent,  brittle  body,  swelling  up,  but  remaining 
undissolved  in  cold  water  ;  heating,  or  the  addition  of  traces  of  acids 
or  alkalis,  readily  effects  its  solution.  When  dissolved  in  water  it 
possesses  a  Isevo-rotatory  power  of  —  130'^,  at  30°  C.  ;  the  addition  of 
strong  alkali  or  acetic  acid  reduces  this  to  —  112°  or — •  114°,  both 
measured  for  yellow  light  3.     Its  solutions  will  not  dialyse. 

Mercuric  chloride  and  tannic  acid  are  the  only  two  reagents  which 
yield  insoluble  precipitates  with  this  body.     Its  presence  prevents  the 

'  De  Bary,  Hoppe-Seyler's  Untersiich,  Hft.  I.  S.  71. 

^  Morochowetz,  Verhand.  naturhist.  med.  Vh'.  Heidelberg.,  Bd.  I.  (1876) 
Hft.  5. 

'  Hoppe-Seyler,  Bdbk.  S.  222. 


APr.]        CHEMICAL   BASIS   OF   THE    ANIMAL   BODY.  75 1 

action  of  Trommer's  sugar  test,  since  it  readily  dissolves  up  the  pre- 
cipitated cuprous  oxide.  The  protcid  reactions  oi  glutin  are  so  feeble 
that  they  are  probably  due  merely  to  impurities.  Heated  with  sulphuric 
acid  it  yields  ammonia,  leucin  and  glycin,  but  no  tyrosin. 

It  appears  improbable  that  glutin  e\ists  ready  formed  in  connective 
tissue  tibres,  since  these  do  not  swell  up  in  water,  and  only  yield  glutin 
after  prolonged  treatment  with  boiling  water  ;  to  which  it  may  be 
added,  that  while  glutin  is  acted  upon  by  trypsin,  the  connective  tissue 
fibres  in  their  natural  condition  resist  its  action  (see  p.  262). 

Elastin.     (0,20-5.     H,  7*4      N,  167.     C,  55'5p.  c.) 

This  characteristic  component  of  elastic  fibres  is  left  on  the 
removal  of  all  the  glutin,  mucin,  &c.,  from  such  tissues  as  "  liga- 
mentum  nuchae,''  advantage  being  taken, of  its  not  being  altered  when 
it  is  heated  with  water,  even  under  pressure,  with  strong  acetic  acid, 
or  with  dilute  alkalis.  When  moist  it  is  yellow  and  elastic,  but  on 
drying  becomes  brittle.  It  is  soluble  in  strong  alkalis  at  boiling  tem- 
peratures, and  concentrated  sulphuric  and  nitric  acids  dissolve  it  even 
in  the  cold.  It  is  precipitated  from  solutions  by  tannic  acid,  but  not 
by  the  addition  of  ordinary  acids.  Notwithstanding  that  it  closely 
approaches  the  proteids  in  its  percentage  composition,  and  gives 
distinct  although  feeble  proteid  reactions,  any  very  close  relation- 
ship between  the  two  appears  improbable,  since  elastin  when 
treated  with  sulphuric  acid,  yields  leucin  (30 — 4op.  c.)  only  and  no 
tyrosin. 

Hilger'  has  obtained  a  similar  body  from  the  shell  membrane  of 
snakes'  eggs. 

Keraiin.  (O,  207 — 25"o.  H,  6-4 — 7-0.  N,  16-2—177.  C,  50-3 
— 52-5-     S,  -7— 5"o  p.  c.) 

This  body,  though  somewhat  resembling  the  proteids  in  general 
composition,  differs  from  them  and  also  from  the  preceding  bodies  so 
widely  in  other  properties,  that  its  description  is  placed  here  for  con- 
venience rather  than  anything  else.  Hair,  nails,  feathers,  horn,  and 
epidermic  scales  consist  for  the  most  part  of  keratin.  Heated  with 
water  in  a  digester  at  150"  keratin  is  partially  dissolved  with  evolution 
of  sulphuretted  hydrogen  ;  the  solution  then  gives  with  acetic  acid  and 
fcrrocyanide  of  potassium  a  precipitate  soluble  in  excess  of  the  acid. 
Prolonged  boiling  with  alkalis  and  acids,  even  acetic,  dissolves  keratin  ; 
the  alkaline  solutions  evolve  sulphuretted  hydrogen  on  treatment  with 
acids.  The  sulphur  in  keratin  is  evidently  very  loosely  united  to 
the -substance,  and  in  all  its  reactions  there  appears  to  be  a  want  of 

'  Ber.  d.  deutsch.  chem.  Gesellsch.  1S73,  S.  166. 


752  PROTEIDS.  [APP. 

similarity  between  keratin  and  either  proteids,  mucin  or  gelatin.  The 
most  common  of  its  products  of  decomposition  are  leucin  (lo  p.  c),  and 
tyrosin  (36  p.c),  and  some  aspartic  acid;  no  glycin  is  formed.  What 
is  generally  known  as  keratin  is  probably  a  compound  body  which  has 
not  yet  been  resolved  into  its  components. 

Ewald  and  Kiihne '  have  described  a  new  body  to  which,  since  it 
occurs  as  a  constituent  of  nervous  tissue  (both  of  nerves  and  of  the 
central  nervous  system),  and  is  yet  closely  identical  with  ordinary 
horny  tissue,  they  give  the  name  of  neuro-keratin.  It  is  prepared  in 
quantity  from  the  brain  by  extracting  this  tissue  with  alcohol  and 
sether,  and  subjecting  the  residue  to  the  action  of  pepsin  and  trypsin. 
The  final  residuum  is  neuro-keratin, 'and  amounts  to  15 — 20  p.c.  of  the 
original  tissue. 

Nuclein.     C29H49N9P3O22.  ' 

Discovered  by  Miescher^   in  the  nuclei  of  pus  corpuscles  and  in  • 
the  yellow  corpuscles  of  yolk  of  &^g.     Other  observers  have  subse- 
quently obtained  it  from  yeast,  from  semen,  from  the  nuclei  of  the 
red  blood-corpuscles  of  birds  and  amphibia,  from  hepatic  cells,  and 
it  is  probably  present  in  all  nuclei. 

When  newly  prepared  it  is  a  colourless  amorphous  body,  soluble  to 
a  slight  extent  in  water,  readily  soluble  in  many  alkaline  solutions  ; 
but  its  solubilities  alter  on  keeping.  If  added  gradually  in  sufficient 
quantity  to  a  solution  of  caustic  alkali  it  first  neutralises  the  solution 
and  then  renders  it  acid.  It  seems  to  possess  an  indistinct  xantho- 
proteic reaction,  but  gives  no  reaction  with  Millon's  fluid.  It  yields 
precipitates  with  several  salts,  e.g.  zinc  chloride,  silver  nitrate,  and 
cupric  sulphate. 

Preparation.  This  is  difficult,  since  nuclein  is  easily  decomposed  \ 
The  most  remarkable  feature  of  this  body  is  its  large  percentage  of 
phosphorus,  5-59  per  cent.  This  phosphorus  is  readily  separated  by 
boiling  with  strong  hydrochloric  acid  or  caustic  alkahs  ;  the  same 
occurs  when  solutions  of  nuclein  are  acidulated  and  allowed  to  stand. 


CARBOHYDRATES. 

Certain  members  only  of  this  class  occur  in  the  human  body  ;  of 
these,  the  most  important  and  wide-spread  is  that  known  as  grape- 
sugar,  or  dextrose  (glucose),  with  which  diabetic  sugar  seems  to  be 

'    Verhand.  naturhist.  med.  Ver.  Heidelberg.  Ed.  I.  (1876)  Heft  5- 

=  Med.  chem.  Untersmh.  Hoppe-Seyler,  Heft  4,  1872,  S.  441  und  502, 

3  Miescher,  op.  cit. 


APP.]        CHEMICAL   BASIS   OF   THE   ANIMAL   BODV.  753 

identical'.  Next  to  this  comes  milk-siirjar.  Inosit  is  another  body  of 
this  cl:iss,  although  it  differs  in  many  important  points  from  the 
prccc'ling  two.  Glycogen  belongs  properly  to  the  sub-class  of  carbo- 
hydrates known  as  starches. 

These  bodies  arc  often  considered  to  be  iiolyatomic  alcohols.  Several  of 
them  stand  in  peculiar  relation  to  mannit,  and  may  be  converted  into  that 
substance  by  the  action  of  sodium  amalgam".  . 

I.    Dfxfrosc  (Grape-sugar).     CoHjoOo  +  HjO. 

Occurs  in  the  contents  of  the  alimentary  canal  to  a  variable  extent, 
dependent  on  the  nature  of  the  food  taken.  It  is  also  a  normal 
constituent  of  blood,  chyle,  and  lymph.  Concerning  its  presence  in 
the  liver  (see  p.  427).  The  amniotic  fluid  also  contains  this  body. 
Bile  in  the  normal  condition  is  free  from  sugar,  so  also  is  urine, 
.though  this  point  has  given  rise  to  great  dispute  3.  The  disease 
diabetes  is  characterised  by  an  excess  of  dextrose  in  the  fluids  and 
tissues  of  the  body  (see  p.  433). 

When  pure,  dextrose  is  colourless  and  crystallises  in  four-sided 
prisms,  often  agglomerated  into  warty  lumps.  The  crystals  will 
dissolve  in  their  own  weight  of  cold  water,  requiring  however  some 
time  for  the  process  ;  they  are  very  readily  soluble  in  hot  water. 
Dextrose  is  soluble  in  alcohol,  but  insoluble  in  aether. 

The  freshly  prepared  cold  aqueous  solution  of  the  crystals  possesses  a 
dextro-rotatory  power  of  +  104°  for  yellow  light.  This,  quickly  on  heating, 
more  slowly  on  standing,  falls  to  -t-  56°,  at  wliich  point  it  remains  constant. 

Dextrose  readily  forms  compounds  with  acids  and  bases  ;  the  latter  are  very 
unstable,  deconipasition  rapidly  ensuing  on  heating  them.  When  its  metallic 
compounds  are  decomposed  the  decomposition  is  in  many  cases  accompanied 
by  the  precipitation  of  the  metals,  eg.  silver,  gold,  mercury,  bismuth.  Caustic 
alkalis  readily  decompose  it,  as  also  does  ammonia. 

Dextrose  is  readily  and  completely  precipitated  by  lead  acetate  and 
ammonia. 

An  important  property  of  this  body  is  its  power  of  undergoing 
fermentations  Cf  these  the  two  principal  are  :  {\)  Alcoholic.  This 
is  produced  in  aqueous  solutions  of  dextrose,  under  the  influence  of 
ye.ist.  The  decomposition  is  the  following  :  C6Hj20o=2C2Hg-f02 
COj,  yielding  (ethyl)  alcohol  and  carbonic  anhydride  Other 
alcohols    of    the  acetic    series    arc    found    in    traces,    as    also    are 

'  The  question,  however,  whether  several  varieties  of  sugar  occurring  in  the 
animal  l)ody  have  not  been  confounded  togetlier  under  the  common  name  of 
dextrose  or  glucose  may  be  considered  at  present  an  open  one. 

"  I.innemunn,  Ann.  d.  Chem.u.  Pharm.  Bd.  123,  S.  136. 

'  See  Seegen,  Z>/.t  Diabetes  Afellitus,  2  Ed,  S.  196. 

F.  P.  48 


754  CARBOHYDRATES.  [APP. 

glycerine,  succinic  acid,  and  probably  many  other  bodies.  The 
fermentation  is  most  active  at  about  25^  C.  Below  5°  or  above 
45°  it  almost  entirely  ceases  If  the  saccharine  solution  contains 
more  than  15  per  cent,  of  sugar  it  will  not  all  be  decomposed, 
as  excess  of  alcohol  stops  the  reaction.  (2.)  Lactic.  This  occurs 
in  the  presence  of  decomposing  nitrogenous  matter,  especially 
of  casein,  and  is  probably  the  result  of  the  action  of  a  spe- 
cific ferment  ^  '  The  first  stage  is  the  production  of  lactic  acid, 
C6Hi20e=2C3He03.  In  the  second  butyric  acid  is  formed  with 
evolution  of  hydrogen  and  carbonic  anhydride  :  2C3Hg03=C4H802+ 
2CO2  +  2H2  The  above  changes,  the  first  of  which  is  probably 
undergone  by  sugar  to  a  considerable  extent  in  the  intestine,  are  most 
active  at  35° ;  the  presence  of  alkaline  carbonates  is  also  favourable 
It  is  moreover  essential  that  the  lactic  ao;tl  should  be  neutralised  as 
fast  as  it  is  formed,  otherwise  the  presence  ot  the  free  acid  stops  the 
process. 

The  detection  and  estimation  of  dextrose  aie  -o  fully  given  in 
various  books  that  they  need  not  be  detailed  nere. 

2.  Maltose.     (C12H22  0^  +  HgO.) 

This  form  of  sugar  was  first  described  by  Dubrunfaut  as  a  product 
of  the  action  of  malt  on  starch.  Its  existence  was  f«r  a  long  time 
doubted  until  Sullivan  repeated  and  confirmed  the  previous  expe- 
riments. According  to  him  it  crystallises  in  fine  acicubr  crystals, 
possesses  a  specific  rotatory  power  of  -j-i5o°  and  a  reducing  power 
which  is  only  one-third  as  great  as  that  of  dextrose.  Musculus  and 
Gruber  =  have  recently  shown  that  it  may  also  be  formed  by  the  action 
of  sulphuric  acid  on  starch,  and  that  it  is  capable  of  underiioing 
alcoholic  fermentation. 

3.  Milk-sugar.     (CiaHggOn  -f  H2  O.) 

Also  known  as  lactose.  It  is  found  in  milk,  and  is  the  only  sugar 
which  enters  into  the  composition  of  this  secretion. 

It  yields,  when  pure,  hard  colourless  crystals,  belonging  to  the 
rhombic  system  (four  or  eight-sided  prisms).  It  is  less  soluble  in 
water  than  dextrose,  requiring  for  solution  six  times  its  weight  of  cold, 
but  only  two  parts  of  boiling,  water ;  it  is  entirely  insoluble  in  alcohol 
and  aether.  It  is  fully  precipitated  from  its  solutions  by  the  addition 
of  lead  acetate  and  ammonia. 

'  Lister,  Path.  Soc.  Trans.  Vol.  for  1878,  p.  425;  also  Quart.  Jl.  of  Micros. 
Science,  Vol.  xviii.  (1878)  p.  177. 

*  Zeitschr.f.physiol.  Chem.  Bd.  TI.  (1878)  S.  1 77. 


APP.]        CHEMICAL   BASIS   OF  THE   ANIMAL   BODY.  755 

When  freshly  dissolvetl,  its  a(|iicnus  solution  j>i)S^csscs  a  specific  dexlro- 
rotntory  power  of  +93'i°  for  yill  )\v  light  ;  thi-dimini.'lie  ,  si  iwlyou  standinij, 
rapidly  on  boitiiifj,  until  it  finally  (Ciuains  constant  at  +  59'3".  The  amount 
of  rotation  is  independent  of  the  c  )ncenlration  of  tin-  s  ilution. 

I  aclo^e  unites  readily  with  hases,  fiirmiiig  unstable  ciinip  unds  ;  frum  its 
metallic  compounds  the  metal  is  precipitated  in  the  reduced  state  on  boiling  ; 
it  reduces  copper  salts  as  readily  as  dextrose. 

Lactose  is  generally  stated  to  admit  of  no  direct  alcoholic  fermen- 
tation ;  this  may  however  sometimes  be  induced  by  a  lengthy  action 
o^  yeast.  By  boiling  with  dilute  mineral  acids  lactose  is  converted 
into  galactose,  which  readily  undergoes  alcoholic  fermentation. 

Galactose  is  very  readily  soluble  in  water,  though  insoluble  in  alcohol.  It 
possesses  a  higher  rotatory  power  than  lactose,  viz.  +<iy2° ;  in  a  freshly 
prepared  solution  the  rotation  is  +I39'6°.  It  may  be  remarked  here  that 
though  iso/iUcii  lactose  is  incapable  of  direct  alcoholic  fermentation,  milk 
itself  may  be  fermented  ;  Berthelot  was  unable  in  this  direct  alcoliolic  fermen- 
tation to  tletect  any  intermediate  change  of  the  lactose  into  another  fermentable 
sugar. 

Lactose  is,  however,  directly  capable  of  undergoing  the  lactic  fer- 
mentation ;  the  circumstances  and  products  are  the  same  as  in  the 
case  of  dextrose  (see  above).  The  action  is  generally  productive  of  a 
collateral  small  quantity  of  alcohol. 

The  tests  for  the  presence  of  this  body  are  the  same  as  for 
de.xtrose,  with  the  exception  of  the  alcoholic  fermcntLtion. 

Preparation.  After  the  removal  of  the  casein  and  other  proteids 
of  the  milk,  the  mother  liquor  is  evaporated  to  the  crystallising 
point ;  the  crystals  are  purified  by  repeated  crystallisation  from  warm 
water. 

4.     Iiiosit.     (CqHi20o  +  2H2O.) 

This  substance  occurs  but  sparingly  in  the  human  body ;  it  was 
founi  originally  by  Scherer '  in  the  muscles  of  the  heart.  Cloetta 
showed  its  presence  in  the  lungs,  kidneys,  spleen,  and  liver*,  and 
Miiller  in  the  brain  3.  It  occurs  also  in  diabetic  urine,  and  in  that  of 
"  Bright's  disease,"  and  is  found  in  abundance  in  the  vegetable 
kingdom. 

Pure  inosit  forms  large  efflorescent  crystals  (rhombic  tables) ;  in 
microscopic  prepaialions  it  is  usually  obtained  in  tufted  lumps  of  hne 
crystals.     Easily  soluble  in  water,  it  is  insoluble  in  aLohul  and  a:ihcr. 

'  Anit.  d.  Chnn.  11.   Pharm.  Bd.  73,  S.  322. 
'  JMii.  Hd.  99,  S.  2S9. 
3  Ibid.  Bd.  103,  S.  140. 

48—2 


756  CARBOHYDRATES.  [APP. 

It  possesses  no  action  on  polarised  light,  and  does  not  reduce  solutions 
of  metallic  salts. 

It  admits  of  no  direct  alcoholic,  but  is  capable  of  undergoing  the 
lactic  fermentation;  according  to  Hilger'  the  acid  formed  is  sarco- 
lactic.     It  is  unaltered  by  heating  with  dilute  mineral  acids. 

Pi-eparatinn.  It  may  be  precipitated  from  its  solutions  by  the 
action  of  basic  lead  acetate  and  ammonia. 

As  a  special  test  may  be  mentioned  the  production  of  a  bright 
violet  colour  by  careful  evaporation  to  dryness  on  platinum  foil,  with  a 
little  ammonia  and  calcium  chloride. 

5.  Dextrin.     Q^yfi^. 

By  boiling  starch-paste  with  dilute  acids,  or  by  the  action  of 
ferments,  the  starch  is  converted  into  an  isomeric  body,  to  which, 
from  its  action  on  polarised  light,  the  name  dextrin  has  been  given. 
It  is  soluble  in  water,  but  is  precipitated  by  alcohol.  It  does  not 
undergo  alcoholic  fermentation  until  after  it  has  been  changed  into 
dextrose,  nor  can  it  reduce  metallic  salts.  It  yields  a  reddish  port- 
wine  colour  with  iodine,  which  disappeai-s  on  warming  and  does  not 
return  on  cooling.  Further  action  of  acids  or  of  ferments  converts 
dextrin  into  dextrose.  Dextrin  is  present  in  the  contents  of  the 
alimentary  canal  after  a  meal  containing  starch,  and  has  also  been 
found  in  the  blood.  Concerning  achroodextrin  and  other  varieties  of 
dextrin,  see  p.  241. 

6.  Glycogen.     Q^yf)^. 

Belongs  to  the  starch  division  of  carbohydrates.  Discovered  by 
Bernai'd  in  the  liver  and  other  organs  (see  p.  425). 

Glycogen  is,  when  pure,  an  amorphous  powder,  colourless  and 
tasteless,  readily  soluble  in  water,  insoluble  in  al:oho]  and  ^ther.  Its 
aqueous  solution  is  generally  though  not  always  strongly  opalescent, 
but  contains  no  particles  visible  microscopically  ;  the  opalescence  is 
much  reduced  by  the  presence  of  free  alkalis.  The  same  solution 
possesses,  according  to  Hoppe-Seyler,  a  very  strong  dextro-rotatory 
power  ;  it  dissolves  hydrated  cupric  oxide  ;  but  this  is  not  reduced  on 
boiling. 

By  the  action  of  dilute  mineral  acids  (except  nitric)  it  is  partially 
converted  into  a  form  of  sugar  very  closely  resembling,  though  pro- 
bably differing  somewhat  from  true  dextrose,  and  the  same  conversion 
is  also  readily  effected  by  the  action  of  amylolytic  ferments.  The  sugar 
into  which  the  glycogen  of  the  liver  is  converted  after  death  (see  p. 

'  Ann,  d.  Chem.  u,  Pharm,  Bd.  1 60,  S.  333. 


APP.]        CHEMICAL   BASIS  OF   THE   ANIMAL    BODY.  757 

428),  appears  to  be  true  dextrose  ;  so  also  the  sugar  of  diabetes. 
Musculus  and  V.  Mcring'  however  state  that  the  reiult  of  the  action 
of  diastase,  or  sahvary  or  pancreatic  ferment,  upon  glycogen  is  a 
mixture  of  achroodcxtrin  and  maltose  ;  the  quantity  of  dextrose 
making  its  appearance  at  the  same  time  being  very  small. 

Opalescent  solutions  of  glycogen  usually  become  clear  on  the 
addition  of  caustic  alkali  :  Vintschgau  and  Dictl"  have  shewn  that 
this  is  accompanied  by  a  change  which  converts  a  portion  of  the 
glycogen  into  a  substance  to  which  they  gave  the  name  of /i.-glycogen- 
dextrin.  (Kiihne^  had  previously  described  a  body  to  which  he  gave 
the  name  glycogen-dextrin.  That  described  by  Vintschgau  anl  Dietl 
differs  slightly  from  Kiihne's  body,  and  hence  the  name).  According 
to  these  authors  one-fifth, of  the  glycogen  is  at  the  same  time  changed 
into  some  other,  at  present  undetermined,  substance.  Normal  lead 
acetate  gives  a  cloudiness,  the  basic  salt  a  precipitate,  in  its  solutions. 

As  tests  for  this  body  may  be  used  the  formation  of  a  port-wine 
colour  with  iodine  ;  this  disappears  on  warming  but,  in  this  rcspe.t 
differing  from  dextrin,  returns  on  cooling.  (The  same  colour  is 
produced  by  dextrin,  but  this  does  not  reappear  on  cooling  after  its 
disappearance  on  warming.) 

Preparation  0/ Glycogen.  The  following  is  Briicke's*  method.  The 
filtered  or  simply  strained  decoction  of  perfectly  fresh  liver  or  other 
glycogenic  tissue  is,  when  cold,  treated  alternately  with  dilute  hydro- 
chloric acid,  and  a  solution  of  the  double  iodide  of  potassium  and 
mercury  5,  as  long  as  any  precipitate  occurs.  In  the  presence  of  free 
hydrochloric  acid,  the  double  iodide  precipitates  proteid  matters  so 
completely  as  to  render  their  separation  by  filtration  easy.  The  pro- 
teids  being  thus  got  rid  of,  the  glycogen  is  precipitated  from  the  filtrate 
by  adding  alcohol  to  the  extent  of  between  60  and  70  p.  c.  Too  much 
alcohol  is  to  be  avoided,  since  other  substances  as  well  are  thereby 
precipitated.  The  glycogen  is  now  washed  with  alcohol  first  of  60 
and  then  of  95  per  cent.,  afterwards  with  a:ther,  and  finally  with 
absolute  alcohol.     It  is  then  dried  over  sulphuric  acid. 

»  Zdlschr.f.  physio'.  Chcm.  Bd.  ii.  (187S)  S.  403. 

»  I'fliigfr'>  Aicli.  r.il.  XVII   (187S)  S.  IS4. 

3  I.chrb.  d.  physiol.  Chan.  (1S6S),  S.  63. 

*■  Si/zitiigsl>,r.  d.  Wiener  Akad.  VA    63  (187 1 )  ii.  Abth. 

5  This  may  I)e  prc|iarcfl  l>y  precii  iiating  potasium  iodide  with  mercuric 
chloride  and  dissolvini^  ihe  washed  preci]  i'ale  in  a  hot  solution  of  potassium 
i  'dide  ns  ii'nn  ns  it  cniiliniies  to  he  'a  en  up.  On  cooling,  sime  a:i  <  iint  of 
j^recipitate  occurs,  which  mu^t  be  fillcrcd  ofi";  the  filtrate  is  then  ready  for 
use. 


758  FATS,  ETC.  [Arp. 

FATS,  THEIR  DERIVATIVES  AND  ALLIES. 

The  Acetic  Acid  Series. 

General  formula  C"H„202  (monobasic). 

This,  which  is  one  of  the  most  complete  homologous  series  of 
organic  chemistry,  runs  parallel  to  the  series  of  monatomic  alcohols. 
Thus  formic  acid  corresponds  to  methyl  alcohol,  acetic  acid  to  ethyl 
(ordinary)  alcohol,  and  so  on.  The  several  acids  may  be  regarded  as 
being  derived  from  their  respective  alcohols  by  simple  oxidation  : 
thus  eth)l  alcohol  yields  by  oxidation  acetic  acid: — CgHgO -j- "^  i  — 
€21^402+  H^O.  The  various  members  differ  in  composition  by  CH.,, 
and  the  bciling  points  rise  successively  by  about  19'^C.  Similar 
relations  hold  good  with  regard  to  their  melting  points  and  specific 
gravities.  The  acid  properties  are  strongest  in  those  where  n  has  the 
least  value.  The  lowest  members  of  the  series  are  volatile  liquids, 
acting  as  powerful  acids  :  these  successively  become  less  and  less 
fluid,  and  the  highest  members  are  colourless  solids,  closely  resembling 
the  neutral  fats  in  outward  appearance.  Conseeutive  acids  of  the 
series  present  but  very  small  differences  of  chemical  and  physical 
properties,  hence  the  diffi-ulty  of  separating  them  :  this  is  further 
increased  in  the  animal  body  by  the  fact  that  exactly  those  acids  which 
present  tl:e  greiite^t  similarities  usually  occur  together. 

The  free  acids  are  found  only  in  small  and  very  variable  quantities 
in  various  parts  of  the  body  ;  their  derivatives  on  the  other  hand  form 
most  important  constituents  of  the  human  frame,  and  will  be  considered 
further  on. 

Formic  acid.     CHO  .  OH. 

When  pure  is  a  strongly  corrosive,  fuming  fluid,  with  powerful  irri- 
tating odour,  solidifying  at  o'' C,  boiling  at  loo'^C,  and  capable  of 
being  mixed  in  all  proportions  ^ith  water  and  alcohol.  It  has  been 
found  in  various  parts  qf  the  body ;  such  as  the  spleen,  thymus, 
P'-increas,  muscles,  brain,  and  blood  ;  from  the  latter  it  nray  be  obtained 
by  the  action  of  acids  on  the  heemoglobin.  According  to  some  authors'^ 
it  occurs  also  in  urine. 

Heated  with  sulphuric  acid  it  yields  carbonic  oxide  and  water ; 
with  caustic  potash  it  gives  hydrogen  and  oxalic  acid. 

'  Buliginsky,  Hoppe-Seyler's  Aled.  Che7n.  Mittheilung.  Heft  2,  S.  240. 
Thudichum,  Journ.  0/  the  Cheni.  Soc.  Vol.  8,  p.  400. 


Al'P.]        CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  759 

Acetic  acid.     C.HoO  .  Oil 

Is  distinguished  by  its  characteristic  odour ;  its  boiling  point  is 
117'  C. ;  it  sohditics  at  5'  and  is  tUiid  at  all  temperatures  above  is'^C, 
It  is  soluble  in  all  proportions  in  alcohol  and  water. 

It  occurs  in  the  stomach  as  the  result  of  fermentative  changes  in 
the  food,  and  is  frequently  present  in  diabetic  urine.  In  other  organs 
and  lluids  it  exists  only  in  minute  traces. 

With  ferric  chloride  it  yields  a  blood-red  solution,  decolorized  by  hydro- 
chloric acid.  (It  differs  in  this  last  reaction  from  sulphocyanide  of  iron.) 
Heated  with  alcohol  and  sulphuric  acid,  the  cliaracteristic  odour  of  acetic 
a;ther  is  obtained.     It  does  not  reduce  silver  nitrate. 

Propionic  acid.     C3  H5  O  .  OH. 

This  acid  closely  resembles  the  preceding  one.  It  possesses  a  very 
sour  taste  and  pungent  odour;  is  soluble  in  water,  boils  at  141°  C, 
and  may  be  separated  from  its  aqueous  solution  by  excess  of  calcium 
chloride. 

It  occurs  in  small  quantities  in  sweat,  in  the  contents  of  the 
stomach,  and  in  diabetic  urine  when  undergoing  fermentation.  It  is 
similarly  produced,  mi.xed  however  with  other  products,  during  alco- 
holic fermentation,  or  by  the  decomposition  of  glycerine.  It  partially 
reduces  silver  nitrate  solution  on  boiling. 

Butyric  acid.     QH-O  .   OH. 

An  oily  colourless  liquid,  with  an  odour  of  rancid  butter,  soluble  in 
water,  alcohol,  and  a;ther,  boiling  at  162'^  C.  Calcium  chloride  separates 
it  from  the  aqueous  solution. 

Found  in  sweat,  the  contents  of  the  large  intestine,  faeces,  and  in 
urine.  It  occurs  in  traces  in  many  other  fluids,  and  is  plentifully 
obtained  when  diabetic  urine  is  mixed  with  powdered  chalk  and  kept 
at  a  temperature  of  35°  C.  It  exists,  as  a  neutral  fat,  in  small  quantities 
in  milk. 

This  is  the  principal  product  of  the  second  stage  of  lactic  fermen- 
tation.    (See  Dextrose.) 

Valerianic  add.     QHoO  .  OH. 

An  oily  liquid,  of  penetrating  odour  and  burning  taste  ;  soluble  in 
30  parts  of  water  at  12'  C,  readily  soluble  in  alcohol  and  a:ther.  Boils 
at  175"  C.  Possesses,  in  free  and  combined  form,  a  feeble  right-handed 
rotation  of  the  ph^ne  of  polarisation. 

It  is  found  in  the  solid  excrements,  and  is  formed  readily  by  the 
decomposition,  through  putrefaction,  of  impure  leucin,  ammonia  being 


y60  FATS,  ETC.  [APP. 

at  the  same  time  evolved ;  hence  its  occurrence  in  urine  when  that 
fluid  contains  ieucin,  as  in  cases  of  acute  atrophy  of  the  liver. 

Caproic  acid.  Cg  H^i  O  .  OH. 
Caprylic  „  Cg  H^jO  .  OH. 
Capric      „        CjoH^gO  .  OH. 

These  three  occur  together  (as  fats)  in  butter,  and  are  contained  in 
varying  proportions  in  the  faeces  from  a  meat  diet.  The  first  is  an 
oily  fluid,  slightly  soluble  in  water,  the  others  are  solids  and  scarcely 
soluble  in  water  ;  they  are  soluble  in  all  proportions  in  alcohol  and 
aether.  They  may  be  prepared  from  butter,  and  separated  by  the 
varying  solubilities  of  their  barium  salts. 

Laurostearic  acid.     C12  H23  O  .  OH. 
Myristic  „        Q^  H,?  O  .  OH. 

These  occur  as  neutral  fats  in  spermaceti,  in  butter  and  other  fats. 
They  present  no  points  of  interest. 

Palmitic  acid.     0^  Hj^  O  .OH.    . 
Stearic       „         C^g  H35  O  .  OH. 

These  are  solid,  colourless  when  pure,  tasteless,  odourless,  crystal- 
line bodies,  the  former  melting  at  62°  C,  the  latter  at  69'2°  C.  In 
water  they  are  quite  insoluble  ;  palmitic  acid  is  more  readily  soluble 
in  cold  alcohol  than  stearic  :  both  are  readily  dissolved  by  hot  alcohol, 
Eether,  or  chloroform.  Glacial  acetic  acid  dissolves  them  in  large 
quantity,  the  solution  being  assisted  by  warming.  They  readily  form 
soaps  with  the  alkalis,  also  with  many  other  metals.  The  varying 
solubihties  of  their  barium  salts  afford  the  means  of  separating  them 
when  mixed'  :  this  may  also  be  applied  to  many  others  of  the  higher 
members  of  this  series. 

These  acids  in  combination  with  glycerin  (see  below),  together  with 
the  analogous  compound  of  oleic  acid,  form  the  principal  constituents 
of  human  fat.  As  salts  of  calcium  they  occur  in  the  fseces  and  in 
'  adipocere,'  and  probably  in  chyle,  blood  and  serous  fluids,  as  salts  of 
sodium.  They  are  found  in  the  free  state  in  decomposing  pus,  and  in 
the  caseous  deposits  of  tuberculosis. 

The  existence  of  margaric  acid ,  intermediate  to  the  above  two,  is  not  now 
admitted,  since  Heintz^  has  shewn  that  it  is  really  a  mixture  of  palmitic  and 
stearic  acid.  Margaric  acid  possesses  the  anomalous  melting  point  of  59'9°^' 
A  mixture  of  60  parts  stearic  and  40  of  palmitic  acids,  melts  at  6o"3°. 

»   Heintz,  Annal.  d.  Phys.  u.  Chefti.  Bd.  92,  S.  588.  =  Op.  cit. 


APP.]        CHEMICAL   BASIS  OF  THE   ANIMAL   CODY.  761 

Acids  of  the  Oleic  (Acrylic)  Series.  1I(C„  Il2„_3)02(monobasic). 

M.iny  acids  of  this  scries  occur  as  glycerine  compounds  in  various 
fixed  fats.  They  are  very  unstable,  and  rexdily  absorb  oxygen  when 
exposed  to  the  air.  The  higher  members  are  decomposed  on  attempt- 
ing to  distil  them.  Their  most  peculiar  property  is  that  of  being 
converted  by  traces  of  NU^  into  solid,  stable  mctL;meric  acids,  capable 
of  being  distilled.  They  bear  an  interesting  relation  to  tlie  acids  of 
the  acetic  series,  breaking  up  when  heated  with  caustic  pjtash  into 
acetic  acid  and  some  other  member  of  the  same  series  : — thus, 

Oleic  acid.  Potassium  acetate.  Pota.ssium  palmitate. 

HCi8H3302+2KHO  =  KC2H302    H»     KQ0H31O2    +     H2. 
O/a'c  acid.     C i,  H 33  O  .  O  H . 

This  is  the  only  acid  of  the  series  which  is  physiologically  important. 
It  is  found  united  with  glycerin  in  all  the  fats  of  the  human  body.  In 
the  sm.dl  intestine  and  chyle  it  exists  also  either  as  a  salt  of  potsssium, 
or  sodium,  or,  it  may  be,  in  the  free  state. 

When  pure  it  is,  at  ordinary  temperatures,  a  colourless^,  odourless, 
tastele:>s,  oily  liqui.l,  solidifying  at  4°  C.  to  a  crystalline  mass.  Insoluble 
in  w:iter,  it  is  soluble  in  alcohol  and  aslher.  It  cannot  be  distilled 
w  thout  decomposition.  It  readily  forms  with  potassium  and  sodium 
soaps,  which  are' soluble  in  water:  its  compounds  with  most  other 
bases  are  insoluble.  It  may  be  distinguished  from  the  acids  of  the 
acetic  series  by  its  reaction  with  NOj  and  by  the  changes  it  undergoes 
Avhen  exposed  to  the  air. 


The  Neutral  Fats. 

These  may  be  considered  as  aethers  formed  by  replacing  the 
exchangeable  atoms  of  hydrogen  in  the  triatomic  alcohol  glycerin  (see 
below),  by  the  acid  radicles  of  the  acetic  and  o'eic  series.  Since  there 
are  three  such  exchangeable  atoms  of  hydrogen  in  glycerin,  it  is 
possible  to  form  three  clisses  of  these  aethers;  only  t,hose,  howevtr, 
which  belong  to  the  third  class  occur  as  natural  constituents  of  the 
human  body  :  those  of  the  first  and  second  are  only  of  theoretical 
importance. 

Tliey  possess  certain  general  characteristics.  Insoluble  in  water 
and  cold  alcohol,  they  are  readily  soluble  in  hot  alcohol,  ivthcr, 
chloroform,  &;  •.  ;  they  also  dissolve  one  another.  They  are  neutral 
bodies,  colourless  and  tasteless  when  pure  ;  are  not  capable  of  being 
distilled  without  undergoing  decomposition,  and  as  a  result  of  this 


762  FATS,   ETC.  [APP. 

decomposition,  yield  solid  and  liquid  hydrocarbons,  water,  fatty  acids, 
and  a  peculiar  body,  acrolein.  (Glycerin  contains  the  elements  of  one 
molecule  of  acrolein,  and  two  molecules  of  water.) 

They  possess  no  action  on  polarised  light. 

They  may  readily  be  decomposed  into  glycerin  and  their  respective 
fatty  acids  by  the  action  of  caustic  alkalis  or  of  superheated  steam. 

/"^/otzV/^  (Tri-palmitin).       /^    u  ^^^    j  ^3*    --*^<*/  ^7</       /f 

The  following  reaction  for  the  formation  of  this  fat  is  typical  for 
all  the  others  : 


Gtycerin.  Palmitic  acid.  Palmitin. 


Palmitin  is  slightly  soluble  in  cold  alcohol,  readily  so  in  hot 
alcohol,  or  in  aether  ;  when  pure  it  crystallises  in  fine  needles ;  if 
mixed  with  steirin,  it  generally  forms  shapeless  lumps,  although  the 
mixtuie  may  at  times  assume  a  crystalline  form,  and  was  then  regarded 
as  a  distinct  body,  namely  margarin.  It  possesses  three  different 
melting  points,  according  to  the  previous  temperatures  to  which  it 
has  been  subjected.     It  solidities  in  all  cases  at  45°  C. 

Preparation.  From  palm  oil,  by  removing  the  free  palmitic  acid 
with  alcohol,  and  crystallising  repeatedly  from  cCther. 

Stearin  (Tri-stearin)      (^^"0)3  }  ""-  ^Cf^  /^^  ^ 

This  is  the  hardest  and  least  fusible  of  the  ordinary  fats  of  the 
body  ;  is  also  the  least  soluble,  and  hence  is  the  first  to  crystaUise  out 
from  solutions  of  the  mixed  fats.  It  crystallises  usually  in  square 
tables.  It  presents  peculiarities  in  its  fusing  points  similar  to  those 
of  palmitin. 

Preparation.  From  mutton  suet,  its  separation  from  palmitin  and 
olein  being  effected  by  repeated  crystallisation  from  aether,  stearin 
being  the  least  soluble. 

(9/«;^  (Tri-olein).        (^is^30)3|  O3.    "^O^^  lo^^^C 

Is  obtained  with  difficulty  in  the  pure  state,  and  is  then  fluid  at 
ordinary  temperatures.  It  is  more  soluble  than  the  two  preceding 
ones.  It  readily  undergoes  oxidation  when  exposed  to  the  air,  and  is 
converted  by  mere  traces  of  NO2  into  a  solid  isomeric  fat.     Oleiu 


APP.]        CHEMICAL   BASIS   OI-"   TIIK   ANIMAL   BODY.  763 

yields,  on  dry  distillation,  a  characteristic  acid,  the  sebacic,  and  is 
saponified  with  much  greater  difficulty  than  are  palmitin  and  stearin. 

Preparation.  From  olive  oil,  either  by  cooling  to  o"  and  pressing 
out  the  olein  that  remains  fluid  ;  or  by  dissolving  in  alcohol  and 
cooling,  when  the  olein  remains  in  solution  while  the  other  fats 
crystallise  out. 

Lilyccrin.  ,,      j-  O3. 

This  principal  constituent  of  the  neutral  fats  may,  as  above  stated, 
be  looked  upon  as  a  triatomic  alcohol. 

When  pure,  glycerin  is  a  viscid,  colourless  liquid,  of  a  well-known 
sweet  taste.  It  is  soluble  in  water  and  alcohol  in  all  proportions, 
insoluble  in  asthcr.  Exposed  to  very  low  temperatures  it  becomes 
almost  solid  ;  it  may  be  distilled  in  close  vessels  without  decom- 
position, between  275' — 280°  C. 

It  dissolves  the  alkalis  and  alkaline  earths,  also  many  oxides,  such 
as  those  of  lead  and  copper  ;  many  of  the  fatty  acids  are  also 
soluble  in  glycerin. 

It  possesses  no  rotatory  power  on  polarised  light. 

It  is  easily  recognised  by  its  ready  solubility  in  water  and  alcohol, 
its  insolubility  in  aether,  its  sweet  taste,  and  its  reaction  with  bases. 
The  production  of  acrolein  is  also  characteristic  of  glycerin. 

CgHgOs  -  2H2O  =  CaHiO  (Acrolein). 

Preparation.  By  saponification  of  the  various  oils  and  fats.  It 
is  also  formed  in  small  quantities  during  the  alcoholic  fermentation 
of  sugar'. 

6'oaps.  These  may  be  formed  by  the  action  of  caustic  alkalis  on 
fats.  The  process  consists  in  a  substitution  of  the  alkali  for  the 
radicle  of  glycerin,  the  latter  combining  with  the  elements  of  water  to 
form  glycerin.     Thus 

Tri-stcarin  Potassic  stearate.  Glycerin. 

Pancreatic  juice  can  split  up  fats  into  glycerin  and  the  free  fatty  acid  (s  e 
p.  263),  and  the, bile  is  known  to  be  capable  of  saponifying  these  fatty  acids. 
The  aaiount  of  soaps  formed  in  the  alimentary  canal  is  however  small  and 
unimportant. 

»  Pasteur,  Attn.  d.  Cheitt.  u.  Pharnt.  Bd.  106,  S.  338. 


764 


GLYCOLIC   ACID   SERIES. 


[APP. 


Acids  of  the  Glycolic  Series. 

Running  parallel  to  the  monatomic  alcohols  (C„H2,j  +  20)  is  the 
series  of  diatomic  alcohols  or  glycols  (C„H2„  +  20  ).  Thus  corres- 
ponding to  ethyl  alcohol  is  the  diatomic  alcohol,  ethyl-glycol.  As 
from  the  monatomic  alcohols,  so  from  the  glycols,  acids  may  be 
derived  by  oxidation  ;  from  the  latter  (glycols)  however  two  series  of 
acids  can  be  obtained,  known  respectively  as  the  glycolic  and  oxalic 
series.  The  first  stage  of  oxidation  of  the  glycol  gives  a  member  of 
the  glycolic  series,  thus  : 

Ethyl-glycol.  Glycolic  acid. 

C2H6O2  +  02  =  C2H4O3  +  H2O,  or  more  generally 
C„H2,i  +  202  +02  =  C„H2»03  +  H2O. 

By  further  oxidation  a  member  of  the  glycolic  series  can  be 
converted  into  a  member  of  the  oxalic  series,  thus  : 

Glycolic  acid.  Oxalic  acid. 

C2H4O3  +02=  C2H2O4  +  HoO,  or  more  generally 
C„H2,.03  +  O  =  C„H2»  -  2O4  +  H2O. 

The  acids  of  the  glycolic  series  are  diatomic  but  monobasic  ;  those 
of  the  oxalic  series  are  diatomic  and  diabasic. 

The  following  table  may  be  given  to  shew  the  general  relationships 
of  alcohols  and  acids  : 


Radical. 

Alcohol. 

Acid. 

Glycols. 

Acid  I. 

Acid  II. 

Formic. 

Carbonic. 

Methyl  (CH3) 

CH3(0H) 

HCHO2 

,, 

H3CO3 

,, 

Acetic. 

Ethyl-glycol. 

Glycolic. 

OxaHc. 

Ethyl  (C2H5) 

C^HslOH) 

HC2H3O2 

QH^iOH)^ 

HC2H3O3 

H2C2O4 

Propionic, 

PropyJ-aflycoI. 

Lactic. 

Malonic. 

Propyl  (C3H7) 

C,¥L,(Oll) 

HC3H5O2 

C3IV.OH), 

HC3H5O3 

H2C3H2O4 

Butyric. 

Butyl-CTlycol. 

Oxybutyric. 

Succinic. 

Butyl  (C^Us) 

C^Hg^OH) 

HC4H7O2 

QHgtuH), 

HC5H,03 

H2C4H4O, 

Glycolic  Acid  Series. 
Lactic  acid.     Q.^^0^. 

Next  to  carbonic  acid,  the  most  important  member  of  this  series, 
as  far  as  physiology  is  concerned,  is  lactic  acid. 

Lactic  acid  exists  in  four  isomeric  modifications,  but  of  these  only 


APP.]        CHEMICAL   BASIS   OK   THE   ANIMAL   BODY.  765 

three  have  been  found  in  the  human  body.  These  three  all  form 
sirupy,  colourless  fluids,  soluble  in  all  proportions  in  water,  alcohol, 
and  aether.  They  possess  an  intensely  sour  taste,  and  a  strong  acid 
reaction.  When  heated  in  solution  they  are  partially  distilled  over  in 
the  escaping  vapour.  They  form  salts  with  metal  j,  of  \vhi:h  those 
with  the  alkalis  are  very  soluble  and  crystallise  with  difficulty.  The 
calcium  and  zinc  salts  are  of  the  greatest  importance,  as  will  be  seen 
later  on. 

1.  Elhylidene-lactic  acid.  This  is  the  ordinary  form  of  the  acid, 
obtained  as  the  characteristic  product  of  the  well-known  '  lactic  fer- 
mentation.' It  occurs  in  the  contents  of  the  stomach  and  intestines. 
According  to  Heintz'  it  is  found  also  in  muscles,  and  according  to 
Gscheidlen'  in  the  ganglionic  cells  of  the  grey  substance  of  the  brain. 
In  many  diseases  it  is  found  in  urine,  and  exists  to  a  large  amount  in 
this  e.\cretion  after  poisoning  by  phosphorus.^ 

It  may  be  prepared  by  the  general  methods  of  slowly  oxidising  the  corres- 
ponding glycol  or  by  acting  on  the  monochlorinated  propionic  acid  with  moist 
silver  oxide.  In  obtaining  it  from  the  products  of  lactic  fermentatijn,  the 
crusts  of  zinc  lactate  are  purified  by  several  crystallisations,  and  the  acid 
liberated  from  the  compound  by  the  action  of  sulphuretted  hydrogen. 

2.  Ethylene-laciic  acid.  This  acid  is  found  accompanying  the  one 
next  to  be  described,  in  the  watery  extract  of  muscles.  From  this  it 
is  separated  by  taking  advantage  of  the  different  solubilities  of  the 
zinc  salts  of  the  two  acids  in  alcohol.  It  seems,  probable,  however, 
that  it  has  not  yet  been  prepared  in  the  pure  state  by  this  method. 

Wislicenus  first  obtained  this  acid  by  heating  hydroxycyanide  of  ethylene 
with  aque  us  solutions  of  the  alkalis*. 

The  same  obsener  found  it  also  in  many  pathological  fluids. 

3.  Sarcolactic  acid.  This  acid  has  not  yet  been  procured  syntheti- 
cally. As  its  name  implies,,  it  is  that  form  of  the  acid  which  occurs  in 
muscles,  and  hence  exists  in  large  quantities  in  Liebig's  'extract  of 
meat.'  It  is  often  found  also  in  pathological  fluids.  This  is  the  only  acid 
of  this  series  which  possesses  any  power  of  rotating  the  plane  of  polar- 
ised light  ;  it  is  otherwise  indistinguishable  from  the  preceding cthyli- 
dene-Iactic  acid,  and  is  generally  represented  by  the  same  formula. 
The  free  acid  has  dextro-,  the  anhydride  tevo-rotatory  action.  The 
specific  rotation  for  the  zinc  salt  in  solution  is  —  7'63°  for  yellow  light. 

'  Ann.  d.  Chc^K  u.  Pharm.  I'd.  157,  S.  320. 

"  Pfluger's  ^//-f///i/,  \'A.  viil.  (1873— 74)  S.  171. 

3  Schultzen  and  Kiess,  L'eber  amte  I  hosphorvcrgftung, 

♦  Ann.  d.  Chan.  u.  Pharm.  Bd.  128,  S.  6. 


J^e  OXALIC  ACID   SERIES.  [APP. 

The  zin:  and  calcium  salts  of  sarcolactic  acid  are  more  soluble  both 
in  water  and  alcohol,  than  those  of  ethylidene-lactic  acid,  but  less  so 
than  those  of  ethylene- lactic  acid  ;  and  the  same  salts  of  ethylene-lactic 
acid  contain  more  water  of  crystallisation  than  those  of  the  other  two. 

Heintz"^  has  compared  the  above  acids  to  the  modifications  capable  of 
existia^  in  tartaric  acid-. 

Hydracrylic  acid,  the  fourth  in  this  series  of  lactic  acids,  is  distinguished 
by  the  nature  of  its  decomposition  on  heating.  It  is  never  found  as  a 
constituent  of  animal  bodies. 


Oxalic  Acid  Series. 
Oxalic  acid.     H2C2O4. 

In  the  free  state  this  acid  does  not  occur  in  the  human  body. 
Calcium  oxalate,  however,  is  a  not  unfrequent  constituent  of  urine, 
and  enters  into  the  composition  of  many  urinary  calculi,  the  so-called 
mulberry  calculus  consisting  almost  entirely  of  it.  It  may  also  occur 
in  faeces,  and  in  the  gall  bladder,  though  this  is  rarely  observed. 

As  ordinarily  precipitated  from  solutions  of  calcium  salts  by  am- 
monium oxalate,  calcium  oxalate  is  quite  amorphous,  but  in  urinary 
deposits  it  assumes  a  strongly  characteristic  crystalline  form,  viz. 
that  of  rectangular  octohedra.  In  some  cases  it  presents  the  ano- 
malous forms  of  rounded  lumps,  dumb-bells,  or  square  columns  with 
pyramidal  ends.  It  is  insoluble  in  water,  alcohol,  and  aether,  also  in 
ammonia  and  acetic  acid.  Mineral  acids  dissolve  this  salt  readily,  as 
also  to  a  smaller  extent  do  solutions  of  sodium  phosphate  or  urate. 
All  the  above  characteristics  serve  to  detect  this  salt  ;  its  microscopical 
appearance,  however,  is  generally  of  most  use  for  this  purpose. 

The  pure  acid  is  prepared  either  by  oxidising  sugar  with  nitric 
acid,  or  decomposing  ligneous  tissue  with  caustic  alkalis. 

Succinic  acid.     H2C4H4O4. 

This  is  the  third  acid  of  the  oxalic  series,  being  separated  from 
oxalic  acid  by  the  intermediate  malonic  acid,  H2C3H2O4.  It  occurs 
in  the  spleen,  the  thymus,  and  thyroid  bodies,  hydrocephalic  and 
hydrocele  iluids. 

According  to  Meissner  and  Shepards,  it  is  found  as  a  normal  constituent  of 
urine.     Tliis  is  contested  by  Salkowski'*,  and  also  by  von  Speyer.     It  seems 

^   Op.  cit. 

^  See  further,  "Wislicenus,  op.  cit.  Also  Ann.  d.  Chem.  u.  Pharm.  Bd. 
166,  S.  3,  Ed.  167,  S.  302,  and  Zeitschr.f.  Chem.  Bd.  XIII.  S.  159. 

3  Untersuch.  iiber  d.  Entsteh.  d.  Bippursdure.      Hannover,  1866. 

4  Y?i^g<ix\  Archiv,  Bd.  ii.  {1869)  S.  367,  and  Bd.  IV.  (1871),  &  95. 


APP.]        CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  767 

probable  however  that  since  wines  and  fermented  liquors  contain  succinic  acid, 
and  this  latter  passes  uncliaiiged  ijito  the  urine,  that  it  may  thus  be  occasionally 
present  in  thU  excretion. 

Succinic  acid  crystallises  in  large  rhombic  tables,  also  at  times  in 
the  form  of  large  prisms  :  they  are  soluble  in  5  parts  of  cold  water 
and  2"2  of  boiling,  slightly  soluble  in  alcohol,  and  almost  insoluble  in 
aether.  The  crystals  melt  at  180°  C,  and  boil  at  235"  C,  being  at  the 
same  time  decomposed  into  the  anhydride  and  water.  The  alkali 
salts  of  this  acid  are  soluble  in  water,  insoluble  in  alcohol  and  oether. 

Preparation.  Apart  from  the  synthetic  methods,  it  may  readily 
be  obtained  by  the  fermentation  of  calcic  malate,  acetic  acid  being 
produced  simultaneously. 

Its  presence  is  recognised  by  the  microscopic  examination  of  its 
crystals,  and  its  characteristic  reaction  with  normal  lead  acetate.  With 
this  it  gives  a  precipitate,  easily  soluble  in  excess  of  the  precipitant, 
but  coming  down  again  on  warming  and  shaking'. 


CHOLESTERIN.     (C2CH44O.) 

This  is  the  only  alcohol  which  occurs  in  the  human  body  in  the 
free  state.  (The  triatomic  alcohol  glycerin  is  almost  always  found 
combined  as  in  the  fats  :  and  cetyl-alcohol,  or  asthal,  is  obtained  only 
from  spermaceti.)  It  is  a  white  crystalline  body,  crystallising  in  fine 
needles  from  its  solution  in  aether,  chloroform,  or  benzol  ;  from  its 
hot  alcoholic  solutions  it  is  deposited  on  cooling  in  rhombic  tables. 
When  dried  it  melts  at  145°,  and  distils  in  closed  vessels  at  360°.  It 
is  quite  insoluble  in  water  and  cold  alcohol  ;  soluble  in  solutions  of 
bile  salts. 

Solutions  of  cholesterin  possess  a  left-handed  rotatory  action  on 
polarised  light,  of  — 32'  for  yellow  light,  this  being  independent  of 
concentration  and  of  the  nature  of  the  solvent. 

Heated  with  strong  sulphuric  acid  it  yields  a  hydrocarbon  ;  with 
concentrated  nitric  it  gives  cholestcric  acid  and  other  products.  It  is 
capable  of  uniting  with  acids  and  forming  compound  jethers.  '' 

Cholesterin  occurs  in  small  quantities  in  the  blood  and  many 
tissues,  and  is  present  in  abundance  in  the  white  matter  of  the 
cerebro-spinal  axis  and  in  nerves.  It  is  a  constant  constituent  of 
bile,  forming  frequently  nearly  the  whole  mass  of  gall-stones.  It  is 
found  in  many  pathological  fluids,  hydrocele,  the  fluid  of  ovarial 
cysts,  &c. 

'  For  further  particulars  see  Mcissner,  op.  cit.,  and  Meissner  and  Solly, 
Zritschr.f.  rat.  Med.  (3)  Bd.  xxiv.  S.  97. 


768  COMPLEX   FATS.  [APP. 

Preparation.  From  gall-stones  by  simple  extraction  with  boiling 
alcohol,  and  treatment  with  alcoholic  potash  to  free  from  extraneous 
matter. 

As  tests  for  this  substance  may  be  given  : — With  conceitrated 
sulphuric  acid  and  a  little  iodine  a  violet  colour  is  obtained,  changing 
through  green  to  red.  This  is  applicable  to  the  microscopic  crystals. 
After  dissolving  in  sulphuric  acid  a  blood-red  solution  is  formed  on 
the  addition  of  chlorofomu,  changing  to  purple  and  finally  becoming 
colourless  ;  the  sulphuric  acid  under  the  chloroform  has  a  green 
fluorescence.  After  evaporation  to  dryness  with  nitric  acid  the  residue 
turns  red  on  treating  with  ammonia. 

This  body  is  described  here  rather  for  the  sake  of  convenience  than  from 
its  possessing  any  close  relationship  to  the  substances  immediately  preceding. 


Complex  Nitrogenous  Fats. 

Lecithin.     C44H9QNPO9. 

Occurs  widely  spread  throughout  the  body.  Blood,  bile,  and 
serous  fluids  contain  it  in  small  quantities,  while  it  is  a  conspicuous 
component  of  the  brain,  nerves,  yolk  of  egg,  semen,  pus,  white  blood- 
corpuscles,  and  the  electrical  organs  of  the  ray. 

When  pure,  it  is  a  colourless,  slightly  crystalline  substance,  which 
can  be  kneaded,  but  often  crumbles  during  the  process.  It  is  readily 
soluble  in  cold,  exceedingly  so  in  hot  alcohol ;  aether  dissolves  it 
freely  though  in  less  quantities,  as  also  do  chloroform,  fats,  benzol, 
carbon  disulphide,  &c.  It  is  often  obtained  from  its  alcoholic  solution. 
by  evaporation,  in  the  form  of  oily  drops.  It  swells  up  in  water,  and 
in  this  state  yields  a  flocculent  precipitate  with  sodium  chloride. 

Lecithin  is  easily  decomposed  ;  not  only  does  this  decomposition 
set  in  at  70°  C,  but  the  solutions,  if  merely  allowed  to  stand  at  the 
ordinary  temperature,  acquire  an  acid  reaction,  and  the  substance  is 
decomposed.  Acids  and  alkalis,  of  course,  effect  this  much  more 
rapidly.  If  heated  with  baryta  water  it  is  completely  decomposed, 
the  products  being  neurin,  glycerinphosphoric  acid,  and  barium 
stearate.     This  may  be  thus  represented  : — 

Lecithin.  Stearic  acid.        Glycerinphosphoric  j^^^ 

Acid. 
C44H9oNr09  +   3H2O  =.  2q8H3602    +     C3H9PO6     +      QH15NO2. 

When  treated  in  an  sethereal  solution  with  dilute  sulphuric  acid,  it 
is  merely  split  up  into  neurin  and  distearyl-glycerinphosphoric  acid. 


\1'P.]        CHEMICAL   BASIS   OF   THE   AxNlMAL    liODY.  769 

Hence  Diakonow  ■  rcjjards  lecithin  as  the  distcaryl-glycerinphosphate 
of  ncurin,  two  atoms  of  hydrogen  in  the  giyceiinphosphoric  acid  being 
eplaced  by  the  radicle  of  stearic  acid.  It  appears  also  that  there 
nobably  exist  other  analogous  compounds  in  which  the  radicles  of. 
:leic  and  palmitic  acids  take  part. 

Prepixration.  Usually  from  the  yolk  of  egg,  where  it  occurs  in 
jnion  with  vitellin.  Its  isolation  is  complicated,  and  the  reader  is 
eferred  to  Hoppe-Scyler^ 

GlyccrinphospJioric  acid.     CjHqPOq. 

Occurs  as  a  product  of  the  decomposition  of  lecithin,  and  hence  is 
ound  in  those  tissues  and  iliuids  in  which  this  latter  is  present  :  in 
eucha^mia  the  urine  is  said  to  contain  this  substance.  It  has  not 
Dcen  obtained  in  the  solid  form.  It  has  been  produced  synthetically 
Dy  heating  glycerin  and  glacial  phosphoric  acid ;  it  may  be  regarded 
as  formed  by  the  union  of  one  molecule  of  glycerin  with  one  of 
phosphoric  acid,  with  elimination  of  one  molecule  of  water.  It  is  a 
dibasic  acid ;  its  salts  with  baryta  and  calcium  are  insoluble  in 
alcohol,  soluble  in  cold  water.  Solutions  of  its  salts  are  precipitated 
by  lead  acetate. 

Protaoon.     C1C0H308N5PO35  (?) 

A  crystalline  body,  containing  nitrogen  and  phosphorus,  obtained 
by  Liebreich^  from  the  brain  substance  and  regarded  by  him  as  its 
principal  constituent.  The  researches  of  Hoppe-Seyler  and  Diakonow 
tended  to  shew  that  protagon  was  merely  a  mixture  ot  lecithin  and 
cerebrin.  A  repetition  of  Liebreich's  experiments  has  led  Gamgee 
and  Bhnkenhorn'*  to  confirm,  the  truth  of  his  results.  Protagon 
appears  to  separate  out  in  the  form  of  very  small  needles,  often 
arranged  in  groups,  from  warm  alcohol  by  gradual  cooling  :  it  is 
slightly  soluble  in  cold,  more  soluble  in  hot  alcohol,  and  aether.  It 
is  insoluble  in  water,  but  swells  up  and  forms  a  gelatinous  mass.  It 
melts  at  200"  C.  and  forms  a  brown  sirupy  fluid. 

Preparation.  Finely  divided  brain  substance,  freed  from  blood 
and  connective  tissue,  is  digested  at  45'  C.  with  alcohol  (85  p.  c.)  as 
long  as  the  alcohol  extracts  anything  from  it.  The  protagon  whi^h 
separates  out  from  the  filtrate  is  well  washed  with  a:ther  to  get  rid  of 

»  IToppe-Scyler's  Med.  ch,ni.  Un'c'such.  Heft  H.  (1S67)  S.  221,  Heft  III. 
(l?68)   S.  405.      O-ufrnlf'.f.  d.  vied.   M'iss.  (186S)  Nr.  1.  7  u.  2S. 

»  Med.  chem.  Unte-uich.  Heft  II.  (1S67)  S.  2 1 5. 

3  Ann.  d.  Client.  11.  Pliarni.  lid    134,  S    29. 

<  Zeilschr.  f.  physwl,  Chem.  Bd.  III.  11879)8.260,  a.n(l  JI.  of  Physiol. 
Vol.  II.  (1874)  p.  113. 

F.P.  49 


770  COMPLEX   FATS.  [APP. 

all  cholesterin  and  other  bodies  soluble  in  aether,  and  finally  purified 
by  repeated  crystallisation  from  warm  alcohol. 

jNcurin  (Cholin).     C5  H15NO2. 

Discovered  by  Strecker^  in  pig's-gall,  then  in  ox-gall.  It  does 
net  occur  either  in  the  free  state  or  apart  from  lecithin.  It  is  a 
colourless  fluid,  of  oily  consistence,  possesses  a  strong  alkahne  re- 
action, and  forms  with  acids  very  deliquescent  salts.  The  salts  with 
hydrochloric  acid  and  the  chlorides  of  platinum  and  gold  are  the 
most  important.  ■ 

Neurin  is  a  most  unstable  body,  mere  heating  of  its  aqueous  solution 
sufficing  to  split  it  up  into  glycol,  trimethylamin  and  ethylene  oxide. 

Preparation.     From  yolk  of  egg.     For  this  see  Diakonow.* 

Wurtz3  has  obtained  it  synthetically,  first  by  the  action  of  glycol  hydro- 
chloride on  trimethylamin,  and  then  by  that  of  ethylene  oxide  and  water  on 
the  same  substance.  The  above,  together  with  the  mode  of  its  decomposition, 
point  to  the  idea  that  neurin  may  be  regarded  as  trimethyl-oxyethyl-ammonium 
hydrate,  ]N(CH3)3(C2H50)OH. 

Crerebin.     C^;  H33  NO3  (?) 

Is  found  in  the  axis  cylinder  of  nerves,  in  pus  corpuscles,  and 
largely  in  the  brain.  In  former  times  many  names  were  given  to 
the  substance  when  in  an  impure  state,  ex.gr.  cerebric  acid,  cerebrote? 
&c.  W.  Miiller'^  first  prepared  it  in  the  pure  form,  and  constructed 
the  above  formula  from  his  analysis;  the  mean  of  these  is  O,  IS'^S- 
H,  1 1 '2.  N,  4'5.  C,  68"45.  Great  doubts  are  however  thrown 
upon  its  purity  by  the  researches  of  later  observers.  According  to 
Liebreich  ^  and  Diakonow^,  it  is  a  glucoside. 

Cerebrin  is  a  light,  colourless,  exceedingly  hygroscopic  powder, 
which  swells  up  strongly  in  water,  slowly  in  the  cold,  pidly  on  heat- 
mg.  When  heated  to  80°  it  turns  brown,  and  at  a  somewhat  higher 
temperature  melts,  bubbles  up  and  finally  burns  away.  It  is  insoluble 
in  cold  alcohol,  or  aether  ;  warm  alcohol  dissolves  it  easily.  Heated 
wit  1  dilute  mineral  acids,  cerebrin  yields  a  sugar-like  body,  possessing 
left-handed  rotation,  but  incapable  of  fermentation. 

Preparation.     For  this  see  W.  Miiller.^ 

'  Ann.  d.  Chem.  tc.  Pharm.  Bd.  123,  S,  353,  Bd.  148,  S.  76. 

^  Op.  cit.  (sub  Lecithin). 

3  Ann.  d.  Chem.  u.  Pha7-m.  Sup.  Bd.  6,  S.  1 16  u,  197. 

■4  Ann.  d.  Chem.  u.  Pharm.  Bd.  105,  S.  361. 

s  Arch.  f.  fathol.  Anat.  Bd.  39  (1S67). 

^  Cenlralb.f.  d.  med.  Wiss.,  1868,  Mr.  7, 

7  Op.  cit. 


API'.]        CHEMICAL   BASIS   OF   THE   ANIMAL   UODY.  771 

NITROGENOUS  METABOLITES. 
The  Urea  Group,  Amides,  and  similar  Bodies. 

Urea.     (NH,)XO. 

The  chief  constituent  of  normal  urine  in  mammalia,  and  some 
other  animals  ;  the  urine  of  birds  also  contains  a  small  amount. 
Normal  blood,  serous  fluids,  lymph  and  the  liver,  all  contliin  the 
same  body  in  traces.  It  is  not  found  in  the  muscles,  as  a  normal 
constituent,  but  may  make  its  appearance  there  under  certain 
pathological  conditions. 

When  pure  it  crystallises  from  a  concentrated  solution  in  the  form 
of  long,  thin  glittering  needles.  If  deposited  slowly  from  dilute 
solutions,  the  form  is  that  of  four-sided  prisms  with  pyramidal  ends  ; 
these  are  always  anhydrous.  It  possesses  a  somewhat  bitter  cooling 
taste,  like  saltpetre.  It  is  readily  soluble  in  water  and  alcohol,  the 
solutions  being  neutral.  In  anhydrous  aether  it  is  insoluble.  The 
crystals  may  be  heated  to  120*^  C.  without  being  decomposed  ;  at  a 
higher  teinpcrature  they  are  first  liquefied  and  then  burn,  leaving  no 
residue.  Heated  with  strong  acids  or  alkalis,  decomposition  ensues, 
the  final  products  being  carbonic  anhydride  and  ammonia.  The  same 
decomposition  may  also  occur  as  the  result  of  the  action  of  a  specific 
ferment  on  urea  in  an  aqueous  solution.'  Nitrous  acid  at  once  de- 
composes it  into  carbonic  anhydride  and  free  nitrogen.  It  readily 
forms  compounds  with  acids  and  bases  ;  of  these  the  following  are  of 
importance. 

Nitrate  of  urea.     ( N  H  2)2C  O  .  H  N  O  3. 

Crystallises  in  six-sided  or  rhombic  tables.  Insoluble  in  aether  and 
nitric  acid,  soluble  in  water,  slightly  soluble  in  alcohol. 

Oxalate  of  urea.     (  (NN2)2  C0)2  .  H.CoO^  +  H,,0. 

Often  crystallises  in  long  thin  prisms,  but  under  the  microscope  is 
obtained  in  a  form  closely  resembling  the  nitrate  ;  it  is  slightly  soluble 
in  water,  less  so  in  alcohol. 

With  mercuric  nitrate  urea  yields  three  salts,  containing  respec- 
tively 4,  3,  and  2  equivalents  of  mercury  to  one  of  urea.  The  first  is 
the  precipitate  formed  in  Liebig's  quantitative  determination  of  urea. 
The  e.\act  constitution  of  these  salts  has  not  yet  been  determined. 

*  MusculuF,  rfliige  's  Archiv,  Bd.  Xll.  (1876)  S.  214. 

49—2 


772  UREA.  [APP. 

Preparation.  Amnionic  sulphate  and  potassic  cyanate  are  mixed 
together  in  aqueous  solution,  and  the  mixture  is  evaporated  to  dryness. 
The  residue  when  extracted  with  absolute  alcohol  yields  urea.  From 
urine,  either  by  evaporating  to  dryness,  and  then  extracting  with 
alcohol,  or  concentrating  only  to  a  syrup,  and  then  forming  the  nitrate 
of  urea  ;  this  is  washed  with  pure  nitric  aciu  and  decomposed  with 
barium  carbonate. 

Detection  in  Solutions.  In  addition  to  the  microscopic  appearances 
of  the  crystals  obtained  on  evaporation,  tha  nitrate  and  oxalate  should 
be  formed  and  examined.  Another  part  should  give  a  precipitate  with 
mercuric  nitrate,  in  the  absence  of  sodic  chloride,  but  not  in  ths  pre- 
sence of  this  last  salt  in  excess.  A  third  portion  is  treated  with 
nitric  acid  containing  nitrous  fumes  ;  if  urea  is  present,  nitrogen  and 
carbonic  anhydride  will  be  obtained.  To  a  fourth  part  nitric  acid  in 
excess  and  a  little  mercury  are  added,  and  the  mixture  is  warmed. 
In  presence  of  urea  a  colourless  mixture  of  gases  (N  and  CO.,)  is 
given  off.  A  fifth  portion  is  kept  melted  for  some  time,  dissolved  in 
water,  and  cupric  sulphate  and  caustic  soda  are  added  ;  a  red  or  violet 
colour,  due  to  biuret,  is  developed. 

Urea  is  generally  considered  as  being  an  amide  of  carbonic  acid. 
Ths  amide  of  an  acid  is  formed  when  water  is  removed  from  the 
ammonium  salt  of  the  acid  ;  if  the  acid  be  dibasic  and  two  molecules 
of  water  be  removed,  the  result  is  often  spoken  of  as  a  diamide.  Thus 
if  from  ammonic  carbonate,  (NH4)9C03,  two  molecules  of  water, 
2H2O,  be  removed,  carbonic  acid  being  a  dibasic  acid,  the  result  is 
urea ;  thus  : 

(NH4)2C03-2Hs,0  =  (NH2),CO, 
which  may  be  written  either  according  to  the  ammonia  type,  as 

H2VN2         or  as         CO|^j.j^ 

two   atoms  of  amidogen  (NHg)    being  substituted  for  two  atoms  of 
hydroxyl  (HO). 

The  connection  between  carbonic  acid  and  urea  is  shewn  by  the 
fact  that  not  only  may  urea  be  formed  out  of  ammonium  cai-bainate  by 
dehydration,  but  also  ammonium  carbonate  may  be  formed  out  of 
urea  by  hydration,  as  when  urea  is  subjected  to  the  specific  ferment 
mentioned  above.  Regarded  then  as  a  diamide  of  carbonic  acid,  urea 
may  be  spoken  of  as  carbamide.  Kolbe  however  is  inclined  to  regard 
it,  not  as  the  diamide  of  carbonic  acid,  but  as  the  ami'le  of  carbamic 
acid.  Ammonium  carbamate  CO2N2HB,  minus  HgO,  gives  urea,  CO, 
N2,  H4 — which,  if  carbamic  acid  be  written  as  CO,  OH,  NH2,  may  be 
written  as  CO,  NHj,  NH2,  one  atom  of  amidogen  being  substituted  for 


APP.]         CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  773 

one  atom  of  hydroxy),  and  not  two,  as  when  the  substnnce  is  reg.irilcd 
as  derived  from  carbonic  acid.  For  the  bearing  of  this  difference  of 
dcrivUiou  sec  p.  451. 

Wanklyn  and  G  imgcc '  however,  since  urea  when  heated  with  a 
large  excess  of  potassium  permanganate  gives  off  all  its  nitrogen  in  a 
free  state  an'l  not  in  the  oxidized  form  of  nitric  acid,  as  do  all  other 
amides,  conclude  that  it  is  not  an  amide  at  all,  that  it  is  isomeric  only 
and  not  identical  with  carbamide. 

It   is   important    to   remember   that    urea   is   also   isomeric  with 

ammonium  cyanate,  C -j  ^.v,  „  ^nd  indeed  was  first  formed  artifi- 
cially by  Wohler  from  this  body.  We  thus  have  three  isomeric  com- 
pounds, ammonium  cyanate,  urea,  an  1  carbamide,  related  to  each 
other  in  such  a  way  that  urea  may  be  obtained  readily  either  from 
ammonium  cyanate  or  from  ammonium  carbamate,  and  may  with  the 
greatest  ease  be  converted  into  ammonium  carbonate.  Now  urea  is 
a  much  more  stable  body  than  ammonium  cyanate,  and  in  the  trans- 
formation of  the  latter  into  the  former,  enetgy  is  set  free  ;  and  it  is 
worthy  of  noti:e  that  though  the  presence  of  sulpho-cyanides  in  the 
saliva  probably  indicates  the  existence  of  cyanic  residues  in  the  body, 
the  nitrogenous  products  of  the  decomposition  of  proteids  belong 
chiefly  to  the  class  of  amides,  cyanogen  compounds  being  rare  among 
them.  Pfliiger*  has  called  attention  to  the  great  molecular  ener^jy  of 
the  cyanogen  compounds,  and  has  suggested  that  the  functional 
metabolism  of  protoplasm  by  which  energy  is  set  free  may  be  com- 
pared to  the  conversion  of  the  energetic  unstable  cyanogen  compounds 
into  the  less  energetic  and  more  stable  amides.  In  other  words, 
ammonium  cyanate  is  a  type  of  living,  and  urea  of  dead  nitrogen, 
and  the  conversion  of  the  former  into  the  latter  is  an  image  of  the 
essential  change  which  takes  place  when  a  living  proteid  dies. 

Compound  Ureas.  The  hydrogen  atoms  of  urea  can  be  replaced  by 
alcohol  and  acid  radicles.  The  results  are  compound  ureas.  Many  of  them 
are  called  acids,  since  the  hydrogen  from  the  amide  group,  if  not  all  replaced 
as  above,  can  he  replaced  hy  a  metal.  Thus  the  substitution  of  oxalyl  (oxalic 
acid)  gives  parabanic  acid, 

(CO 
No  \  Mj  or  CO,  NII2,  N .  Co0.j ; 
■  /  C.,0„ 

oftartronyl  (tartronic  acid),  diakiric  acid,  CO,  NII„,  N.CjHjOj'.of  mesoxalyl 
(mcsoxalic  acid),  alloxan,  CO,  NHj,  N  .  C;)03.  These  bodies  are  interesting 
as  being  also  obtained  by  the  artificial  oxidation  of  uric  acid. 


'  Jotirtt.  Chnn.  Soc.  2,  Vol.  vi,  p.  25. 
'  rnUger's  AnJiiv,  Bd.  X.  (1875)  S.  337. 


774  URIC  ACID.  [app. 

•Uric  acid.     C5H4N4O3. 

The  chief  constituent  of  the  urine  in  birds  and  reptiles  ;  it  occurs 
only  sparingly  in  this  excretion  in  man  and  most  mammalia.  It  is 
normally  present  in  the  spleen,  and  traces  of  it  have  been  found  in 
the  lungs,  muscles  of  the  heart,  pancreas,  brain  and  liver.  Urinary 
and  renal  calculi  often  consist  largely  of  this  body,  or  its  salts.  In 
gout,  accumulations  of  uric  acid  salts  may  o:cur  in  various  parts  of 
the  body,  forming  the  so-called  gouty  concretions. 

It  is  when  pure  a  colourless,  crystalline  powder,  tasteless  and 
without  odour.  The  crystalline  form  is  very  variable,  but  usually 
tends  towards  that  of  rhombic  tables.'  When  impure  it  crystalhses 
readily,  but  then  possesses  a  yellowish  or  brownish  colour.  In  water 
it  is  very  insoluble  (i  in  14,000  or  15,000  of  cold  water) ;  aether  and 
alcohol  do  not  dissolve  it  appreciably.  On  the  other  hand,  sulphuric 
acid  takes  it  up  without  decomposition,  and  it  is  also  readily  soluble 
in  many  salts  of  the  alkalis,  as  in  the  alkalis  themselves.  Ammonia 
however  scarcely  dissolves  it. 

Salts  of  Uric  acid.  Of  these  the  most  important  are  the  acid 
urates  of  sodium,  potassium,  and  ammonium.  The  sodium  salt 
crystallises  in  many  different  forms,  these  not  being  characteristic, 
since  they  are  almost  the  same  for  the  corresponding  compounds  of 
the  other  two  bases.  It  is  very  insoluble  in  cold  water  (i  in  1100  or 
1200),  more  soluble  in  hot  (i  in  125).  It  is  the  principal  constituent 
of  several  forms  of  urinary  sediment,  and  composes  a  large  part  of 
many  calculi ;  the  excrement  of  snaVes  contains  it  largely.  The 
potassium  resembles  the  sodium  salt  very  closely,  as  also  does 
the  compound  with  ammonium ;  the  latter  occurs  generally  in  the 
sediment  fi^om  alkaline  urine. 

Preparation.  Usually  from  guano,  or  snake's  excrement.  From 
guano  by  boiling  with  caustic  potash  (i  part  alkali  to  20  of  water)  as 
long  as  ammonia  is  evolved.  In  the  filtrate  a  precipitate  of  acid 
urate  of  potassium  is  formed  by  passing  a  current  of  carbonic  anhy- 
dride, and  this  salt  is  then  decomposed  by  excess  of  hydrochloric 
acid. 

The  presence  of  uric  acid  is  recognised  by  the  following  tests.  The 
substance  having  been  examined  microscopically,  a  portion  is  evapo- 
ra4:ed  carefully  to  dryness  with  one  or  two  drops  of  nitric  acid.  The 
residue  will,  if  uric  acid  is  present,  be  of  a  red  colour,  which  on  the 
addition  of  ammonia  turns  to  purple.  This  is  the  murexide  test,  and 
depends  on  the  presence  of  alloxan  and  alloxantin  in  the  residue. 
Schiff^  has  given  a  delicate  reaction  for  uric  acid.     The  substance  is 

'  See  Ultzmann  and  K.  B.  Hoffman,  Atlas  der  Harnsedimente,  Wien,  1872. 
-    "  A7in.  d.  Chem.  u.  Pharvt.  td.  109,  S.  65. 


API'.]        CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  7/5 

dissolved  in  sodic  carbonate,  and  dropped  on  paper  moistened  witli  a 
silver  salt.  If  uric  acid  be  present  a  brown  stain'  is  formed,  due  to 
the  redu;tion  of  the  silver  carbonate.  An  alkaline  solution  of  uric 
acid  can,  like  dextrose,  reduce  cupric  sulphate,  with  precipitation  of 
the  cuprous  oxide. 

Unlike  urea,  uric  acid  cannot  be  formed  artificially  ;  and  unlike 
urea  and  the  uroa  compounds,  it  resists  very  largely  the  action  of 
even  strong  acids  and  alkalis.  This  last  fact  would  seem  to  indicate 
that  urea  residues  do  not  pre-exist  in  uric  acid  ;  nevertheless  by  oxida- 
tion uric  acid  does  give  rise  not  only  to  ordinary  urea,  but  also,  and  at 
the  same  time,  to  the  compound  ureas  spoken  of  above.  Thus  by 
oxidation  with  acids. 

Uric  acid.  Alloxan.  Urea. 

CgH^N.Oa  +  H2O  +  O  =  C4N2H2O4  +  CNjHiO.    - 

Now  alloxan,  as  was  stated  above,  is  a  compound  urea,  viz. 
mesoxalyl-urea,  and  by  hydration  can  be  converted  into  mesoxalic 
acid  and  urea,  thus  : 

Alloxan.  Mesoxalic  acid.  Urea. 

C4N2H2O4  +  2H2O  =  C3H2O5  +  CN2H4O  ; 

and  by  the  action  of  chlorine  uric  acid  can  be  split  up  directly  into  a 
molecule  of  mesoxalic  acid  and  two  molecules  of  urea  : 

Uric  acid.  Mesoxalx  acid.  Urea. 

C5H4N4O3  +  CI.,  +  4H2O  =  C3H2O6  +  2CN2H4O  +  2HCI. 

By  oxidation  with  alkalis,  uric  acid  is  converted  into  allantoin  and 
carbonic  acid. 

Uric  acid.  Allantoin. 

QH4N,03  +  H2O  +  O  =  QHcN,03  +  CO2  ; 

and  allantoin,  by  hydration,  becomes  allanturic  or  lantanuric  acid 
and  urea, 

All.intoin.  Urea.  Allanturic  acid. 

C^HcN^Oa  +  Ho  O  =  CH^NoO  +  C3H4N.P. 

Now  allanturic  acid  is  a  compound  urea,  with  a  residue  of  glyoxylic 
acid.  By  other  oxidations  of  uric  acid,  parabanic  acid  (oxalyl-urea), 
oxaluric  acid  (which  is  hydrated  parabanic  acid),  and  dialuric  acid 
(tartronyl-urea)  are  obtained.  In  fact  all  these  decompositions  of  a 
molecule  of  uric  acid  lead  to  two  molecules  of  urea  and  a  carbon  acid 
of  some  kind  or  other. 

There  are  however  reasons  for  thinking  that  before  the  urea  can 
be  obtained  from  the  uric  acid  a  molecular  change  takes  place  ;  that 


'J']6  THE   UREA   GROUP.  [APP. 

part  of  the  nitrogen  of  uric  acid  exists  as  a  cyanogen  residue,  which 
on  the  sphtting  up  of  the  uric  acid  is  converted  into  the  same  condi- 
tion as  the  rest  of  the  nitrogen,  viz.  into  the  amide  condition.  It  has 
been  supposed  indeed  that  uric  acid  is  tartronyl  cyanamide,  in  which 
two  molecules  of  amidogen  have  been  replaced  by  the  radical  of 
tartronic  acid,  and  two  others  by  two  atoms  of  cyanogen,  thus  : 

rCsH^Os 

If  this  be  so,  since  the  metabolism  of  the  animals  in  which  uric  acid 
replaces  urea  cannot  be  supposed  to  be  fundamentally  different  from 
that  of  the  urea-producing  animals,  we  may  infer  that  the  antecedent 
of  both  uric  acid  and  urea  in  the  regressive  metabolism  of  proteids 
is,  as  we  suggested  above,  a  body  containing  some  at  least  of  its 
nitrogen  in  the  form  of  cyanogen, 

K}-eaiin.     C4H9N3O2. 

Occurs  as  a  constant  constituent  of  the  juices  of  muscles,  though 
possibly  it  may  be  formed  during  the  process  of  extraction  by  the 
hydration  of  kreatinin.  Kreatin  is  not  a  normal  constituent  of  urine, 
but  it  is  said  to  occur  in  traces  in  several  fluids  of  the  body.  When 
found  in  lyine  its  presence  is  probably  due  to  the  conversion  of 
kreatinin,  a  constant  constituent  of  urine,  into  kreatin  during  its  ex- 
traction, since  Dessaignes  ^  has  shewn  that  the  more  rapidly  the 
separation  is  effected,  the  less  is  the  quantity  of  kreatin  obtained,  and 
the  greater  the  amount  of  kreatinin. 

In  the  anhydrous  form  it  is  white  and  opaque,  but- crystallises  with 
one  molecule  of  water  in  colourless  transparent  rhombic  prisms.  It 
possesses  a  somewhat  bitter  taste,  is  soluble  in  cold,  extremely  soluble 
in  hot  water,  is  less  soluble  in  absolute  than  in  dilute  alcohol,  and  is 
insoluble  in  aether. 

It  is  a  very  weak  base,  scarcely  neutralising  the  weakest  aids.  It 
forms  crystalline  compounds  with  sulphuric,  hydrochloric  and  nitric 
acids. 

Preparation.  From  extract  of  muscle  by  precipitating  completely 
with  basic  lead  acetate,  and  crystallising  out  the  kreatin,  mixed  with 
kreatinin.  From  this  latter  it  is  separated  by  the  formation  of  the 
zinc-salt  of  kreatinin,  kreatin  not  readily  yielding  a  similar  compound. 

Kreatin  may  be  converted  into  kreatinin  under  the  influence  of  acids,  the 
transformation  being  one  of  simple  dehydration. 

'  y.  Pharm.  (3)  Bd.  xxxil.  S.  41. 


APP.]        CHEMICAL    BASIS   OF   THE   ANIMAL    BODY.  JTJ 

Kreatin  may  be  decomposed  into  sarcosin  (methyl-glycin)  and 
urea  : 

C4H,,Np,  +  H2O  =  C3H7NO2  +  CH4N2O  ; 
it   may  be   formed    synthetically '    by   the   action    of    sarcosin   and 
cyaaamide  : 

C3H7NO2  +  CH2N2  =  C4lIyN.,0. 

Sarcosin  is  glycin  in  which  one  atom  of  hydrogen  has  been  replaced 
by  the  alcohol  radical  methyl,  thus  : 

^,     .     C,H,0\^  ,  C2Hi,(CH3)0 1  ^ 

Glycin     LA     \0  becomes        mu  f^' 

like  glycin,  sarcosin  has  not  been  found  in  a  free  state  in  the  body. 

Kreatinin.     C4H7N3O. 

This,  which  is  simply  a  dehydrated  form  of  kreatin,  occurs  normally 
as  a  constant  constituent  of  urine  and  of  muscle  extract.  It  crystallises 
in  colourless  shining  prisms,  possessing  a  strong  alkahne  taste  and 
reaction.  It  is  readily  soluble  in  cold  water  (i  in  11  "5),  also  in  alcohol, 
but  is  scarcely  soluble  in  aether.  It  acts  as  a  powerful  alkali,  forming 
with  acids  and  salts  compounds  which  crystallise  well.  Of  these  the 
most  important  is  the  salt  with  zinc  chloride  (C4H7NjO)2ZnCI.u  It  is 
formed  when  a  concentrated  solution  of  the  chloride  is  added  to  a 
not  too  dilute  solution  of  kreatinin.  Since  the  compound  is  very  little 
soluble  in  alcohol,  it  is  better  to  use  alcoholic  rather  than  aqueous 
solutions.  It  crystallises  in  warty  lumps  composed  of  aggregated 
masses  of  prisms,  or  fine  needles. 

Preparation.  Either  by  the  action  of  acids  on  kreatin,  or  from 
human  urine  by  concentrating,  and  precipitating  with  lead  acetate  ; 
in  the  filtrate  from  this,  a  second  precipitate  is  caused  by  the  addi- 
tion of  mercuric  chloride,  and  consists  of  a  compound  of  this  salt 
with  kreatinin.  The  mercury  is  removed  by  sulphuretted  hydrogen, 
and  the  kreatinin  purified  by  the  formation  of  the  zinc  salt,  and 
washing  with  alcohol. 

Kreatinin-zinc  chloriie  may  be  converted  inlo  kreatin,  by  the  action  of 
hydrated  oxide  of  lead  on  its  boiling  aqueous  solution. 

Allantoin.     C4HQN4O3. 

The  characteristic  constituent  of  the  allantoic  fluid  of  the  foetus  ; 
it  occurs  also  in  the  urine  of  animals  for  a  short  period  after  their 
birth.  Traces  of  it  are  sometim.es  detected  in  this  excretion  at  a 
later  date. 

■  Sitzungsber.  d.  bayersch.  Akad.  1868,  lift.  3,  S.  472. 


7/8  THE   UREA   GROUP.  [APP. 

It  crystallises  in  small,  shining,  colourless  prisms,  which  are  taste- 
less and  odourless.  They  are  soluble  in  i6o  parts  of  cold,  more 
soluble  in  hot  water,  insoluble  in  cold  alcohol  and  sether,  soluble  in 
hot  alcohol.  Carbonates  of  the  alkalis  dissolve  them,  and  compounds 
may  be  formed  of  allantoin  with  metals  but  not  with  acids. 

Allantoin,  as  already  stated,  p.  653,  is  one  of  the  products  of  the 
oxidation  of  uric  acid,  and  by  further  oxidation  gives  rise  to  urea. 

Preparation.  This  is  best  done  by  the  careful  oxidation  of  uric 
acid  either  by  means  of  potassium  permanganate  or  ferrocyanide,  or 
by  plumbic  oxide. 

Hypoxanthin  or  Sarkin.     C5H4N4O. 

Is  a  normal  constituent  of  muscles,  occurring  also  in  the  spleen, 
liver,  and  medulla  of  bones.  In  leuch^mia  it  appears  in  the  blood 
and  urine.  It  crystallises  in  fine  needles  which  are  soluble  in  300 
parts  of  cold,  more  soluble  in  hot  water,  insoluble  in  alcohol,  soluble 
in  acids  and  alkalis.  It  forms  crystalline  compounds  with  acids  and 
bases.  It  is  precipitated  by  basic  acetate  of  lead,  the  precipitate  being 
soluble  in  a  solution  of  the  normal  acetate.  Its  preparation  from 
muscle-extract  depends  on  its  precipitation  first  by  basic  acetate  of 
lead,  and  then  by  an  ammoniacal  solution  of  silver  nitrate  after  the 
removal  of  kreatin. 

Both  hypoxanthin  and  the  next  body,  xanthin,  can  also  be  obtained  from 
proteids  by  the  action  of  putrefactive  changes,  of  water  at  boiling  temperature, 
of  dilute  hydrochloric  acid  ("2  p.  c.)  at  40°  C,  and  by  the  action  of  gastric  and 
pancreatic  ferments^.  Chittenden  has  noticed  a  peculiar  difference  between  fibrin 
and  egg-albumin  when  submitted  to  the  above  processes  ;  he  finds  that  the 
latter  does  not  yield  hypoxanthin  when  treated  with  boiling  water,  with 
dilute  hydrochloric  acid,  or  gastric  ferment,  while  the  former  does.  Egg- 
albumin  on  the  other  hand  yields  hypoxanthin  by  the  action  of  pancreatic 
ferment  in  alkaline  solution,  but  not  so  readily  as  fibrin  does. 

Xanthin.     C5H4N4O2. 

First  discovered  in  a  urinary  calculus,  and  called  xanthic  oxide. 
More  recently  it  has  been  found  as  a  normal,  though  scanty,  con- 
stituent of  urine,  muscles,  and  several  organs,  such  as  the  liver,  spleen, 
thymus,  &c. 

When  precipitated  by  cooling  from  its  hot,  saturated,  aqueous 
solution  it  falls  in  white  flocks,  but  if  the  solution  be  allowed  to 
evaporate  slowly  it  is  obtained  in  small  scales.     When  pure  it  is  a 

•  Salomon,  Zeitschr.  f.  physiol.  Chem.  Bd.  11.  (1878-1879),  S.  90.  Kranze, 
Inaug.  Diss.,  BerUn,  1878.  Chittenden,  Journ.  of  Physiol.  Vol.  11.  (1879), 
p.  28. 


Arr.j         CHEMICAL    BASIS    OF    THIi    ANIMAL    hu\)\.  779 

colourless  powder,  very  insoluble  in  water,  requiring  1500  times  its 
bulk  for  solution  at  100'' C.  Insoluble  in  alcohol  and  a.thcr,  it  readily 
dissolves  in  dilute  acids  and  alkalis,  foiining  crystalli--.able  compounds. 
Mypoxanthin  by  oxidation  becomes  xanthin.  Both  these  bodies^ 
as  well  as  the  following,  guanin  .^iid  carnin,  are  evidently  closely 
allied  to  uric  acid  ;  indeed,  uric  acid  by  the  action  of  sodium-amalgam 
may  be  converted  into  a  mixture  of  xanthin  and  hypoxanthin. 

Preparation.  It  is  obtained  from  urine  and  the  aqueous  extract  of 
muscle  by  a  process  similar  to  that  for  hypoxanthin,  and  is  then 
separated  from  the  latter  by  the  action  of  dilute  hydrochloric  acid  ; 
this  separation  depends  on  the  different  solubilities  of  the  hydro- 
chlorates  of  the  two  bodies.     For  further  information  see  Neubauer.' 

Carnin.     C7H8N4O3. 

Discovered  by  Weidel-  in  extract  of  meat,  of  which  it  constitutes 
about  one  per  cent. 

It  crystallises  in  white  masses  composed  of  very  small  irregular 
crystals  ;  it  is  soluble  witii  difficulty  in  cold,  more  easily  soluble  in  hot 
■water,  insoluble  in  alcohol  and  ?ether.  Its  aqueous  solution  is  not 
precipitated  by  normal  lead  acetate,  but  is  by  the  basic  acetate  of 
this  metal.  It  unites  with  acids  and  salts  forming  crystalline 
compounds. 

Preparation.  Is  found  in  the  precipitate  caused  in  extract  of 
meat  by  basic  acetate  of  lead.^ 

This  body  possesses  an  interesting  relation  to  hypoxanthin,  into  which  it 
may  be  converted  by  the  action  either  of  nitric  acid,  or  still  better,  of  bromine. 

Guanin.     CgHgNjO. 

First  obtained  from  guano,  but  recently  observed  as  occurring  in 
small  C[uantities  in  the  pancreas,  liver,  and  muscle  extract. 

It  is  a  white  amorphous  powder  insoluble  in  water,  alcohol, 
Ether  and  ammonia.  It  unites  with  acids,  alkalis  and  salts,  to  form 
crystallisable  compounds. 

Preparation.  From  guano  by  boiling  successively  with  milk  of 
lime  and  caustic  soda,  precipitating  with  acetic  acid,  and  purifying  by 
solution  in  hydrochloric  acid  and  precipitation  by  ammonia. 

Guanin  may,  by  the  action  of  nitrous  acid,  be  converted  into 
xanthin.     By  oxidation  it  can  be  made  to  yield   principally  guanidine 

'  Ham- Analyse,  Bd.  vii.  (1876)  S.  24. 

»  Anu.  li.  Clum.  u.  Pharm.  Bd.  158,  S.  365. 

3  Sec  Wfidcl,  op.  dt. 


7^0  AMIDES,   &C.  [a PP. 

and  parabanic  acid,  accompanied  however  by  small  quantities  of  urea, 
xanthin,  and  oxalic  acid. 

Its  separation  from  hypoxanthin  and  xanthin  depends  on  its 
insolubility  in  water  and  behaviour  with  hydrochloric  acid. 

Kynurenic  acid.     C2oHi4N20g  +  2H2O. 

Found  in  the  urine  of  dogs,  and  first  described  by  Liebig.'  When 
pure  it  crystallises  in  brilliant  white  needles,  insoluble  in  cold,  soluble 
in  hot  alcohol.  The  only  S3,lt  of  this  body  which  crystallises  well  is 
that  formed  with  barium.  For  preparation  and  other  particulars  see 
Liebig^  and  Schultzen  and  Schmiedeberg.^ 

Glycin.     C2H2(NH2)0(OH).    Also  called  Glycocoll  and  Glycocine. 

Does  not  occur  in  a  free  state  in  the  human  body,  but  enters  into 
the  composition  of  many  important  substances,  ex.  gr.  hippuric  and 
bile  acids.  It  crystallises  in  large,  colourless,  hard  rhombohedra, 
which  are  easily  soluble  in  water,  insoluble  in  cold,  slightly  soluble 
in  hot  alcohol,  insoluble  in  jether.  It  possesses  an  acid  reaction? 
but  a  sweet  taete.  It  has  also  the  property  of  uniting  with  both 
acids  and  bases  to  form  crystalhsable  compounds.  In  this  it  exhibits 
its  amide  nature,  and  that  it  is  an  amide  is  rendered  evident  from 
the  methods  of  its  synthetic  preparation  ;  thus  mono-chlor- acetic  acid 
and  ammonia  give  glycin  and  ammonium  chloride  : — C2H3CIO2  + 
2NH3  =  C2H2'NH2)0(OH)  -I-  NH4CI.  It  is  amido-acetic  acid. 
Heated  with  caustic  baryta  it  yields  ammonia  and  methylamine. 

Prepa7-ation.  From  glutin  by  the  action  of  acids  or  alkalis  ;  from 
hippuric  acid  by  decomposing  this  with  hydrochloric  acid  at  a  boiling 
temperature  and  removing  by  precipitation  the  simultaneously  formed 
benzoic  acid. 

Taurin.     CjH^NOgS. 

In  addition  to  entering  into  the  composition  of  taurocholic  acid 
(see  p.  786),  taurin  is  found  in  traces  in  the  juices  of  muscle  and  of 
the  lungs. 

It  crystallises  in  colourless,  regular,  six-sided  prisms  ;  these  are 
readily  soluble  in  water,  less  so  in  alcohol.  The  solutions  are  neutral. 
It  is  a  very  stable  compound,  resisting  temperatures  of  less  than 
240°  C.  ;  it  is  not  acted  on  by  dilute  alkalis  and  acids,  even  when  boiled 
with  them.     It  is  not  precipitated  by  metallic  salts. 

Taurin    is    amido-isethionic    acid ;     and    may    be    synthetically 

'  Ann.  d.  Chem.  u.  Phai-m,  Bd.  S6,  S.  125,  and  Bd.  108,  S.  354. 

^  up.  cit. 

3  Ann.  d.  Chem.  u.  Pharm.  Bd.  164,  S.  155. 


APP.J        CliDMlCAL   BASIS   OK   THE   ANIMAL   BODY.  78 1 

prepared    from    iscthionic    (cthyl-sulpliuric)   acid    by    the    action    of 
ammonia  ;    thus  : 

I.scthiunic  ac  d.         Amm  nia.  T.iurii. 

%"^}  SO,  +  NH3  =   ^?[|^}  so  +  n,o. 

Preparation.  As  a  product  of  the  decomposition  of  bile,  and  is 
purified  by  removing  any  traces  of  bile  acids  by  means  of  lead 
acetate,  and  then  successively  crystallising  from  water. 

Lettcin.     CqHijNOj. 

Is  one  of  the  principal  products  of  the  decomposition  of  nitro- 
genous matter,  either  under  the  influence  of  putrefaction  or  of  strong 
acids  and  alkalis.  It  occurs  however  normally  in  the  pancreas,  spleen, 
thymus,  thyroid,  salivary  glands,  liver,  &c.,  and  is  one  of  the  pro- 
ducts of  the  tryptic  (pancreatic)  digestion  of  proteids  ;  in  a:ute 
atrophy  of  the  liver  it  is  present  in  the  urine  in  large  quantity,  in 
company  with  tyrosin. 

As  usually  obtained  in  an  impure  form  it  crystallises  in  rounded 
lumps  which  are  often  collected  together,  and  sometimes  exhibit 
radiating  striation.  When  pure,  it  forms  very  thin,  white,  glittering 
flat  crystals.  These  are  easily  soluble  in  hot  water,  less  so  in 
cold  water  and  alcohol,  insoluble  in  aether.  They  feel  oily  to  the 
touch,  and  are  without  smell  and  taste.  Acids  and  alkalis  dissolve 
them  readily,  and  crystallisable  compounds  are  formed. 

Carefully  heated  to  170°  it  sul)linies,  hut  at  a  higher  temperature  is  decom- 
posed, yielding  amylamin,  carbonic  anhydride  and  am  nonia.  In  the  presence 
of  putrefying  animal  matter  it  splits  up  into  valeric  acid  and  ammonia  j  in  this 
it  exhibits  its  amide  nature. 

Leucin  is  amido-caproic  acid,  and  may  be  written  thus  : 


Preparation.  From  horn  shavings  by  boiling  with  sulphuric  acid, 
neutralising  with  baryta  and  separating  from  tyrosin  by  successive 
crystallsation.  Sec  also  Kijhne  ',  who  prepares  it  by  the  action  of 
pancreatic  ferments  on  proteids. 

Schercr  has  given  the  followmg  test  for  leu:in.  The  suspected 
substance  is  evaporated  carefully  to  dryness  with  nitric  acid  ;  the 
residue,  if  it  is  leucin,  will  be  almost  transparent  and  turn  yellow  or 
brown  on  the  addition  of  caustic  soda.  If  heated  again  with  the 
alkali  an  oily  drop  is  obtained,  which  is  quite  chara.teristic  of  this 
substance.     Leucin,  if  not  too  impure,  may  be  easily  recognised  by  its 

'  Virchow's  Arc/iw,  Bd.  39,  S.  130. 


782  THE   AROMATIC   SERIES.  _  [APP. 

subliming  on  being  heated ;  a  characteristic  odour  of  amylamin  is  at 
the  same  time  evolved. 

Cystin.     C3H7NSO2. 

Is  the  chief  constituent  of  a  rarely  occurring  urinary  calculus  in 
men  and  dogs.     It  may  also  occur  in  renal  concretions,  and  in  gravel. 

From  calculi  it  is  obtained,  by  extractiori  with  ammonia,  as 
colourless  six-sided  tables  or  rhombohedra,  v^^hich  are  neutral  and 
tasteless.  It  is  insoluble  in  water,  alcohol  and  aether,  soluble  in 
ammonia  and  the  other  alkalis,  and  also  in  mineral  acids.  The  fact 
that  this  body  is  one  of  the  few  crystalline  substances,  occurring 
physiologically,  which  contain  sulphur,  renders  its  detection  very 
easy.  Apart  from  its  insolubility  in  water,  &c.,  it  yields  with  caustic 
potash  and  salts  of  either  silver  or  lead,  a  brown  coloration  due  to 
the  presence  of  the  sulphides  of  these  metals. 

According  to  Dewar  and  Gamgee'  cystin  is  amido-sulpho-pyruvic  acid,  and 
its  formula  is  C3H5NSO2 — pyruvic  being  lactic  acid  minus  two  atoms  of 
hydrogen. 


The  Aromatic  Series. 


Benzoic  acid.     HC^H^Og. 

This  is  not  found  as  a  normal  constituent  of  the  body,  but  owes 
its  presence  in  urine  to  the  decomposition  of  hippuric  acid,  whereby 
glycin  and  benzoic  acid  are  formed  : 

Hippuric  acid.  Glycin.  Benzoic  acid. 

C2H4(QH50)N02+  H2  O  =  C2H5NO2  +  QHeO^. 

The  sublimed  acid  is  generally  crystallised  in  fine  needles,  which 
are  light  and  glistening  ;  any  odour  they  possess  is  not  due  to  the 
acid,  but  to  an  essential  oil,  with  which  they  are  mixed.  When  pre- 
cipitated from  solution,  the  crystalline  form  is  always  indistinct.  This 
acid  is  soluble  in  200  parts  cold,  or  25  parts  of  boiling  water,  but  is 
easily  soluble  in  alcohol  or  aether.  It  sublimes  readily  at  145°  C.  ;  it 
also  passes  off  in  the  vapours  arising  from  its  heated  solutions. 

P7'epa7-ation.  Either  as  above  from  hippuric  acid  by  fermentation, 
or  the  action  of  hydrochloric  acid,  or  by  sublimation  from  gum- 
benzoin. 

'   jfourn,  of  Anat.  and  Physiol, ,  Nov,  1870,  p.  143. 


Al-P.]         CHEMICAL    UASIS    OV    THE    ANIMAL    BODY.  783 

Tyrosin.     CjHuNOj. 

Generally  accompanies  leucin,  and  is  perhaps  found  normally  in 
small  quantities  in  the  pancreas  and  spleen.  It  is  also  usually 
obtained  in  large  quantities  by  the  decomposition  of  proteid  matter, 
either  by  putrefaction  or  the  action  of  acids. 

The  researches  of  RadziejewsUy'  render  it  probable  that  tyrosin  does  not 
occur  normally  in  any  part  of  the  human  organism,  except  as  a  product  of 
pancreatic  digestion. 

It  crystallises  in  exceedingly  fine  needles  which  are  usually  collected 
into  feathery  masses.  The  crystals  are  snow-white,  tasteless  and 
odourless,  almost  insoluble  in  cold  water,  readily  soluble  in  hot  water, 
acids  and  alkalis,  insoluble  in  alcohol  and  aither.  If  crystallised  from 
an  alkaline  solution  tyrosin  often  assumes  the  form  of  rosettes  com- 
posed of  fine  needles  arranged  radiately. 

Tyrosin  does  not  sublime  by  heating,  but  is  decomposed  with  an 
odour  of  phenol  and  nitrobenzol.  On  boiling  with  MiUon's  reagent 
it  gives  a  reaction  almost  identical  with  that  for  proteids  (Hoffmann's 
lest);  Treated  with  strong  sulphuric  acid  and  gently  warmed,  it 
yields,  on  the  addition  of  chloride  of  iron,  a  violet  colour  (Piria's 
test). 

Tyrosin  is  an  ammonia  compound  belonging  to  the  aromatic 
(benzoic)  series. 

Preparatioi.  By  means  similar  to  those  employed  for  leucin,  the 
separation  of  the  two  depending  on  their  solubilities.  According  to 
Kiihne's  fncthod''  large  quantities  are  easily  obtained  as  the  result  of 
pancreatic  digestion.     It  has  not  yet  been  formed  synthetically. 

Hippitric  acid.    CgHgNOs.  Or  Benzoyl-glycin.    C2H4(QH50)N02. 

Is  found  is  considerable  quantities  in  the  urine  of  herbivora,  and 
also,  though  to  a  much  smaller  amount,  in  the  urine  of  man.  It  is 
formed  in  the  body  by  the  union  with  dehydration  of  glycin  and 
benzoic  acid,  see  p.  453. 

Crystallised  from  a  saturated  aqueous  solution,  it  assumes  the  form 
of  fine  needles  ;  if  from  a  more  dilute  solution,  white,  semi-trans- 
parent four-sided  prisms  are  obtained.  These  when  pure  are  odour- 
less, with  a  somewhat  bitter  taste.  They  are  soluble  in  600  parts  01 
cold  water,  readily  soluble  in  alcohol,  less  so  in  ajthcr.  All  the  solu- 
tions redden  litmus. 

Hippuric  acid  is  monobasic,and  forms  salts  which  are  readily  soluble 

'  Archivf.  path.  Anal.  Bd.  %6,  S.  i.  Zeitsch.  f.  anal.  Chan.  Bd.  5, 
S.  466. 

'  Op.  cit.  (sub  Leucin). 


784  THE   AROMATIC   SERIES.  [APP. 

in  water  (except  the  iron  salts)  ;  from  these,  if  in  sufficiently  concen- 
trated solutions,  excess  of  hydrochloric  acid  precipitates  the  acid  in 
fine  needles.  When  heated  with  concentrated  mineral  acids  it  is 
resolved  into  benzoic  acid  and  glycin.  The  same  decomposition 
occurs  in  presence  of  putrefying  bodies.  Strong  nitric  acid  produces 
an  odour  of  nitrobenzol. 

Preparation.  Fresh  urine  of  horses  or  cows  is  boiled  with  milk 
of  lime,  filtered,  and  the  filtrate  evaporated  to  a  small  bulk ;  the 
hippuric  acid  is  then  precipitated  by  adding  an  excess  of  hydrochloric 
acid. 

When  heated  in  a  small  tube,  hippuric  acid  gives  a  sublimate  of 
benzoic  acid  and  ammonium  benzoate,  accompanied  by  an  odour  like 
that  of  new  hay,  while  oily  red  drops  are  observed  in  the  tube.  This 
is  very  characteristic,  and  distinguishes  it  from  benzoic  acid. 

Phenylic  {Carbolic)  acid.     CgHyO, 

This  acid  occurs  only  as  a  urinary  constituent.  According  to  the 
older  view  it  was  a  normal  constituent  of  this  excretion  ;  it  seems, 
however,  more  probable  that  it  is  due  to  some  decomposition  occurring 
in  the  urine,  by  the  processes  requisite  for  its  isolation. 

Buligin>ky'  says  the  urine  of  many  animals,  of  cows  and  horses  always, 
contains  a  substance  insoluble  in  alcohol,  and  not  precipitated  by  lead  acetate 
and  ammonia,  which  by  the  action  of  dilute  mineral  acids  gives  carbolic  acid. 
The  same  acid  applied  to  the  body  exteroally  or  internally  also  passes  into  the 
urine^  Similarly  benzol  (CgHg)  when  taken  into  the  stomach  appears  as 
carbolic  acid  in  the  urines. 

The  pure  acid  crystallises  in  long,  colourless  prismatic  needles  ; 
they  melt  at  35°  C,  and  boil  at  180°  C.  It  is  readily  soluble  in 
alcohol  and  jether,  slightly  soluble  in  water  (i  part  in  20).  In  most 
cases  it  acts  as  a  weak  acid,  forming  crystalline  salts  with  the  alkalis. 
With  nitric  acid  it  yields  picric  acid.  Its  solutions  reduce  silver  and 
mercury  salts. 

Preparation.  By  the  dry  distillation  of  salicylic  acid,  als  3  from 
the  acid  products  of  the  distillation  of  coal. 

'  Hop]3e-Seyler,  Med.  chem.  Unterstcch.  Heft  2  (1867),  S.  234. 

^  Almen,  Neues  Jahrb.  d.  Pharm.  Ed.  34,  S.  III.  Salkowt,ki,  Pfliiger's 
Archiv,  Bd.  v.  (1871-72)  S.  335. 

3  Schultzen  and  Naunyn,  Keichert  u.  .Du-Bois  Reymond's  Archtv,  1867, 
Heft  3,  S.  349. 


APP.J        CHEMICAL   BASIS   OF   TIIK    ANIMAL    BODY. 


/o? 


The  Bile  Series. 

Cholic  {or  Cholalic)  acid.     H.CoiHg^Oj  +  HjO. 

Occurs  in  traces  in  tha  small  intestine,  in  larger  quantities  in  the 
contents  of  the  large  intestine,  and  the  excrements  of  men,  cows,  and 
dogs.  In  icterus,  the  urine  often  contains  traces  of  this  acid.  But  its 
principal  interest  lies  in  its  being  the  starting  point  for  the  various 
bile  acids  (see  below).  The  pure  acid  may  be  amorphous,  or  crystal- 
line, in  the  latter  case  crystallising  from  hot  alcoholic  solutions  in 
tetrahedra.  These  crystals  are  insoluble  in  water  and  aether.  In  the 
amorphous  form,  it  is  somewhat  soluble  in  water  and  a;ther.  Heated 
to  2oo~  C,  it  is  converted  into  water  and  dyslysin  (C,4H^.j0.j). 

This  acid  possesses,  in  the  anhydrous  condition,  a  specific  rotatory 
power  of  +  50'  for  yellow  light  :  when  it  crystallises  with  HoO,  the 
rotation  is  -|-  35°.  The  rotatory  power  of  the  alkali  salts  is  always  less 
than  the  above,  and  when  in  solution  in  alcohol,  the  rotation  is  inde- 
pendent of  the  concentration.  For  the  alcoholic  solution  of  the  sodium 
salt  the  rotation  is  4-  3r4'. 

Preparation.  By  the  decompositions  of  bile  acids  by  means  of 
acids,  alkalis,  or  fermentative  changes. 

Bayer'  has  recently  examined  the  bile  acids  obtained  from  human  bile,  and 
has  prepared  from  them  cholalic  acid.  To  this  he  assigns  the  formula 
CigHogO^.  If  this  be  so,  then  cholalic  acid  of  huuian  bile  would  seem  to 
be  a  body  entirely  different  from  that  obtained  from  ox  bile,  and  analysed  by 
Strecker.     Bayer's  results  however  require  further  confirmation. 

Pettenkofer's  test. 

This  well-known  test  for  bile  acids  depends  on  the  reaction  of 
cholalic  acid  in  presence  of  sugar  and  sulphuric  acid  If  to  a  solution 
of  the  acid  a  little  sugar  be  added,  and  then  sulphuric  acid,  keeping 
the  temperature  below  but  not  much  below  70"  C,  a  beautiful  reddish 
purple  is  obtained.  This  gives  a  characteristic  spectrum  with  two 
absorption  bands,  one  between  D  and  E,  nearest  to  E,  the  other  close 
to  F  on  the  red  side  of  F. 

Protcids,  and  other  bodies  easily  decomposed  by  sulphuric  acid  such 
as  amyl-alcohol,  give  a  similar  coloration,  and  the  reaction  is  much 
impeded  by  the  presence  of  colouring  matters-. 

»  Zeitschr.  f.  phyiiol.  Chem.  Bd,  ll.  (1878-79)  S.  35S. 

*  For  further  information  on  this  subject  see  :  liischotT,  Zeitsch.  f.  rat,  Mtd. 
Ser.  3,  Bd.  21,  S.  126.  Schenk,  Anatom.  physiol.  Untcrstich.  Wien,  1S72, 
S.  47- 

F.  P.  50 


y^6  THE   BILE   SERIES.  [APP. 

Glycocholic  acid.     C26H43NO6.  * 

This  is  the  principal  bile-acid  of  ox-gall  ;  it  is  also  present  in  the 
bile  of  man,  but  has  so  far  not  been  observed  in  that  of  carnivora.  In 
icterus,  the  urine  may  contain  traces  of  this  acid. 

It  crystallises  in  fine,  glistening  needles.  These  are  slightly 
soluble  in  cold  water ;  readily  so  in  hot  watar  and  alcohol  ;  insoluble 
in  3sther.  They  possess  a  bitter  and  yet  sweet  taste,  and  a  strong 
acid  reaction. 

The  salts  of  this  acid  are  readily  soluble  in  water  and  crystallise 
well.  The  salts,  as  well  as  the  free  acid,  exert  right-handed  polarisa- 
tion amounting  to  +29-0°  for  the  acid,  and  -+-257°  for  the  sodium 
salt,  both  measured  for  yellow  light. 

Glycochohc  acid  is  a  compound  of  glycin  and  cholalic  acid  ;  thus  : 

Cholalic  acid.  Glycin.  Glycocholic  acid. 

C24H40O5+  C2NH502-H20  =  C26H,3N06. 

Prolonged  boiling  with  dilute  mineral  acids  or  caustic  alkalis  decomposes 
this  body  into  glycin  and  cholic  acid ;  if  dissolved  in  concentrated  sulphuric 
acid  and  then  warmed,  one  molecule  of  water  is  removed,  and  cholonic  acid 
obtained,  C2gH4iN05,  The  barium  salt  of  this  last  acid  is  insoluble  in  water, 
which  fact  is  of  importance,  since  cholonic  acid  possesses  nearly  the  same 
specific  rotatory  power  as  glycocholic. 

Preparation.  From  ox-gall,  by  evaporating  to  a  syrup,  decolorising 
with  animal  charcoal,  extracting  with  strong  alcohol,  and  precipitating 
by  a  large  excess  of  aether.  Its  separation  from  taurocholic  acid 
depends  on  the  precipitation  of  its  solution  by  normal  lead  acetate. 

Taurocholic  acid.     C26H45NSO7. 

Occurs  also  in  ox-gall,  but  is  found  especially  plentiful  in  human 
bile  and  that  of  carnivora. 

It  has  not  yet  been  obtained  in  the  crystalline  form,  although  its 
salts  crystallise  readily.  When  dried  it  is  an  amorphous  powder, 
with  pure  bitter  taste,  easily  soluble  in  water  and  alcohol,  insoluble  in 
aether.  All  its  salts  are  soluble  in  water,  and  are  precipitated  by  basic 
lead  acetate  only  in  the  presence  of  free  ammonia.  The  sodium  salt 
dissolved  in  alcohol  has  a  specific  rotatory  power  of  -j-  24'5°  ;  if  dis- 
solved in  water  this  rotation  is  less,  and  in  this  respect  it  resembles 
glycocholic  acid. 

This  acid  is  far  more  unstable  than  the  preceding  one,  being 
decomposed  if  boiled  with  M'ater.  The  products  of  decomposition  are 
taurin  and  cholalic  acid. 

'  Neubaneru.  Vogel,  Ham- Analyse,  Ed.  Vll.  (1876)  S.  97. 


APP.]        CHEMICAL   BASIS   OF   THE   ANIMAL   BODY.  787 

Taurocholic  acid  is  a  compound  of  taurin  and  cholalic  acid  ;  thus: 

Cholalic  acid. '  Taurin.  T.iurocholic  acid. 

CjiH^oOs  +  C2H7NO3S-  Hi,0  =  C2„H^5NO;S. 

Preparation.  From  the  gall  of  dogs  by  a  process  similar  to  that 
for  glycocholic  acid.  It  is  separated  from  traces  of  this  latter  and 
from  cholic  acid  by  preparation  with  basic  lead  acetate  and  ammonia. 


The  Indigo  Series. 
Indicaii. 

There  often  occurs '  in  the  urine  and  sweat  of  men  and  animals  a 
certain  substance  which  has  not  yet  been  satisfactorily  isolated,  but 
which  yields  by  the  action  of  acids  the  blue  colouring  matter  indigo  as 
one  product  of  the  decomposition.  A  similar  substance  is  found  in 
several  plants  (Indigo-fera,  Isatis),  and  the  two  were  considered  by 
Schunck  to  be  identical.  Hoppe-Seyler  -  on  the  other  hand,  having 
regard  to  the  greater  ease  with  which  the  indican  from  plants  under- 
goes decomposition,  regards  them  as  most  probably  different  sub- 
stances. Baumann  shewed  3  that  the  two  were  really  different,  and 
has  confirmed  his  previous  results  in  a  recent  publication-*.  According 
to  him,  the  indican  obtained  from  urine  is  not  a  glucoside  (so  also 
Hoppe-Seyler)  and  yields  sulphuric  acid  by  the  action  of  hydrochloric 
acid.     He  assigns  to  it  the  formula  KCgHcNSO^. 

Indican  appears  in  urine,  according  to  Jaffe  and  other  observers, 
as  the  result  of  the  presence  of  indol  in  the  alimentary  canal. 

It  is  always  estimated  by  conversion  into  indigo. 

Indigo.     C3H5N9O. 

It  is  formed,  as  stated  above,  from  indican,  and  gives  rise  to  the 
bluish  colour  sometimes  observed  in  sweat  and  urine. 

It  may,  by  slow  formation  from  indican,  be  obtained  in  fine 
crystals  ;  these  are  insoluble  in  water,  slightly  soluble  with  a  faint 
violet  colour  in  alcohol  and  a:!ther.  Chloroform  also  dissolves  them  to 
a  slight  extent.  Indigo  is  soluble  in  strong  sulphuric  acid,  forming  at 
the  same  time  two  compounds  with  this  acid  ;  these  are  soluble  in 
water.     It  possesses  a  pure  blue  colour  ;  when  pressed  with  a  hard 

'•Schunck, /'/4j7.  Ma^.VoX.  x.  p.  73;  xiv.  p.  228;  xv.  pp.  29,  117, 
183.  Chan.  Centralb.  1S56,  S.  50  ;  1S57,  S,  957  ;  1858,  S.  225.  Hoppe- 
Seyler,  Arch.  f.  path.  Anat.  Bd.  xxvii.  S.  388.  Jafle,  Pfluger's  y4r<-A.  Bd. 
III.  (1870)  S.  44S. 

=  Hatidb.  d.  path.  chem.  Anal.  Ed.  IV.  (1875)  S.  191. 

3  Pllugcrs  Arch.  Bd,  XIII.  (1876)  S.  301.  Zcitschr.f.  phystol.  Chem.  Bd. 
I.  (1877-78)  S.  60. 

*  Zeitschr.  f.  physiol.  Chem.  Bd.  III.  (1879)  S.  254. 

^  50 — 2 


^88  THE   INDIGO   SERIES.  [APP. 

body  a  reddish  copper-coloured  mark  is  left,  and  the  crystals  exhibit 
the  same  colour  if  seen  in  reflected  light. 

The  soluble  compounds  with  sulphuric  acid  give  an  absorption 
band  in  the  spectrum  which  lies  close  to  the  D  line  and  to  the  rei 
side  of  it.     This  may  be  used  to  detect  indigo. 

Treated  with  reducing  agents,  indigo  is  decolorised;  being  reduced 
to  indigo-white.  The  latter  contains  two  atoms  more  hydrogen  than 
indigo. 

Indol     CgHyN. 

To  this  body  the  specific  odour  of  the  f^ces  is  partly  due.  It  is 
obtained  as  the  final  product  of  the  reduction  of  indigo;  and  also  by 
the  distillation  of  proteid  matter  with  caustic  alkalis. 

It  often  occurs  among  the  products  of  the  action  of  pancreatic 
ferment  on  proteids  ;  its  presence  in  such  cases  appears  however  to  be 
due,  not  to  the  action  of  the  trypsin,  but  to  a  simultaneous  putrefaction 
under  the  influence  of  bacteria,  etc'.  If  the  pancreatic  digestion  be 
carried  on  in  the  presence  of  sahcylic  acid,  indol  does  not  make  its 
appearance  ;  see  p.  261.  Indol  gives  a  characteristic  red  colour  with 
nitrous  acid. 

Skatol.  Noticed  by  Brieger'  as  one  of  the  products  of  the  action 
of  putrefactive  changes  in  the  small  intestine.  Secretans  had  pre- 
viously described  a  similar  substance  as  arising  from  the  putrefaction 
of  albumin. 

Skatol  is  crystalline  and  contains  nitrogen  ;  it  is  more  soluble  in 
water  than  indol  and  does  not  give  rise  to  any  red  coloration  with 
nitrous  acid.     No  formula  has  as  yet  been  assigned  to  it. 

Skatol  readily  passes  into  the  urine  when  it  occurs  in  the  ali- 
mentary canal,  and  then  gives  a  violet-red  reaction  with  strong 
hydrochloric  acid. 

v.  Nencki-*  prepares  this  substance  by  the  putrefaction  of  a  mixture 
of  finely  divided  pancreas  and  muscle  substance.  After  the  addition 
of  acetic  acid  the  mass  is  distilled,  when  the  skatol  readily  passes 
over.  From  the  distillate  it  is  precipitated  by  picric  acid,  and  the 
precipitate  when  again  distilled  with  ammonia  gives  off  pure  skatol 
which  may  be  finally  purified  by  crystallisation. 

'  Kiihne,  Verhand.  d.  Heidlb.  naturhist.   tned.  Ver.  N.S.    Bd.  I.  Hft.  3 
Bericht.  d.  Daitschen  chem.  GeseUschaft,  1875,  S.  206. 

'  Ber.  d.  Deutsch.  chcm.  GeselL,  Jahrg.  X.  (1877)  S.  1027. 
3  Recherches  sur putrefaction  de  Valbumine.     Geneva,  1876. 
*  Centralb.f.  d  wed.  Wiss.,  1878,  S.  849. 


INDEX. 


I  N  D  E  X. 


Aberration,  spherical,  of  the  eye,  525 

Absorption  by  the  skin,  405 

Absorption  of  products  of  digestion,  316 — 
328 

Absorption  of  food  by  diffusion,  326 

Accelerating  fibres,  133 

Acrclcrat  ir  nerves,  194,  200,  233 

Accommodati  n,  power  of,  in  the  eye,  317 

Acetic  ac.d,  758 

Achro  dextrin,  241,  436 

Acid-albumin,  730,  747 

Acidity  of  urine,  410 

Acids,  decomposition  of  proteids  by,  744 

Acids  in  perspiration.  400 

Aousiic  apparatus  of  the  ear,  575 

Adami'K  on  the  bra.n,  657 

Adipose  tissue  (See  Fat) 

Afferent  impulses,  129,  130,  193,  599  ;  of 
vaso-motor  action,  207,  210,  211  ;  of  de- 
glutition, 295  ;  in  respiration,  369 ;  in 
micturition,  419  ;  nerves  conveying,  499 

After-images  of  vi>ion,  551 

Air,  tidal,  stationary  and  residual,  in  respira- 
tion, 310;  its  changes  in  respiration,  335, 
388  :  effects  of  an  increased  supply  of.  392  : 
effects  of  changes  in  the  composition  of, 
394  ;  effects  of  changes  in  the  pressure 
of,  .194 

Aladoff  on  di.abetes,  434 

Albertoni,  the  brain,  644 

Albumin,  action  of  gastric  juice  on,  247 

Albumins,  728,  747 

Albumin.ates,  730 

Alimentary  canal,  239  ;  changes  of  food  in 
the,  307—316 

Alimentary  mechanism,  8 

Alkali-albumin,  731,  748 

Alkaline  urine  •  f  herbivora,  410 

Allantoic  vessels,  696 

AUantoin,  775,  778 

Ammonia  in  expired  air,  343 

Amoeba;,  properties  of,  292,  319 

Amylolyiic  action  of  pancreatic  juice,  258; 
of  saliva.  242,  285 

Analysis,  of  perspiration,  399;  of  the  com- 
posi;ion  of  the  animal  body,  454,  707 

Anelcctrotonus,  93 

Aneurism,  26 

Animal  body,  chemical  basis  of  the,  725 

Antipeptone,  262 

Antiperistaltic  action,  298 


Anus,  302 

Aorta,  pressure  in,  163 

Aortic  valves,  166 

Apnoea,  21)7,  392 

Appreciati  m  of  apparent  size,  557 

Arterial  blo)d,  344,  353,  358,  360,  375,  381 

Arterial  pulse.  (Sc-e  Pulse) 

Arteries,  137,  139,143.  147,  151,  153,  154; 
contractility  and  dilation  of,  200,  267; 
renal.  412 

Artificial  diabetes,  433 

Ascending-  aorta,  pulse-wave  in,  179 

Asphyxia,  297,  334.  371,  388,  390,  394 

Aspirates  (voice),  680 

Astigmatism,  526 

Atr.pm,  its  effects,  190,  524 

AuBEKT  on  cutaneous  respiration,  401 

Auditory  sensations,  577 

AuEivBACH.  nervous  plexus  in  the  intestines, 
128  ;  peristaltic  movements  in  digestion, 
297 

Augmenting  fibres,  133 

Auricles,  blood-pressure  in,  161 

Auriculo-ventricle  valves,  164 

Automatic  action,  2,  124,  126,  128,  193;  of 
peristaltic  m  )vemc:nts,  296  ;  ( f  the  re- 
spiratory centre,  370  ;  the  spinal  cord  as  a 
centre  of  thi-;  action,  610 

Automatic  tissues,  6 

Axillary  arterj'  of  the  tortoise,  its  con- 
tractility, 202 


Bacteria,  313,  31s 

Balogh,  cerebral  convolutions,  640 

Banting's  dietetic  system.  <j65 

Bat,  movement  of  veins  in  its  wing,  aoa 

Bauer,  absorption  of  products  of^digestion, 

316 
Baxt,     cardiac     accelerator    nerves,    19  j ; 

velocity  of  nervous  impulses,  504 
Beat  of  the  heart  {See  Heart-beat) 
Beau.mo.nt,  Dr.,    researches  on  digestion, 

3"8,  317 
Bechbk,  on  respiration,  342,  362 
Bed-sores,  489 
Bec<,  temperature  of,  478 
Behaviour  of  brainless  anim.als,  599.  609 
Bell,   Sir   Chas. ,   roots  of  spinal  nerres, 

500  ;  motor  and  sensory  fibres,  670 
Benzoic  acid,  78a 


792 


INDEX. 


Bernard,  Claude,  on  the  '  internal  me- 
dium,' 14 ;  section  of  the  cervical  sym- 
pathetic, 223,  235  ;  pancreatic  juice,  258  ; 
secretin  n  of  saliva,  267  ;  mechanism  of 
digestive  Recretion,  269,  274 ;  digestion, 
314,  328;  haemogljbin,  355;  cutaneous 
secretion,  403 ;  glycogen,  425  ;  thermo- 
genic and  frigorific  nerves,  4S6 ;  olfactory 
organs,  586 

Bernoulli's  model  of  respiratory  move- 
ments, 337 

Bernstein,  muscular  contraction-wave,  58  ; 
muscular  c  jntracti.n ;  his  differential 
rheotome  (d.agram),  105 

Bernstein,  N.  O.,  pancreatic  juice,  258, 
264,  278 

Berzelius,  researches  on  digestion,  327 

BiCHAT,  on  death,  721 

Bidder  and  Schmidt,  en  digesticn,  312, 
327  ;  on  nutrition  and  starvat.on,  456, 495 

Bidder,  nerves  of  the  submaxillary  gang- 
lion, 269 

Bile,  33,  239,  254 — 257 ;  its  colour,  254 ; 
constituents,  pigments,  254  ;  bile-salts.  254; 
action  on  food,  257  ;  secretion  of,  277.  290  ; 
its  effect  en  fat,  311  ;  in  the  699  ;  foetus, 
bile  acids,  785 

Bilirubin,  39,  255 

Bilivcrdin,  255 

Binocular  vision,  559 — 572 

Birds,  brainless,  their  behaviour,  625,  6;8 

Birds,  temperature  of,  478 

Birds,  uric  acid  in,  452 

BisCHOFF,  on  nutrition  and  starvation,  457, 
495  .      . 

Black's  discovery  of  carbonic  acid  in  air, 
397 

Bladder,  420 

Blagden,  Dr.,  effects  of  heat,  480 

Blastoderm,  696 

Blind  spot,  530 

Blood,  7,  13 — 41  ;  its  chemical  composition, 
30  ;  coagulation,  14  ;  fibrin,  31  ;  fibrino- 
plastin  and  fibrinogen,  19  ;  fibrin  ferment, 
22  ;  gases  of,  344 ;  influence  of  the  living 
blood-vessels,  23  ;  sources  of  the  fibrin- 
factors,  26  ;  history  of  the  corpuscles,  35  ; 
quantity  and  distribution  of  blood  m 
animals  and  man,  40 ;  velocity  of  flow ; 
Volkmann's  haemadromometer,  144  ;  Lud- 
wig's  stromuhr  (diagram),  144  ;  Vierordt's 
haematach: meter,  145  ;   sugar  in.  325 

Blood,  changes  in  quantity  and  quality, 
229 — 235  ;  effects  of  its  condition  on  peri- 
staltic movements,  297  ;  respiratory  changes 
in  it,  343  ;  relations  of  oxygen  in  the  blood, 
344;  Ci,bur  of  arterial  and  venous,  353; 
effect  cf  respiration,  357,  361,  375;  rela- 
tions of  carbonic  acid  and  nitrogen  in 
blood,  357,  360 

Blood,  circulation  of  the,  136 — 235 

Blood,  in  inenstruaticn,  692 

Blood- of  the  foetus,  700 

Blood-pressure,  139 — 235  ;  apparatus  for  in- 
vestigating (diagram)  ;  endocardiac  pres- 
sure ;  Fick's  manometer,  142  ;  curves  of 
pressure  in  cavities  of  heart,  left  ventricle 
and  aorta  (diagram),  163  ;  its  relation  to 
heart-beat,  197,  198  ;  effect  of  bleeding  and 
injection  of  blood,  229,  271,  376 ;  in 
asphyxia,  390:  in  secretion  of  urine,  411 


Blood-supply,  its  influence  on  muscular 
contraction,  97 

Blushing,  208 

Body,  metabolic  phenomena  of  the,  4*4; 
energy  of  the  body,  468 

Bochefontaine,  cerebral  convolutions,  640 

Boll,  visual  purple  of  the  retina,  536 

Bjne.  6,  8 

B-nes,  broken,  6Sg 

BovLE,  tn  ret  piratic  n,  397 

Brachial  plexus,  section  of,  204 

Brain,  the,  and  automatic  reflex  action  in, 
132  ;  carbonic  acid,  its  action  on  higher 
parts  of  the,  378  ;  kreatin  m,  447  ;  a  source 
of  heat,  477  ;  its  functions,  622 — 671  ; 
cerebral  convolutions  in  the  dog  and  men 
(diagrams),  639—642  ;  growth  of  the,  713 

Brainless  animals,  behaviour  of,  603,  611, 
624 

Bread  (See  Dietetics,  Nutrition) 

Breathing  (See  Respiration) 

BkEUEu,  respiratory  action  of  vagus,  372 

'  Bright '  colours,  545 

Brodie,  bodily  heat,  nutrition,  482    • 

Brown-Sequard,  vascular  mechanism,  235  : 
on  the  spinal  cord,  614 ;  cerebral  convolu- 
tions, 641 
BrOcke,  on  blood-clotting,  27;  semilunar 
valves  of  the  heart,  165 ;  digestion  of 
s.arch,  241  ;  peptone  and  pepsin,  251,  261, 
262  ;  abs.rpti  m  of  proteids,  324 

'  Buffy  coat '  in  blood,  15 

Bunge,  hippuric  acid,  454 

BuscH,  movements  of  the  stomach,  302,  308  ; 
digestion,  312 

Butyric  acid,  759 


Cascum,  314 

Calcareous  degeneration,  714 

Cane  changed  into  grape-sugar  by  Succus 
Entericus,  265 

Capillary  circulation,  137,  148,  235  ;  changes 
in  peripheral  resistance,  226 — 229  ;  blood- 
pressure  in  renal  secretion,  411 

Caproic  acid,  760 

Capric  acid,  760 

Caprylic  acid,  760 

Carbohydrate  food,  effects  of,  464 

Carbohydrates,  in  the  human  body,  752 

Carbol.c  acid,  784 

Carbonic  acid,  in  expired  air,  330,  341,  342, 
343;  in  the  ILod,  344,358;  exit  from 
blood,  361 ;  in  the  tissues,  364 ;  effects  of 
excess  of,  377 

Cardiac  impulse,  ts6,  169 

Cardiac  inhibition,  190 

Cardiac  muscles.  120 

Cardiac  sound,  for  measuring  blood-pressure 
(d.agram),  159 

Cardiograph,  157 

Cardio-inhibitory  centre,  193,  198,  233 

Carnin,  779 

Carnivorous  animals,  nutrition  of,  466 

Carotid  artery,  blood-pressure  in,  139,  140 

Carpenter,  on  the  brain,  653 

Cartilage,  5,  8 

Cartilages  of  the  ribs,  their  action  in  respira- 
tion,  336 

Cartilages,  nasal,  340 


INDEX. 


793 


Carvills,  on  the  brain,  655,  056 

Casein.  733 

Cat,    saliva   of,    344;     blood-cryslals,    348; 

rtspiration,    403^    405  ;      composition    of 
dy.  273 
Cells,   mivirating,   laa  ;    cclodermic  and  en- 

d  >tlcrjiir,  123;  epithelium,  of  alimentary 

Oinal,  2  ^9 
Cclliil  isr,  241 

Central  ncrv  >iis  mechanism,  9,  125 
Centre<    of    organic   function-!    in    medulla 

obi  'ni^ata.  664 
Ceradini,  on  valves  of  the  heart,  16C 
Cerebfllum.  660 

Cerebral  acti  ns,  rapidity  of,  605 
Cerebral  convolutions  of  the  dog  and  man 

(■  I  iajjram  ■;).  639—642 
Cervical  sympathetic  nerve,  sccti  n  of  the, 

314 

ChapCron,  spinal  cord,  604 

Chauveau,  instrument  for  measuring  blood 

prcs-iiire.     146,    157  ;     movements    of    the 

oe^  >phagus.  joo 
Chemical    Action,     Tissues    of,     239—397; 

Digestion,    215—328;    Resp!ra'ion,    329 — 

397.  ,  .      . 

Chemical  aspects  of  respiration,  367 
Chemical  basis  of  the  animal  b  dy,  725 
Chemical  changes  in   muscular  contraction, 

68 
Chemical  changes  in  tissues,  6 
Chemical  composition  of  blood,  30 
Chemical  substances  in  muscle,  71 
Chkv\e-S POKES,  re'^piration.  378 
Children,  temperature  of.  486 
Chi  >ral.  IS  effect  on  cerebral  functions,  210 
Cholesterin,  7(17 
Cholic  acid,  785 
Chonirin,  749 

Chorda  and  sympathetic  saliva,  274 
Chorda   tymptni.    siinulaiion   of    the,   216, 

222  ;  secre  ing  effects,   273,    287  ;    thermic 

effects.  486 
Chordas  voc.ales,  672 
Chord*  tendiniae.  164 
Chrom.atic  aberration  of  the  eye,  527 
Chyle.  317.  318 
Chyme,"  3d8,  310.  313,  315 
Cih.ary  g.anglia,  521 
Ciliary  m  )vement,  121 
Ciliary  muscl.',  519 
C  liaied  cells.  122 
Circiilition  >  f  the  blood,  7;  136 — 235  ;  effects 

(f  respiration  on.  378;  in  asphy.xia,  390; 

in  the  foetus.  700 
Coagulati  n  of  the  blood,  14,  17 
CoagiiHted  pr  teids.  741.  748 
Cochlea,  functions  of.  580 
CiLvsANPi,  effect  of  cold  on  guinea-pigs, 

4^3 
Col  I   effect  of  on   temperature  of  the  body, 

48},  486;  on  rabb.is  and  guinea-pigs,  483, 

485 
C  Ion.  302 

Colo  ir  blinJncss,  549 
Colour  sensaions.  54^— SS' 
Colo  ir,  ■  pale,'  '  rich.'  '  deep,'  'bright,'  545 
Colour  of  the  retina,  536 
f  oloiir  of   venous  and  arterial  blood,   353, 
^358 
Colour  vision,  538,  548 


Compensating  action  for  local  disturbance, 
234 

Composition  of  the  animal  body,  454 

Consciousness  and  intelligence,  60a 

Consonan  s.  679 

C  nstricli  .n  <  f  arteries  (See  Contraction) 

Contractile  tissues.  42—122;  chemical  sub- 
stances in  muscle,  71:  phcn  jmena  of 
muscle  and  nerve.  75  ;  unstriated  muscular 
ttssiie,  119;  cardiac  muscles,  lao ;  cilia, 
121  ;  migrating  cells,  122 

Contractile  tissues,  illustrated  by  the  pcndu- 
lun  my  'graph,  47  ;  the  m.agnetic  inter- 
ruptor.  54 

Contr.actility  of  the  amoeba,  i 

C  ntracti  n,  law  of  muscular,  42;  con- 
tr.actility  of  blojd-vesscis,  201,  211,  aai, 
223.  232 

Contract i'n  r{  the  walls  of  the  stomach,  301 

C'niraction  (See  Muscular  Contrac.ion) 

Contrast,  visual  sensati  ns  of,  555 

Convulsions  in  asphyxia,  388 

Convulsive  centre.  664 

Coordination  <(  visu.al  m  vements,  564 

Coronary  arteries,  165,  198,  23a 

C'  rp  >ra  Arantii.  165 

Corpora  qu.adrigemina.  657,  65o 

C  >rpora  striata.  654.  656 

Corpuscles  (  f  the  blood,  13,  14  ;  their  history, 
33.  138.  347  . 

Corpusclts,  in  indaTimation,  228 

C  rpu-.cles,  in  >rganic  salts  in,  15 

Corpuscles,  salivary.  240,  271 

Corpuscles,  s'.arch,  241 

Corpus  luteum.  691 

CouTl.  rods  of,  580 

Coin'iSART,  researches  on  digestion,  328 

Coughing,  396 

Cranial  nerves,  503,  663 

Crassamentum,  or  blood-clot,  15 

Crerebin.  770 

Crura  cerebri,  section  of,  663 

Crj'ing.  396 

Currents  (See  Electric  currents,  Nerve 
currents) 

Curves,  pulse  (with  tracings).  180.  181 

Curves,  resp.r.atory  (with  tracings),  33a 

Cutaneous  respira'.on,  401 

CvoM.  diabetes.  434;  urea  in  the  liver,  450 

CvoN,  E.,  en  va.so-motor  fibres,  223 

Cyst  n.  782 

CzEKMAK,    effects    cf   chorda     stimulation, 


Danii-Ewsky,  on  pancreatic  juice,  263 
Da.mlewski,    Ji;,\.,     on     corpora    quadri* 

gemin.a,  (60 
Devils  A,  on  ur.ari  stimu'ati-  n,  2to  ;  blood- 

pressure,  234 
Death,  720;   death  agny,  perspiration  in, 

401 
Dei  idua,  695 

D-c  mp  siii  n  of  protrids,  744,  746 
Debn,  Van.  on  the  spinal  Cord,  621 
'  Deep'  c  lours.  545 
Di'fa;caiion.  302 
Deglutition,  293 

Demtschen'Ko.  secretion  of  te.ars,  57? 
Denis,  on  coagulation  of  the  bl  lod,  18 
Dentition,  711 


794 


INDEX. 


Depressor  nerve,  209 

Derived  proteids,  748 

Detrusor  urinse,  420 

Dextrin,  240,  241,  757 

Dextrose,  241,  753 

Diabetes,  433 — 437 

Diabetic  centre,  664 

Diagrams  :  apparatus  for  experiments  with 
muscle  and  nerve,  46  ;  pendulum  myo- 
graph, 48  ;  muscle-curves,  47,  52,  53 ; 
nervous  impulses,  50  ;  the  magnetic  inter- 
ruptor,  55  ;  muscular  fibre  undergoing  con- 
traction, 59  ;  nonpolarizable  electrodes, 
62 ;  muscle-nerve  preparations,  80  ;  illus- 
trating electrotonus,  82  ;  simplest  forms  of  a 
nervous  system,  123  ;  Du  Bois-Reymond's 
electro-motive  molecules,  loi  ;  in  their 
bipolar  condition,  ic2  ;  the  fall-rheotorae, 
104;  Bernstein's  differential  rheotome,  105, 
107  ;  electrotonic  currents,  113 ;  kymo- 
graph, 143  ;  Ludwig's  stromuhr,  for 
measuring  velocity  of  hovf  of  blood,  144 ; 
Marey's  tambour,  with  cardiac  sound,  159  ; 
blood-pressure,  140  ;  Kick's  spring  mano- 
meter, 142  ;  curves  of  pressure  in  cavities 
of  heart,  163;  sounds  of  the  heart,  169; 
pulse-curves,  175  ;  cardiac  inhibition,  190, 
200,  201  ;  cervical  and  thoracic  ganglia  of 
rabbit,  195  ;  of  dog,  196  ;  submaxillary 
gland  of  dog,  268  ;  secretion  of  pancreatic 
juice,  278  ;  pancreas  of  the  rabbit,  281 ; 
sections,  of  mucous  glands,  286  ;  of  a  serous 
gland,  287  ;  the  parotid  of  the  rabbit,  287  ;  the 
spectra,  314  ;  respiratory  movements,  332  ; 
apparatus  for  taking  tracings  of  movements 
of  air  in  respiration,  333  ;  Ludwig's  mercu- 
rial gas-pump,  346  ;  blood-pressure  curves 
and  intra-thoracic  pressure,  382  ;  Traube's 
respiratory  curves,  385  ;  Scheiner's  experi- 
ment, 515  ;  chromatic  aberration,  528 ; 
Purkinje's  figures,  531,  533  ;  muscles  of 
the  eye-balls,  563  ;  the  horopter,  567  ; 
areas  of  spinal  nerves,  613,  614;  cerebral 
convolutions,  of  the  dog,  639,  640 ;  of 
man,  641,  642  ;  the  larynx,  673 

Diaphragm,  its  action,  157,  335,  339,  369,  372 

D.astole  of  heart,  length  of,  160 

Dicrotic  pulse-wave,  180,  181 

Dietetics,  491 

Diet  of  an  animal,  normal,  457 

Digestion,  tissues  and  mechanisms  of,  8,  239 — 
328  ;  succus  entericus,  237  ;  saliva,  239  ;  gas- 
tric juice,  245;  bile,  254;  pancreatic  juice, 
257 ;  secretion  of  digestive  juices,  265, 
289  ;  mucous  and  serous  glands,  287  ;  mus- 
cular mechanism,  293 — 307  ;  changes  of 
food  in  alimentary  canal,  307  ;  absorption 
of  products,  316 ;  decomposition  of  pro- 
teids,  746 

Digestive  secretion,  mechanism  of,  265 

Dilation  of  blood-vessels,  203,  231,  271,  278 

Dioptric  mechanisms  of  sight,  510 

Dioptric  apparatus,  imperfections  in,  525 

Distribution  of  bLod  in  the  body,  40 

Divers,  respiration  of,  390 

Dock,  on  glycogen,  427  ;  on  sugar  in  urine, 
435 

Dog,  quantity  and  distribution  of  blood  in 
the,  40;  arterial  pressure,  141,  201,  381; 
velocity  of  the  circulati  n,  152  ;  section  of 
vagi,  193  ;  cervical  and  thoracic  ganglia  of 


(diagram),  196 ;  saliva,  245 ;  bile,  255  ;  pan- 
creatic juice,  258;  submaxillary  gland  (dia- 
gram), 268;  vomiting,  307;  blood  crystals, 
348  ;  perspiration,  403  ;  cerebral  convolu- 
tions (diagrams),  639 — 64c 

DoGiEL,  on  blood  circulation,  146  ;  sounds 'of 
the  heart,  170 

DoNDERS,  length  of  the  cardiac  systole,  169, 
173  ;  pulse-waves,  176  ;  inhibition  of  heart- 
beat, 190  ;  movements  of  the  eye-balls,  559  ; 
the  rapidity  of  mental  operations,  666 

Drowning,  390 

Du  Bois-Revmond,  pendulum  myograph, 
46;  on  muscle-currents,  66  ;  eleciro-motive 
molecules,  loi,  102 ;  muscle  and  nerve, 
114,  116 

Dumas,  on  nutrition,  438 

Duodenum,  298,  300,  305,  310 

DlTRHAM,  sleep,  717 

Dyspepsia,  715 

Dyspeptone,  262 

Dyspnoea,  334,  371,  376,  378,  388,  394 


Ear,  the,  574 — 584 

Ebstein,  on  pepsin,  284 

EcKHARD,  action  of  submaxillary  ganglion, 
269  ;  on  secretion  of  saliva,  275 ;  diabetes, 
435  ;  morphia  diabetes,  436  ;  spinal  cord, 
610  ;  cerebral  convolutions,  641  ;  the  cere- 
bellum, 663 

Ectodermic  cells,  124 

Edgren,  movements  of  the  pupil,  521 

Edwards,  W.,  respiratory  changes,  341,  367, 
397 

Eel,  caudal  vein,  202  ;  iris,  521 ;  contraction 
of  the  pupil,  521 

Efferent  impulses  in  secretion  of  saliva,  129, 
130,  270 ;  vomiting,  306 

Egg-albumin,  728 

Eichhorst,  nutrition,  trophic  nerves,  490 

Elastm,  751 

Electric  currents  of  nerve  and  muscle,  62,  78, 
loi  ;  the  fall-rheotome,  104  ;  Bernstein's 
differential  rheotome,  105 

Electrodes,  non-polanzable,  illustrating  nerve- 
currents  (diagram),  62 

Electrotonic  currents,  112,  113 

Electrotonus,  80 

Emetics,  effect  of,  307 

Emmetropic  eye,  516,  525 

Emminghaus,  movements  of  chyle,  321 

Emotions  causing  micturition,  421 

Endo-cardiac  pressure,  157  —  164  ;  Fick's 
spring  manometer,  142 

Endodermic  cells,  124 

Energy  of  the  body  (income  and  expenditure), 
468,  469  ;  muscular,  470 

Engelmann,  on  muscle-currents,  58  ;  auto- 
matic action  of  ureter,  128 ;  ciUary  move- 
ment in  the  frog,  121 ;  peristaltic  move- 
ments, 299 

Entoptic  phenomena  of  sight,  528 

Epiglottis,  294 

Ep.thelium  cells,  239,  265,  272,  319,  415,417, 

574 
Erect  posture,  683 

Erismann,  on  cutaneous  secretion,  402 
Eructation,  309 
Erythrodextrin,  241 
Erythrogranulose,  241 


INDEX. 


795 


EsTOR,  scat  of  oxidation  in  respiration,  364 

litliylcnc-lactic  acid,  765 

Etliyl>dcne-laciic  acid,  765 

Lusiai:lii:in  tube.  577 

Excrcli   n  uf  uiine,  407  ;  of  milk,  441  ;  of  ni- 

tr,gen,  in  muscul.ir  exercise,  472  (See  De- 

fxc:tti"n.  Micturition) 
Kxcrct  ry  tissues.  5,  6 
Exhaustion,  muscular,  93 
ExNBR,    on   visual  sensations,   535  ;    reflex 

acti  ms,   608  ;    on    the    rapidity   of  mental 

opcrati  -ns,  665 
Expiration,    330,   333 ;    movements   in,  338 

36S,  380,  ^87 
Explosives  (v,  ice),  680 
Eye.  the  (See  Sight) 
Eye-balls,  movements  of  the,  560,  657 


Facial  respiration,  339 

Faxe<,  302,  304.  315 

Fainting,  193 

Fall  >pian  tubes.  691,  694 

Fall-rheotjine  (di.-igram),  104 

Falsetto  v.iice.  677 

Fat,  history  of.  437 — 441 

Fat  of  milk.  442 

Fats,  omplcx  nitrogen  us,  768 

Fats,  I  heir  derivatives  and  cllies,  758 

Fats  ill  serum.  31  ;  action  of  bile  on,  257  ;  ot 
pancreatic  juice,  263  ;  digestion  of,  308, 
311,  326 

Fatty  degeneration,  714 

Fatty  fjud,  etTects  of,  464 — 467,  491 

Fauces,  294.  295,  306 

Fechneh  s  r  r.iiula  of  visual  sensations,  542 

Feel.ng  and  Tc  uch,  589 

Ferments,  organized  and  unorganized,  243 ; 
saliva,  243  ;  gastric  juice,  246 ;  of  pan- 
creatic juice,  259,  282  ;  in  the  small  in- 
testine, 313 

Feknet,  on  respiration,  397 

Ferkieh,  on  the  brain.  645.  647,  648,  659.  6^1  ; 
cerebral  c  mvoluti  ^ns  if  the  dog  and  man 
(diagra:iis).  639.  640—642 

Fibrin,  15 — 22,  117,  247,  250,  736,  748 

Fihrin-ferment,  21 

Fibr.pogen,  20,  736 

Fibnn^plastin,  19.  20.  735 

FiCK.  on  blo.id-circulation,  163,  164;  spring 
manometer  (diagram).  142  ;  nutrition,  ani- 
nal  heat,  474  ;  urea  and  muscular  exercise. 
471  ;  muscles  of  the  eye-balls,  564  ;  spinal 
cordi  621 

Flatulency,  310 

Fleischi.,  nervous  irritability,  90 

Flouken's,  on  the  respiratory  centre,  370  ; 
en  the  brain,  638 

Focfj:;  (Sie  Embryo) 

Food,  acuun  of  bile  and  pancreatic  juice  on, 
257 

Fo>  d,  effects  of  gelatine,  467  ;  effects  ofi 
salis  .IS,  467 

Food,  fatten. ng  diet,  438 ;  potential  energy 
of  f  od,  468,  493 

Fiod.  glyc  'gen  produced  by,  426,  432 

Food,  Its  eOert  on  the  stomach,  300  ;  absorp- 
tion by  diffusiL>n,  326 ;  effects  of  carbo- 
hydrate, 464 

Food,  tissues  and  mechanisms  of  digestion, 
235 — 328  ;  changes  of  food  in  the  alimentary 


canal,  307  :  absorption  of  products  of  di- 
gestion, 316 

Force  of  heart-beat,  173 

FOKUVCK,  Dr.,  effect  of  heat,  480 

Formic  acid,  758 

Fkanklanu,  on  the  potential  energy  of 
f  )od,  468 

p'reqiicncy  of  heart-beat.  173 

FkEMCHs,  on  digestion,  327 

F'rigorific  nerves.  486 

Fkitsch,  cerebral  convolutions  of  the  dog 
(diagram).  571 

Frog,  experiments  on  the  ;  nerves,  43,  44,  70, 
92,  05 ;  skeletal  muscles,  43 ;  the  rhco- 
scopic  frog,  66,67;  lymphatic  heart,  131, 
132;  he.-irt,  186,  187,  190,  193;  contract- 
ility of  arteries.  202  ;  blood-vessels,  227  ; 
capillary  circulati' n,  235  ;  cutaneous  respi- 
ration. 40t  ;  contraction  ■  f  the  pupil,  521  ; 
visual  purple  in,  538  ;  spinal  cord,  602,  620  ; 
lymph-heart,  609 

Frog,  bra;nless.  its  behaviour,  130,  603,  624 

FunctK  nal  activity,  its  influence  en  muscular 
irr.tability,  98 

FuNKE.  on  succus  entericus,  264 ;  Sugar  in 
blood  and  urine,  325  ;  respiration,  387 ; 
quantity  of  perspiration,  399 


Gai.abin,  Dr.,  diagrams  of  pulse-ourves, 
i8o,  181 

Galvanic  current,  its  effect  on  muscular  con- 
traction, 53,  62 

Ganglia,  128,  132,  188,  301,  501  ;  cervical 
and  thoracic,  of  rabbit  and  dog  (diagrams), 
195.  196 

Gauuod,  on  pulse-waves,  177;  heart-beat, 
233  ;  quantity  and  flow  of  blood,  233 

Gases,  in  eructaticjn,  309  ;  in  the  large  intes- 
tine, 314  ;  in  the  blood,  344 

Gases  in  urine,  409 

Gases,  pcisi  n  us,  respiration  of,  394 

Gas-pu:np,  mercurial,  Ludwig's  (diagram), 
346 

Gaskell,  W.  H.,  contraction  and  dilation  of 
arteries,  223 

Gastric  compared  with  pancreatic  digestion, 
260 

Gastric  digestion,  circumstances  affecting,  250 

Gastric  juice,  239,  246,  247,  27s,  308;  arti- 
ficial, 708 

Gastric  juice,  action  on  proteids,  247 

Gastric  movements,  nervous  mechanism  of, 

.301 
Gaulk  and  Goltz,  their  maximum  mano- 
meter, 162,  163 
Gelatin,  750  ;  as  food,  467 
Geklacii,  on  cuiaiieous  respiration,  401 
Gestation,  703 
Giddiness,  633 
Gii.nEKT  and  Lawes,  on  the  formation  of 

fat.  438,  467     .,  .         •,       .. 

Glands,   submaxill.-iry,   secretion    of   saliva, 

266  ;  submaxillary  of  dog  (diagram),  268 ; 

gastric,  283  ;  salivary,  285  ;  of  rabbit,  287  ; 

secreting     sweat,    ^02;     mammary,    441; 

L-ichryinal.  Meibomian,  572 
Gi.issoN,  on  muscular  contraction,  46 
Globin,  356 
Globulin,  in  muscular  tissue,  and  saliva.  340, 

356,  734.  748 


796 


INDEX. 


Globulins,  734,  748 
Glomeruli,  renal.  411 

Glottis,  its  action  in  respiration,  339,  370, 
673  ;  c  ntractions  of  the  (diagram),  673 

Gljttis,  narrowing  t  f  the,  674 

Glottis,  widening  of  the,  675 

Glutm,  750 

Glycerin,  763 

Glycerinphosphoric  acid,  769 

Glycin,  7S0 

Glycoch-lic  acid,  786 

GlycoHc  acid  scries,  764 

Glycogen,  425 — 433.  698,  756  _ 

Gmelin,  researches  on  digestion,  327 

GoLTZ,  his  maximum  manometer,  162,  163, 
164  ;  on  vaso-motor  actions.  221 ;  move- 
ments of  ihe  oesophagus,  300,  301  ;  defjeca- 
tion,  303;  moveiuents  of  lymph,  321  ;  mic- 
turition, 421  ;  reflex  actions,  607  •  lymph- 
hearts,  610  ;  the  cerebral  conv  lulions,  646  : 
menstruati  jn,  618;  impregnation,  694 

Goose,  bile  of,  255  ;  blood-crystals,  348 

Graaffian  follicle,  691 

Granulose,  241 

GuEHANT,  on  urea,  449 

Grey  matter  of  the  spinal  cord,  619 

Growth,  phases  of  life,  713 

GrOtznen,  on  pepsin,  284 ;  afferent  and 
efferent  nerve  fibres,  505 

GscHEiDLEN,  OH  the  Origin  of  urea,  449,  430 

Guanin,  779 

Guinea-p.g,  saliva  of  the,  244  ;  blood-crystals, 
348  ;  effect  of  cold  on,  483 

Gustatory  fibres,  5S8 

Gyekgyai,  absorption  of  proteids  in  di- 
gestion, 325 


Haberman,  on  proteids,  747 
Hjemadromometer  of  Vclkmann,   for    mea- 
suring blood-pressure,  144 

Haeraatachometer,  for  measuring  blood- 
pressure,  145 

Haematin,  356 

Hsematoidm,  39 

Hsemoglobin,  33,  39,  291,  348,  351,  356,  359 

Hemorrhage,  effects  of,  on  vascular  mecha- 
nism, 230 

Haeklin,  on  paralbumin,  729 

Hales,  Dr.  Stephen,  circulation  of  blood, 
125.  235 

Halfond,  sounds  of  the  heart,  170 

Hai.lek-,  on  muscular  contraction,  46 ;  on 
physiology  of  muscle  and  nerve,  118 

Hali.ste.n,  cntractile  tissues,  90 

Hamcekgeu's  model  of  respiratory  move- 
ments, 337 

Hammahste.v,  coagulation  of  blood,  22; 
ga.stric  ju.ce  in  new-born  animals,  708 

Hauvev,  circulatii  n  of  the  bloud,  235 

Have.m,  red  bljod-corpuscles,  37 

Heanng,  574 

Heart,  the,  154 — 173 ;  phenomena  of  the 
normal  beat,  155 ;  curves  of  pressure  in 
cavities  of  heart.  184  ;  mechanism  of  the 
valves,  164 ;  sounds  of  the  heart,  i58 ;  its 
failure  before  de.ith,  721 

Heirt-beat,  normal,  136,  155;  variations, 
in,  172,  198,  391,  411 

Heart-beat  in  fcetus,  699 

Heart-murmurs,  169 


Heart  of  the  babe,  709 

Heart  of  the  frog,  132 

Heat,  loss  of  energy  from,  469 

Heat,  sources  and  distribution  of,  474 

Heat,  varying  pr^-duction  of,  480 

Hedgehog,  blood-crystals  of  the,  348 

Heidenhain',  on  pancreatic  digestion.  259  ; 
mechan.sm  of  digest.ve  secretion,  268,  274, 
276,  285  ;  mucous  and  serous  glands,  287, 
290,  309  ;  researches  on  digestion,  32S  ;  en 
renal  secretion,  416 ;  on  nutrition,  472, 
483  ;  bodily  heat,  479,  483  ;  lymph-hearts 
of  the  frog,  610 

Heller,  movements  of  chyle,  320 

Helmholtz,  on  muscular  contraction,  75; 
vel-C.ty  of  nervous  impulses,  118;  loss  of 
energy  from  heat,  478;  dioptric  mechan- 
isms. 529 ;  colour  sensations,  546  ;  the 
horopter,  567  ;  vision  and  musical  sounds, 
598  .        .  ■ 

Helmont,  Van,  on  carbonic  acid  gas,  397 

Hemipeptone,  262 

Hensen,  on  auditory  hairs,  580 

Hensen  and  Volkers,  sight,  movements  of 
the  pupil,  524 

Hepatic  artery,  and  the  secretion  of  bile, 
291  ;  hepatic  cells,  4,  291.  425,  433 

Herbivorous  animals,  nutrition  of,  466 

Hering,  respiratory  action  of  vagus,  372; 
nervous  mechanism  of  respiration,  372 ; 
colour  sensations,  552  ;  sensations  of  tem- 
perature, 593 

Hermann,  on  muscular  contraction,  58; 
rigor  mortis,  and  electrical  theory  of 
muscle,  74,  108,  116,  118 ;  respiration  of 
muscle,  118 

Herzen,  inhibition  of  reflex  action,  603 

Herzem.stei.v,  secretion  of  tears,  572,  573 

HiccvjUgh,  396 

Hippuric  acid,  783 

HiKSCH,  on  rapidity  of  cerebral  operations, 
666 

HlusCHMANN,  on  visual  sensations,  543 

HiTZiG,  on  the  cerebral  convolutions  of  the 
dog  (diagram),  639,  640  ;  cerebellum,  661 ; 
vertigo.  662 

Hlasiwitz,  on  proteids,  747 

Holmgren,  movements  of  the  pupil,  521, 
524  ;  electric  currents  of  the  optic  nerve. 

Hook,  on  artificial  re.spiration,  397 

Hoi'I'e-Sevler,  on  the  composition  of  blood, 
S'-  33)  34 1  '^'^  b''^>  25s  ;  hEemoglobin, 
358  ;  respiration,  397 ;  nutrition,  463 ; 
analysis  of  proteids,  726 

Horopter,  the,  566 

Horse,  blood-circulaticn  in  the,  27.  29,  32, 
139,  146.  152  ;  (diagram),  15S  ;  saliva,  244, 
307  ;  blood-crystals,  348  ;  locomoticn,  684 

HoKVATH,  death  from  extreme  heat,  487 

Houckgeest,  Va.n"  Braam,  peristaltic  ac- 
tion, 29S 

H0FNE15,  on  influence  of  bacteria  in  diges- 
tion. 261 

H  UTCHiiN'SON,  vital  capacity  of  the  lungs,  33K 

HuxLEV,  blojd  corpuscles,  37 

Hydra,  124 

Hydracrylic  acid.  766 

Hydraulic  principles  of  blood  circulation, 
148 

Hydrobilirubin,  39 


INDEX. 


797 


Hydruzoa,  ciliary  movement  in,  iii,  134 
Hydriiria,  or  e.xccsMvc  rcnul  secrctiun,  413 
Hyt.crpnoea.  388 

H  ypjtj'  '^sal.  vasi>-m  tor  action  of  the,  204 
HypjxanLh.n,  446,  77S 


Ileo-caccal  valve,  298,  30a,  314 

lmprcj;nati  n,  694 

IinpuUo,  nerv.ius,  134  ;  efferent  and  affer- 
ent, 129  ;  afferent,  499  ;  conduction  of,  by 
the  sp.nal  c  nl,  616;  nerv^jus  in  respira- 
tK.n,  36):  sensory  and  md.r,  134 

Inc  >me  and  uuic^me  uf  diet,  458 

Income  of  energy,  468 

Jnci.nt.ncncc  if  urine,  43a 

JnJic.in  in  urine,  409,  787 

Indigo,  787 

Indij?  .-carmine,  excretion  of,  416 

Ini  .1,788 

Induction-machine.  54  ;  induction-shock,  ef- 
fects of.  46,  77.  83,  191 

Inert  layer  in  capillary  c.rculation,  138 

Infants,  temperaturo,  486 

Inllammaiion,  us  cffccis.  227,  489 

Infusoria,  cil.ary  movement  in,  121 

Inh.b.tion,  132  ;  of  heari-beat,  189,  194  ;  of 
peri-taltic  action.  297 ;  of  reflex  action, 
633  :  panurition,  704 

Inhibitory  fibre-,  133 

Inject. .,n  of  bb.^d,  effects  of,  198 

Ino^en,  117 

In.s.t,755 

Insen>ible  perspiration,  .jod 

Inip  rati>.n,  mjchan  csof,  330,  335  ;  laboured, 
338  ;  nsrvous  niechan.sm  cf,  369  ;  effects 
oil  circulation,  381;  asphyxia,  388 

Integrat.on  of  fundamental  tissues,  7 

Intercj^tal  muscles,  their  acti.^n  in  respira- 
ti  n.  336.  339 

Intestine,  large,  movements  of.  302,  314 

Interline,   small,   310  ;  peristaltic  action  of. 

Irradiation  of  visual  sensations,  555 

Irriia'ile  tissues,  6,  7 

Irniab.lity  of  nerve  and  muscle,  43—46,  61, 

83.  92 
Isthmus  faucium,  394 


Jab'irandi,  its  effect  on  heart-beat,  191 

Jacobso.n,  on  bbod-pressure,  147 

Jaffe,  urobiLa  in  unne,  39;    pigments  of 

bile.  25s 
Jaundice.  292 

Jones,  Whakton,  bio  d-orpusclcs,  37 
JOuELi.,  c  .mpjsitii.n  1  f  red  c  rpuscles,  33 
Judgments,    visual,     568;      auditory,     583; 

tactile,  594 
Juices,  digestive,  339 — 265 
Jumping,  684 


Katelectrotrnus,  82 — 85,  93 

Kemmekich,  •  n  the  S'.-crcti  ^n  of  milk,  443 

Kenoal,  on  cutaneous  secretiL.n,  402 

Kendall,  vaso-motor  action,  321,  233 

Kerat.n,  751 

Kidneys,  secretion  by  the,  407—419 

Kidneys,  certain  diseases  of,  448 

Klsin,  origin  of  white  blood-corpuscles,  38 


Knock,  bodily  heat,  486 
Knoll,  on  the  corpora  quadrigemina,  583, 
,657.659 

KohlschOtter,  sleep,  717 
Kollikek,  red   corpuscles,   37,    38;   succus 

entcricus,  264 
KoKNEK,  on  uterine  conlracti'  nf,  705 
Kreaiin,  krcatinin,  447,  448,  776,  777 
KuONECKEtj,  on   lllu^.cular  co.itraciijn,  83; 

funcii..nal  activity  of  muscles,  100 
KCiiNE,   on    t'   :  chemistry    of    muscle,  70, 

13s  ;  gastric  juice,   253  ;  pancreatic  juice. 

25(5;    proteids.    261,    363;    mechani-in    of 

salivary   secretion,  274;    secretion   in   the 

pancreas,    280  :      visual     purple     of     the 

rcti  la.  537 
KtX'FFER,  on  end.ngs  of  nerves  in  salivary 

glands,  272 
KOkschner,  on  heart-beat,  155 
Kymjgraph   fjr  recording  arterial  pressure 

(diagram;,  143 
Kyaurenic  acid,  780 


Labour,  loss  of  energy  by,  469 

Labour-pains,  704 

Laboured   respirat.on,    330,   334,    338,    339, 

Lachrymal  glands,  573 

L.icteals.  318 

Lactic  ac.d,  764;  in  muscle,  71  ;  converted 
from  cane-sugar  by  succus  entericus,  265 

Lactose,  754 

Lagkange,  on  respiration,  397 

Landois,  en  blooil-circulation,  161 ;  cere- 
bral c  nvolutions,  640 

Langendokf,  nervous  mechanism  in  re- 
spiration, 375  ;  inhibition  of  reflex  action, 
604 

Langlkv,  salivary  secretion,  273 

Lardacein.  745.  748 

Laryngeal  nerve,  superior,  in  respiration, 
372 ;  in  vo.cc,  676  ;  inferior,  in  respiration, 

Laryngeal  respiration,  333 
Laryngjscope.  340 

Larynx.  294,  672:   d.agram  of  the.  673 
Latschenbekgek,    oil     urari    stimulation, 
2IO  ;  bbod-pressure,  23j  ;  respiration,  387 
Laughing.  31,6 
Laurostearic  acid.  760 
Lavoisier,  on  respiration.  397 
Lawes  and  Gilbert,  on  the  formation  of 


fat,  438,  471 
.EA  ; 
280 


Lea  and 


471 
KOhne, 


secretion  in  the  pancreas. 


Lecithin,  33.  768 

Legg.  Wickham,  on  diabetes,  436 

Lemoigne,  on  the  brain,  656 

Leucin,  260,  261,  313.  446.  439.  781 

Leuwenhqek.  capillary  circulation,  235 

Levat  rescosianim.  337 

LiEBiG,  on  f^rmauon  uf  fat,  43S ;  nutrition, 

.470.  47.?.  495 
Life,  the  phases  of.  707 
Lingual  nerve.  204.  260 

LuTEK,  J.,  coagulati  n  of  the  bIoc>d.  23,  27 
Listing,  movements  of  the  eye-balU,  562 
Liver    secretion   of  bile,   290;    a  source   of 

sugar,  425 
Locomotor  ataxy,  598 


798 


INDEX. 


Locomotor  mechanisms,  erect  p;siticn,  682, 
walking,  683  ;  running,  684 

LoRTET,  instrument  for  measuring  blood- 
pressure,  146 

LovEN,  constriction  and  dilation  of  arteries, 
zii,  215 

Lower,  on  respiration,  397 

LucHsiNGER,  vaso-motor  action,  220,  221 ; 
cutaneous  secretion,  405 ;  perspiration  in 
the  cat,  405 

LuDWiG,  blood  velocity  in  dog  and  rabbit, 
146  ;  his  stromuhr,  144 ;  s^^unds  of  the 
heart,  170  ;  vascular  mechanism,  235 ; 
mechanism  of  salivary  secretitn,  273 ; 
peristaltic  action,  298 ;  mercurial  gas- 
pump,  (diagram),  346  ;  respiration,  397 ; 
renal  secretion,  4 15 ;  temperature  of 
submaxillary  gland,  4S6 

Lumbar  cord,  693,  703,  705 

Lungs,  the:  mechanics  of  pulmonary  re- 
spiration, 330;  elast.c  force  of,  331,  380; 
respiratory  changes  m,  360 

Lunulse  of  heart-valves,  165 

LussANA,  on  the  brain,  656 

Lutein,  39 

Lymph,  Lymph-vessels,  Lymphatic  glands, 
38.  317.  319    ^ 

Lymph-hearts  of  the  frog,  127,  610 

Lymphatic  system  in  infancy  and  youth,  710 


Magnetic  interrupter  (d.agram),  54 

Magnus,  on  resp.ration,  397 

Majendie,  on  vomiting,  305  ;  sensory 
nerves,  500;  olfactory  nerve,  586 

Malpighi,  capillary  circulatijn,  235 

Malpigh.an,  bodies  i_f  the  kidney,  407,  411 

Maltose,  241 

Mammary  gland,  442 

Man,  temperature  of,  478 

Manometer  applied  to  blocd-circulation,  139, 
161  ;  to  heart-beat,  162,  163,  198  {See 
Diagrams) 

Marching,  684 

Marey,  on  blood-circulation,  152 ;  blood- 
pressure,  157  ;  pulse  waves  (diagram),  175, 
177 ;  heart-beat,  174 ;  Marey's  tambuur 
(diagram)  159,  333;  pneumograph  (dia- 
gram), 332  ;  locomotion  of  the  horse,  684 

Mastication,  293 

Mayer,  respiration,  386 

Mayow,  on  changes  of  air  in  respiration, 
341  ;   on  oxygen,  397 

Maxwell,  on  colour-sensations,  546 

Meat  (See  XJietetics,  Nutrition) 

Mechanical  tissues,  6 

Mechanism  of  digestive  secretion,  266 

Mechanisms  of  respiration,  329 — 397 

Mechanisms  of  reproduction,  689 

Meconium,  699 

Medulla  oblongata,  664 ;  cardio-inhibitory 
centre,  193  ;  centre  for  secretion  of  saliva, 
270 ;  for  deglutition,  295  ;  for  movements 
of  oesophagus  and  stomach,  299 ;  convul- 
sive centre,  388  ;  as  a  centre  of  co-ord.nation 
in  the  frog,  636  ;  in  the  mammal,  606 

Meibomian  glands,  572 

Meissner,  plexusof  the  intestines,  128  ;  pep- 
tic digestion,  261,  262  ;  peristahic  action  in 
digestion,  297  ;  urea  and  urates  in  the  liver, 
450 ;  hippuric  acid,  453  ;  peptones,  742 


Menstruation,  691 

Mental    emotions    producing    perspiration, 

4°3    . 

Mercurial  gas-pump,  Ludwig  (diagram).  3^6 

Mercury  manometer  applied  to  blood-c.rcu- 
lation,  140,  162,  163,  190,  198  {See 
Diagrams) 

Metabolic  tissues,  5,  6,  425 

Metabolic  pruductj  in  urine,  410 

Metabolic  phenomena  of  the  body,  424 

Metabolism  of  the  embryo,  6g8 

Metabolites,  nitrogenous,  771 

Metapeptone,  262 

Meyer,  Lothar,  en  respiration,  397 

Michieli,  the  cerebral  convolutions,  644 

Micturit.on,  419,  604 

MlESCHER,  on  blood-corpuscles,  34 ;  nu- 
clein,  752  ;  spinal  Curd,  616,  621 

Migrating  cells,  122 

Milk,  442 — 444  ;  action  of  gastric  juice  on, 
249,  253 

Milk-sugar,    754 

Minerals,  act.on  of  gastric  juice  on,  246 

MoLESCHOTT,  normal  diet  of  man,  457 

Monkey,  cerebral  convolutions,  639 

Morphia  diabetes,  436 

Mosso,  changes  in  the  circulatii  n,  229  ; 
movements  of  the  oesophagus,  299 ;  sleep, 
716 

Motor  fibres,  205 

Motor  nerves,  125,  135 

Mouth,  its  action  in  digestion,  307 

Mucin,  749 

Muciparous  cells,  285 

Mucous  glands,  285 

MOller,  J.  J.,  researches  on  respiration, 
363 

MOller,  Worm,  effects  of  bleeding,  230 

Muller,  W.,  changes  of  air  in  respiration, 
341 

MOller,  J.,  on  the  senses,  598  ;  on  reflex 
actions,  670 

MuNK,  en  cerebral  localisation,  648 

Muscarin,  its  effect  on  heart-beat,  191 

Muscle  and  nerve,  81,  92,  94,  101 

Muscle  and  nerve,  electrical  phenomena  of, 
loi  ;  energy  of,  116  ;  chemical  changes  in, 
116 

Muscle-nerve  preparation  as  a  machine,  86 

Muscle-currents,  62  ;  in  frog,  66 

Muscle-curves,  diagrams  of,  46,  47,  50,  52,  53 

Muscles,  42 — 122  ;  chemical  substances  in 
muscle,  68  ;  energy  of  muscle,  116;  glyco- 
gen in,  426  ;  kreatin  in,  447  ;  respiratory 
changes  in,  363  ;  phenomena  of  muscle  and 
nerve,  43 ;  irritability  of,  92 ;  unstriated 
muscular  tissue,  119  ;  cardiac  muscles,  120  ; 
cilia,  121;   m.gratory  cells,  122 

Muscles  of  defaecation,  303 

Muscles  of  mastication  and  deglutition,  293, 
294, 

Muscles  of  micturition,  420 

Muscles  of  respiration,  336,  338,  340,  369 

Muscles  of  the  eye-balls,  562 

Muscles  of  the  foetus,  698 

Muscles  of  the  larynx,  675 

Muscular  contraction  : — shewn  by  the  pen- 
dulum myograph,  48,  50;  changes  m  a 
muscle  during  contraction,  57 ;  change  of 
form,  57  ;  electrical  changes,  62  ;  physical 
changes,  67  ;  chemical  changes,  68  ;  law 


INDEX. 


799 


of  contractiiin,  84  ;  circumstances  niTccting 
its  amount  and  character.  86 

Muscular  energy,  sources  of,  116,  470 

Muscular  fibre  cells,  laj 

Muscular  fibres  in  artcnes,  joo 

Muscular  mccliaiiisms,  8 

Mu-cuLir  mechanisms  of  digestif  n,  293 — 307  ; 
mastication,  293  ;  deglutition,  igi ;  peri- 
staltic action  of  the  sm.ill  intestine,  296: 
movements  of  the  ocNophagus,  29^  ;  of  the 
stomach,  300;  of  the  large  intestine,  303  ; 
defxcatiin,  302  ;  vomiting,  304 

Muscular  mechanisms,  special,  673 

Muscular  irritability,  43,  45,  83,  84 

Muscular  sense,  596 

Muscular  s  >und,  600 

MuscuLar  tissues,  6 

MuscuLi;s,  action  of  saliva  on  starch,  241  ; 
maltose,  754 

Musical  sounds,  nature  of,  578 

Myograph,  pendulum  (diagram)  47,  48 

Myosin  in  muscular  tissues,  75,  737 

Myristic  acid,  760 


Native  albumins,  728 

Nausea,  304 

Nawrocki.  cutaneous  secretion,  405 

Negative  variation  l  f  muscle-currents,  66 

Ner\'e  and  muscle,  phenomena  of,  43 

Ner\'e  currents,  illustrated  by  non-polarizable 
electrodes  (diagram),  62  ;  negative  varia- 
tion, 66 

Nerve-rirts.  126 

Nerves,  irritability  of,  92  ;  accelerator,  194, 
233  ;  experiments  with  pendulum  myo- 
graph, 47,  48 ;  cardiac,  of  the  dog,  196  ; 
thermogenic,  486  ;  frigorific,  486 

Nerves,  chemical  changes  in,  116 

Nerves,  cranial,  503,  663 

Nerves,  energy  of,  1 16 

Nerves,  their  effect  on  c^nstricti'^n  and  dila- 
tion of  arteries,  203 

Nerves  employed  in  defxcation,  302 

Nerves  in  c  nnection  with  striated  muscles, 

43 

Nerves,  thc.r  influence  on  the  secretion  and 
ejection  of  milk.  444 

Nerves  of  mastication  and  deglutition,  293 

Nerves  of  sight,  520 

Nerves  of  the  eye,  572 

Nerves  of  xiuch,  589,  596 

Nerves,  renal,  413 

Nerves,  sensory,  499 

Nerves,  spinal.  539,  572,  612 

Nerves,  splenic,  445 

Nerves,  trophic,  488 

Nerves,  vasj-motor,  203 

Nervi  erigentes,  217 

Ncrvi  mesenterici,  193 

Xervjus  action  in  vomiting.  305 

Nervous  influences  on  peristaltic  action,  297 

Nervous  impulses,  curves  illustrating  their 
velocity,  50  ;  changes  in  the  nerve  during 
their  passage.  53.  54,  86 

Nervous  irritability.  8),  84 

Nervous  mechanism  for  secreting  digestive 
juices,  265.  275,  278 

Nervous  mechanism  of  the  gastric  move- 
ments, 301 

Nervous  mechanism  of  perspiration,  40a 


Nervous  mechanism  of  respiration,  369 
Nervous  system,   7,  8,  9  ;  simplct  forms  of 

(diagram),  123  ;  its  influence  on  heart-beat, 

minute  arteries,  and   capillaries,    187  :    its 

influence  uii  nutrition,  4b8  ;  in  infancy  and 

youth,  710 
Nervous  tissues,   properties  of,  4,  12 j — 135; 

metabol.sm  of,  447 
Nervous  tissues,  general  properties  of,  125 
Neu.mann,  red  corpuscles,  37 
Neurin,  770 
Neutral  fats,  761 
Neutral  salts,  23 

Nlcoi^Kl,  vaso-motornerves,  215 
Nicotin,  its  effect  on  heart-beat,   191  ;  pen- 

staltic  acti'.n,  296 
Nitrate  of  urea,  771 

Nitrogen  of  inspired  and  expired  air,  341 
Nitrogen,   quantity   .n   arterial   and    venous 

blood,  3^5 
Nitrogen,  its  relati..ns  in  the  bl  od,  360 
Nitrogenous  crystalline  bodies  in  urine,  408 
Nitrogenous  f  oJ.  470 
Nitrogenous  metabolism.  ^C^i 
Nitrouenous  metabolites,  771 
Nceud  vilai,  370 
Non-nitrogenous  metabolism,  464 
Non-p  il.irizable  electrodes  (diagram),  6a 
Normal  blood  plasma,  20 
Normal  diet,  457,  493 

Nostrils,  their  action  in  respiration,  340,  370 
NoTH.v.\GEL,  on  the  brain,  656,  C61 
Nuclein,  752 

NussBAUM,  renal  secretion,  418,  419 
Nutrition,  425  ;  production  of  glycogen,  426  ; 

of  the  embryo,  696 

Ocular  spectra,  556 

Odour  of  the  breath,  343 

Oehi.,  movements  of  the  pupil,  523 

OJsophagus,  movements  of,  299,  305 

Old  age,  714 

Oleic  acid,  761 

Oleic  (acrylic)  series  of  acids,  761 

Olein.  762 

Olfactory  organs,  584 

( )PPLEK,  on  renal  secretion,  462 

Optic  thalami,  652,  655,  656 

Otic  ganglia,  132 

Ovanes.  691,  693 

Ovum,  690 — 695,  7?o 

OwsjAN.NiKOW.  vaso-motor  centre,  318  ;  on 
reflex  actions.  608 

Ox,  saliva  of  the,  244;  bile,  255;  blood- 
crystals,  .348 

Oxalate  of  urea,  771 

Oxalic  acid,  766 

Oxidation,  seat  cf,  in  respiration,  363 ; 
oxygen  inhaled  in  respiration,  330,  341, 
343  ;  quantity  and  condition  in  arteri.al  and 
venous  blood.  344,  34.7,  358,  J77  ;  its  en- 
trance into  the  lungs  in  respirati  ^n,  360, 
368 ;  the  cause  of  dyspnoia,  asphyxia,  and 
apnoea.  393 

Oxygen  tension.  361,  368 

Oxyhscmoglobin,  350,  353 

Palate  in  deglutition,  393 
■  Pale  '  Colours.  545 
Palmitic  acid,  760 


8oo 


INDEX. 


Pal.nitin,  762 

Pancreatic  digestion,  312 

Pancreatic  juice,  239,  257,  278,  310,  311,  312, 

437 

Paraglobulin,  20,  22,  29,  30,  735 

Paralytic  saliva,  274,  279 

Parapetone,  249,  257,  261,  312 

Pakinaud,  bodily  heat,  482 

Parkes,  on  urea  and  muscular  exercise,  471 

Parotid  saliva,  244,  274 

Parturition,  703 

Paschutin,  on  the  action  of  saliva,  242  ; 
movements  of  lymph,  321 ;  inhibition  of 
reflex  action,  603 

Paw,  nutrition,  glycogen,  428 

Pendulum  myograph  (diagram),  48 ;  dia- 
grams obtained  by  it,  47 

Penicillium,  467 

Penis,  mechanism  of  erection,  216,  694 

Peptic  digestion.  247,  259 

Peptic  glands,  283 

Pepsin,  the  ferment  of  gastric  juice,  257,  260, 
284. 

Peptone,  249 

Peptones,  257,  259,  261,  271,  741,  747 

Peptones  in  gastric  juice,  247 

Perceptions,  tactile,  589  —596  ;  visual,  552 — 

554 
Periodicity  in  the  phenomena  of  the  body, 

715  ... 

Peripheral  resistance  m  blood-circulati_n, 
154,  179,  199.  208.  210 

PeriSialtic  action  of  ureter,  132 

Peristaltic  contractions  :  in  defsecation,  304 ; 
in  digestion,  296  ;  in  the  oesophagus,  299; 
in  the  stomach,  300 

Perspiration,  nature  and  amount  of,  399  ;  se- 
cretion of,  402 ;  nervous  mechanism  of, 
402  ;  average  loss  by,  472 

Pettenkofek,  on  changes  of  air  in  respira- 
tion, 342  ;  on  nutrition,  460 — 465,  472,  495  ; 
sleep.  718 

Pettenkofer's  test  for  bile  ac'.ds,  785 

PflOgek,  blood.  20,  22  ;  nervous  irritability 
during  electrotonus,  65,  82,  87  ;  endings  of 
nerves  in  salivary  glands,  272 ;  inhibition 
of  peristaltic  action,  297 ;  pump  for  ex- 
tracting gas  from  bl  lod,  344  ;  hsemoglobin, 
356  ;  seat  of  oxidation  in  respiration,  364  ; 
respiratory  changes  in  tissues,  366 — 397  ; 
spinal  cord,  607  ;  sleep,  718 

Pharynx  in  deglutition,  294 ;  vomiting,  299, 
304 

Phases  of  life,  707 

Phenylic  ac»d,  784 

Philipeaux.  en  union  of  sensory  and  motor 
nerves,  506 

Pha=phorus  as  an  element  of  food,  467 

Photochemistry  of  the  retina,  533 

Phrenic  nerve  of  rabbit,  its  effect  on  respi- 
ration, 369 

Phthisis,  cold  sweats  in,  403 

Phys.ology  of  respiration,  our  knowledge  of, 

397 

Physostigmin.  its  effects  on  the  pupil,  535 

Pig,  saliva  of  the,  244 ;  bile,  255 ;  blood- 
crystals,  348 

Pigments,  in  bile,  254  ;  in  urine,  409 

Placenta,  69s,  698 

Planer,  gases  of  intestine,  313 

Plasma  of  the  blood,  20,  28,  31 


Plasmine,  18 

Plateau,  on  af.er-images,  553 

Plethysmograph,  for  measuring  changes  in 

the  circulation,  229 
Plusz,  absorption  of  proteids  in  digestion, 

325 
Pneumogastric  nerve,  its  influence  in  respira- 
tion, 371 

Pneumographs,  Marey's  and  Pick's,  333 

Pvjison,  effect  of  urari,  44,  435  ;  carbonic 
oxide,  435 

Polyuria,  or  excessive  renal  secretion,  413 

Pons  Varolii,  659 — 663 

Potential  energy  of  food,  468 

Pre-e.'cistence  theory  of  muscle  and  nerve,  loi 

Predicrotic  pulse-wave  (diagram),  181 

Pregnancy, 694 

Pressure,  Ijlood,  139 — 235,  377  {See  Blood 
pressure) 

Pressure  of  air  in  respiration,  394 

Pressure,  sensations  of,  591 

Prever,  on  blood-corpuscles,  39  ;  on  hsemo- 
globln  and  haematin,  356,  358  ;  sleep,  717 

Priestley,  on  respiration,  combustion  and 
oxygen,  397 

Propionic  acid,  759 

Protagon.  769 

Protective  mechanisms  of  the  eye,  572 

Proteid  food,  metabol.c  effects  of,  467,  492 

Proteids,  725 — 752;  action  of  gastric  juice 
on,  244,  253  ;  action  of  pancreatic  juice  on, 
259 ;  changes  in  stomach,  308 ;  in  the  in- 
testine, 313 ;  absorption  of  indigestion, 
324  ;  as  sources  of  fat,  439 

Proteolysis,  digestive,  theory  of,  261 

Protoplasm,  properties  of,  i,  123 ;  in  adipose 
tissue,  437  ;   sfinal,  601 

Protoplasm  of  en  bry^nic  tissues,  698 

Prout,  on  digestion  327 

Ptyalin  of  saliva,  243,  252 

Puberty,  691,  712 

Pulmonary  respiration,  mechanics  of,  430 

Pulmonary  tissues.  6 

Pulsation  of  the  brain,  379 

Pulie,  the,  143,  173,  17s  ;  sphygmograph 
tracings  of  pulse-waves,  175,  180,  181 ; 
predicrotic  and  dicrotic  waves,  182 

Pulsus  venosus,  379 

Pump  action  on  the  heart,  174,  179 

Pupil  of  the  eye,  its  movements,  520,  657 

Purgative  action  of  salts,  327 

Purkinje's  figures,  530,  531,  533;  on  the 
effects  of  galvanic  currents  on  the  brain, 
662 

Purple,  visual.  536 

Purpurin  in  urine,  409 

Pyloriis,  298,  300,  305.  309,  312 

Pyrexia,  485 

Pyrosis,  305 

Python,  temperature  of,  478 


Quetelet,  phases  of  life,  708 
Quinine,  action  of  on  reflex  action,  604 

Rabbit,  quantity  and  distribution  of  blood  in 
the,  25,  32,  41  ;  arter.al  pressure,  146;  cir- 
culation, 152;  heart-beat,  194;  cery.cal 
and  thoracic  ganglia  (diagram),  195.;.  inhi- 
bition of  heart-beat,  200  ;  contractility  of 


INDEX. 


80I 


the  arteriu  of  the  ear,  aoa  ;  stimulation  <•( 
depres'-or  nerve,  aog ;  saliva.  344 ;  sub- 
maxillary gl.-ui<l,  aS;  ;  blood-crystals,  348 ; 
bloocl-prcisure  in  respiration,  384  ;  section 
of  spinal  curd,  4-44 ;  etVcct  of  cold  on.  483  ; 
moveiiients  of  liic  pupil,  524  ;  spinal  corJ, 
6ao 

Rankk,  on  distribution  of  blood  in  the  rab- 
bit and  dog,  41;  perspiration.  400;  nutri- 
tion. 469.  471 

Ranso.mb,  l)r.  A.,  power  ff  g.ostrc  juice, 
251  ;  movemcnl  of  ribs  in  respiration.  336 

Rat,  saliva  of  the.  244  ;  blood-crystals,  348 

Reaction  |>criod,  665 

Rectum,  in  Uefa:cation,  30a 

Red  ci^n'u^clcs  of  b'ood.  their  chemical  com- 
position. 33,  37  ;  their  fate,  38,  348 

Reflex  actions,  126 

Reflex  actions,  the  spinal  cord  as  a  centre  of, 

Reflex  actions,  inhibition  of,  603 

Reflex  action,  parturition,  703 

Reflex  centres,  657,  664 

Keflex  inhibition.  193  ;  of  heart-beat,  193 

Reflex  micturition.  421 

Regener.ition  i^f  tissues.  689 

Regnault  and  Keiskt,  on  cutaneous  respi- 
ration, 401  ;  on  nutrition,  495 

Rbich,  secretion  of  tears,  573 

Renal  secretion,  407 

Rennet,  252 

Reproduction  of  the  amoeba,  3 

Reproduction,  tissues  and  mechanisms  of,  6, 
689 

Resonants  (voice).  681 

Respirati.n  of  the  ainccba,  3.  4 

Respiration,  our  knowledge  of  the  physiology 
or.  397         .  .         , 

Respiration,  tissues  and  mechanism  of,  329 — 
397  ;  mechanics  of  pulmonary  respiration, 
330  ;  rhythm  of,  332  ;  apparatus  for  taking 
tracings  of  movements  of  air  (di.igram). 
333  :  facial  and  laryngeal,  339 ;  ch.inges  of 
air  in.  340 ;  changes  in  blood.  343  ;  in  the 
lungs,  360;  in  the  tissues,  361  ;  nervous 
mechanism,  369  ;  eflectson  the  circulation, 
37S  ;  effects  of  changes  in  the  air  breathed, 
333  ;  modified  respiratory  movements,  395 

Respiration,  cutaneous,  401 

Respiration  as  a  regulator  of  temperature, 
479 

Resjiiration  of  the  foetus,  701,  703 

Resp. ration,  failure  of  before  death,  720 

Respiratory  centre,  375.  376 

Kesi)irat  iry  mechanisms,  8,  329 

Respiratory  move:iients,  334,  395 

Respiratory  muscles,  129 

Rest,  muscular  exhaustion  restored  by,  100 

Retina  (6V<f  .Siijht) 

Retching,  304 

Rheometcr  of  Ludwig,  for  measuring  blood- 
pressure,  144 

'  Kheoscopic  Frog.'  66,  170 

Rheotomes  :  —  Fall-rheo:ome,  104  ;  Bern- 
stein's Differential  Rheotome,  105 

Rhythm  of  heart-beat,  173  ;  of  respiration. 
^32„340.  370.  372,  376.  38S  ;  in  .asphyxia,  3S8 

RiSs.  movement  in  respiration,  336 — 338 

'  Rich  '  colours,  545 

Rigor  mortis,  57,  68,  96,  97,  1 18,  jgi,  478, 
721 

F.  P. 


RiNCRR,  on  di.abetes,  436;  daily  variation 
in  the  temperature  of  the  body,  487 

Rittkk's  tetanus,  85 

Ritter-Vai.li,  law  of  irritability  of  nenres, 
94 

R6hnig.  on  perspiration,  402 ;  effect  of  cold 
on  rabbits,  484  :  urari  p<.isoning.  4S4 

Ro.%fA.NES,  on  cunti;9ctile  tissues,  86 

RosE.NTiiAi.,  respiratory  functi/n  of  vagus, 
and  theory  of  nervous  mechanism  of  re- 
spiration, 373  ;  on  reflex  actions,  609 

RuGE,  gases  in  the  large  intestine,  314 

Running.  684 

Ri;THEKFOKr>,  vaso-motor  nerves  of  stomach. 
277 


Saikowksv,  diabetes,  435 

St.  PiiJKKE  and  Kstor,  seat  of  oxidation  in 
respiration,  364 

Saliva,  239—245  ;  purpose  in  digestion.  340; 
on  fats  and  proteids,  240 ;  its  action  on 
starch,  240,  251  ;  quantity  of.  266  ;  action 
of  submaxill.iry  saliv.a.  239,  264,  276;  ia 
vomiting.  304  ;  relation  to  taste,  588 

Saliva  of  infants,  70S 

Salivary  cell,  nutrition  of  the,  488 

Salts,  as  food,  467 

Salts,  in  bile,  253  ;  in  blo'^d,  32.  33  ;  in  urine, 
i07 ;  abs  irpiion  into  bijod  and  urine,  326 

Salts  of  uiic  acia,  774 

Samuel,  elTect  of  c^ld  on  rabbits,  485 

Sandehson'.  Bi;kdon.  dicrotic  pulse-w.ave, 
182  ;  recording  stcthometer,  333  ;  cerebral 
convolutions,  644 

Saphena  artery  of  the  rabbit,  its  contrac- 
tility, 202 

Sarcolaciic  acid,  71,  76s 

Sarkin.  778 

Scaleni  muscles,  333.  336 

Sen  A  PER,  red  corpuscles.  36 

ScHARLi.N'G,  on  cutaueous  respiration,  401 

SCHECH,  on  the  larynx,  676 

Scheinek's  experiment  on  sight,  514 

ScHE.MEMETjEWSKi,  changes  in  the  tissues 
in  respiration,  366 

ScHERER,  paralbumin  and  metalbumin,  729 

ScHiFF,  mechanism  of  digestive  secreti.n, 
268;  on  secretion  of  bile,  291  ;  movements 
of  the  oisophagus,  300 ;  vomiting,  305  ; 
spinal  cord,  616 ;  functions  of  the  brain, 
671 

Schmidt,  A.,  fihrinoplastin  and  fibrinogen, 
20,  21,  23  ;  view  of  function  of  paraglobu- 
lin.  30 ;  red  corpuscles.  36,  3^  :  relations  of 
neutral  salines  and  of  gastric  juice,  250 ; 
albumins,  730 

Schmidt  and  Bidder,  absorption  of  fat  in 
digestion,  31a ;  researches  on  digestion, 
327 

Schmidt,  C,  composition  of  blotxl,  33:  on 
lard.icein,  745 

SciiMiEDEDEKG,  cardiac  accelerator  nerves, 
194  ;   hippiiric  acid,  454 

ScHt;i.TZE.  Max.  on  dimensions  of  retinal 
cones,  543  ;  olfactory  cells,  584 

ScHi'LTZK.s'.  on  urea,  451 

SchOtze.n'urkger.  on  proteids.  747 

ScHWA.N.v.  researches  on  digcsti  m,  327 

Sciatic  nerve,  vaso-motor  action  of,  303,  aoif 

Secretion  by  the  skin,  398 — 406 


51 


8o2 


INDEX. 


Secretion  by  the  Iddneys,  407 

Secretion  by  the  renal  epithelium,  414 

Secretion  of  milk,  441 

Secretion  of  urine,  411 

Secretions,  digestive  {See  Saliva,  Bile,  Pan- 
creatic juice) 

Secreting  tissues,  4,  S>  6 

Semen,  694 

Semilunar  valves  of  the  heart,  165 — 167 

Sensations,  auditory,  577 

Sensations,  tactile,  591 

Sensations,  visual,  529 

Sense,  muscular,  598 

Sense-organs,  507 

Sensible  perspiration,  399 

Sensitive  cells,  125 

Sensory  fibres,  502 

Sensory  nerves,  125,  134,  499 — 509 

Sequin,  on  perspiration,  393 

Serum,  its  chemical  composition,  20,  31,  33 

Serum-albumin,  729 

Setschenow,  inhibition  of  reflex  action, 
603 

Sexual  generation,  689,  694 

SHARPEy,  sounds  of  the  heart  (diagram), 
169 

Sheep's  blood,  26,  147,  348 ;  saliva,  244 

Shepard,  hippuric  acid,  453 

Sighing,  395 

Sight,  .510 — 573  ;  dioptric  mechanism,  510  ; 
visual  sensations,  529  ;  visual  perceptions, 
552;  binocular  vision,  559;  visual  judgments, 
568 ;    protective   mechanisms  of  the  eye. 

Singing,  672 

SiNiTZEN,  on  trophic  nerves,  489 

Sinus  venosus,  191 

Size,  appreciation  of  apparent,  557 

Size  of  the  body  ;  phases  of  life,  707 

Skatol,  788 

Skeletal  muscles,  43,  610,  682,  714 

Skeleton,  growth  of  the,  713 

Skin,  5,  6  ;  absorption  by  the,  405  ;  secretion 

by  the,  398 — 406 
Skin,  loss  of  heat  from  the,  479 
Skin,  terminal,  organs  of  the,  589 
Sleep,  715 
Smell,  584 

Snake,  behaviour  when  decapitated,  602 
Sneezing,  396 

Snellen,  inflammation  of  the  eye,  489 
Stokes-Cheyne,  respiration,  378 
Soaps.  763 
Sobbing,  396 

Solidity,  judgment  of,  569  _ 
SoLTMANN,  cerebral  areas  in  the  newly-bom, 

711 
Sound,  the  voice,  672 
Sounds,  musical,  578 
Spallanzani,  researches  on  digestion,  327 ; 

respiratory  charges  in  the  tissues,  361 
Special  muscular  mechanisms,  675 
Spectra  of  hsemoglobin,  350,  352  ;  haematin, 

356,  357 

Speech  :  vowels,  678  ;  consonants,  679  ;  ex- 
plosives, 680 ;  aspirates,  680 ;  resonants, 
681,  682  ;  vibratory,  682 

Spermatozoa,  43,  692,  694.  695 

Spherical  aberration  in  the  eye,  526 

Sphincter  vesicae,  420 

Sphygmograpti,  157  (diagnuii)^  180 


Spiess,  temperature  of  submaxillary  glaHd, 

486 
Spinal    cord,   section    of,   effect    on   blood- 
preiisure,  210,  220;  its  action  on  respiration, 
370  ;  of  rabbit,  section  of,  435 ;  as  a  centre 
of  reflex  action,  599;  in  the  frog,  599;  in 
the  mammal,  606 ;  as  a  centre  of  automatic 
action,  609 ;  as  a  conductor  of  afferent  and 
efferent  impulses,  611 ;  parturition,  705 
Spinal  nerves,  500 ;  roots  of,  500 
Spirometer,  332 

Splanchnic  nerve,   vaso-motor  action,   206 ; 
relation  to  gastric  secretion,  277 ;  relation 
to  peristaltic  movements,   297,  301 ;    and 
renal  secretion,  413 
Spleen,  the,  444 
Sporadic  ganglia,  128,  131 
Sprengel's  pump  for  extracting  gas  from 

blood,  344 
Stannius,  experiments  on  heart-beat,  192 
Starch,  action  of  saliva  on,  240,  252,  307,  310, 
431;  action  of  gastric  juice  on,  246;  cor- 
puscles,  241  ;   action  of  pancreatic  juice 
on,  238  ;  as  food,  464,  467 
Starvation,  effects  of,  455,  456 
Stasis  in  inflammation,  227,  228 
Statistics  of  nutrition,  454 
Stearic  acid,  760 
Stearin,  440,  762 
Stereoscope,  565 
Stethometer,  recording,  333 
Stimulation,  impulses  in  nerves  produced  by, 

124 
Stimulation  of  afferent  nerves,  effect  on  vaso- 
motor centre,  208 
Stimulation  of  the  chorda  tympani,  222,  272 
Stimuli,  character  of  reflex  actions  dependent 

on  the  nature,  604 
Stimuli  in  aid  of  parturition,  703 
Stimulus,  as  affecting  muscular  contraction, 

90,  95  ;  in  unstriated  muscles,  119 
Stirling,  the  muscle-nerve  machine,  88 
Stokes,  on  the  spectra  of  haemoglobin,  35;^ 
Stomach,  secretion  by,  274  ;  action  of  gastric 
juice  on   the,   292  ;  its  movements  in  di- 
gestion, 301  ;  its  action  in  vomiting,  304; 
Its  action  on  food,  308 ;  digestion  in  the, 
308—310  (See  Digestion) 
Strassburg's    researches    on    respiration, 

360,  362 
Stroganow,  oxygen  in  the  lungs  in  respira- 
tion, 361 
Stromuhr,  or  rheometer,  for  measuring  blood- 
pressure,  144 
Strychnia,  action  of,  602,  603 
SuBBOTiN,  fat  of  man  and  the  dog,  439 ;  the 

secret. on  of  milk,  440 
Sublingual  saliva,  244 

Submaxillary  gland,  secretion  of  saliva,  266, 
285;  of  dog  (diagram),  268 ;  of  rabbit,  287 
Submaxillary  saliva,  244 
Succinic  acid,  766 
Succus  entericus,  239,  264,  265,  279 
Sugar,   conversion    of   starch   into,  by  the 
saliva,  240,  242  ;  digestion  of,  307  ;  in  small 
intestine,  310 
Sugar  in  urine,  325,  413,  434  ;  in  the  hepatic 
blood,  425 ;  in  the  blood  and  urine,  325, 
428,  431 
Sugar,  milk-sugar,  442 ;   cane,  26$  ;  gtxpe, 
365 


INDEX. 


803 


Sanr  u  food,  ^64,  467 

Sulphur  as  an  clement  of  food,  468 

Suppression  of  urine,  419,  448 

Svsi.oWA,  lymph-hearts  of  the  frog,  610 

Swallowing.  299.  ^09 

Sweat  (See  Perspintlion) 

Sympaihciic  action,  ait 

Syntonin.  70,  a6i 

Systole  of  heart,  duration  of,  160,  173 


Traubo'j  curves  of  Wood-preMure  in  respira* 

lion,  385 
Tricuspid  valves  of  the  heart,  165,  167 
Trophic  centres,  503 
Trophic  nerves,  488—491 
Trypsin,  259,  26a 
TscHHscmciiis,  bodily  heat,  483 
Tuliuti  urini/eri,  407 
Turtle's  heart-beat,  34,  187 
Tyrosia,  a6o,  a6i,  313,  446,  783 


T.ictile  judgments,  594 

Tactile  perceptions,  589,  594 — 596 

Tactile  sensations.  591.  615,  666 

Tambour,  Marey's,  for  measuring  blood- 
pressure  (diagram),  150,  333 

Takchanopf,  on  the  bpleen,  445 

Tartar  emetic,  effects  of,  307 

Taste.  586 

Taurin.  780 

Taurocholic  acid,  786 

Tears,  572 

Teeth,  action  in  mastication,  293 

Temperature,  its  intliience  on  muscular  irri- 
tability, 95  ;  on  ciliary  action,  121  ;  on  the 
saliva.  242  ;  on  the  gastric  juice,  250 

Temperature  of  man,  478  ;  birds,  478 ;  bees, 
478 ;  wolf.  478  ;  fish,  478 

Temjieratuie,  its  effect  un  animals,  480 — 488 

Temperature,  sensations  of.  592 

Temperature  (5^^  Cold,  Heat) 

Tension  of  the  gases  of  blood  and  pulmonary 
air,  360,  365,  366,  368 

Terminal  orj^ans  of  the  skin,  589 

Tests  f  jr  proteids,  727 

Tetanic  contractions,  52 

Tetanus,  56,  57,  73,  88,  99;  sound  in,  170 

Tetanus,  Rittcr's,  85 

Thermogenic  ner%es,  486 

Thiky.  on  succus  entericus,  264 

Thoracic  duct,  317 

Thoracic  respiratory  movements,  332  ;  effect 
of  on  circulation.  379 

Thuuichum,  on  pigments  in  urine,  409 

Thymus,  713 

Thymus  bodies,  446 

TtuDKMANN,  researches  on  digestion,  327 

Time  re  luired  for  reflex  actions,  608 

Tissues,  fundamental,  5 

Tissues,  contractile,  42 — laa 

Tissues,  embr^'onic.  698 

Tissues.  metaboLc,  425 

Tissues,  nervous,  properties  of,  123,  134 

Tissues  of  chemical  action  and  their  mechan- 
isms. 239—328;  digestion,  239 — 328;  re- 
p.ration.  329 — 397 

Tissues  of  reproduction.  689 

Tissues,  resp.ratory,  changes  in  the,  360 

Tissues,  the  death  of,  721 
'  Tone '  of  arteries.  204 

Tongue,  its  action  in  mastication  and  de- 
glutition, 293.  39s 

Tonicity  of  skeletal  muscles,  610 

Torricellian  vacuum  for  extracting  gas  from 
blood,  344 

Touch,  S89 

Tracings  of  respiratory  movements,  33a ; 
blood-pressure  curves  and  intra-thoracic 
pressure.  382  {See  liiagrams)   ,. 

Tnnsfusion  of  blood,  39,  36 


Undulations  of  blood-pressure  in  respiration, 
386 

Unstriated  muscular  tissua,  119 

Urzmic  poisoning.  448 

Urari  poison,  its  effects  on  contractile  tissues, 
44,  85  ;  its  effect  on  heart-be.it,  191  ;  its 
ctfect  on  cerebral  functions.  210  :  on  vomit- 
ing, 305;  on  respiration,  382;  in  producing 
diabetes,  435 

Urea.  398  ;  presence  in  perspiration,  400  ;  the 
history  of,  446 ;  relation  to  muscular 
exercise,  471 

Urea,  771 ;  nitrate  of.  771  ;  oxalate  of.  771 ; 
compound,  773  ;  detection  of,  in  solutions, 
772 

Ureter,  peristaltic  contraction  of  the,  128, 
132  ;  in  micturition,  420 

Urethra,  420 

Uric  acid.  774  ;  source  of,  432  ;  in  the  spleen, 
452;  salts  of.  774  ...        , 

Urine,  composition  of,  407 — 410  ;  acidity  of, 
410 ;  constituents  of,  410 ;  secretion  of, 
411;  act  of  micturition,  419;  kreatin  in, 
447  ;  hippuric  acid  in,  453 ;  loss  of  nitro- 
gen, 459 

Urine  in  infancy,  710 

Urine,  sugar  in,  325 

Uriniferous  tubules,  411 

Urobilin  in  urine,  39,  409 

Urochroine,  409 

Uroerythrin  in  urine,  409 

'  Uterine  milk,'  698 

Uterus,  in  menstruation,  691  ;  in  parturition, 
7°^ 


Vagus,  cardio-inhibitory  action  of.  its  effect, 
193 ;  relation  to  movements  of  stomach. 
300 ;  to  vomiting,  307  ;  respiratory  function 
of  the,  370 

Valerianic  acid.  759 

Valves  of  the  heart,  164 — 166 

Varnishing  of  anim:Us,  its  effects,  401 

Vascular  mc-chanism,  7,  136  ;  physical  pheno- 
mena of  the  circulation.  136;  the  heart, 
154;  the  pulse,  173;  vital  phenomena  of 
the  circulation,  184  ;  ch.inges  in  the  heart- 
beat, 186;  in  the  calibre  of  the  minute 
arteries,  vaso-motor  actions,  200  ;  constric- 
tion and  dilation,  224 :  changes  in  the 
capillary  districts,  326  ;  in  the  quantity  of 
blood,  23^ 

Vaso-constrictor  and  vaso-dllator  nerves, 
220 

Vaso-motor  actions,  200 

Vasj-moior  action,  relating  to  secreting 
activity,  271 

Vaso-moior  centre,  224 

Vaso-motor  nerves,  303,  329 


8o4 


INDEX. 


Veins,  138,  147 ;  effect  of  respiratory  move- 
ments on  the,  381 

Velocity  of  the  flow  of  blood,  143,  148,  152  ; 
of  the  pulse-wave,  176 ;  of  sensory  im- 
pulses, 504 

Vea^us  blood,  343,  353,  358,  360,  368,  375 

Venous  pulse,  184 

Ventricle  of  the  heart,  155 

Vertigo,  632,  662 

ViERORDT,  numeration  blood-corpuscles,  35  ; 
hseraatachometer  for  measuring  blood- 
pressure,  14s 

Vision,  region  of  distinct,  SS4 ;  the  reaction 
period  {See  Sight)  665 

Visual  impulses,  origin  of,  529 

Visual  judgments,  568 

Visual  perceptions,  552 

Visual  purple,  536 

Visual  sensations,  529,  542 

'  Vital  capacity  '  of  the  lungs,  332 

Vital  phen  >mena  of  the  circulation,  184 

Vitellin,  738 

Vocal  cords,  263  ;  tightening  of,  675 ;  slack- 
ening of,  67s 

Voice,  the,  672 

VoiT,  changes  of  air  in  respiration,- 342  ; 
effects  of  starvation,  45s  ;  nutrition,  459 — 
465,  471—472,  495  ;  sleep.  718     _ 

VoLKMANN,  researches  on  blood-circulation, 
144,  146,  235  ;  lymph-hearts,  609 

Vomiting,  304 

Vowel-sounds.  678 

VULHIAN,  vaso-motor  action,  224  ;  on  union 
of  motor  and  sensory  nerves,  506  ;  on  con- 
duction of  impulses  in  the  spinal  cord,  615 


Waldeyer,  lymph  hearts,  610 
Walking,  683 

Waller,  A.,  vascular  mechanism,  235 
Wasmann,  researches  on  digestion,  327 


Weber,  pulse-waves,  177 ;  muscular  con- 
traction, 118;  on  visual  sensations,  542 ;  on 
tactile  perceptions,  594 

Weight  of  the  body ;  phases  of  life,  707 

Weiske  and  Wildt,  on  nutrition,  465 

Weiss,  on  glycogen  in  starving  hens,  431 

Wharton's  duct,  27X 

Wheatstone,  on  binocular  vision,  598 ;  bino- 
cular vision  instrument,  570 

Whispering,  682 

White  corpuscles,  21,  28,  34,  37,  38,  42 

Williams,  on  menstruation,  692 

WiNOGRADOFF,  diabetes,  435 

Winking.  572 

WisLiCENUS,  on  urea  and  muscular  exercise, 
471 

WiTTiCH,  diabetes  and  digestion,  328, 436 

Wolf,  temperature  of,  478 

WoLFERZ,  secretion  of  tears,  572 

WoLFFBERG,  researches  on  respiration,  360 

WoROSCHiLOFF,  On  reflex  actions,  608,  616, 
617 

WuNDT,  spinal  ganglia,  502 


Xanthin,  446,  454,  778 


Ya\vning,  395 

Yellow  spot  in  eye,  543 ;  influence  of  the 

pigment  of,  550 
Young-Helmholtz,  theory  of  colour  sensa* 

tions,  548 


Zaleskv,  on  renal  secretion,  448 
Zawilski.  digestion  of  fats,  322 
ZuNTZ,  alkalescence  of  shed  blood,  30;  effect 
of  cold  on  rabbits,  484 ;   urari  poisoning, 


Zymogen,  383 


